ML19327A008

Responds to NRC 790627 Ltr Re Violation Noted in IE Insp Repts 50-491/79-10,50-492/79-10 & 50-493/79-10.Corrective Actions:Corrected Procedure for Determining Bulk Density of Test Sand & Increased Testing of Filter Matl

ML19327A008
Person / Time
Site:	Cherokee
Issue date:	06/25/1980
From:	Dail L DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19327A007	List: ML19327A008
References
NUDOCS 8008010044
Download: ML19327A008 (3)

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DUKE POWER COMEAy.h. ,

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ELECTHIC CENTEH, Box 33180, CHAntoTtEc Ni 0 p .- - - -48242 " '

..:inidEh. M ..in i A8: 59 June 25, 1980 Mr. J. P. O'Reilly, Director U.S. Nuclear Regulatory Commission 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 i

Re: Cherokee Nuclear Station IE:II JPO Inspection Report: 50-491, 492, 493/79-10 Duke File: CK-1412.11-1

Dear Mr. O'Reilly:

Enclosed is Duke's final report concerning the item of non-compliance identified in the referenced inspection report.

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a. C. Dail, Vice' President Design Engineering EKM/pam Enclosure 800801oggy 0FFICLE COM

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CHEROKEE NUCLEAR STATION DOCKET NOS: 50-491, 50-492. 50-493 FINAL REPORT TO INFRACTION 79-10-01 Restatenent of Non-Compliance (Reference Duke letter dated July _20, 1979)

During an NRC inspection on May 8-10, 1979, a question was raised concerning the " sensitivity" of the correlation curves for each of the filter materials.

During an evaluation of the " sensitivity" an error was discovered in the determination of the bulk density of the sand cone sand used in determining the in-situ density of the filter materials. A study was made of the significance of-this error and it was determined that, after correction, certain originally passing. tests became'failing tests.

, After thorough study including additional laboratory and field testing, it 1

was concluded that remedial work would be necessary in certain areas of the

existing filter zones of the dam.

At a meeting with NRC inspector, Mr. Jack Harris, on July 7, 1979, Duke's

, proposed remedial actions were outlined. The dam filter zones were divided into three parts for this work. The remainder of this report states the actions

. -taken in these three areas.

Remedial Work (Reference Duke Drawing CK-0026-07) i t Area I

Area I work consisted of the removal of the chimney drain between stations 14+50 and 16+00. The work began July 17, 1979, and the excavation was completed and -i the contractor started replacing material on August 16, 1979 This a'rea was  !

brought back.to original grade about January 4, 1980. The required testing frequency'in the chimney drain and~ transition zones was increased to the following:

one test per 100 tons of material placed, one test per three feet increase in elevation, or one test per shift, whichever gave the most tests. This was

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done to insure that no loose zones were placed in this confined area. The required testing frequency will be increased proportionally for the remainder

.. of the chimney'and transition materials in the dam. All material was placed in accordance with the specification. Test results are available on site for review.

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Area II Area 11. consisted of'the low-level downstream blanket. drain which was already covered by soil. .This area was dewatered and those zones which indicated failing tests were retested. It was confirmed that there were some areas which were ,

still:below the required relative density. Non-Conforming item _(NCl) 0842 was I written on these falling tests and sent to Design Engineering. The resolution  !

, was to remove the Group 1 soll and recompact the blanket drain. Removal. began i on March 10, 1980, and recompaction began on April-2, 1980. After all the ,

retests' met the specification,'the placment of Group 1 fill began and the area was completed back to original grade on or about May 14, 1980. Results of tests'taken in this area are available on site'for review.

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i Area Ill

, Area Ill consisted of the remainder of blanket drain which was still exposed.

The area was recompacted and retested during the fall of 1979 and spring of 1980.

The retests met the specification and the area has been covered with Group I fill.

Sensitivity Study On June 27, 1979, a sensitivity study concerning the relative density control of the filters on the NSW dam was sent to Design Engineering. This report was reviewed by both Design Engineering and Law Engineering Testing Cdmpany. After evaluation, it was concluded that the present method for determing maximum and minimum density of the filter material was acceptable. Studies for this evaluation are available on site.

Summary As stated before, all retests of the filter materials are available on site for review. Changes in procedures which were taken to preclude recurrence of the problem are as follows:

a) Method for determining bulk density of test sand used in relative density test has been corrected.

b) Technical control of Contractor's operations is now under direct supervision of the Project Geotechnical Engineer.

c) Specifications now require increased testing frequency of filter materials.

Based upon t e results of recent retesting, or recompaction and testing, all filter materials in the dam are now constructed in full compliance with the specifications, and work is continuing.

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