ML20027A499

Forwards Interim Rept to Document Current Status of Util Investigation of Low Strength 90-day Concrete Cylinders Described in Insp Rept 50-483/78-04.Conclusion:base Mat Concrete Meets 5000psi Design Requirement

ML20027A499
Person / Time
Site:	Wolf Creek
Issue date:	05/25/1978
From:	Koester G KANSAS GAS & ELECTRIC CO.
To:	Seidle W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20027A495	List: ML20027A497 ML20027A498 ML20027A499 ML20027A500 ML20027A501
References
NUDOCS 7812110276
Download: ML20027A499 (4)

Text

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May 25,1978 Mr. W.C. Seidle , Chief -

Reactor Construction and Engineering ,

Support Branch U.S. Nuclear Regulatory Coranission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011

Subject:

Interim Report - Investigation of*

Iow Strength 90-day Concrete Testi Cylinders - 50-482 i

Dear Mr. Seidle:

In accordance wi'th the agreement made with Mr. C. Oberg on M'ay 19, the attached Interim Report is provided to

! document the current status of our investigation of the i low strength 90-day concrete cylir.ders described in Inspection Report 78-04, i

Also attached is a tentative report on the testing per-formed at the Portland Cement Association laboratory in 4

Skokie, Illinois. ,

Please advise if you need additional information.

Yours very truly,

$$f(/- W N-CIJ.tbb Attach .

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cc: JOArterburn/ attach EWCreel/ attach WEHitt (Daniel) / attach DTMcPhee (KCPL)/ attach 1

9 79- y 1 o 2yg,

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INTERIM REPORT INTRODUCTION 1.0 .

l 1.1 To comply with the NRC's request for additional information, this interim report is being submitted regarding the :esults of the 90 day compressive strength tests associated with the Reactor Building base mat.

1.2 On March 15, 1978 Kansas Gas and Electric Company (KG&E) verbally notified the assigned NRC reactor

• inspector that the 9 0 thy <=nnt-rat-a t yl i nd er com-

, pressive strength tests indicated that the cylinder strengths were below the specified value .of 5000 psi.

(Reference Nuclear Regulatory Commission Inspection .

Report No 78-04) 1.3 On May 3, 1978 Mr Seidle was advised of the status of the cylinder break investigation and that, because of f avorable data from our investigations we judged this situation as not being reportable per 10CFRSO.55(e) .

(Reference Mr- Glenn L Koester letter to Mr W C Seidle dated May 3,1978)

• 1.4 This interim report gives the current status of investi gations regrrding the Reactor Building base mat 90 day a

concrete cylinder breaks. ,

2.0 DESCRIPTION

OF DEFICIENCY

! 2.1 Sixty-six pairs of concrete cylinders were destructive 1 l

tested 90 days after the base mat was poured. The strength values when computed in accordance with ACI 318 criteria were approximately 350 psi below the 5000 psi specified strength.

I 3.O CHRONOLOGY OF EVENT 3 3.1 On February 2,1978 an analysis of the 7 and 28 da'y compressive test data was made following the guidance of ACI-214-65. This analysis indicated that the Coefficient of Variation was excellent and the within test variation was good, and that the concrete strengtis at 28 days was nearly up to the value specified for 90 days.

3.2 On March 13,1978 the 90 day cylinders were destructive tested.  ?

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[ . 3. 3 On March 14, 1978 nonconformance report No 1-0229-C was prepared to document that the 90 day cylinders failed to meet the 5000 psi strength requirement.

3.4 On March 15, 1978 the NRC was advised of the lu test.

strengths. . .

3.5 On March 20, 1978 an analysis of the 90 day concrete strength data wa s pc rformed by Kansas Gas and Electric Company in accordance. wit h ACI-214-65. Results showed that the within test s P.andard deviation and within test coefficient of variation for the' 90 day tests were larg than should have been experienced indicating a possible p'roblem in the testing procedure and/or equipment.

3.6 On March 27, 1978 an examination of the cylinder cc:E-pressive test machine was made. The hydraulic measurin system of the machine was found to be within calibratio tolerance, however, the lower wear plate was found to be loose from the lower platen with the space between filled with cylinder debris which had been crushed to a fine powder. This ' material caused the lower plate to be at a slight angle from the front to the back of I

the machine. The material was removed and the wear

, plate returned to'its correct position.

3.7 During the period March 23 to April 10, 1978 Kansas Gas and Electric Company, Bechtel, Daniel, and Portland Cement Association personnel developed a schedule of tests and investigations to be conduc'ted. Some of the more significant investigations / tests which were scheduled are:

(a) Air content of concrete * '

(b) Petrographic analysi's of concrete .

(c) Admixture analysis .

I (d) Cement content analysis (e) Comparison of results between on-site testing mach and machine in Fortland Cement Association Laborat

' (f) Comparison of strengths of 2* x 2" cubes made frcr 90 day cylinder remnants versus the strength of th cylinders as measured by the on-site testing nachi (g) Windsor probe testing of the base mat concrete (h) Correlation test.tng of compressive test cylinders, and cores, and Windsor probe measurement:a using tc pads of the same' concrete mix used in the base mat (i) Investigations / tests to attempt to quantify the ef fects of applying compressive loads on test cyli where the bottom plate is not normal to the direct of the applied force with the angle being a functi

, of the applied load. ,

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$'40 PRELIMINARY RESULTS ,

All of the above tests have been completed except for h and i It is expected that these will be completed by mid-July. Ech ever, preliminary results from the completed tests give stro positive indication that the concrete in the reactor' base ma .

has a compressive strength well in excess of 5000 psi and al other chemical and physical properties are as expected for .

high strength concrete. -

5.O CORRECTIVE ACTIONS 5.1 As described above, extensive testing and investigation is being conducted to . determine the properties of the base mat concrete and to determine the cause of tha. low:

indicated cylinder strengths at 90 days. ~

5.2 The compression testing machine has undergond exter.sive maintenance and calibration chec'ks. This. program will be continued to assure the machine stays in good workinc order.

. 5.3 Increased attention is being directed to the trends of r the 7, 28, and 90 day compressive strength test results.

6. O

SUMMARY

6;l Investigations completed as of this time indicate that the base mat concrete meets the 5000 psi design require-ment and the disparity in strength values is most likell due to an error in measuring the strength of the 90 day cylinders.

6.2 Because of the evidence available which indicates the Reactor Building base mat concrete meets design require-ments, Kansas Gas and Electric Company does not regard

.this condition as being reportable to the Nuclear Regulatory Commission per 10CFR50.55 (e) .

6.3 Testing and investigation is still being conducted. The estimated completion date is now set for mid-July. At

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this time the complete data package will be made avail-able to Bechtel for their evaluation.

6.4 A final report on this condition will be submitted to tt i

Nuclear Regulatory Commission upon return of NCR No 1-02 l C from Bechtel. A final report should thus be completed i

about August 1,1978.

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