ML19207B525
| ML19207B525 | |
| Person / Time | |
|---|---|
| Site: | Cherokee  |
| Issue date: | 07/20/1979 |
| From: | Dail L DUKE POWER CO. |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML19207B521 | List: |
| References | |
| NUDOCS 7908300119 | |
| Download: ML19207B525 (4) | |
Text
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DUKE POWEH CO31PANY
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GENERAL OFFICES 422 Souf M CMURCH STRtti CII ARLOTTE. N. C. 28242 U
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w Mr. J. P. O'Reilly, Director U. $. Nuclear Regulatory Commission 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re:
Cherokee Nuclear Station IE:II:JP0 Inspection Reports: 50-491/492/493-79-10 Duke File: CK-1412.ll-1
Dear Mr. O'Reilly:
In the referenced inspection report, an item of non-compliance was identified. Duke Power's response to this item is enclosed.
Duke Power does not consider any of the information contained in the report to be proprietary.
Very truly yours,
-e 4 L. C. Dail, Vice-President Design Engineering Department JDW/sr Enclosure 852 154 796'76 7908300 / / G r
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DUKE'S RESPONSE TO INFRACTION 79-10-01 8
1.
Description of Non-Compliance The acceptance criteria for compaction of filter materials in the NSW e
Dam is 80% Relative Density as defined by ASTM D-2049 Prior to filter placement, correlation curves were developed from laboratory tests relating the Uniformity Coefficient (Cu = D60/D10) to the maximum and
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minimum dry density for each type of filter material, i.e.
fine, coarse, and transition material.
During an NRC inspection on May 8-10, 1979, the Inspector raised a question concerning sensitivity of the correlation curves for each of the filter materials. Duke agreed to evaluate the sensitivity and the NRC inspector issued an " unresolved ited'.
During the sensitivity study, a discrepancy was discovered in calculating the bulk density values for the sand used in the in-situ testing of the filter materials.
ASTM D-1556 a110ws two methods of calibrating sand density:
(a) in the A modified sand cone Jar or (b) in a container of known volume.
version of method (b) had been used and it was determined that this gave
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a higher bulk density than method (a), therefore, a higher in-situ All density tests in the filter material were then recomputed s
density.
using corrected bulk density values. This analysis showed that the corrected test results fell below the 80% relative density requirement of the specification as follows: 27.9% of the tests in the fine fil ter, 15.4% of the tests in the coarse filter, and 57.1% of the tests in the transition material.
On an inspection by the NRC on June 12-13, 1979, the unresolved item was changed to an item of non-compilance, to which this report is a response.
Since laboratory testing has not been completed, the evaluation of the sensitivity study will be included in an addendum report.
Beginning June 7, 1979, a systematic program of additional field testing was implemented to determine the in-situ density of the filter materials.
The zones of the filter material already in the dam were considered in three parts:
1) the chimney drain, 2) the filter blanket which has been covered with soII, and 3) the filter blanket still exposed.
In the first area, the chimney drain, the test results, corrected for hulk density, showed a grouping of 4 in-situ tests at various depths that were below 80% relative density. Two s
near Station 15+12 L 30' ( d at this location, indicated a low relative
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borings wi th SPT's performe Additional borings were drilled on cach side of this station g^
density.
g to define the area of low relative density.
Comparison of SPT values in the suspect zone with those at Station 16+22 and Station 16+72, Indicated that there existed zones of poorly compacted fine filter between approximately Station 14+50 and 16+00 in the chimney drain.
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I In the area of the filter blanket which is covered with soil, a dewatering program was initiated to permit additional in-situ density testing. Also, Standard Penetration Tests (SPT) are being performed for the evaluation of the filter material conditions, in the area of the filter blanket which still is exposed, additional in-situ density testing was done to determine if additional compaction has occurred in the lower layer of the fine filter due to the subsequent in some cases, the placement of coarse and upper fine fil ter layers.
density was found to have increased since the original test.
The SPT's were performed in the chimney drain in holes about four inches in diameter using drilling mud to stabilize the walls.
To verify that the drilling fluid was not loosening the sands and causing erroneous SPT's, a static penetration test, the " Dutch Cone," was used.
The Dutch Cone requires no drilled holes and is pushed through the sand in incre-ments by applying a force from the drill rig.
The " Dutch Cone" test results verified the weak sands in the same locations as determined by SPT.
The construction records were reviewed and it was determined that this general area had received considerable rework, in the period August to November 1978, during the tying in of the blanket and chimney drains.
The SPT tests and construction records indicate that the reworked areas did not receive adequate compaction and testing.
The low SPT values show that the in-situ relative densities in the weak zone of the chimney drain are in the " loose to very loose" descriptive This indicates that the relative densities are probably less range.
than 50% and would be a discontinuity in the completed structure if left in-place. Review of the finite element analysis calculations also indicates that the weak zone would be overstressed by the shear strains induced in the embankment during the SSE. Therefore, it was concluded that the weak zone should be removed and replaced with adequately compacted material to provide an embankment whose safe performance during SSE will be assured.
Duke notified NRC by letter on June 15, 1979, that field work would be discontinued until the problems had been evaluated and a resolution acceptable to the NRC had been agreed upon.
II.
Corrective Action Proposed in Progress in a meeting with the NRC Inspector on July 6,1979, proposed corrective action was presented as follows:
In Area 1, the chimney drain between Station 14+50 and 16+00, the loosely compacted fine filter and transition material will be removed or re-compacted. The affected zone will be replaced and compacted as shown on the attached Drawing CK-0026-07 dated 7-10-79 In Area 2 the blanket drain covered by soil, verification in-situ density testing will be performed when the water has been lowered sufficiently.
Our evaluation of these testing results will be available for NRC review prior to any further work in this area.
852 156
The upper fine filter Area 3 blanket drain exposed, will be recompacted.
In areas of the coarse layer will be retested after recompaction.
filter and lower layer of fine filter which presently show densities After less than 80%, relative density retesting will be performed.
acceptable results are determined, work will resume in this area.
Corrective Steps Taken to Avoid Further Non-Compilance Ill.
is our opinion that by using the correct method for determining the itbulk density of the test sand, the problem associated witn the non-In addition, design specirications will be compliance will be resolved. revised to require increased frequency of in-situ t to prevent small quantitles of material in narrow zones to go untested.
In addition, an organizational change will be implemented so that all technical control of the contractor for the nuclear safety related earthwork will be under the direct supervision of the Project Geo-technical Engineer or his representative.
Schedule for Completing Work and Addendum Report IV.
is estimated that the additional testing in the At the present time it 15 Area 2 retesting blanket drain, Area 3, will be completed by August and Area 1 remedial work will be completed between September 15 to Our estimated date to be in full compliance will be October 15, 1979 An addendum report covering testing and proposed October 15, 1979 remedial work for Area 2 will be provided in September when tests are completed and an action plan has been approved.
852 157
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