ML20003C519

Final Deficiency Rept Re Structural Backfill Matl,Initially Reported on 800321.Four Isolated Areas in Unit 2 Power Block Found to Have Densities Below Specified QC Criteria. Corrective Action Not Required Due to Adequacy of Backfill

ML20003C519
Person / Time
Site:	South Texas
Issue date:	02/27/1981
From:	Oprea G HOUSTON LIGHTING & POWER CO.
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
ST-HL-AE-627, NUDOCS 8103060337
Download: ML20003C519 (6)

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4 The Light Company m,-n ueino n>m m a<> moo u<>-n. rms nom onesmn February 27, 1981 ST-HL-AE-627 SFN: V-0530

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/g Mr. Karl Seyfrit

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Director, Region IV 4 8ttu = %

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Nuclear Regulatory Commission 9

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Arlington, Texas 76012 O

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Dear Mr. Seyfrit:

South Texas Project Units l&2 Docket Nos. STN 50-498, STN 50-499 Final Report Concerning Structural.

Backfill Material On March 21, 1980, pursuant to 10CFR50.55(e), Houston Lighting & Power Company notified your office of an item concerning non-conforming backfill material areas located adjacent to the South Texas Unit 2 power block.

Attached is the final report on this item, describing the cause and extent of the problem.

The Ir.'fependent Expert Comittee Report which further substantiates the conclusions contained within this Final Report has been transmitted separately as a response to NRC Show Cause Item No. 2.

Further questions should be directed to Mr. M. E. Powell, (713) 676-8592.

Very truly yours, rW r.

Dl Ex cutive ice President S

MEP/RRH/ par Attachment 8103060 DE F

Houston Lighting & Power Company February 27, 1981 ST-HL-AE-627 cc:

J. H. Goldberg SFN: V-0530 D. G. Barker Page 2 i

Howard Pyle R. L. Waldrop H. R. Dean r

D. R. Beeth J. D. Parsons G. B. Painter L. K. English J. W. Briskin R. A. Frazar H. S. Phillips (NRC)

J. O.

Read (Read-Poland,Inc.)

i M. D. Schwarz (Baker & Botts)

R. Gordon Gooch (Baker & Botts) i J. R. Newman (Lowenstein, Newman, Reis & Axelrad) l Director, Office of Inspection & Enforcement Nuclear Regulatory Comission Washington, D. C.

20555 h.

Borchelt Charles Bechoefer, Esquire

?xecutive Vice President Chaiman, Atomic Safety & Licensing Board Central Ptwer & Light Company U. S. Nuclear Reg'.htory Comission P. O. Box 2121 Washington, D. C.

20555 Corpus Christi, Texas 78403 R. L. Range Dr. James C. Lama, III Central Power & Light 313 Woodhaven Road P. O. Box 2121 Chapel Hill, North Carolina 27514 i

Corpus Christi, Texas 78403 R. L. Hancock Dr. Emeth A. Luebke Director of Electrical Utilities Atomic Safety & Licensing Comission City of Austin U. S. Nuclear Regulatory Comission P. O. Box 1088 Washington, D. C.

20555 Austin, Texas 78767 T. H. Muehlenbeck Citizens for Equitable Utilities City of Austin c/o Ms. Peggy Buchorn P. O. Box 1088 Route 1, Box 1684 Austin, Texas 78767 Brazoria, Texas 77422 J. B. Poston Pat Coy Asst. General Manager of Operations Citizens Concerned About Nuclear Power City Public Service Board 5106 Casa Oro P. O. Box 1771 San Antonio, Texas 77422 San Antonio, Texas 78296 A. vonRosenbarg Betty Wheeler City Public Service Board Hoffman, Steeg & Wheeler P. O. Box 1771 1008 S. Madison San Antonio, Texas 78296 Amarillo, Texas v

Brian E. Berwick Bernard M. Bordenick i

Asst. Attorney for the State of Texas Hearing Attorney P. O. Box 12548 Office of the Executive Legal Director Capitol Station U. S. Nuclear Regulatory Comission Austin, Texas 78711 Washington, D. C.

20555 l

4 FINAL REPORT Concerning Structural Backfill on the South Texas Project I.

SUMMARY

During the period of January 28 to February 8,1980, Woodward Clyde Consultants drilled twenty one (21) borings into the structural backfill surrounding South Texas Project Units 1&2 in order to determine the ade-quacy of the in situ structural backfill. During this investigation four small isolated areas within the Unit 2 power block were identified 33 haying densities below the specified quality control criteria of 80s rel-ative density as interpreted from the Standard Penetration Tests.

As a result, an extensive evaluation has been conducted by Houston Lighting

& Power Company which has determined that the backfill is indeed adequate and that no remedial action is required. As part of the comprehensive eval-uation conducted by the Independent Expert Committee in response to NRC Show Cause Item No. 2, it was concluded by the Committee that:

"The studies establish that these zones ha 'e adequate factors of ' safety against liquefaction and that negligible pore pres-sures which might build up in these zones during the Safe Shut-down Earthquake are not significant with respect to the adequacy and safety of the userall structural backfill."

II.

DESCRIPTION OF THE INCIDENT

/+ tts? iption of the incident has been previously provided in Houston hmr ng & Power Company's first Interim Report concerning Structural tBaisdil. The following information has been extracted from the first Interim Report.

"During the period of January 28 to February 8,1980, Woodward Clyde Consultants drilled twenty-one (21) borings into the structural back-fill surrounding Units 1&2. Through the initial field investigation, the structural backfill within the Unit I area was found to be in con-formance with the backfill specification criteria. However, the field investigation also identified four (4) areas within the Unit 2 e ea where densities are potentially below the specified quality control cri-teria of 80% relative density, as iaterpreted from Standard Penetration Tests.

- Area 1 was identified by W;odward Clyde Consultants as an area West of the Unit 2 Reactor Containment Building near the tendon gallery main access shaft at a depth of about 70 feet (boring 204).

- Area 2 was identified by Woodward Clyde Ccnsultants as an area Northwest of the Unit 2 Reactor Containment Building at a depth of about 34 feet (berang 205).

- Area _3 was identified by Woodward Clyde Consultants as an area East of the Unit 2 Mechanical Electrical Auxil-iary Building at a depth of about 30 feet (borings 208 and 209).

- Area 4 was identified by Woodward Clyde Consultants as an area West of the Unit 2 Fuel Handling Building (boring 203).

Figure 1 identifies the specific boring area investigated during the initial field investigation.

Subsequently, during the period of March 24 to April 11,1980, a second field investigation was conducted by Woodward Clyde Consultants in order to determine more precisely the extent and characteristics of tne four (4) potentially non-confoming areas creviously identified. The second field investigation involved the dril. ing of twenty-eight additional borings. The sampling depths and int rvals within the second field in-vescigation were selected in order to arovide better definition of the extent and praperties of the non-conf ming areas. The structural back-fill was tested by Standard Penetrati.n Testing starting at a depth of about 5 feet above the zone of interest and continued to a depth of about 5 feet below or until subgrade was encountered."

Area l_ has several small isolated zones and pockets with a density less than construction quality control criteria.

Zones with densities less than construction criteria within Areas 2 and 3 are limited to one compacted lift thickness (approximately 16 inches).

They are judged to be one rolling lane wide (about 6 feet wide based on the 7-foot drum width of vibratory rollers at the South Texas Project (STP) site). The length of zones is small, estimated to be less than 10 feet long as detemined by borings.

Area 2 had one such zone and Area 3 contain-ed two such small zones.

Area 4 has two small zones less than construction quality control criteria, separated by '.pproximately 18 feet of structural backfill that exceeds the construction quality control criteria. The lower zone is about 6 by 20 feet in plan view size, with the upper zone about 6 by 10 feet in horizontal dimensions. Both zones were limited to one compacted lift thickness.

III. CORRECTIVE ACTION Corrective action has not been required due to the adequacy of the structural backfill, as discussed in the following section.

IV. SAFETY ANALYSIS r

A boring prog,.m was perfomed to detemine the extent of the non-confom-ing structura backfill.

Information obtained from this program has been evaluated by i e Expert Comittee. The evaluation by the Expert Committee considered the overall properties of the backfill material, the construction criteria and operations, and the in-place density test construction quality

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control results. The Expert Committee also concluded that in spite of i

isolated locations where the relative density of the fill may be less t;ian the value of 80% originally specified, the fill is sufficiently dense at all points to provide a high degree of safety against lique-faction during the postulated SSE. The Expert Committee concluded, furthennore, that "...since the condition of the backfill, as placed l

is judged to be adequate, there is no need for remedial action to take pl ace. "

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2co 4co s.::o (4) P.e hanical Auxiliary Building (5) Turbine Generator Building 3.c u., m (6) Diesel Generator Building i

O soil Boring Location

'*78 sorings mita A, a and v sorrixes SOUTH TEXAS PROJECT drilled in vicinity"of other boring UNITS 1 &. 2 with same boring nt:.ber, eg., 205, 205A, 205B and 205v1. See Figures SOIL BOR.IN LCCATICN PLAN 2, 3, 4 and 5 f or detailed boring FIGUTd; 1 lo:atien plan in Unit 2.

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