ML20213D853

Forwards Draft Branch Input to Sections 2.5.4,2.5.5 & 2.5.6 of SER Re Soil Backfilling,Compaction & Testing

ML20213D853
Person / Time
Site:	Columbia, North Carolina State University
Issue date:	10/13/1981
From:	Lear G Office of Nuclear Reactor Regulation
To:	Tedesco R Office of Nuclear Reactor Regulation
References
CON-WNP-0398, CON-WNP-398 NUDOCS 8110300412
Download: ML20213D853 (14)

Text

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l OCT 131981

• Docket flo. 50-397 ftE"0 rat!DU'1 FOR: Robert L. Tedesco, Assistant Director for Licensing Division of Licensing THRU: James P. Knight, Assistant Director for Components and Structures Engigeering Division of Engineering George Lear, Chief ' I "5 FR0ft:

liydrologic and Geotechnical Engineering Dr -

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Division of Engineering

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SUDJECT: DRAFT SER If;PUT - GE0 TECH:!ICAL E!:GIf;EERIliG11 0C714 Net.

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i Plant flame: HPPSS fluclear Project !!o. 2  % .'

Licensing Stage: OL 4. N Docket tiumbers: 50-397 P.esponsible Branch: Licensing Branch !!o. 2; R. Auluck, LPI

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Review Status: Applicant's Response to Open Iten is fieeded for SSER Ue have reviewed Sections 2.5.4, 2.5.5 and 2.5.C of the UPPSS Iluclear Project tio. 2 (l.HF-2) FSAR through Amendment !;o.17 dated September 1,1931 provided by ifashington Public Power Supply System (tlPPSS) in support of their application for an operating license. On the basis of this review, we have prepared the enclosed draft geotechnical engineering input to the Safety Evaluation Report.

In the enclosed draft, we have indicated that the applicant has inforned the flRC staff, in interim reports dated April 22, 1981 and September 1, 1981, that there is a potentially reportable condition concerning soil backfilling, compaction and testing. The report describing the deficiency indicates that the laboratory naxinun density testing for the Class I. backfill performed since May 1976 nay have been perfomed incorrectly. The applicant is compiling a list of all the affected areas and plans to evaluate if any area needs retesting. The staff will review the applicant's final report on this open itcn and provide an evaluation in a supplement to this SER.

Other than the open iten indicated above, the geotechnical staff finds that the applicant's design and construction criteria of the 12;P-2 for the plant foundations and the ultinate heat sink systen nect the requircaents of Appendix A to 10 CFR Part 103.

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• Robert L. Tedesco OCT 131981 This review has been perforTned by Dr. Dinesh C. Gupta, Geotechnical Engineering Section, Hydrologic and Geotechnical Engineering Dranch.

Ot!ginal signed Ly Geetie Lear George Lear, Chief Hydro logic and Geotechnical Engineering Dranch Division of Engintfering

Enclosure:

Draft SER cc: w/ enclosure R. Vollner A. Schwencer F. Schauer R. Jackson G. Lear L. Heller I1. Fliegel D. Gupta R. Auluck 4

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r SER Input - Geotechnical Engineering WPPSS Nuclear Project No. 2 (WNP-2)

Docket Number 50-397 Prepared by: D. Gupta, GES, HGEB, DE The following sections present the staff's geotechnical engineering review of the WNP-2 site and plant features as presented by the applicant, Washington Public Power Supply System (WPPSS), in the Final Safety Analysis Report. The stability of subsurface materials and foundations (Section 2.5.4), the stability of slopes (Section 2.5.5) and embankments and dams (Section 2.5.6) have been evaluated in accordance with the criteria given in Appendix A to 10 CFR Part 100, Regulatory Guide 1.70, Revision 3, and the current Standard Review Plan.

2.5.4 Stability of Subsurface Materials and Foundations 2.5.4.1 General The WPPSS Nuclear Project No. 2 (WNP-2') is located within the Hanford Reservation of the U.S. Department of Energy, approximately 12 miles north of Richland, Washington. The site is approximately 3 miles west of the Columbia River. Two other nuclear power plants, WNP-1 and WNP-4, are under construction about 1 mile east of the WNP-2 site.

l The safety related structures, systems and components (SSC) which have been reviewed for foundation stability are listed in Table 3.2-1 of the WNP-2 FSAR.

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The Category I structures include the reactor building, radwaste and control building, and diesel generator building located in the main powerblock area.

l The seismic Category I ultimate heat sink (UHS) system consists of two concrete l

spray ponds, two standby service water (SSW) pumphouses, and pipelines and conduits

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between the pumphouses and the powerblock structures. The spray ponds and the SSW pumphouses are located about 900 ft from the reactor building. A gravity flow makeup water supply line is provided from the circulating water pumphouse

, to the spray ponds to maintain the pond water at the required level.

The area around the site is a flat, semi-arid plateau./ The original ground surface elevation ranged from about 420 feet to 450 feet (msl). The final plant grades in the powerblock area and around the seismic Category I spray ponds are at elevation 440 feet (msl) and 434 feet (msi), respectively.

2.5.4.2 Subsurface Conditions Except for a 2 to 3 foot thick zone of surficial soils, the material from the ground surface down to a depth of approximately 45 feet, or to elevation 395 ft (msl), consists of loose to medium dense sand with occasional pieces of gravel. Below approximate elevation 395 ft (msl) the soils consist of very dense gravel or sandy gravel, assumed to be the middle member of the Ringold Formation. Though this gravelly zone contains relatively thin silt and sand seams at various depths, it is very dense throughout with standard penetration resistance blow counts consistently greater than 100 blows per foot. This 200 ft l thick middle member extends to about elevation 190 ft (msl), where it is underlain l

l by a 300 ft thick lower member of the Ringold Formation, a very dense, interbedded l gravel, sand and silt. Basalt bedrock underlies the lower member at a depth of l

557 feet (elevation -117 ft ms1).

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The subsurface conditions at the WNP-2 site were determined from extensive field and laboratory investigations. Some information gathered for the adjacent WNP-1 and WNP-4 projects was also utilized to define these conditions.

Field Investigations To establish the stratigraphy and engineering propertf'es of the soil and rock beneath seismic Category I structures, 32 borings were drilled at the plant site and near vicinity. Three of these bore holes were deep borings ranging in depths from 846 feet to 947 feet below original ground surface; the other 29 borings were drilled to depths ranging from 58 feet to 250 feet below the original ground surface.

Because of the granular, cohesionless nature of the soil at the site, only a few undisturbed samples were attempted and recovered. A specially fabricated 4.5 inch outside diameter steel thick-wall, drive-barrel sampler was used to advance the hole. The barrel was driven, extracted from hole, emptied, reinserted in the hole and the operation repeated. Samples of soil were obtained at 2.5 feet death intervals by driving 3-inch diameter thin walled steel tubes into the soil at the bottom of the hole. The caving of the hole was prevented by advancing a six-inch inside diameter steel casing with the hole and continuously adding drilling mud during drilling. Emphasis during this

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investigation was placed on obtaining soil penetration test values at 5 feet intervals using a conventional split spoon sampler.

The rock was cored in the three deep borings. Wireline diamond coring tools were used to obtain continuous core. Coring time in minutes per foot as well as percentage recovery were recorded.

Field explorations included 4 Dutch Cone penetration probes to depths ranging s

from 32 feet to 43 feet, 2 test pits (8 feet deep) and a test trench,15 feet deep, diagonally across the reactor site.

Geophysical studies performed at the site included seismic refraction surveys, uphole/ downhole and cross-hole seismic velocity measurements and a suite of neutron and gamma ray logs in boreholes.

The applicant's field exploration studies show that there are no areas of actual or potential subsurface uplift, subsidence or collapse, no deformation zones, shears, joints, fractures or folds, and no zones of alteration, irregular weathering or structural weakness which could adversely affect plant safety.

The staff finds these conclusions to be reasonable and acceptable.

Laboratory Investigations Soil and rock characteristics required for the analyses of the static and dynamic stability of subsurface materials and foundations under seismic i Category I structures were established using laboratory tests which included moisture content, grain size tests. classification tests, maximum / minimum i

density tests, compaction characteristics, permeability, triaxial, resonant column, and stress and strain controlled dynamic triaxial tests. Chemical analyses l

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on rock samples were also performed. Test procedures and results of these tests are described by the applicant in Appendix 2.5G of the WNP-2 FSAR. The test procedures used by the applicant on in situ soil and rock samples are in accordance with the state of the art and are acceptable to staff. The laboratory test results are reasonable and are, therefore, also acceptable; the staff's evaluation of the laboratory maximum density t4sts performed on compacted backfill material is presented in Section 2.5.4.3.

Subsurface Soil and Rock Procerties Applicant's field and laboratory investigations indicated that the upper 40 feet of the in situ glacio-fluvial soils ranged from moderately dense to very loose. Therefore, it was decided to excavate down to about 40 feet (elevation 395 feet), or' lower, to the top of Ringold Formation and to backfill up to the base of the seismic Category I foundations with granular soil compacted by vibratory compacting equipment to a minimum of 75% relative density and an average of 85% relative density, as determined by ASTM D2049-69. Staff's

! evaluation of the backfill under various seismic Category I structures is presented in section 2.5.4.3 of the SER.

The underlying Ringold Formation below approximate elevation 395 feet was determined by the applicant to have been preloaded by several hundred feet of overburden which has been subsequently eroded. This Formation is very dense, l exhibiting standard penetration resistance blow counts consistently greater than 100 blows per foot. Between a depth of 45 and 105 feet from the surface, the compressional wave velocity averages 5,600 fps. At depths of over 105 ft, the P wave velocity is greater than 10,000 fps. Based on the standard penetration resistance data as well as the geophysical wave velocity data, the applicant l

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concluded, and staff agrees, that the Ringold Fonnation has " rock like" seismic characteristics.

For static analyses of seismic Category I foundations, the applicant used the modulus of elasticity (E) of the soil deposit underneath the foundations to s

calculate settlements. The following conservative values (for settlement calculations)

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were used by the applicant (FSAR Appendix 2.5E).

Depth 0 to 40 ft, E = 25,000 psi Depth 40 to 107 ft, E = 60,000 psi Depth 107 to 420 ft, E = 90,000 psi Based on the geophysical tests, resonant column tests and the dynamic triaxial tests, the applicant obtained the strain dependent shear moduli and damping curves for these soils. These results are presented in the FSAR Appendix 2.5G.

The following values of dynamic shear moduli for the soils were selected on the basis of calculations for the soil strain levels developed in the soil-structure interaction analyses which used a lumped mass model on an elastic half space with strain independent soil properties.

Shear Modulus, osi l

Mode Lower bound Averaae Uccer bound Horizontal Translation 50,000 75,000 100,000 and Rocking Vertical 80,000 120,000 160,000

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- Based on computed' strain levels, the applicant selected a value of 5 percent for the internal damping of the soil. The geometric damping was computed ,

using the formulas given by Richart, Hall, and Woods (1970). However, to be conservative, the applicant did not use geometric damping values, but used soil damping values in the analytical model for soil structure interaction which did not exceed the following: #

Soil Damping Coefficients Used in SSI Model (Percent of Critical Damping)

Mode Operating Bases Safe Shutdown Earthauake Earthcuake Rocking 5 7 Translation (horizontal 10 10

.and vertical) ,

The staff considers the static and dynamic soil parameters used by the applicant for stability and seismic response evaluations of foundations to be reasonable and acceptable.

Groundwater Level The groundwater level at the plant site is at about elevation 380 feet (msl).

Seasonal variations are less than 10 ft. However, the design basis groundwater l

level is based on the possible construction of the Ben Franklin Dam at River

! Mile 348 on the Columbia River. Because of this consideration, a groundwater elevation of 420 feet (msl) has been assumed for design. Staff's evaluation of the groundwater conditions at the site are presented in Section 2.4 of the SER.

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2.5.4.3 Evaluation of Foundations ,

Beneath all seismic Category I structural foundations, the existing upper loose sandy ma,terial was excavated down to the underlying very dense Ringold gravel ,

and replaced in a denser state by compaction, The excavations to the Ringold formation extended down to 385 feet (m:1) to 392 feet (msl) with some 1ccalized areas as deep as 375.8 feet (msl). ThethicknessoftIecompactedbackfill and the main foundation features of the principal seismic Cateccry I plant structures are shown on Table 1.

Comoacted Backfill The applicant informed the NRC Staff on April 22, 1981 and September 1,1981 that there is a potentially reportable condition concerning soil backfilling, compaction and testing. The applicant's interim reports describir.; the deficiency indicate that the laboratory maximum density testing for the Class 1 backfill performed since May 1976 may have been performed incorrectly. The applicant is formulating a list of all the affected areas and will evaluate if any of these areas have to be retested. The staff will review the applicant's conclusions and provide evaluation of the applicant's study ir. a supplement to this SER.

Bearina Capacity The applicant has provided for a safety factor in excess of 3 in calculating allowable static design bearing capacity. The staff agrees that this margin of safety is adequate for the support of the plant facilities.

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2 Table 1 Foupdation Features of Principal Seismic Category I Structures Approximate Foundation Thickness of Soil Area Load Area Load Foundation length Width Elevation, Backfill Beneath DL + LL DL + LL + EQ Structure Type (ft) (ft) ft (MSL) Foundation, ft (tsf) (tsf)

Reactor Building Mat 157 147 406 15 S.70 20.5 s Radwaste & Control Mat 212 163 429 37 3.5 11.5 Bldg.

Diesel Generator Strip 124 60 435 45 3.8 4.6 Bldg. Footing

, Spray Ponds Strip 250 250 417 27 0.25 3.0 Footing

& Slab Category I pipe Continuous

• Duct Bank Continuous

• A Final grade is at elevation 440 feet around the plant structures and elevation 434 feet around the spray ponds.

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• varying thicknesses

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Settlements The applicant has presented the estimated static and dynamic settlements of Seismic Category I structures in FSAR Tables 2.5-12 and 2.5-13, respectively.

The allowable settlement criterion is presented on Figure 21 of the FSAR Appendix 2.5F. The measured settlement data are given in Appendix 2.5H of the FSAR and in response to staff question Q362.010. The' data indicate that the maximum total and differential settlements of various seismic Category structures are less than 0.6 inches. Also the total settlements in 2.5 years since completion of structures has been less than 0.1 inch, and thus the rate of post-construction settlements has been very small. The applicant has concluded and the staff agrees that these small amounts of total and differential settlemen.ts and the small rate of post-construction settlements should be of insignificant consequence to the safety of the plant structures and their appurtenances.

Earth Pressures The applicant has designed all subsurface walls to resist static and dynamic lateral earth pressures exerted by compacted backfill. The computation procedure is consistent with the method described by Seed and Whitman (1970) to calculate dynamic lateral loads in combination with static at-rest pressures (coefficient of static earth pressure at rest equal to 0.5). This procedure is in accordance with the state-of-the-art and is acceptable to the Staff.

Liquefaction Potential The studies made by the applicant to evaluate liquefaction potential show that the four.dation soils are not potentially liquefiable. The undisturbed Ringold gravel is very dense. Except for the areas under investigation, the compacted backfill has been placed tc a relative density in excess of 75

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percent and the backfill has been shown to be stable when subjected to the design safe shutdown earthquake loading of 0.25g effective peak acceleration (see Section 2.5.2 of the SER).

2.5.4.4 Conclusion Based on the applicant's design criteria and construction reports and on the results of applicant's investigations, laboracory and field tests, and analyses presented in the FSAR, the staff has concluded that the site and plant foundations will be adequate to safely suppert the WFPSS Nuclear Project No. 2 (WNP-2), and to pemit the safe operation of the ultimate heat sink system in accordance with the requirements of Appendix A to 10 CFR Part 100, pending satisfactory resolution of the open item identified in Section 2.5.4.5.

2.5.4.5 Coen Iten The applicant infomed the NRC staff in interim reports dated April 22, 1981 t

and Septemter 1, 1981 that there is a potentially reportable condition concerning sbil backfilling, compaction and testing. The report describing the deficiency

! indicates that the laboratory maximum density testing for the Class 1 backfill performed since May 1976 may have been performed incorrectly. The applicant is compiling a list of all the affected areas and plans to evaluate if 61y area needs retesting. The staff will review the applicant's final re: ort and provide an evaluation in a supplement to this SER.

11-2 5.4.6 References R'ichart, Jr. , F.E. , Hall, Jr. , J.R. , and Woods, R.D. , Vibrations of Soils and F,bendatior.s, Prentice-Hall Inc., New Jersey,1970.

Seed H.B., and Khitman, R.V. (1970), " Design of Earth Retaining Structures for Dynamic Loads," ASCE Specialty Conference, Latera4 Stresses and Earth ,

Retaining Structures,1970.

2.5.5 Stability of Slopes _ ,

There are no slopes, either natural or mannade, the failure of which could adversely affect the safety of WhP-2.

2.5.6 EmbanAments and Dams There are no echankments and ca.T.s at the WhP-2 site for ficcd protection or for i

i impounding ccoling water required for the operation of the nuclear power plant.

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