Modular design and construction techniques for nuclear

Nuclear Engineering and Design

ELSEVIER Nuclear Engineering and Design 172 (1997) 327 349

Modular design and construction techniques for nuclear power plants

Christopher W . Lapp, Michael W. Golay *

Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, MA 02139, USA

Received 24 October 1995; received in revised form 22 August 1996; accepted 9 January 1997

Abstract

Modularization has been proposed as a nuclear power plant design-fabrication approach for increasing the quality and reducing the costs of future plants. The work reported describes a methodology for making the modular design and construction process more systematic and efficient. This methodology is applied to both the design and fabrication processes for power plant modules. The design process is enhanced by the utilization of a matrix reordering technique that reveals natural groupings in complex data sets. This technique allows a layout which groups plant systems functionally so that modules increase self-sufficiency and minimize inter-module interaction costs.

In an illustration of modular design the ship fabrication methods of product work breakdown structure are applied to a modular nuclear power plant to be built at an on-site factory facility. A comparison of a new modular power plant and a conventional power plant design is performed. Cost penalty indices are defined in order to guide maximization of the economic benefits of a modular design. Economic analyses, for both modular and conventional construction methods, are performed over a range of construction schedules and monetary interest rates to illustrate the potential savings of modular construction. The results of the analyses reported here indicate a typical potential savings of 15% in the capital cost of the modular nuclear power plant versus a conventional one. The most interesting result of this work is that the potential savings derive equally from the design and construction processes. © 1997 Elsevier Science S.A.

1. Introduction

This p a p e r descr ibes a m e t h o d for designing modu la r i zed nuclear power plants . This design and cons t ruc t ion t r ea tmen t can be useful in reducing the costs o f fu ture nuclear power plants . In the Un i t ed Sta tes and, to a lesser degree, else- where the high capi ta l costs o f nuclear power

*Corresponding author. Fax: + l 161 172588863; e-mail: [email protected]

p lan ts have con t r ibu t ed to a h ia tus in new nuclear p lan t orders. M a n y factors have con t r ibu ted to these high costs inc luding pers is tent r egu la to ry changes, and the absence o f s t andard ized p lan t designs.

A m a j o r p r o b l e m dur ing the cons t ruc t ion o f m a n y large nuclear p lan ts was low mora le o f the l a b o r force assoc ia ted with low worke r p roduc t iv - i ty and low cons t ruc t ion quali ty. A s tudy (Borcherd ing et al., 1980) o f the mot iva t ion and p roduc t iv i ty o f c ra f t smen at five large nuclear

0029-5493/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S0029-5493(97)0003 1-9

328 C.W. Lapp, M.W. Golay Nuclear Engineering and Design 172 (1997) 327 349

projects identified six factors which influenced their productivity: low material availability, low tool availability, high rework rates, needless interference with other crews, overcrowded work areas, and time consuming inspection delays. In order to reduce the capital costs of nuclear plants, it can be important to develop a method of plant construction which can increase productivity and quality. Reducing the amount of on-site labor with factory produced power plant modules is one avenue for doing this. The real capital cost is composed of the following elements: engineering and construction labor, rework, hardware; allowance for funds used during construction (AFUDC); and indirect and owner's costs.

All except the last can be reduced via modular fabrication techniques. Modular construction allows the relocation of work from a crowded plant site to the more controlled and productive environment of a factory. The benefits of modularization have been widely recognized; however, the literature is largely silent about how to create a modular plant in a systematic way. In order to implement modular fabrication effectively both the design and construction phases of a project must be addressed. Thus, consistent methods must be developed for: design of the plant for modular construction, efficient construction of the designed modules, simplified installation of modules within the power plant, and evaluation of the economic performance of modular methods. This paper illustrates how this can be accomplished.

In this paper, first, methods are presented for creating an efficient modular design which lends itself to simplified construction. Second, the methods of part one, along with established guidelines for plant layout, are combined in a systematic manner to produce a 'methodology of modular design.' Third, to illustrate the use of this design methodology an existing conventional plant (the Shearon Harris Pressurized Water Reactor (PWR) plant) is redesigned for modular fabrication. Fourth, the design is described of an on-site factory for the fabrication of power plant modules. Finally, a comparison of design cost indices is made for two power plants, which considers the factors of modular compatibility. An economic sensitivity analysis is then performed over a range

of construction schedules and interest rates to illustrate the potential savings of modular construction.

These methods are used to design the example power plant for modular construction from the point of project inception. This design process is contrasted to that of conventional methods where power plant designs are divided into geometrical regions to be supported by space frames, termed modules, but where plant components are not necessarily grouped functionally. The result of this latter approach is a design which can require much on-site installation work in order to connect components between modules. We anticipate that these methods would be used iteratively throughout the design, initially in a very approximate fashion and more elaborately as the level of available design detail increases.

Matrix clustering analysis can help in grouping plant components functionally. Such matrix clustering techniques are applied to power plant systems in order to group functionally those systems which have many physical connections. The technique uses information describing the number of systems with which a given system interconnects. The system interface information is placed in a matrix form and reordered so as to group systems which have close functional association.

The economics of modular construction would be enhanced through the use of a prelicensed standard plant design, thus reducing regulatory intervention. Reduced intervention is important so that the status of plant design and compliance is not changed substantially after the start of detailed design. The US NRC's design certifica- tion process promises this benefit, but it has not yet been used in a constructed plant.

2. Design methods

For high engineering efficiency it is valuable to optimize plant layout and it is essential in modular design. However, more preplanning and detailed computer aided design (CAD) information (i.e., drawings or computer bits) are required in advance of starting modular construction. The modular methodology discussed here can allow

C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327-349 329

the plant designers to optimize modularization from the beginning of the design process.

2.1. Matrix clustering analysis

Large amounts of information must be treated in characterizing complex plant systems and their interdependencies. A valuable optimization technique utilizes a matrix characterizing the mutual importance of related systems. These matrix data are reordered in order to cluster together systems of large mutual importance. Such reordering methods are able to identify natural groups of matrix elements in a large data set, where such groups might not be apparent upon casual exami- nation. Grouping of plant systems or components is accomplished using the bond energy algorithm (BEA) (McCormick et al., 1972). It does this by reordering the rows and columns of a matrix so as to cluster the array elements having large values. This task is accomplished by multiplying an element A(id) of the matrix by the elements sur- rounding it to the left, right, top and bottom (McCormick et al., 1972). Then, summing over columns (or rows) of the resulting values from this calculation gives the column (or row) value of the BEA. Rows and columns are moved within the matrix until the arrangement giving the largest value of the BEA is obtained for that row or column. This procedure is then repeated until all columns (rows) have been placed in their optimal locations. The optimal matrix clustering is obtained by maximizing the measure of effectiveness (ME), defined as (McCormick et al., 1969):

n

ME 2 A(ij) i = l j = l

x {A(i , j-- l ) + A ( i , j + 1) +A( i - - 1,j)

+ A ( i + 1,j)} (1)

or for a symmetric matrix (McCormick et al., 1972):

M E = ~ ~ A(i , j ) x { A ( i , j - 1 ) + A ( i , j + l ) } i - - 1 / = 1

(2)

An example of the relationship between the ME and matrix degree of clustering is shown in Fig. 1,

where a progression of matrix configurations is formed, going from unclustered to highly clustered arrays. It is seen that as the value of the ME increases the degree of clustering within the matrix also increases. When the maximum ME value is determined for a given matrix, the optimal clustering is also found.

For example, system interface importance data used in modular plant designs are obtained from system flow path diagrams, showing how many times and with which other systems a particular system interfaces. The values of an interface matrix element, A (id'), indicates the number of times that a system (i) interfaces with system (j). Ma- trix symmetry is maintained by reordering the rows and columns simultaneously. By performing a matrix clustering analysis, the systems which are functionally linked are grouped together.

2.2. The cost penalty method

A major focus of nuclear power plant design optimization is economic. It is desirable to find the least construction cost modular plant layout. To do this we use the matrix clustering technique, in conjunction with a set of cost weighting factors, for interacting components and systems to identify their least-cost configurations.

Cost factors used in our example analyses include those of fluid systems and structural connections at modular interfaces, and of piping

A B C D

A I 0 1 0

0 1 0 1

i 0 1 0

0 1 0 1

A B C D

A I 0 1 0

I 0 1 0

0 1 0 1

0 1 0 1

A 1

B 1

C 0

C D

0 0

0 0

1 1

1 1

ME= 8

i B C D A 0 1 0

B 1 0 1

C 1 0 1

D 0 0 0

ME=2

B C D A 1 0 0

B 0 1 1

C 0 1 1

D 1 0 0

ME = 6

Fig. 1. Illustration of ME sensitivity to the degree of matrix clustering McCormick et al., 1969. ME, method of effectivenss (for matrix clustering).

330 C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327 349

materials. These system connections are needed because of the functional interactions of plant systems, especially between pr imary and support systems. The cost penalty values used in the analysis presented here are approximate and illustrative. More detailed and accurate cost analyses would be required in actual practice.

2.2.1. Piping system cost penalties Creation of an optimal design is guided by

assignment of a cost penalty value to each system interface, reflecting the not only the number of interfaces between systems, but also the relative cost of an interface. For example, in the case of a piping system the diameter of the pipe and its construction safety class will affect the cost of an interface. For ease of analysis pipe sizes are divided into four categories based on diameter as listed below:

Table 1 Safety classes of piping systems

Safety class No. Description

I Highest rating, for in-containment components directly associated with the primary coolant system (e.g., piping, safety coolant accumulators). For components required for emergency purposes (e.g., safety coolant injection system). For components which support class 2 equipment or a primary system (e.g., the CVCS). For systems related to non-safety bal- ance of plant functions (i.e., condensate or waste process systems).

Penalty = number of interfaces

× pipe size cost penalty

× safety class number. (3)

Category Pipe outer diameter

1. Small - < l0 cm 2. Medium - < 2 5 cm 3. Large - <46 cm 4. Extra Large - >46 cm

Piping safety class categories reflect the increase of a component ' s cost as its safety importance increases. This cost escalation is a result of using more expensive materials, better documentation, higher standards of construction and more inten- sive quality control inspections. In piping systems four basic construction safety classes are also used for components as listed in Table 1. Such cost categorizations could be extended to much finer detail, but are limited here, for illustrative purposes. In order to assign an overall cost penalty value to a system interface the individual cost penalties must reflect the size and safety class categories of the piping.

This is done in Table 2 where the values of an interface cost penalty matrix element is a function of the number of interfaces, the size of pipe, and its safety class penalty, per Eq. (3):

Table 2 Cost penalty matrix values

Safety class cost penalty values

Safety class Cost penalty value

1 6 2 4 3 2 NNS 1

Pipe size cost penalty value

Pipe diameter size class Cost penalty value Small, diameter < 10 cm 1 Medium, diameter <25 cm 3 Large, diameter <46 cm 5 Extra-large, diameter >46 cm 7

Cost Penalty = {No. of interfaces} x {Pipe size indexl x {Safety index}. NNS, Non-Nuclear Safety. Example Case: residual heat removal low pressure safety injection and suction piping connected to reactor coolant system interconnection cost penalty. Safety class 2: cost penalty value, 4; pipe size medium: cost penalty value, 3; number of system interfaces, 6. Cost Penalty (RHR connection to RCS) - (4) x (3) x (6) - 72.

C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327 349

Table 3 Advantages of prefabrication/preassembly

331

Advantage Explanation

Improved quality Use of high-accuracy machinery leads to greater manufacturing precision and better process control. control

Improved production control

Inventory control Improved labor

control Improved work site

climate control

Programmed production and coordinated material delivery reduce inventory.

Factory setting gives more control of small parts production with better tracking of materials. Coordination between labor trades is enhanced, the labor force is made more stable and the factory environment increases labor morale and productivity. Work continues to be performed throughout the seasons and is not dependent upon weather conditions.

For example the residual heat removal (RHR) system which interfaces with the reactor coolant system (RCS) as shown in Table 2 has a relative cost penalty value of 72. The relative cost value then becomes an element A(i$) in the matrix indicating the costs of connections between different plant systems. Such a process is repeated for the rest of the systems under analysis to create an interface cost penalty matrix for the power plant piping network.

A system design which minimizes the number of inter-module connections for the pipe in ques- tion is desirable. Subsequent clustering analysis of the cost penalty matrix groups those items which mutually have high relative cost penalty values. This process assists a designer in assigning priority to them in component and piping placement.

3. Modular fabrication methods

Prefabrication of components into modules ap- plies manufacturing technologies to the construction process. Mass production techniques help to reduce the costs of a product due to the productivity and quality improvements of this method. In modular fabrication one builds elemental pieces of a plant, which are then assembled to form the final product to be installed on-site. The categories of items suitable for prefabrication can range from building elements (wall sections, etc.) to the total building (entire rooms or regions of the building). Different levels of prefabrication, preassembly and modularization are used to esca-

late module size from building elements, to components, to systems and finally to the total building. The advantages of prefabrication/preassembly are listed in Table 3 (Tatum et al., 1986). However, not all aspects of modular construction are positive, as is noted in Table 4.

3.1. Productivity and modular construction

A major benefit of modular fabrication is increased construction labor productivity by means of serial production. This can be augmented in the modular design process by requiring less material and fewer assembly steps.

Utilizing the group technology (Product Work Breakdown Structure, 1982) approach for module fabrication in a factory setting should also increase the productivity of factory workers and inspectors. This can be done by improving the following six factors of worker productivity: 1. Material availability; in factory fabrication all

required supplies are contained in the material supply pallets sent to each work lane.

2. Tool availability; in an assembly line all tools are set in their required locations.

3. Rework; through improved work conditions and more precise tools the work quality is increased.

4. Interference with other crews; in the factory each crew has its own work location, thus inducing inter-crew interferences.

5. Overcrowded work areas; in the factory process enough space is allocated for each task while modules allow easy access for outfitting before site installation.


Table 4 Disadvantages of preassembly/prefabrication

Disadvantage Explanation

Increased initial cost

More complete engineering required

Greater discipline required

Increased vulnerability to changes

A greater initial capital investment is needed in order to erect buildings and obtain machinery for fabrication of modules. More engineering effort is needed initially in order to develop more complete project plans and to account for the concerns of manufacturing in the design of the facility. Greater discipline is needed in planning to coordinate all of the factors involved with production and assembly at the plant site. Plant changes during design and construction are more costly to accommodate.

6. Inspection delays; inspection delays are reduced as the workers start tasks on another item in the assembly lane while the previous item is inspected.

The third variable affecting a project's progress, rework, depends upon the quantity of work as it is performed. Improved quality in a modular construction process appears likely to result from alleviation of many of the problems associated with conventional on-site construction and from access to more automated and accurate assembly and inspection tools. Worker morale should also be higher in the factory setting since this clean and controlled environment provides comfort not afforded to workers in outdoor construction.

3.2. Construction concerns specific to nuclear power

Conventional nuclear construction involves additional factors which can hinder efforts to increase productivity. These arise from the high degree of regulation which is required to assure public safety from radiological incidents. The inspections necessary for regulatory compliance in- terfere with the construction process and reduce productivity. The design and construction process must allow for many inspections and equipment qualification tests during fabrication. By using modular techniques an improvement of productivity can be achieved because such inspection and testing can be integrated into the fabrication process.

The relocation of work from the plant construction site to a modular factory (which could be built next to the construction site) could allow many of the required quality assurance or quality control (QA/QC) activities to be performed in the assembly flow lanes. In conventional field assembly work productivity is reduced as workers wait for inspections to be performed. With use of a rationalized production facility standardized inspections can be performed in a more timely manner. For instance, inspections could be performed on products in various stages of assembly as workers continue with tasks at another stage. Pipe subassemblies, for example, could be inspected before they are incorporated into more complex assemblies at succeeding levels of fabrication.

3.3. Defining modular boundaries

Defining module boundaries and module sizes are important considerations which should be re- solved early in the design process. Placement of module boundaries affects the entire production and installation process. Module size could range from the very large down to that of a small skid-mounted equipment module. For example, a floating nuclear plant could be composed of a few large modules assembled at a shipyard. Alterna- tively, a factory could make medium-sized modules, with size determined by transportation limitations. In another option, skid mounted machinery could be delivered to the site for modular installation. Use of such small skids, however,

C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327 349 333

does not take full advantage of the modular concept and would still require a great deal of on-site labor for installation. The large module concept such as a floating power plant takes the greatest advantage of the modular process and its associated economic savings. However, the facility needed for such large scale module fabrication would also require the greatest initial capital investment. The facility would have to build numerous floating plants in order to amortize its capital expenses successfully. The need for such investment constitutes a barrier to large-scale modularization. A third alternative, the on-site factory producing medium-sized modules, appears to provide a more attractive and realistic near-term prospect.

The determination of optimal modular boundaries requires a more detailed analysis than is available in the current literature. It is important to note that modular boundaries do not simply define geographic subdivisions of a given plant layout. Rather an optimization process is employed here to determine which modular boundaries reduce the amount of required on-site construction work. In order to determine valuable module boundaries some basic initial questions concerning how a module is defined need to be answered.

In order to accommodate regulatory and safety requirements the buildings and their modules are divided between the nuclear island and secondary portions of the plant. The primary or nuclear island portion of the plant consists of the buildings associated with the nuclear reactor and related radioactive systems (for a pressurized water reactor). A power plant's secondary side consists of the electrical generating and non-radioactive systems. Primary systems are then divided into safety and non-safety related equipment. Subse- quently, the following questions are addressed: (i) should the modules be organized upon a structural basis or a systems basis?, (ii) for structurally- based designs will the defining boundary be based upon module volume or mass? and (iii) for systems-based designs will the module boundary be defined by system function or by the most complex/largest system?

In answering these questions the following goals should be considered: (i) reducing the total amount of on-site work required, (ii) reducing the total length of pipe, cable, ducting and simplifying their routing geometry and (iii) ensuring that the modules used are standard in size and geometry

In deciding between structurally-based and systems-based modules it appears that the structural option is not a clearly attractive one. This is because the division of the plant into a set of structural space frame regions would not meet the goal of minimizing the total costs of on-site work associated with module interconnections. How- ever, the systems option is not totally satisfactory either because it would be impossible to separate systems into completely individual modules. There exist many support systems which connect components throughout the plant. Also, many of the plant systems are highly interconnected with each other, so that the goals of individual modular autonomy may not be met. The size of systems also varies greatly. This system-based approach would make uniform module size difficult to accomplish. As a result neither option is attractive by itself. Rather a combination of the two options is found to offer an attractive compromise. The grouping of systems within some standard-sized structural modules is able to satisfy well the goals set above.

3.3.1. Modularization cost measures

3.3.1.1. The measure o f modularity. In contrasting alternative modular plant designs it is valuable to employ scalar measures of the economic implications of different aspects of modularity. The dis- cussion here presents several such measures as follows: measure of modularity (MOM), which reflects the costs of modular interconnections for the entire power plant; module alignment index (MAI), which reflects the cost of structurally connecting the modules in a plant; pipe routing index (PRI), which reflects the cost of a particular modular piping network; concrete volume index (CVI), which reflects the amount of concrete used, and thus, the cost of concrete, design quality index (DQI), which summarizes the plant-wide cost penalty indices listed above, where:

3 3 4 C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327 349

DQI = MOM + MAI + PRI + CVI. (4)

In order to meet the previously stated design goals a method is needed to measure how effective the cost penalty matrix clustering is in making modules self sufficient. Because of their high costs, piping systems are of particular interest for power plant designers.

Typically, less emphasis is given to electrical cable design since cables are installed after the plant is complete. Cables are pulled through the finished plant in one piece since, for safety reasons, they are not allowed to be spliced. Thus reducing the on-site labor factor based upon an analysis using cable modular boundary interfaces would not be meaningful. This situation would most likely be altered in the future by the use of multiplexed fiber optic signal transmission.

However, piping that runs from module to module must be connected and inspected in the cramped confines of an almost completed plant. The larger the pipe, and the more important is its safety class, the more time-consuming and expensive is the process of interconnection. For this reason the modular boundary interface index (MBII) combines a set of cost penalty indices reflecting the pipe size, safety class and number of pipe interfaces associated with a module. The values of the MBII factor are the same as those used in the cost penalty matrix except for an added penalty, P (elevation), which reflect the costs of piping which traverses between different elevations [P (e levat ion)=2 for an elevation change, and = 1 for no change]. The number of modular boundary interfaces is determined by following a pipe route from component to component within a system and summing the number of times that it crosses a module boundary. There- fore, application of this optimizing technique is possible only after an initial plant design is completed.

A good modular design will have relatively few systems connections between interfacing modules. For a particular module the cost implications of such interfaces is quantified by the MBII, defined a s :

Ns

MBII = ~ N i x (P~ize × Scl,ss x Pele,ation), (5) i l

where N,, is the number of systems; Ns, number of interfaces; Psize, relative pipe diameter cost penalty; Sd .... relative pipe safety class cost penalty; and Pdevation, elevation penalty value.

The piping value of the MBII for each system is obtained from Eq. (5), summed over the modular interfaces encountered throughout the system piping network. Then, the respective values of MBII for the different plant systems are summed to yield the value of the MOM, as follows:

Ns MOM = ~ (MBII)/. (6)

/ = l

The value of MOM reflects the relative cost of module interfaces for plant piping systems. The value of MOM gives a relative, but not absolute, economic comparison of the degree of modularity of a design. An example of a inter-module pipe piece connector that might be used to connect systems is illustrated in Fig. 2.

3.3.2. Module alignment index In order to simplify structural module integra-

tion, or inter-modular transmission, designers need to consider how adjacent modules align. The areas of concern are the corner and side structural steel supports of each module. It is important that these elements be aligned vertically for two reasons. First, since modules are composed of struc-

Pump Module Pipe Route ModuLe

I'-I I-'ll'-I I.'1 x

Horizontal Span Distance

Fig . 2. T y p i c a l p i p e p i e c e f o r o n - s i t e m o d u l e c o n n e c t i o n .

C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327-349 335

tural steel it is likely for these members to be used as structural components. For this approach to be structurally effective the steel members have to align vertically so as to transmit tensile building loads without introducing needless bending and shear loads. Second, placing and anchoring modules within and between building levels becomes more difficult if structural members do not align vertically. The associated difficulty in construction arises as workers have to add extra bed plates and structural supports in order to compensate for each structural misalignment. In order to compare the merits of various modular designs a measure of the cost of such misalignments is required.

The MAI is a measure of the quality of module alignment. It is calculated using the module vertical alignment index (MVAI) and the module horizontal alignment index (MHAI). The MVAI sums over all vertical anchoring points in a plant and adds a cost penalty (equal to a value of two in this example) for each point which does not align directly, according to the relationship:

N v

MVAI = ~ FvAi + (FNvA, X 2), (7) i = 1

where, Nv, is the number of vertical connection points; Fvai, number of points that are vertically aligned; Fyvai, number of points not vertically aligned.

Horizontal integration of modules is not quite as important economically as vertical integration. Modules may be linked horizontally by welding or bolting structural steel corners and/or side columns. An overall MAI is the sum of the MVAI and MHAI indexes. A greater weight, R, is given to the MVAI to reflect the actual ratios of work required in the field to accomplish both types of alignment. The MAI is defined as follows:

MAI = {(R) x MVAI + {MHAI}, (8)

where R = (work to install vertical connection)/(work

to install horizontal connection). The ratio, R, could be equal to a value of three

or four, depending upon how much horizontal integration is required for structural purposes.

3.4. Elements of the pipe routing penalty index

For efficient modular fabrication it is important that the pipe routing be simple and uncongested. Piping should be designed to have few bends, crossovers and elevation changes so that it can be easily fabricated and installed in the module. This is because piping with numerous bends requires more subassembly stages and work at the stage of outfitting in the module. If the pipes tend to cross over one another frequently the pipe rack can become congested and difficult for workers to outfit, resulting in lower productivity and longer construction schedules. The number of different building elevations that a pipe passes through should also be reduced since it requires more on-site labor to connect piping which runs between levels.

A design must also address how to route the pipe in order to satisfy these design criteria while also reducing the total pipe length. Shorter piping runs reduce material costs and the costs to build, install and inspect pipe supports. Considerations of costs of pipe length, bends, elevation changes and crossovers are balanced in order to achieve an optimal design. Though it is more costly to use a longer piping run, doing so may, in some cases, simplify the geometry enough to allow quicker prefabrication and installation. In order to reflect these economic tradeoffs each of the qualities previously mentioned is given a cost penalty value which represents its relative construction cost.

3.4.1. Determination of pipe routing cost penalties The cost penalty values assigned for each of the

pipe characteristics is determined in terms of how they influence the plant fabrication and construction process. In order to detail the penalty assignments fully each PRI component is addressed separately in the following sections. The concept of routing penalties is derived from attempts at very large scale integration (VLSI) of complex integrated circuits, where many of the same concerns of routing connections are encountered (Sherman, 1986).

The PRI consists of the sum of the following cost penalty indices, which are discussed subse- quently: the pipe length penalty (PLP), reflecting

3 3 6 C.W. Lapp, M.W. Golay / Nuclear Engineer#1g and Design 172 (1997) 327 349

the direct costs of piping materials; the pipe bend penalty (PBP), reflecting the cost of pipe fabrication; the pipe crossover penalty (PCP), reflecting the cost of prefabrication and assembly of pipe sub-modules; the pipe elevation penalty (PEP), reflecting the cost of connecting pipes between building elevations on-site.

3.4.2. Pipe length penalty The PLP component of the PRI reflects the

costs of materials and of labor and inspection for installation of additional pipe supports. The cost penalty value is a function of pipe size (diameter), safety class and length, according to the relationship, for a single run of pipe in a particular system:

N s

P L P = ~ L ; X F L × F D X F s , (9)

where Ns, is the number of systems; L;, pipe length in the ith system; FL, relative cost per unit length; FD, relative pipe diameter category cost factor; Fs, relative pipe safety class cost factor.

3.4.3. Pipe bend penalty (PBP) The number of pipe bends has an influence on

the fabrication process as more subassembly steps are required in order to obtain a finished pipe piece. This is somewhat important to the overall fabrication process, but not as much as some of the other design concerns. The value of the penalty, FB, is equal to two in piping sections having bends. Thus, the PBP is defined by the following equation:

Ns

PBP = ~ (FB x NBi) x PLP;, (10) i 1

where, Ns, is the number of systems; NB;, number of pipe bends in the ith system; F B, pipe bend cost penalty in ith system; PLP;, Pipe length penalty in the ith system.

3.4.4. Pipe crossovers penalty Piping crossovers influence the outfitting of

modules at the assembly stage. As more pipes cross one another the module becomes more congested, and piping installation becomes more difficult. Because of the importance of making

outfitting easier for workers, a higher penalty value is assigned to a pipe crossover than to a pipe bend. In the work reported here a penalty factor value, Fc, of four is assigned to each pipe crossover. The PCP is defined by the following equation:

Ns

PCP = ~ (F c × Nci) × PLP;, (11) t = l

where, N~, number of systems; F c, piping crossover penalty; No;, number of crossovers in ith system and PLP;, pipe length penalty in the ith system.

3.4.5. Pipe elevation penalty The PEP depends upon the cost efficiency of

on-site installation of piping connecting modules. Aligning and connecting pipes between building levels is more difficult than is inter-module connection on the same level. Because it is important to reduce the amount of on-site work this work component is assigned a larger penalty than those given to pipe bends or crossovers. A piping elevation change cost penalty factor, FE, value of seven is used in the work reported here. The value of the total PEP is shown in the following PEP equation:

Ns

PEP = ~ (NE x FE) x PLP;, (12) i - - I

where, N s, is the number of systems; ARE;, number of pipe elevation changes in the ith system; FE, individual piping elevation change penalty and PLP;, pipe length penalty in the ith system.

3.4.6. Total pipe routing cost penalty index The sum of the above piping penalty compo-

nents provides the PRI which is expressed as:

PRI = {PLP + PBP + PCP + PEP}. (13)

3.4.7. Purpose of the design quality index Another index of the plant design is the CVI.

The CVI considers the volume of concrete in a particular power plant design and relates it directly to the cost of the plant as follows:

CVI = F~ x Vc, (14)

c.w. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327 349 337

where, Fc, is the concrete cost per volume; Vc, plant concrete volume.

In the analysis presented here consideration is given to the quantity of concrete used in vertical and horizontal applications because of the cost difference in the two applications. In order to compare the merits of one design to another the need arises for a measure of the overall cost implications of modular design. This then leads to the development of a DQI which summarizes various aspects of a design taking into account economic as well as construction concerns. The DQI is defined by the relationship below:

DQI -- A,(MOM) + A2(MAI) + A3(PRI)

+ A4(CVI). (15)

The values of the coefficients A I - A 4 can be ad- justed subjectively to reflect the relative importance to the designer of economic and other considerations. This adjustment prevents the influence of one index from inappropriately over- whelming those of the others. The DQI can also be related to costs and schedule estimates and can contain additional items besides those mentioned here. This is done in order to obtain a cost function which reflects the values of material and time savings.

4. Illustration of the design process

Accomplishing the goals of modularization requires design innovation and use of a systematic procedure for design evaluation resulting in a design process which is rationalized and made reproducible.

This new approach to design allows optimization for modular fabrication from the beginning of the design process. Since more preplanning and detailed 3D CAD models (or drawings) are required in order for modularity to be effective, it is imperative that this augmented engineering effort be made as efficient as possible. To do this the design is advanced in a step-by-step procedural process which allows design feedback. The procedure helps to eliminate duplication and converges to a new optimal design sooner than do trial and error techniques.

At this stage of the process the design is formulated independent of the plant construction and concerned only with the functional system requirements. These system designs determine the material requirements and any constraints upon system operability. It is in the design layout of the plant that a system-oriented design process becomes focused upon modular construction. This approach employs the process of Product Work Breakdown Structure (PWBS) using a zone-oriented (i.e., module) basis (Product Work Break- down Structure, 1982).

In the example presented here, this process is applied in modifying the Shearon Harris Nuclear Power Plant design for modular construction. The resulting design is then compared to the original design. The steps of this process are outlined below.

4.1. Step I: division o f the plant into nuclear and non-nuclear buildings

First, the site buildings are divided into those needed for nuclear and non-nuclear functions, as the following categorization illustrates for a pressurized water reactor (PWR):

Nuclear Buildings • Reactor Auxiliary Building (RAB) • Control Building (CB) • Reactor Containment Building (RCB) • Waste Process Building (WPB) • Fuel Handling Building (FHB)

Non-nuclear Buildings • Turbine Building • Intake Structures • Water Treatment Building • Other Warehouse Buildings.

Buildings containing systems which are related directly to the reactor, which are safety-related and which are radioactive become segregated for construction purposes.

4.1.1. Step 2: assignment o f plant systems to various buildings

In the work reported here only nuclear-related buildings and their associated systems are considered. However, the methods of design analysis illustrated in this work are equally applicable to

338 C.W. Lapp, M.W. Golay / Nuclear Engineer&g and Design 172 (1997) 327 349

both classes of buildings. Within a building category some plant systems extend between more than one building, and must be assigned to all of the buildings with which they interact. A list of the nuclear-related buildings and their respective systems is presented in Table 5. Only hydraulic systems are addressed here because such systems are sufficient for an illustration and they are important in the economics of the entire plant. For these reasons only the RAB is analyzed since it contains most of the nuclear- related piping systems (listed in Table 6).

4.1.2. Step 3: interJace cost matrix analysis of system interconnections

The costs of interconnections of the major plant systems can be minimized using the cost penalty matrix clustering analysis. For each plant system a table of the costs of each interface is created according to the procedure described previously, and placed in a symmetric matrix relating the cost of connecting each system to every other one. For the case studied here the cost matrix generated is that shown in Fig. 3. Then a clustered matrix is produced which identifies naturally grouped systems, as shown in Fig. 4. The clustered systems of this matrix having high numerical cost index values are then given priority for adjacent placement in the plant, as a means of reducing the number of the more costly interfaces.

4.1.3. Step 4: defining building regions In this step regions of the building are di-

vided into areas designated for performance of specific tasks associated with the systems within them. First, any major plant components and their mutual interconnections should be established so that other less significant systems can be routed or placed near them. In defining building regions the following criteria are used: (i) systems are segregated according to whether they are safety-related, (ii) safety systems are divided into two redundant safety trains, (iii) areas within a building are defined which can be built in a modular fashion and those which may benefit more from on-site assembly and (iv) safety-related cable runs are confined to

Table 5 Shearon Harris plant system and building assignments

Building System Component types

Reactor Reactor coolant system Accumulator~ building

Safety injection system Accumulator: Residual heat removal Piping Containment spray Piping Main steam Piping

Reactor Safety injection system Equipment auxiliary

Fuel handing

Turbine building

Waste process

Containment spray Equipment Residual heat removal Equipment Chemical and volume Equipment control Boron thermal Equipment regeneration Boron recycle system Equipment Component cooling Equipment water Emergency serive water Equipment Auxiliary feedwater Equipment Main steam Piping Feedwater Piping Demineralized water Piping and make-up

Fuel pool cooling and Equipment cleanup Component cooling Piping water

Steam dump system Equipment

Condensate Equipment Feedwater Equipment Normal service water Piping Extraction steam Equipment Feedwater heater Equipment vents/drains Gland seal steam Equipment system Auxiliary steam Piping Main turbine Equipment Steam generator Equipment blowdown

Waste process Equipment Demineralized water Piping and make-up Auxiliary steam Piping

Control Electical components Equipment building

Note: equipment also indicates piping.

c.w. Lapp, M.W. Golay /"Nuclear Engineering and Design 172 (1997) 327 349 339

safety areas within the building in order to reduce their total length and to meet spatial separation requirements.

The application of this concept is illustrated in Figs. 5 and 6 for the RAB and CB. In order to determine the overall building size an initial esti- mate of space requirements is made using information regarding the number and types of components required for this plant.

Table 6 Shearon Harris power plant systems

Identification System Abbreviation No.

1 Reactor coolant system RCS 2 Safety injection system SIS 3 Residual heat removal RHR 4 Containment spray CS

system 5 Chemical and volume CVCS

control system 6 Boron thermal BTRS

regeneration system 7 Boron recycle system BRS 8 Component cooling CCW

water 9 Emergency service ESW

water 10 Auxiliary feedwater AFW 11 Fuel pool cooling FP and C

and cleaning 12 Main steam MS 13 Steam dump system SD 14 Auxiliary steam AS 15 Feedwater system FW 16 Condensate system COND 17 Feedwater heater FWHV and D

vents and drains 18 Steam generator SGBD

blowdown 19 Main turbine MT 20 Gland seal steam system GSSS 21 Normal service water NSW 22 Demineralized and DM,RWMU

reactor water make-up 23 Waste process system Liquid, solid,

gas 24 Condenser systems 25 Extraction steam ES

4.1.4. Step 5: systems placement The results from the system clustering analysis

and the general area layout reflecting that analysis are presented in Fig. 7, which shows the placement of systems within the RAB and CB. To begin the process systems which are safety-related must be distinguished from the other primary coolant-related systems which are also mutually identified in the clustering analysis. These safety- related systems are: the safety injection system (SIS), component cooling water (CCW), residual heat removal (RHR), emergency service water (ESW), containment spray (CS) and auxiliary feedwater (which is related to the secondary coolant system located in the RAB).

Those systems having high numerical clustering values in the RAB are the RHR, SIS and CCW (cluster no. I in Fig. 4). Another cluster of systems (cluster no. II in Fig. 4) reflects the close relationship between the safety systems, ESW and CCW, as well as the primary coolant-related BRS and CVCS. It is apparent that of the systems mentioned above the CCW, RHR, SIS, and ESW should be closely located. For the non-safety areas which contain primary coolant-related systems the following are considered in the design analysis: chemical and volume control system (CVCS), boron recycle system (BRS) and boron thermal regeneration system (BTRS).

From the system clustering analysis it is apparent that the CVCS interfaces with many systems (both safety and non-safety-related) in the RAB, RCB and WPB. The CVCS placement should take into account these relationships in order to select a location convenient to all of these buildings and systems. As shown in the system clustering results most of the primary systems have numerous interfaces with waste process systems. This result indicates beneficial placement of the CVCS next to the WPB.

4.1.5. Step 6: assigning route ways Allowance is required within the system spaces

for the routing of piping, cable and heating venti- lation and air conditioning (HVAC) ductwork. These route ways should allow piping (and duct/ cable) to have access to all components within the building. Reflecting its dual function, the route

340 C.W. Lapp, M.W. Golay .Nuclear Engineering and Design 172 (1997) 327 349

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

1 96 72 0 33 0 0 36 0 0 0 0 0 0 0 0 0 0 0 0 0 2 7 0 0 96 1 18 27 9 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 72 18 1 0 6 0 0 24 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 27 0 1 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 33 9 6 0 1 10 20 12 32 0 0 0 0 0 0 0 0 0 0 0 0 2 6 0 0

0 0 0 0 10 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 0 0 0 6 0 0 20 0 1 36 0 0 4 0 9 0 0 0 0 0 0 0 0 4 19 0 0

36 0 24 0 12 0 36 1 40 0 40 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 32 0 0 40 1 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 10 0 54 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 4 40 0 0 1 0 0 0 0 0 0 0 0 0 0 5 4 0 0 0 0 0 0 0 0 0 0 0 10 0 1 0 9 0 40 9 40 1 0 0 0 0 18 99 0 0 0 0 0 0 9 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 54 0 9 0 1 6 15 1 0 0 4 0 0 0 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 6 1 60 1 0 3 8 60 0 0 30 54 0 0 0 0 0 0 9 0 0 0 0 40 0 15 60 1 0 0 0 8 0 0 0 66 0 0 0 0 0 0 0 0 0 0 0 0 9 0 1 1 0 1 0 0 0 0 0 1 3 0 0 0 0 0 0 0 0 0 0 0 0 40 0 0 0 0 0 1 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 3 0 0 6 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 12 0 0 0 0 4 8 8 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 60 0 0 0 0 0 1 0 3 0 0 2 0 0 0 2 2 4 2 0 0 5 0 0 0 0 0 0 0 0 0 0 1 0 0 0 7 3 0 0 6 1 19 0 0 0 4 0 2 0 0 0 1 0 0 0 3 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 18 0 6 30 66 3 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 99 0 6 54 0 0 0 0 0 0 0 0 0 1

Fig. 3. Shearon Harris plant systems cost penalty matrix. Note: numbers on vertical and horizontal axis represent systems (see Table 6 for identification).

way must also allow for the access of personnel and equipment for repair and replacement of components. The route ways should have a simple geometry in order to be compatible with the modular concept. Placement of route ways should respect the goals of the Pipe Routing analysis which attempts to minimize the total economic penalties due to the combination of pipe length, bends, crossovers and piping elevation changes. Route ways must also satisfy the requirements of safety system spatial separation in order to ensure safety-related redundancy (i.e., lbr protection of these systems from fires and internal accidents). System area definitions are then refined with the placement of route ways.

A new design reflecting these principles is illustrated in Fig. 8 which shows the initial route ways

that allow access to all regions of the plant for pipe, cable, duct and maintenance personnel. The further division of these spaces into individual function-based cubicles is shown in Fig. 9.

4.1.6. Step 7: analyzing the results o f clustering of the components requirements matrix

The next crucial step in the design process is placement of individual components within system spatial volumes. Cost component attribute penalties are summed for each of the components within the RAB. The determination of the cost penalty rankings of these component attributes was performed reflecting the judgment of the au- thors, staff members of the Stone and Webster Engineering Corporat ion and from the review of a set of PWR general arrangement drawings.

C.W. Lapp, M.W. Golay // Nuclear Engineering and Design 172 (1997) 327-349 341

1 3 2 8 5

23 7

-Q 9 E 11

Z 22

E 13

¢n 18 o3 25

16 21 24 15 12 14 10 20 19 17 6

S y s t e m N u m b e r

4 1 3 2 8 5 23 7 9 11 22 13 18 25 16 21 24 15 12 14 10 20 19 17 6

1 0 0 0 1 7~ 0 72

---6 0

2 7 ~ 0 0@0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 96 36 33@7 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 18 24 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

96 18 1 o 9 a 6 @ 0 0 0 ® 0 0 0 0 0 0 0 0 0 0 0 0 0 0 36 24 0 1 1 2 0 36 40140]®2-- 0 0 0 0 0 0 0 0 0 0 0 0 0 0

/

33 6 9 12 1 6 [201321fi30 2 0 0 0 0 0 0 0 0 0 0 0 0 0 10 0 7 0 3 0 6 11 9 0 4 0 2 0 0 0 3 0 0 0 0 0 0 0 1 1

I 1 0 4 4 0 0 0 6 36 20 19 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 ]400~_~_J 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 2 0 0 0 4 0 0 0 1 4 0 1 0 4 4 0 1 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 2 2 0 4 0 5 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 2 9 0 0 0 1 0 0 0 0 0 0 c . _ ~ O ( ~ O 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 I 0 0 0 0 ,0~1401~0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 541991 6 , ~ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0166 601401151-0'' ~°J 8 0 0 0

I

0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 1 0 601 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 ~ i 1 3 0 1 1 8 6 0 0 1 3 0 ' [ 9 1 1 - ~ 4 0 0 0 0 0 0 0 0 0 0 0 0 0 ]54 60 30 1 0 ~ 3 1 0 0 0 0 0 0 0 0 0 0 0 0 0 ]40 99 18 o 119 lOl-O 1 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 6 6 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 110 5 4 l i 0 0 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 8 0 0 8 0 4 0 I 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 6 0 0 0 1 3@)1 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 3 1 9 1 0 0 0 1 0 0 0 0 0 0 10 1 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 1

Cluster Matina Systems and Identifvina Number

I SIS and (CS, RCS, RHR) (RCS and RHR) and (SIS, CCW and CVCS)

II BRS and (CCW, CVCS and WPS) (BRS and ESW) and (CCW and CVCS) CVCS and (BRS, ESW and (FPC & P))

III COND and (Condenser, FW, MS and AS) FW and (ES, COND, NSW and COND) MS and (SGBD, ES and COND)

IV (AS and AFW) and (AS and MS)

Fig. 4. Shearon Harris plant systems cost penalty matrix clustering results circled Roman numerals denote system clusters circled arabic numerals denote system sub-clusters. LL = 25, MAXME = 112370.

A component cost penalty matrix for this case was formulated to relate components with cost weighted component attributes. These attributes

correspond to safety class, maintenance requirements and other pertinent considerations. The value of a particular cost matrix element (at loca

342 C.W. Lapp, M.W. Golay / Nuclear Engineering and Design 172 (1997) 327 349

Fuel Handling Building I I

~ / ~ Switch GearA P

W B m a a Cable a s t r t t Spread Y e e

r Room A p y r r e o a c Switch Gear B

e s s

Switch Gear NNS

O t h e r and Primary Area Battery NNS

I Control Building

Turbine Building I ~ 80f t .

2 0 0 ft. I Fig. 5. Modular Shearon Harris power plant level 1 building areas (elevation 190 ft.).

tion i , j) reflects the relative cost weight, as evaluated by a designer, of the j-th component due to the i-th attribute of that component. The results of the component clustering analysis are used to determine component locations in attempting to reduce costs associated with their most important attributes. For brevity this analysis is not shown here (Lapp, 1995). The component clustering analysis has identified three major groupings of

Fuel Handling Building

RHB CS A SIS C C W ~ A CVCS

CCW B BTRS

Electd~%oE~i p . . . . AFW BRS

I TurbineBu,0,ng I I 200 $1 t

w a s t

2 e P r

ft.

Fig. 7. Modular Shearon Harris power plant level 2 system placement (elevation 216 ft.).

components, which correspond to the elevation at which different components are placed. The groupings shown occur because requirements to avoid piping elevation changes are assigned the greatest cost penalty rankings.

4.1.7. Step 8: d@'ning modular boundaries An important step in the design process is

defining the modular boundaries within the plant.

i Fuel Handling Building

Ele~,,&a, Aro,, l ~ ~ ~rea Pr [

i w Control Room m

and a r Computer Y 0 2

Area A 0 r e ft a o

Electdcal Area e B Safety s s

Etect dcal Area NNS Other and Pdmary Area

Control Building I Turbine Building

F - °o.. i 2ooft

Fig. 6. Modular Shearon Harris power plant level 2 building areas (elevation 216 ft.).


Switch GearA

B a Cable t t Spread e r Room Y

Switch Gear B

Switch GearNNS Baflery NNS

Control Building

I ~ 8 0 f t .

UlIIII

A 8

C

W R

B S

r•j Elect nc & AFW BRS BTBS Equipment

Turbine Building I 200 ft. I

I i -

[ l l l l l l

Fig. 8. Modular Shearon Harris power plant level 2 route way placement.

C.W. Lapp, M.W. Golay / Nuclear Engineering and Design 172 (1997) 327-349 343

i Fuel Handling Building

Switch Gear Room-A cc I~ ~al,~,

3artery C Cable ~) C W Room a Roorr

A b A - - Cntrl. I e Cable Room R Ro~m - - 2 e

Switoh Ge, r , ~ ~ o

, ~ . . s s

Switch Gear BR~ttep h Equip Elec. Roo Roe

, [ ] ®

Control Building I Turbine Building I

I ~ 8oit. ] 2o0 , .

Fig. 9. Modular Shearon Harris power plant level 2 component placement. (1) emer. service water booster pump A, (2) component cooling water pump A, (3) component cooling water HX-A, (4) residual heat removal HX-A, (5) containment spray additive tank, (6) component cooling water pump B, (7) component cooling water HX-B, (8) emer. service water booster pump B, (9) residual heat removal HX-B, (10) fire protection water pump, (11) motor driven AFW pump-A, (12) motor driven AFW pump-B, (13) turbine driven AFW pump- SAB, (14) boron recycle evaporator, (15) BTRS chiller pump, (16) BTRS chiller unit, (17) BTRS letdown reheat HX, (18) BTRS modering HX, (19) BTRS letdown chiller HX, (20) gross failed fuel detector, (21) SIS boron injection tank, (22) CVCS seal water HX, (23) CVCS letdown HX.

The basic cr i ter ia for design used in this process are the fol lowing: (i) the m o d u l e geomet ry should be simple, (ii) the n u m b e r o f different modu le geometr ic styles should be kep t small , (iii) modu le sizes o f a pa r t i cu l a r geomet r ic style should be changed in un i fo rm increments , (iv) m o d u l a r spaces wi th in the p lan t should be geomet r ica l ly in te rchangeab le in o rde r to a l low design flexibil i ty and (v) the to ta l n u m b e r o f modu les should be kep t small .

I m p o r t a n t m o d u l a r cons t ra in t s include: size, which should not be so large as to impose difficulties in hand l ing and p lacement in the plant ; and weight, which should be low enough for ease o f lifting. The ini t ial modu le bounda r i e s for the example design are shown in Fig. 10 a long with each m o d u l e ' s ident i f ica t ion number .

4,1.8. Step 9: applying the pipe routing cost index in design refinement

In the work r epor t ed here a P R I analysis has been pe r fo rmed only for the R A B since the CB conta ins lit t le p ip ing o f significance. This cost pena l ty index is used for c o m p a r i s o n o f designs, and to indicate whether m o d u l a r i z a t i o n can be expected to yield large capi ta l cost savings. The resul t ing value o f the P R I for the new (modu la r ) design is 2773 as c o m p a r e d to the or ig inal design value o f 5901. Thus, the new design is ind ica ted to more economica l to bui ld.

4.1.9. Step 10: using the measure o f modularity in design refinement

In o rde r to test whether the M O M reflects the increased m o d u l a r i t y o f the new design the sum, for bo th designs, o f the M B I I over all systems gives the final value o f the M O M . Resul ts o f the


I ...,e

~Req ~ v RoAom a Room i

Penetrat=on Penetration 3( e able 3~ n oorn ~

R Calves

o NNS ~ ] m : ~

ROO~)B talves

has AFW ~ cm Switch r Batten

Control Building I Turbine Building

m

, o . . I 2ooit.

Y 2 e

Op r

It. o

Fig. 10. Modular Shearon Harris power plant level 2 module boundaries. (A) emer. service water booster pump A, (B) component cooling water pump A, (C) component cooling water HX-A, (D) residual heat removal HX-A, (E) containment spray additive tank, (F) component cooling water pump B, (G) component cooling water HX-B, (H) emer. service water booster pump B, (I) residual heat removal HX-B, (J) fire protection water pump, (K) motor driven AFW pump-A, (L) motor driven AFW pump-B, (M) turbine driven AFW pump- SAB, (N) boron recycle evaporator, (O) BTRS chiller pump, (P) BTRS chiller unit, (Q) BTRS letdown reheat HX, (R) BTRS modering HX, (S) BTRS letdown Chiller HX, (T) gross failed fuel detector, (U) SIS boron injection tank, (V) CVCS seal water HX, (W) CVCS letdown HX. MOM, total of all system, MBIIs = 1180.

344 C.W. Lapp, M.W. Golay . Nuclear Engineering and Design 172 (1997)327 349

Table 7 Modular Shearon Harris plant system modular boundary interface index values and measure of modularity

System No. of MBII Interfaces

I. Component Cooling 43 246 Water

2. Chemical and Volume Control Letdown and Charging 21 78 BTRS 5 10 BRS 4 14 PMS/BA 7 IN Total CVCS 37 120

4.1.11. Step 12: refining the design using the design quality index

The initial design has now been evaluated in terms of its respective values of MOM, MAV and PRI penalty. These are some of the components needed to calculate the value of the DQI. This quantity is used in evaluating design alternatives after the initial conceptual design has been completed.

5. Application of group technology to nuclear plant construction

3. Residual Heat Removal 14 207 4. Containment Spray 12 122 5. Safety Injection

High Pressure 15 96 Low Pressure 5 100 Total SIS 20 196

6. Auxiliary Feedwater 7 51 7. Emergency Service Water 29 220 8. Steam Generator 9 18

Blowdown Totals for all systems 171 (MOM)1180

MOM, total of all System; MBIIs = 1180.

system MBII values are presented in Table 7. They show that the value of MOM for the Modu- lar Shearon Harris Plant design to be 1180, as compared to a value of 2112 for the original Shearon Harris Plant design. This lower value reflects a better functional grouping of components in the new design.

4.1.10. Step 11: cak'ulating the value oJ'module alignment index Jor a new design

With the module boundaries defined in the initial plant design the value of the MAI is calculated to be 2895. As the original design is not structurally modular the concept of the MAI is moot, and a value is not calculated. However, the MAI can be used for comparison of alternative modular designs.

It is important to advance techniques for the fabrication of modules in order to complete the modular design and construction process described here. The modules of a power plant contain mostly machinery, pipes, cable and ducting. Another industry having similar fabrication concerns is that of shipbuilding. One of the more advanced forms of ship construction utilizes the methods of group technology (Product Work Breakdown Structure, 1982) and PWBS.

Basically group technology is a method of applying mass production techniques in the assembly of a variety of items in varying quantities. This approach permits a more efficient assembly process while also allowing flexibility in production. The techniques of group technology which permit efficient fabrication are the lbllowing: (i) plant site labor requirements are reduced by moving construction work off-site to a module factory, allowing a controllable work environment, resulting in improved worker morale, reduced em- ployee turnover and better process control in factory manufacturing lanes, (ii) work product quality is improved, through application of factory-based quality control techniques such as Deming Quality Circle concepts (Hashimoto, 1988), easier material control and achievement of greater fabrication precision, (iii) cost reduction and assembly time savings are achieved due to reduced rework and greater pretesting prior to delivery and (iv) work scheduling is improved due to use of a more controlled production process which imcorporates feedback from production to design.

C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327 349 345

5.1. Basic elements of product work breakdown structure

The main advantage of group technology is that most of the detailed plant construction work (i.e., outfitting of components) is accomplished on the module before it is assembled and installed on-site. This technique allows workers to have better access in order to install equipment than if they were in the congested confines of a ship or power plant. As an example, overhead work or work at an elevation, can be accomplished 'hands- down' (working with the module inverted on the assembly line). The module assembly lanes are more efficient than is conventional fabrication because of PWBS. PWBS logically separates the fabrication of products according to their common attributes.

The PWBS technique divides the work involved in the production of an item by grouping common characteristics of tasks according to material or manufacturing attributes. These material attributes could be similar component types, shapes or sizes while manufacturing attributes could be similar assembly methods (e.g., welding or bolting). The basic premise of PWBS lies in the division of fabrication according to the successive categories of system/zone/area/stage (Seubert, 1988). This division is accomplished by answering what/where/how/when in describing the assembly work.

5.1.1. Fundamentals of P WBS: defining the work package

The basic element of this fabrication process use work packages as elements for work, material division, and assignment in controlling the flow of a product from initial fabrication to final assembly. Work packages also monitor progress and cost. PWBS defines work packages into three areas (Seubert, 1988). First, it divides the assembly process into specific tasks. Second, it classifies PWBS in terms of its intermediate products, based upon the resources needed for their production (i.e., material and manpower). Third, it classifies a work package according to its four product aspects, system (item), zone (location), area (work type) or stage (sequence) (Product

Work Breakdown Structure, 1982). This process can also be applied to power plant

construction by analyzing the different types of work involved in its fabrication. First, prepara- tion of site civil works would be separated from the fabrication of modules. Then the construction of modules can be divided into structural assembly, component installation, and outfitting assembly stages. Each of these work stages then again can be subdivided into fabrication and assembly sub-stages. The result is a division of work as follows: (a) site works construction, consisting of fabrication of reinforcing bar and plate steel, assembly of concrete and installation of modules and (b) module construction, consisting of structural steel assembly and installation of components.

The PWBS has a dual nature in that it catego- rizes work packages in terms of product aspects; and cost classifications in terms of product resources. This means that material costs can be estimated on a system basis while construction personnel are allocated on a zone/area/stage basis. The PWBS organizes work by classes of problems for the final integration of parts into modules according to a parts zone identification. Construc- tion trade workers are not segregated according to a particular product (i.e., piping), but rather according to any work requiring a common tool or skill. Teams of workers are formed to produce intermediate products for each product class, with the result of less work force specialization. Reduc- ing work specialization enhances the flexibility of the construction process.

5.2. Application of PWBS to modular nuclear construction

The application of the PWBS process to nuclear construction is relatively straightforward. It is important to have a finished modular design before construction begins so that all material and design requirements are known. This information is then used to develop a process flow path utilizing PWBS for fabricating the power plant modules. The process flow path is similar to that used for ship construction except for some added features which must be taken into account as follows


(Seubert, 1988): (i) requirements for added inspection and testing in construction, (ii) use of safety- related equipment in the plant, (iii) use of radioactive components which require shielding and (iv) requirements for designs to accommodate the structural and support loads of postulated accidents, (v) requirements, in construction, for handling of very large, heavy components (i.e., steam generator, reactor vessel).

The following goals should be met by the production outfitting planners in order to achieve a more efficient prefabrication process (Seubert, 1988): (i) maximize pre-outfitting of the module with components of systems within the module zones at the assembly stage, (ii) maximize assembly of components within the module zones, (iii) minimize at-site outfitting within the power plant itself, (iv) invert modules and assemblies requiring fittings or structural steel support to be mounted on ceilings or in elevated regions to positions that are easier to reach and (v) transfer work environ- ments from closed, narrow unsafe locations to open, safe conditions.

5.2.1. Total component process work lanes The use of production lanes is illustrated in Fig.

11, showing the successive positions of a module as it is built and outfitted, and how various stages of work relate to module fabrication. The lower portion of this diagram represents the component work lanes. Note that some flow path lines pass around the different process steps. In this figure the sequence of manufacturing flows from left to

T 6 0

o

f t

[ Structural Shops

I

Module Assembly and Outfit Shops

I I Component Shops k

I-" 150 ft. -q I 300 ft.

FttB IWPB

".( .llll

I 300 ft.

Fig. 11. Module factory process work flow lanes for modular nuclear construction.

right as parts are assembled into successively larger units. Some of the production from one work lane may enter other lanes at different points in the process. This fact reflects the interde- pendency of the production process. The products from these component lanes are incorporated with the products of the structural fabrication lane in the integration phase in order to produce a complete module.

5.2.2. Relating process flow lanes to design In designing a facility for production of the

power plant modules the following manufacturing design goals should be considered (Breteton, 1988): (i) personnel and machine utilization must be kept high, (ii) process flexibility must be re- tained and (iii) material flow and varieties of available handling equipment must be kept high.

Another goal for a hypothetical on-site factory is the utilization of existing on-site buildings for module fabrication. Dual building use is one way of reducing the initial capital investment of the project. An example of such dual utilization is the outfitting of a warehouse, required for subsequent plant operations, as a factory facility during the construction phase. Such operational facilities can be built at the project's inception so as to maximize their use for modular fabrication.

5.3. Construction cost implications

In order to illustrate the potential monetary savings from modular construction, a sensitivity analysis was performed over a range of construction schedules and interest rates. Modular construction schedules for three different cases are estimated, respectively to be 80, 70 and 60% of the conventional construction schedule. The assumed conventional construction schedule for this analysis is 6 years (less than the most recent US schedules of 10 years). The interest rates applied to the different construction schedules were 6, 10 and 14%. The assumed cost for all materials, labor and engineering is $2 billion. The potential savings from modular construction for these different cases ranged from 6.7 to 26.7%. As a median case, the 10% interest rate and modular construction schedule that is 70% of the conven-

C.W. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327-349 3 4 7

tional schedule would lead to a potential savings of 15.8% on this project. If this analysis were compared to a 10-year construction schedule, the potential savings of the median case would be on the order of 25%. A savings of 15.8% on this hypothetical project represents a monetary savings of approximately $500 million.

6. Design of an on-site module factory

6.1. Relating the process flow path to the factory layout

The main object of a factory designer is to enhance the efficiency of the production process. One of the primary requirements for an efficient factory design is to minimize the material handling required between work lanes. Location of production work lanes is based on the amount of interaction and the amount of material to be transferred between product lanes. Most of the needed information can be obtained from the simplified process flow path diagram previously developed (Fig. 11). The flow path shows where the products go in the process path and in what sequence. However, the flow path does not indicate the amount and distance of material movement. The goal of material handling is to minimize the cost of moving material within the fabrication facility. The cost of material handling can be related by the following equation (Brete- ton, 1988):

C . . . . = ~ Ci x Di x F,., (16) i = 1

where, Np, is the number of parts to be moved; C~, the cost of a move per unit distance; Di, the distance which a part moves; Fg, the frequency of moves.

The objective of the process design is to minimize the costs of movement. The required analysis is that of the quadratic assignment problem (QAP) in which the cost of movement is minimized. However, this problem could also be solved by utilizing the matrix clustering technique. Since the goal of the initial facility layout is to group work lanes which have strong interactions

the problem is analogous to that of grouping of power plant systems having many interconnections. However, the method of solution must take into account not only the number of interactions, but also the distance and amount of material moved. After an initial design has been developed it can be refined until an optimal design is found.

In the example presented here, the clustering analysis was performed utilizing a cost per unit distance, since the total distances involved in the factory are not yet known. The value of Ci is determined by the following:

C~ = M i x F, x/~, (17)

where, M~, is the mass of material to be moved, product (i); F~, the frequency of material to be moved, product (i); and Ii, the factory interactions within various work lanes, lane (i).

The relative costs of moving all of the materials listed in the process flow chart have been evaluated. The value of Ci gives a measure of the relative cost of handling material of type (i). It is assumed that the such costs increase with an object's weight and frequency of movement. The relative scales that are used for assignment of values to mass (M) at frequency (F) are from 1 (low) to 5 (high), with I being equal to either 0 or 1.

6.1.1. Definition of factory work lanes-arrangement of buildings and shops

An initial arrangement of component work lanes and shops was determined using the results from the material cost penalty matrix analysis. Information regarding the relative sizes and production lane location were incorporated from shipyard fabrication experience (Lardy, 1988) and nuclear plant construction sites (Nuclear Regula- tory Commission, 1983). The results show two basic groupings for component lanes, according to the piping or electrical categories. For this region of the factory several buildings are required, as shown in Fig. 12.

6.1.2. Initial building and flow lane positioning The buildings of interest in designing the site

module fabrication facility are the following: (a) warehouses, for receiving incoming material and

348 C.W. Lapp, M.W. Golay /Nuclear Engineering amt Design 172 (1997) 327 349

Plate Steel Shop - - 2oo, . I l o o , . - t

_. 1_ llo,+++,

StructuraISide StructuraIshop Steel [ [ J ~/ p She~o~etal '

+! a w 7 + +mi'Y MT'+ °u"' T ' o ~ s o , i Ar,a i i Are, [ 0 o ft. u

e Sort Sort Module Assembly/Outfit Facility

COmsiP'nent ~ . ~ ~ /~ ~

13 12 10 15 Insul

+1 T°°++r !1 ++ F-lOO.. I too~. I 12s~.--tsoft.

130 ft. - - Work Lanes 1 Work Lanes 2 550 ft.

Fig. 12. Detailed factory work lane arrangement (9) electrical unit lane, (10) heat exchanger unit lane, (11) panel unit lane, (12) filter unit lane, (13) valve unit lane, (15) vessel unit lane, (16) machine unit lane.

components, (b) a structural fabrication facility, for cutting and assembly of the material required for satisfaction of structural concerns, (c) a component assembly facility, for outfitting component skids and palletizing parts, (d) an outfit and integration facility, for combining components/structural items in order to produce modules, (e) a blast and paint facility, for surface preparat ion of structural items and (f) shops, for piping, ducting, etc., which are then supplied to the work lanes.

In addition to these buildings support facilities such as supply shops, administrative quarters and outside lay-down areas for material storage are also built on-site. Whenever possible, existing site structures should be utilized for construction facilities. Initial building placements are then determined by the material flow interactions between them.

6.1.3. Module assembly and outfit Jacility The module assembly and outfitting building is

where the items from the structural and compo-

nent lanes merge to become power plant modules. Since a great deal of work is performed in this facility it should have abundant space for workers to outfit and assemble modules. The module assembly facility is centrally located in order to receive material from all site work lanes and shops. The size of this facility should accommodate at least four of the largest modules for simultaneous fabrication and outfitting.

7. C o n c l u s i o n s

This paper illustrates how modular design and construction techniques could be used to reduce the capital cost of nuclear power plants. Several new relative cost measures and concepts (i.e., MOM, PRP1, etc.) are introduced in our work to quantify factors to be considered in reaching an optimal modular design, and to make the design process more systematic. These design indices indicate a relative merit between different power plant designs, which is related to the cost of the power plant.

In the example cited here the value for the MOM between the original Shearon Harris facility design and the Modular Shearon Harris facility design decreased by about 45%. Other components of the DQI (MAI, PRPI, CVI) also show reductions ranging from 30 to 46%. This indicates a potential savings in using modular design techniques. The potential savings resulted both from improved design for easier construction and reduced material requirements.

It is assumed, in this economic analysis, that the total number of tasks involved in building the power plant with either method is approximately the same, but that labor productivity is higher in the modular case. This assumption of improved productivity is based on the fact that factory work is usually more efficient than field work. A range of modular construction schedules (60-80% of a conventional 6 year schedule) were analyzed using a range of real interest rates (6 14%). It should be noted that using a more typical 10 year construction schedule (for the USA) results in a greater cost advantage for modular construction. For the median case analyzed here (70"/,, of the nominal

c.w. Lapp, M.W. Golay /Nuclear Engineering and Design 172 (1997) 327-349 349

schedule and 10% interest) the potential construction cost savings was about 15%. The following conclusions can be made f rom the work reported here: (i) a potential for substantial cost savings exists using modula r design and construct ion, and (ii) a systematic method for creating effective modu la r designs exists, which has been demonstra ted.

The application o f this me thodo logy to nuclear power plants is impor tant if the next generat ion o f reactor designs are to be economical ly competit ive with other fuel sources. An increased market for nuclear power may result if the methods described here can be implemented economically. This modular design method is applicable to any reactor type that might be built. Some plants (i.e., large LWRs) would benefit f rom the design and construct ion phases while others would benefit more f rom the fabricat ion process (i.e., the factory-buil t modula r gas-cooled reactor). Most o f the concepts developed here could be implemented with existing C A D programs that contain power plant design information. A detailed design analysis could be efficiently formulated using these computer applications.

It is impor tan t that the capital costs o f nuclear power plants be reduced while also maintaining a high quality o f work. For this modula r design process to be effective in achieving such cost reductions, various nuclear power industry organi- zations must col laborate and decide on a agenda for enhancing the envi ronment o f nuclear plant design and construction. These organizat ions include the architect engineers, regulators, builders, reactor manufacturers , electric utilities and other govern- ment agencies. Work ing together these interested parties could p romote the modula r process as a means to achieve the aims described above.

References

Borcherding, J.D., Sebastian, S.J., Samelson, N.M., 1980. Improving Motivation and Productivity on Large Projects, J. Constr. Division, March 1980.

Breteton, M.F., 1988. A Logic Based Approach to Factory Design, SM Thesis, Technology and Policy Program, M.I.T., May 1988.

Hashimoto, F.Y., 1988. Improving Productivity in Construc- tion through QC and IE, Class Notes 1.421, Productivity and Competitiveness in Construction, Civil Engineering Deptartment, M.I.T., Fall 1988.

Lapp, C., 1995. A Methodology for Modular Nuclear Power Plant Design and Construction, Thesis Project Report., Department of Nuclear Engineering, M.I.T., MIT-ANP- TR-038, October 1995.

Lardy, S., 1988. Personal communication, Bath Iron Works, Shipyard Layout and Design Drawings, February 2, 1988.

McCormick Jr., W.T., Deutsch, S.B., Martin, J.J., Schweitzer, P.J., 1969. Identification of Data Structures and Relation- ships by Matrix Reordering Techniques, Research Paper P-512, Institute for Analyses, December 1969.

McCormick Jr., W.T., Schweitzer, P.J., White, T.W. 1972. Problem Decomposition and Data Reorganization by a Clustering Technique, Operations Research, Vol. 20, No. 5, September 1972.

Nuclear Regulatory Commission, Shearon Harris Nuclear Power Plant Final Safety Report, Carolina Power and Light Co., Vol. 1, 1983.

Product Work Breakdown Structure, National Shipbuilding Research Program, US Department of Transportation, Maritime Administration, December 1982.

Seubert, T.W., 1988. Modular Shipbuilding and its Relevance to Construction of Nuclear Power Plants, SM Thesis, Department of Nuclear Engineering, M.I.T., May 1988.

Sherman, A.T., 1986. Cryptology and VLSI; A Two Part Dissertation, Ph.D. Thesis, Deptartment of Computer Sci- ence., M.I.T., October 1986.

Tatum, C.B., Vanegas, J,A., Williams, J.M., 1986. Con- structability Improvements Using Prefabrication, Pre- assembly and Modularization, Construction Industry Institute Technical Report, November 1986.

Documents

Modular design and construction techniques for nuclear