ML20126A256

Evaluation Rept Re Concrete Strength of Reactor Bldg Base Mat at Facility

ML20126A256
Person / Time
Site:	Wolf Creek
Issue date:	07/10/1979
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20126A095	List: ML20126A093 ML20126A097 ML20126A120 ML20126A148 ML20126A167 ML20126A205 ML20126A208 ML20126A242 ML20126A256 ML20126A267
References
NUDOCS 8002140520
Download: ML20126A256 (5)

Text

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E'iALUATIO;' REFORT REGARD!!!G THE CONCRETE STRENGTH OF THE h REACTOR SU!LDING BASE MAT b'OLF CREEK GENERATING STATION On Decer.ber 12 and 13,1977, the K'oif Creek reactor buiicing base ma: was

. placed as a conclithic pour of approximately 6603 cubic yards of cor.: rete.

At the end cf the 90-cay curing period, thirty-four out of a to ai cf  ;

sixty-six sets cf ccncrete cylinders tested exhibited strengths belen he 1 1

specified ccncrete strength of 5000 pounds per square inch. Thirty sets l of the cor. crete cylinc'ers tested a t 90 c'ays had strengths which were lower than the streng;hs previously determined f or the sane batch of concrete af te r 25 c ays. The SC30 pounds per scuare inch streng r. for the con: rete l l

wa s specified b;. Bechtel (architect-engineer f or the plan:), in ccn;ur.: tion 1

with ctber cesign carameters (e.g. , base me. thickness anc re:ar arrar.ge er.t), I in order to satisfy the design criteria spe:ified in the h'ol f Creek Pre-l iminary Sa fety k.a'ys i s F.epor t (PS '? )'. inese criteria require tr.a: the base mat be able to withstand, without ir.pairmen: of its structurei integrity cr its safety func:icn, the specified design loads and loadinc contina.icns.

Subsequently, the a;piicant condu:ted several investications to determine the possible causes of the anomaly and suber.itted the results of the investicatiors in a report, ca;ed 'k:cber 26, 1978. The applicant con:l uded in its re;:rt that the 90-day strength cf the con: rete in the reactor builcing base ma; was above 5000 pounds per square in:h and that .he apparent low strength of a portion of the 93 day cylinders was attributed to errors in .estinc.

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-c-The matter was investigited by the ,'i-~ Offi:e of Inspection and Enforcerert (:E )

with the help of an cutside consultant. As a result of the investiga: 1cn, :(

d ete nninec: tha: the ccn:lusions made by the applicant in its report of Octcber 26,197E, were ,.ct sufficien:iy sup:or:ed by the f acts contained setal,i e. tindings c; the investigation per,.ormed by 1 I n . .h e re p o rt .

are described ir. a report , cated Fe:ruary 15, 1579. Subsecuently, the applicant studies in crder to resos ve the issues and concerns pe rferci, a acy;;;ona expressed by the NRC staff. At our request the applicant al so performed a reanalysis c# the bas = ca , bisec cr. :he c:rcrete strength inoicate by :h e r e s ui: s c f : he 9 r. - cay c y'. i ..c e r : s s s , t o d e t a rm i r.e i f t h e d e s i c n stresses are within all:wable I frits and he:her the base mat desien sa:isfies c)]

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ne ac 1t1Cnal con:r:te tes:s Consisted Of Compressive Cement s37 .es.

streng:n tests en two-irch cubes sa red fro- }.he cylinder remnants , anc' petrocraphic exar.inatior and chemical analysis of a selected group of cy:1nce. remnan:s . r >.1 c . : ness test resul:s are described in ceta11 in rep;rts subri::ed by the applican; by letters, cated February 2c, 1979 a nd F'ay 3, 19 79. In actition, the 5:ruc ures Laboratory of the Corps of

.'z;erveys ,txperimen; s,tatien, engi ne'ers , U g c.: .- e \,;. cx sburg , Mis si ss i ppi , conduct ed a petrographic exar..ination cf cer.: rete thin sections and documented its c on:l us i o r.s i r, a re p ort , da t e d J t'y 2, 19 7 9.

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We have completed our review of the results of the tests performed by the Portland Cement Association and the evaluation perfcrmed by the Corps c:

Engineers. E,ased on our review of the test data, we concl ude that there is no evidence of degradation of concrete strength nor is there any sign of substandard cr f aulty cement. Hcaver, ite cannot concl ude that the lov SG-day strencths cbtained with the cylinder tests are attributed to testing machine f actors er testinc ccnditions as claimed by the applicant.

We note tha; the 90-day cylinder streng:h tsst results correlate very well with the twc-inch cube compressive screncth test res u'i ts. In fact if So .h s ets of results are plottec , th! w: c u ves would almost be parallel .

Eecause of :his excellent correla*.icn betwetn :ne s.rencths of cubes and cylincers , we con 1ude that the 90-day :y;inder test resuits shouid ce censicered as valid and that these resul.s shoulc be used in assessing the load carrying capacity cf the base a.

Tne ap;iicant c;m;ieted the requested reena~ysis of the base mat and.the results were suomitted by letter, datec' May 10, 1979. In crder to perform the reenalysi s, the a:plicant first detemi .ed I ccncret.e strength for the met based en the 90-day cylinder test risul.s by utilicine the established ecceptance criteria in Section 4.3 of Americ2n Concrete Institute ( ACl) {

St andard 313-71. We concur with the applicant that the resultant strencth is 4450 pounds per scuare inch.

Tne reanalysis of the base mat was then pedormed in accordance with the l

. 1 criginal cesign comitments of the 'sif Creek P3AP, by using the calculated l l

concrete strencth of 4450 pounds per scuare inch. A seismic soil-strue:ure l interaction analysis was performed by using the co ?vter code FLUSH based l l

1

4-en a finite el ement approach. Since the We'.f Creek plant is one of the five SZ?PS standard plant units, the SNUPPS envelope design earthquak e ground motior.s of 0.209 for the safe shutdown earthquake (SSE) and 0.129 for the c;eratir; basis earthcuake (OEE) were used c generate the seismic cesign forces for the base mat. Tne SSE ard OEE fer the Wolf Creek site are 0.129 and O.Cr.'c, respectively.

The seismic f orces generated by the finite element apprcach were compared wit'.r th:se cenerated by another established metroc cf analysis, the fixed

ase a;; cach, to cemenstrate that :ne seisric icads usec in the reanalysis a re cc ns erva t i ve ior the 'r.'ol f Creek pi a nt . For the fixed base approach, the '.icif Creek site specific design sar;hcuike ;rcund m:tions of 0.12 c f or

• he ES E and 0.0'g for the OEE were used as 'n;u: mo. i ons .

Tne es'.its of the reanalysis by bo:h a;proa:hes i ncica:e that the case mat mes:s the desien criteria for the W:1f Creek. f acility and that the tensile stress es cf the reinfcrcing steel are cen:r:liir.c. Thus, the base cat cesi;r. is ::ntrolled by tension ar.d the lead carryng capacity of the ma: is ;cverned primarily by the am:ur.: cf reinforcing bars provided in the bas e mat. Lowering the specific concrete desion strength f rom 5000

o 4460 pcunds per square inch has very lit:le effe:t on the load carrying capacit;. cf the base mat.

Eased on cur review of the test results and the results of the reanalysis,

. we conc ude that the base met concrete strer.gth has not retrogressed, tha*. the strength of the base mat meets the original design criteria

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1 in the V:if Creek PSAR, and that the me; will withstand the specified design leads and Icading ccmbinatior.s witho;t impairment of its structural integrity or its s afety function. '

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