ML20213E092
| ML20213E092 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 03/11/1982 |
| From: | Lear G Office of Nuclear Reactor Regulation |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| CON-WNP-0491, CON-WNP-491 NUDOCS 8203230168 | |
| Download: ML20213E092 (9) | |
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MAR 11 199~
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/0 MEMORANDUt FOR:
A. Schwencer, Chief Licensing Branch flo. 2 Division of Licensing N
g FROM:
George Lear, Chief liydrologic and Geotechnical Engineering Branch Division of Engineering SUCJECT:
REVIEU OF DRATT SER FOR WNP-2 A menc from R. Tedesco to NRR A/b's dated March 10, 1982, subject
" Review / Concurrence of,'NP-2 5.ER" asked for our comments.
Dr. Gupta of ny HGES staff has reviewed Sections 2.5.4, 2.5.5 and 2.5.0 of the Attachment to the above memo. t!e have annotated our corrections on T.hc attachment to this memo for incorporation into the final SER.
Originc! tigne:! ty George Icar George Lear, Chief Hydrologic and Geotechnical Engineering Branch Division of Engineering Attechrdent: As stated cc w/o attaclynent:
G, Lear R. Tedesco L. lieller D. Gupta cc w/attachaer,t:
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the efforts of DOE since 1977, the knowledge of the area has been greatly enhanced.
The applicnat has undertaken numerous studies and investigations and has provided an extensive amount of new information and interpretation.
The staff review of this information has lead to an understanding and resolution of many issues relating to the site vibratory ground motion determination.
The increasing amount of new information, however, may require the reinterpreta-tion of some previous positions of the staff, the USGS and the applicant.
Although most of'the geologic and seismic issues are resolved, there are several outstanding issues that are still open.
The applicant and the staff met on February 10, 1982 to discuss the open issues ard the applicant has undertaken a rigorous program of investigations to collect the information which will allow the staff to confirm that the open issues are resolved.
The staff, the USGS, and Dr. Slemmons will undertake at least one and probably several site visits to review the applicant's additional field investigations.
Upon the applicant's submission and the staff's review of the new information, the Geosciences Branch will issue an extensive SSER.
This SSER will discuss in detail all the geologic and seismic issues including the regional and site geology, capable faulting, seismicity, operating and safe shutdown earthquakes, and the vibratory ground motion.
Reports by the USGS and Dr. Slemmons will be incorporated as appendices and will be discussed in the SSER.
2.5.4 Stability of Subsurface Materials and Foundations The following sections present the staff's geotechnical engineering review of the WNP-2 site and plant features as presented by the applicant in the FSAR.
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 100, NRC Regulatory Guide 1.70, Revision 3, and the current Standards Review Plan, NUREG-0800.
2.5.4.1 General WNP-2 is located within the DOE Hanford Reservation 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, have been under construction about 1 mile east of the WNP-2 site.
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.
The Category I structures include the reactor building, radwaste and control building, and diesel generator builting located in the main powerblock area.
The seismic Category I ultimate heat sink (VHS) system, consists of two concrete spray ponds, two standby service water (SSW) pumphouse, and pipelines and d
conduits between the pumphouses and the powerblock str,uctures.
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 (msl), 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 (ms1), 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 thick middle member extends to about elevation 190 ft (msl), where it is underlain by a 300 ft thick lower member of the Ringold Formation, a very dense, interbedded gravel, sand and silt. Basalt bedrock underlies the lower member at a depth of 557 feet (elevation -117 ft msl).
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 used to define these conditions.
Field Investications To establish the stratigraphy and engineering properties 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 depth 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 l
hole and continuously adding drilling mud during drilling.
Emphasis during l
this investigation was placed on obtaining soil penetration test values at
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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 from 32 feet to 43 feet, 2 test pits (8 feet deep) and a test trench, 15 feet i
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 riy logs in boreholes'.
The applicant's field exploration studies show that at and near the site 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 NRC staff finds these conclusions to be reasonable and acceptable.
Laboratory Investications Soil and rock characteristics required for the analyses of the static and dynamic stability of subsurface materials and foundations under seismic Category I structures were established using laboratory tests which included moisture content, grain size tests, classification tests, maximum / minimum 4
densitytests,compactioncharacteristics, permeability, triaxial,relsonant column, and stress and strain controlled dynamic triaxial tests.
Chemical analyses 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
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in accordance with the state of the art and are acceptable to NRC staff.
The laboratory test results are reasonable and are, therefore, also acceptable; the staf f's evaluation of the laboratory maximum density tests performed on compacted
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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 insitu 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 _ yo g average of 85% relative density, as determined by ASTM GM445;69.
The NRC 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 elavation 395 feet was determined by the applicant to have been preloaded ty qveral hundred feet of overburden which has been subsequently eroded. This formation is very dense, 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 avgrages 5,600 fps. At depths of over 105 ft the P wave velocity is greater than 10,000 fps.
Based on the standard penetra-tion resistance data as well as the geophysical wave velocity date, the apnli-cant concluded, and NRC staff agrees, that the Ringold Formation 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 calculate settlements. The following conservative values (for settlement calculations) 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 mode! on an elastic half space with strain independent soil properties.
Shear Modulus, psi Mode Lower bound Averaoe Upoer bound Horizontal Transalation 50,000 75,000 100,000 and Rocking Vertical 80,000 120,000 160,000 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 conserva-tive, 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 ir SSI Model (Percent of Critical Damping)
Operating Basgs Safe Shutdown
- IS Mode Earthouake Earthouake Rocking 5
7 Transalation (horizontal 10 10 and vertical) i The staff considers the static and dynamic soil parameters used by the appli-cant for stability and seismic response evaluations of foundations to be reasonable and acceptable.
Grounowater Level l
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 level is based on the possible construction of the Ben Franklin Dam at River l
Mile 348 on the Columbia River.
Because of this consideration, a groundwater elevation of 420 feet (mil) has been assumed for design. The NRC staff's evaluation of the groundwater conditions at the site is presented in Section I
l 2.4 of the SER.
l 03/05/82 2-28 WNP 2 SER SEC 2 r
2.5.4.3 Evaluation of Foundations Beneath all seismic. Category I structural foundations, the_ existing upper loose sandy material was epxcavated down to the underlying very dense Ringold gravel and replaced in a denser state by compaction. The excavations to the Ringold formation extended down te 385 feet (msl) to 392 feet (msl).with some localized areas as deep as 375.8 feet (msl). The thickness of the compacted backfill and the main foundlfion features of the principal seismic Category I plant structures 4 are shown in Table 2.5.1.
Comoacted Backfill The backfilling, compaction and testing of soils under and around the seismic Category I structures were specified to conform to a minimum relative density
) p t d of 75 percent and an average relative density of 85 percent, as determined by ASTM h 69.
Tnis backfill was placed before May 1976 and was found by the 4
applicant to conform to the specification requirements. The NRC staff con-eludes that the compacted backfill to the above specified requirements should provide adequate support for the plant facilities.
After May 1976, excavations were made in this backfill for installation of the remote air intake piping, the remote air intake structures, and the standby service water pipeline with parallel duct banks.
Backfill subsequently used in these excavations was found by the applicant not to conform to the above Quality Class I specifications with respect to gradation and compaction.
The specifications called for the excavation backfill material to be compacted to an average relative density of 85 percent, with a minimum relative density of 75 percent.
In addition, the backfill materials were specified to consist of inorganic sand or sand and gravel mixtures to be free of b'culders and cobbles greater than 3 inches and contained 5 percent or less fine grained, non plastic materials passing a 250 mesh sieve. The applicant's investigations of the backfilled excavation areas indicated that the majority of this backfill was poorly graded sand containing from 4 to 10 percent fines. Also, the compacted density was found to be erratic and varied from loose to very dense with extreme values of SPT blow counts ranging from 3 to 100.
The design ground water table at the site is lower than the bottom of the excavation for the pipelines, ducts and air intake structures, and therefore, the backfill in question is above the plant design water table.
The applicant has investigated the effect on safety-related utilities and structures of the backfill that does not fully meet the above specification and has concluded that these backfill soils will have no detrimental.effect on safety-related buried piping and seismic Category I structures. The NRC staff finds that, since the piping is adequately supported on backfill compacted to the required specified density and-the backfill above the piping is unsaturated with no potential for liquefaction, the non-conforming fill should have no detrimental effect on safety-ielated buried piping.
The NRC staff has also concluded that, since none of the backfill in question is used to support seismic Category.I buildings, the safety of these structures is not affected.
t FoundationfeaturesofprincipalsQicCategoryIstructures 4--
Table 2.5.1 Foundation Thickness of soil Area Load Area Load Foundation Length Widtli Elevation backfill beneath DL + LL DL + LL
- EQ i
Structure type (ft)
(ft) ft (ms1) foundation, fL (tsf)
(tsf)
Reactor Building Mat 157 147 406 15 6.8 22.5 Radwaste & Control Bldg.
Hat 212 163 429 37
- 3. 5 11.5 Diesel Generator Bldg Strip Footing 161 80 435 45 3.8 4.6 Spray Ponds Strip footing 250 250 417 27 1.1 3.6 and slab e
Category I pipe Continuous Duct Bank Continuous Final grade is at elevation 440 feet around the plant structures and elevation 434 feet around the spray ponds.
CVar ng thicknesses. g s
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t 5
Bearina Capacity The applicant has pr'ovided for a safety ' factor in excess of-3 in calculating allowable static design bearing capacity. The NRC staff agrees that this margin of safety is adequate for the support of the plant facilities.
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 NRC staff agrees that these small amounts of total and differential settlements and the small rate of post-construction settlements should be of insignificant consequence to the safety of the plant structures anc' 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 NRC staff.
Liouefaction Potential The studies made by the applicant to evaluate liquefaction potential show that the foundation soils are not potentially liquefiable.
The undisturbed Ringold gravel is very dense.
The compacted backfill under seismic Category I structures has been placed to a relative density in excess of 75 percent and the backfill has been shown to be stable when subjected to M design safe shutdown earth-quake of 0.25g effective peak acceleration /g ; E.;rtier 1E ^ :M-N 4 N @*
2.5.4.4 Conclusion Based on the applicant's design criteria and construction reports and on the results of applicant's investigations, laboratory and field tests, and analyses presented in the FSAR, the NRC staff has concluded that the site and plant foundations will be adequate to safely support the WPPSS Nuclear Project No. 2 (WNP-2), and to permit the safe operation of the ultimate heat sink system in accordance with the requirements of Appendix A to 10 CFR 100.
l 2.5.5 Stability of Sloces There are no slopes, either natural or manmade, the failure of which could adversely affect the safety of WNP-2.
2.5.6 Embankments and Dams There are no embankinents and dams at the WNP-2 site for flcod protection or for impounding cooling water required for the operation of the nuclear power plant.
O 03/05/82 2-32 WNP 2 SER SEC 2
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