Greg Gibson 750 East Pratt Street, Suite 1600

Vice President, Regulatory Affairs Baltimore, Maryland 21202

UnnStar"NUCLEAR ENERGY

10 CFR 50.410 CFR 52.79

July 9, 2010

UN#10-185

ATTN: Document Control DeskU.S. Nuclear Regulatory CommissionWashington, DC 20555-0001

Subject: UniStar Nuclear Energy, NRC Docket No. 52-016Response to Request for Additional Information for theCalvert Cliffs Nuclear Power Plant, Unit 3,RAI 229, Question 02.05.04-18, Stability of Subsurface Materials andFoundations

Reference: 1) Surinder Arora (NRC) to Robert Poche (UniStar Nuclear Energy), "FINAL RAI229 RGS1 4566" email dated April 30, 2010

2) UniStar Nuclear Energy Letter UN#10-139 from Greg Gibson to DocumentControl Desk, U.S. NRC, Response to Request for Additional Information forthe Calvert Cliffs Nuclear Power Plant, Unit 3, RAI 229, Question02.05.04-20, Stability of Subsurface Materials and Foundations, dated May20, 2010.

The purpose of this letter is to respond to the request for additional information (RAI) identifiedin the NRC e-mail correspondence to UniStar Nuclear Energy, dated April 30, 2010(Reference 1). This RAI addresses Stability of Subsurface Materials and Foundations, asdiscussed in Section 2.5.4 of the Final Safety Analysis Report (FSAR), as submitted in Part 2 ofthe Calvert Cliffs Nuclear Power Plant (CCNPP) Unit 3 Combined License Application (COLA),Revision 6.

Reference 2 anticipated that the responses to Questions 02.05.04-17 through 02.05.04-19would be provided to the NRC by July 9, 2010.

T) 0 cq

UN#110-185July 9, 2010Page 2

The enclosure provides our response to RAI 229, Question 02.05.04-18.

UniStar Nuclear Energy requires additional time to finalize the responses to RAI 229, Questions02.05.04-17 and 19. The response to these questions will be provided by July 23, 2010.

Our response does not include any new regulatory commitments and does not impact COLA

content.

This letter does not contain any sensitive or proprietary information.

If there are any questions regarding this transmittal, please contact me at (410) 470-4205, orMr. Wayne A. Massie at (410) 470-5503.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on July 9, 2010

Greg Gibson

Enclosure: Response to NRC Request for Additional Information RAI 229, Stability ofSubsurface Materials and Foundations, Question 02.05.04-18, Calvert CliffsNuclear Power Plant, Unit 3

cc: Surinder Arora, NRC Project Manager, U.S. EPR Projects BranchLaura Quinn, NRC Environmental Project Manager, U.S. EPR COL ApplicationGetachew Tesfaye, NRC Project Manager, U.S. EPR DC Application (w/o enclosure)Loren Plisco, Deputy Regional Administrator, NRC Region II (w/o enclosure)Silas Kennedy, U.S. NRC Resident Inspector, CCNPP, Units 1 'and 2U.S. NRC Region I Office

GTG/SJS/mdf

UN#10-185

Enclosure

Response to NRC Request for Additional Information

RAI 229, Stability of Subsurface Materials and Foundations,

Question 02.05.04-18,

Calvert Cliffs Nuclear Power Plant, Unit 3

EnclosureUN#10-185Page 2

RAI 229

Question 02.05.04-18

FSAR Section 2.5.4.10.6 presents the calculation of static and seismic lateral pressures. Since severalassumptions were used in the calculations,

1. Please evaluate the pressure induced by compaction of side backfill in the lateral earthpressures calculation.

2. Please justify the use of a Poisson's ratio value of 0.3 for the saturated portions of the backfill inyour calculation of seismic lateral earth pressures.

3. Please discuss how the site-specific lateral earth pressure analysis is consistent with thestandard design.

Response

The lateral pressure induced by compaction of the side backfill was not initially evaluated in the lateralearth pressure calculation. The calculation has been updated as described below. In addition, thePoisson's ratio for thesaturated portion of the backfill and the subsurface was updated to 0.45 in orderto address item 2 above.

It is expected that heavy compaction equipment will operate near the below-grade walls and mayinduce additional lateral pressures to the walls surrounding the NI below the site grade. The earthpressure due to the compaction of the backfill was calculated based on the methodology described bythe U.S. Army Corp of Engineers (USACE, 2004)1. The USACE method provides the magnitude anddistribution of the lateral earth pressure increase due to a compactor operating within six inches of thebelow-grade wall. The excess lateral pressure due to compaction was calculated based on thepressure distribution shown in Figure 1. In this calculation, a 3.2 ton vibratory roller compactor wasselected as a representative of typical structural backfill compaction. As can be seen from the secondgraph in Figure 1, the compactor-induced lateral pressure is largest when the compactor is at thenearest location to the wall. Therefore, six inches will provide a conservative lateral pressureestimation. The critical lateral pressure due to compaction, in excess of active and at-rest pressure,was taken as 400 psf. The critical depth for the critical pressure as recommended is 1.7 ft from theground surface. However, the critical depth was conservatively selected as zero feet from the groundsurface.

The pressure distribution due to compaction is shown on Figure 2(a) for active lateral earth pressuredistribution and on Figure 2(b) for at-rest lateral earth pressure distribution.

In addition to the extra load imposed by compaction, the backfill selected for the CCNPP Unit 3 site hasa dry weight of 145 lb/ft3 versus the 110 lb/ft specified for dry soil in the U.S. EPR FSAR. Thisdeparture and the evaluation of the Nuclear Island Common Base Mat structures, the EmergencyService Water Buildings (ESWBs), and Emergency Power Generation Buildings (EPGBs) using sitespecific lateral earth pressure loads will be provided with the reconciliation of FSAR Sections 3.7

1 (USACE 2004) Unified Facilities Criteria (UFC 3-220-04FA), Backfill for Subsurface Structures. U.S. Army Corps of

Engineers, Naval Facilities Engineering Command, Air Force Civil Engineer Support Agency, January, 2004. This UFCsupersedes TM 5-818-4, dated 1 June 1983.

EnclosureUN#10-185Page 3

and 3.8 with the proposed update to the U.S. EPR FSAR that will utilize an embedded finite elementmodel currently in preparation.

FIGURE 1COMPACTION INDUCED LATERAL PRESSURE ESTIMATION

(USACE, 2004)

LA TERAL PRESSURE,IN EXCESS OF ACTIVEPPESSURE, INDUCEDBY COMPACTION

DC = CRITICAL DEPTH

I(H)C - CRITICAL LATERAL PRESSUREEARTH PRESSURECOEFFICIENTS:KA - ACTIVE

KO - AT REST

OV - VERTICAL STRESS(SOIL UNIT WEIGHT X DEPTH)

CRITICAL (CHIcCOMPACTION EQUIPMENT DEPTH Dc, FT p.f

10-TON SMOOTH WHEEL ROLLER3.'-TON VIBRATORY ROLLER1.4-TON VIBRATORY ROLLER400-KG VIBRATORY PLATE12-- KG VIBRATORY PLATE

1.91.71.21.51.0

420400260340240

a. MAXIIVUM INDUCED LATERAL PRESSURES

FT

=-I-- a

•z-

0

15

10

3.6.

2 4 6 8 10

2. I-TON DUAL DRUM, WALKBEHIND VIBRATORY ROLLERSTATIC WEIGHT/DRUM=2100 LB.

1 NAMIC FORCE/DRUM=7380 LB.

.BACKFILF'

7 20 PCF -

1 1-- LU

0 0.5 1.0 1.5 2.0 2.5 3.0

CLOSEST DISTANCE OF COMPACTOR TO WALL ,M

b. EFFECT OF DISTANCE FROM WALL

EnclosureUN#10-185Page 4

FIGURE 2ACTIVE AND AT-REST LATERAL EARTH PRESSURE DISTRIBUTION

Active Lateral Earth Pressure (psf) At-rest Lateral Earth Pressure (psf)0 500 1000 1500 20000 500 1000 1500 2000

00

Static Active Earth - Static At-rest Earth PressurePressure 5

- - - - Hydrostatic Pressure - - - - Hydrostatic Pressure

10 Compaction Induced 10 Compaction Induced LateralLateral Pressure Pressure

15 15

4_20 F20

ct25 025

30 Nb 30 ,

35. % 35%

403 %% 403 %5

45 45

(a) (b)

COLA Impact

The following changes will be made in FSAR Section 2.5.4.10.6 and Section 2.5.4.10.6.2 to incorporatethe information described above. Note that this markup is to the FSAR text provided in UNE letterUN#09-427 2 dated October 9, 2009.

2.5.4.10.6 Earth Pressure

Section 2.5.4.10.6 is added as a supplement to the U.S. EPR FSAR.

Static and seismic lateral earth pressures are addressed for below-grade walls. Seismic earthpressure diagrams are structure-specific. They are only addressed generically herein. Specificearth pressure diagrams are developed for specific structures based upon each structure's finalconfiguration. Passive earth pressures are not addressed; they are excluded for conservatismfor general purpose applications. Engineering properties for structural fill are used to estimateearth pressures. The properties of backfill are provided in Section 2.5.4.2.5.9. Structural backfill

2 G. Gibson (UniStar Nuclear Energy) to Document Control Desk (U.S. NRC), "Update to Calvert Cliffs Nuclear Power Plant, Unit 3 FSAR

Sections 2.5.4 and 2.5.5," Letter UN#09-427, dated October 9, 2009.

EnclosureUN#10-185Page 5

material is verified to meet the design requirements prior to use during construction. Asurcharge pressure of 500 psf applied at the ground surface is assumed. The validity of thisassumption will be confirmed during detailed design. Lateral prossure. due to compact.in arenet included; these prescures are controlled by compacting backfill with light equipment noarMFUGt~res. In addition to earth pressures associated with the effective pressure distribution ofthe backfill materials, subsurface structures and walls may also be subiected to surcharge loadscaused by heavy equipment operating close to the structure and by increased permanent lateralearth pressures caused by compaction of backfill material with heavy equipment. Compaction-induced earth pressures can cause a significant increase in the permanent lateral earthpressures acting on a vertical wall of a structure. The magnitude of the increase in lateralpressure is dependent, among other factors, on the effective weight of the compactionequipment and the weight, earth pressure coefficient, and Poisson's ratio of the backfill material.

The lateral pressure that will be generated due to the compaction of the backfill is calculatedbased on the assumption that the equipment can operate to within 6 inches of the wall.Significant reductions in lateral pressures occur as the closest allowable distance to the wall isincreased. A 3.2-ton vibratory roller compactor is used to estimate lateral pressures due tocompaction. The critical lateral pressure in excess of active and at-rest pressure associated withthis equipment is considered to be 400 psf; the critical depth at which this critical pressure isreached, Dc, is 1.7 ft. However, the critical depth is conservatively considered as Dc = 0.

In developing the earth pressure diagrams, the following are assumed:

2.5.4.10.6.2 Seismic Lateral Earth Pressure

The active seismic pressure, PAE, is given by the Mononobe-Okabe equation (Whitman, 1991),represented by:

PAE = AKAEY(H - z)

Where:

PAE "- Active seismic pressure;AKAE --> Coefficient of active seismic earth pressure (KAE - KAS);

KAE "* Mononobe-Okabe coefficient of active seismic earth thrust

cos 2 (0' - e)KAE = 2

CS() +sin sin (' - e)cos2e(1+ cose

e -- e = tan-1 (kh)

EnclosureUN#10-185Page 6

kh -- Seismic coefficient (0.15 g)

Y -- Unit Weight of backfill;H -- Below-grade height of wall;

z -> Depth below the top of the backfill;

The value AKAE can be estimated as 0.75 kh for kh values less than about 0.25 g, regardless of

the angle of shearing resistance of the backfill (Seed, et al., 1970).

The seismic at-rest pressure AKOE, for below-grade walls for Category I structures is evaluatedusing a method that recognizes the frequency content of the design motion, limited building wallmovements due to the presence of floor diaphragms, and uses the soil shear wave velocity anddamping as input (Ostadan, 2004). To predict lateral seismic soil pressures for below-gradestructural walls resting on firm foundations and assuming non-yielding walls, the methodinvolves the following steps:

1. For conservatism, define the ground motion as the CCNPP Unit 3 Safe ShutdownEarthquake (SSE) peak ground acceleration. This value is the maximum spectralacceleration of the site specific spectra (See Section 3.7).

2. Compute the total mass for a representative Single Degree of Freedom (SDOF) systemusing Poisson's ratio and the mass density of the soil, m:

M 1 Y H2 4jV

Where:

Y- -- Total mass density of the structural backfill;gH -> Height of walltl4v -- Factor to account for Poisson's ratio (v), with I v = 0.3 adopted for structural

backfill for unsaturated conditions, and 0.45 was considered for saturatedconditions

2LPv = 1(1-v)(2-v)

3. Obtain the lateral seismic force as the product of the total mass obtained from Step 2,and 0.15 g.

4. Obtain the maximum lateral seismic soil pressure at the ground surface by dividing thelateral force obtained from Step 3 by the area under the normalized seismic soilpressure, or 0.744 H.

EnclosureUN#10-185Page 7

5. Obtain the soil pressure profile by multiplying the maximum pressure from Step 4 by thefollowing pressure distribution relationship:

p(y) = -0.0015 + 5.05y - 15.84y' + 28.25y 3 - 24.59y 4 + 8.14y 5

Where:

y -- Normalized height ratio (y/H) "y" is measured from bottom of the wall and y/Hranges from a value of zero at the bottom of the wall to a value of 1.0 at thetop of the wall.

For well-drained backfills, seismic groundwater pressures need not be considered (Ostadan,2004). Since granular backfill is used for the project, only hydrostatic pressures are taken intoconsideration. Seismic groundwater thrust greater than 35 percent of the hydrostatic thrust candevelop for cases when kh>0.3g (Whitman, 1990). Given the relatively low seismicity at theCCNPP Unit 3 site (kh<0. lg), seismic groundwater considerations can be ignored.

Representative earth pressure diagrams are provided in Figure 2.5-197.

EnclosureUN#1O-185Page 8

Figure 2.5-197 is replaced with a new figure as shown:

Figure 2.5-197--{Earth Pressure Representative Diagrams)

Active Lateral Earth Pressure [ psf]

1000 2000 3000 4000 5000 0

At Rest Earth Pressure [ psf ]

1000 2000 3000 4000

EnclosureUN#1 0-185Page 9

Figure 2.5-197--{Earth Pressure Representative Diagrams)

Active Lateral Earth Pressure (psf) At-rest Lateral Eart

0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 200

- Static Active Earth\ Pressure I

-- - Hydrostatic Pressure

10 I10 - - - SurchargeActive i

, ,, Pressure

15 =: Total Active Earth I

Pressures•- SeismicActive Earth

"20 - Pressure.=I. I

. I Compaction Lateral0 25 I. Pressure

'. Ikl..

35 I-

% I

40 % %

h Pressure (psf)

0 2500 3000 3500 40001 1 1

45