1 Presentation L.Kupca Podolsk May 2007 AGEING MANAGEMENT OF SAFETY RELATED COMPONENTS OF WWER-440 UNITS OPERATED IN SLOVAK REPUBLIC The 5-th International

1 Presentation L.Kupca Podolsk May 2007

AGEING MANAGEMENT OF SAFETY AGEING MANAGEMENT OF SAFETY RELATED COMPONENTS OF WWER-440 RELATED COMPONENTS OF WWER-440

UNITS OPERATED IN SLOVAK REPUBLICUNITS OPERATED IN SLOVAK REPUBLIC

The 5The 5--th International Conferenceth International Conference “ “Safety Assurance of NPP with WWER”Safety Assurance of NPP with WWER”

FSUE OKB “GIDROPRESS”, Podolsk, RussiaFSUE OKB “GIDROPRESS”, Podolsk, Russia

29 May-1 June, 200729 May-1 June, 2007


Introduction

• During the NPP`s operation occurs a gradual degradation of structural materials properties.

• Trends of material problems monitoring on the operated NPP`s VVER-440 are to the growing of requirements for knowledge of its degradation properties.

• Strict requirements for safety of NPP`s operation, need clear define the critical parts and its continuous monitoring.

• For the ageing management and lifetime optimization, is necessary to monitor these processes in advance, which enables the evaluation of exposed surveillance specimen in real operational conditions.

• The most of the degradation mechanisms are monitored by special projects, but a lot of other degradation mechanisms, are not monitored.

• For the monitoring all degradation mechanisms on safety operation of NPP, was prepared and realized the special research project (R&D):

„ Ageing management and life-time optimization of NPP`s WWER-440“ during the years from 2002 to 2005.


The main goals of R&D project:

Identify the ageing mechanisms of the safety related components.

Development of the database for the rest of life-time evaluation.

Extension of the operated monitoring systems for important degradation mechanisms.

Development of the ageing management program for minimizing the degradation of the safety related components.

Development of the software tools which have implemented the ageing processes.

Development of the software for the technical and economical evaluation of the NPP components repair and replacement management from the life-time prolongation point of view.


„Research and analysis of ageing mechanisms“ Task 01:

„The ageing management programs“ Task 02:

„The research of the sophisticated systems for the degradation processes monitoring“

Task 03:

„The legislation for the ageing management program“Task 04:

Task 05:

Task 06:

Task 07:

„The database for the ageing management program “

„The efficiency of the NPP units life-time prolongation “

„The legislation limits for the re-commissioning of NPP units after planned life-time“

Task 08: „Coordination and management of R&D project“

Project was divided to the eight tasks:Project was divided to the eight tasks:


Task E 01: Research and analysis of the ageing mechanisms

Milestones:

Design of the degradation processes database for safety related components and systems during the ageing process.

To set the predominant degradation processes and critical parts from the ageing point of view.


Task E 02:

The ageing management programmes

Milestones:

• To prepare the methodology and tools for safety related components of the rest of life-time evaluation.

• Optimization of the input data of the specific components.


Task E 03:

Milestones: • Analysis of the operated monitoring systems. • Implementation of the newest information's for ageing monitoring

systems.

The research of the sophisticated systems for the

degradation processes monitoring


Task E 04The legislation base for the ageing management program

Milestones: The preparation of the programmes set for the ageing processes mitigation. The preparation of specific programmes with the aim of the NPP units life-time prolongation.


Task E 05The database for the ageing management program

Milestones: Specification of the input and output data and criterions.

• The extension of the used databases for the life-time of the safety related components evaluation.


Task E 06The efficiency of the NPP units life-time prolongation

Milestone: Development of the technical and economical tools for the ageing

management.


Task E 07The legislation limits for the re-commissioning of NPP units after planned life-time

Milestone: The development of the validated methods and software with the

implementation of the ageing processes by standard and critical operational regimes.


Present status of irradiation damage monitoring of RPV`s VVER‑440 type structural materials

Still don’t exist suitable theoretical model for reliable forecasting of the various RPV`s material properties changes during its operation.

The main reason is fact that on the irradiation damage of RPV`s steels influenced many individual factors like: irradiation temperature, fast neutrons fluence and flux density, energetic spectrum of neutrons, chemical composition of RPV`s steels, microstructure of steels after final heat treatment, inhomogeneous properties through the RPV wall, operational history of individual RPV`s etc.


This is main reason, for implementation on the power reactors “surveillance specimen programs”(SSP), which enable continuous evaluation of material parameters with aim to ensure the nuclear safety.

In the present time, on the Slovak NPP units, there were (are) realized four types of surveillance programs:

In Jaslovské Bohunice V-2 NPP (Units 3 and 4) was finished the „Standard Surveillance Specimen Program “(SSSP),

„Extended Surveillance Specimen Program“ (ESSP), was prepared with aim to validate the SSSP results, is in its final stages now,

For the Mochovce NPP Units 1 and 2, is running completely new surveillance program “Modern Surveillance Specimen Program” (MSSP),

For the Bohunice V-1 NPP was realized “New Surveillance Specimen Program” (NSSP) coordinated by IAEA. This program was finished at the end of 2004.


Critical analysis of realized SSP

During the analyses of experimental results from finished programs (SSSP, NSSP) and still running programs (ESSP, MSSP) in the Slovak NPP`s, there were asses several aspects:

1. Methodical:Associated with the creating period, and that time concepts and possibilities of irradiation embrittlement of RPV`s monitoring.

2. Design:The irradiation capsule placement on the core barrel what markedly influenced these factors: dimensions of irradiation capsules, high lead factors of its irradiation, dimensions of tested samples, irradiation capsules placement along the core axis, differences of the irradiation conditions for individual sets of samples.


3. Material: Associated with the lack of convenient recognized reference material. The austenitic RPV`s cladding was not involved to the irradiation

monitoring program. The technical possibilities for the monitoring of structurally narrow

zones of RPV`s as HAZ, which represents the most sensitive parts off all weld joints.

4. Legislation: Associated with the requirements of our and Russian regulatory in that

time and by the international standards and recommendations of IAEA as well.

Originally shorter projected NPP`s lifetime, whereby actual world trend is aimed to the long-term operation of NPP`s over the planned values, till 60 years.


Advanced surveillance specimen program (ASSP)

Main goal of the prepared ASSP is continuous monitoring of the irradiation RPV material degradation, but not for BM and WM only but for the HAZ and austenitic cladding material properties evaluation too.

The project ASSP is based on:

main requirement – RPV material mechanical properties changes have to be monitoring during the all RPV lifetime,

results from critical analysis of the SSSP for the reactor type V 213,

concept of the realized project ESSP in NPP EBO,

know-how obtained during the realization of several project (e.g. ESSP, MSSP, NSSP).


The main goals of the ASSP are following:

• mechanical tests on the un-irradiated samples,• new methods application with the better description of the material properties,• evaluation of the RPV material thermal ageing above the active zone in the reactor.

Base methods for evaluation of the mechanical property changes due to irradiation will be following:

• Charpy testing (KCV),• static fracture toughness testing (COD),• Small Punch Test (SPT) on specimens Φ 8 x 0,5 mm - to test the HAZ properties.


Irradiation temperature measurement

In ASSP will be used three methods of irradiation temperature measurement: melting monitors (all irradiation capsules), thermocouples (one chain of ASSP capsules), combination (capsule with melting monitors and thermocouples). Application of thermocouples measurement method is rather complicated and expensive for power reactors, but has best accuracy. Melting monitors are not so precise, but widely used because of its simplicity. In ASSP will be used melting monitors for temperature range: 290-305°C.


Neutron fluence monitoring

Improved ASSP neutron dosimetry is based on:

new sets of activation foils and wires for each irradiation capsule,

improved symmetry of monitors inserted in irradiation capsules,

fixed orientation of irradiation capsules to the reactor core,

neutron fluence monitoring opposite the irradiation chains on the outside surface of RPV.


The design of irradiation chains for ASSP

Verified design of irradiation chain will be basically used for ASSP because of following advantages:

results of ESSP, MSSP and ASSP will be compared, uniform placement of capsules along the reactor core (lead factor), fixed orientation of irradiation capsules to the core center, complete set of specimens in irradiation capsule for one transition

temperature curve, samples from HAZ will be placed opposite the weld No.4 .

Design of ASSP includes 12 chains, for every unit, i.e. 6 sets with 2 chains. The exposition time will be 1, 2, 3, 5, 7 and 10 campaigns. The scheme of one chain set is illustrated on the figure 1.


Scheme of the ASSP one chain set

Scheme of the instrumented chain


The thermal ageing processes monitoring

• The thermal embrittlement is one of the most important degradation mechanisms.

• The leading roles in this type of degradation have the impurities, originated during the manufacture of NPP`s great components.

• The temperature ageing is not monitored during the operation of Slovak NPP`s units until now.

• Monitoring of temperature ageing for the RPV`s materials including its internal structures is essential from the planned prolongation of NPP`s lifetime point of view and of course with respect of its reliable and safe operation.

• It is still more discussed issue for continuous monitoring of all degradation mechanisms during the all-operational life-time as it is recommended by IAEA too.


The project proposal for monitoring of NPP`s structural materials thermal ageing

The proposal of project for monitoring of the NPP`s V-2 EBO and EMO12 thermal ageing was solved in R&D program: „Ageing management and lifetime optimization for the NPP`s units VVER-440 type”. Similar system is planned for the units EMO34.

The main arguments for the project implementation are following:

to gain the arguments of NPP`s lifetime prolongation for the 20 years, evaluation of RPV`s materials properties according to the planned up-

rate of the units power output, to avoid the cutting parts of primary circuit loops after 200 000

operation hours in NPP`s.


For the thermal ageing monitoring system proposal were settled following technical requirements:

The possibility to monitor the long-term thermal loads on the nominal reactor power level.

The possibility of the long-term monitoring and archiving the thermal loads during the very long time of experiment.

After detailed analyses was for the realization proposed the outer surface of primary circuit hot leg.


The arguments for this selection are following:

For the MCP Ø 500 mm was prepared and proven the technology for fixing the thermocouples for the surface of primary circuit temperature measurement.

These measurements were on the Mochovce unit 1 realized till now.

The design of supporting structure is possible to use for the surveillance specimen fixing to the primary circuit surface too.

The temperature differences of primary surface piping and primary coolant measured by special temperature gauge from Control System of Reactor Temperature Measurement (CSRTM) is less than 1°C.

Using the CSRTM enables reliable archiving of the data during the long-time exposure.


The ring with surveillance samples for the temperature ageing monitoring system

The design of supporting ring


The main advantages for system of thermal ageing on the primary circuit are following:

zero induced activity of exposed samples, which enables the evaluation without hot cells utilization,

significantly lower price of designed system according to the other monitoring possibilities,

simplified access by placement, removing and changing of individual exposed samples sets,

practically identical exposition parameters during the units operation, the possibility to evaluate all materials of safety related primary circuit

components.


In capsules will be one complete set of materials with proposed exposition time 5, 10, 15, 20 and 25 years, and the individual exposition time will be possible to change according to the demands of operator and the current results of monitoring.

Innovation according to the old design of RPV`s materials monitoring proposal is the exposition of compact part from RPV`s reference materials, it means the block from RPV`s including base metal, weld metal and austenitic cladding.


This approach enables comparing with the exposition of prepared testing samples following:

the evaluation of RPV`s materials parameters as compact block it means all transient ranges raised due to the RPV`s welding procedures,

the implementation of current methods and procedures according to the period of individual set evaluation after relatively long exposition time (after 10 till 20 years), according to the development of new more effective methods of evaluation.


Conclusions

For the monitoring systems of the NPP`s material degradation due to the irradiation and thermal ageing processes is possible to conclude, that this systems will meet the requirements of:

Slovak Regulatory Authority (UJD SR), recommendations of IAEA, internationally approved standards used for evaluation of thermal

ageing, the possibility to compare the results between the operated

individual units not in Slovak Republic only, but with the other nuclear technologies in the world too.


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Documents

1 Presentation L.Kupca Podolsk May 2007 AGEING MANAGEMENT OF SAFETY RELATED COMPONENTS OF WWER-440 UNITS OPERATED IN SLOVAK REPUBLIC The 5-th International