ML20085G487
| ML20085G487 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Browns Ferry |
| Issue date: | 10/29/1973 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Kruesi F US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20085G474 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8308290103 | |
| Download: ML20085G487 (4) | |
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Y Mr. F. E. Krucsi, Director Directorate of Regulatory Operations U.S. Atoctic Energy Commission Washington, D.C.
20545
Dear Mr. Krucsi:
An initial report of a possible deficiency involving inverted control rod absorber tubes for Browns Ferry Nuclear Plant units 2 and 3 was made by L. D. Weber to AEC-DRO Inspector B. J. Cochran on August 21, 1973. The initial report was followed by an interim report, J. E. Gilleland to F. E. Kruesi, dated September 19, 1973, in compliance with paragraph 50.55(e) of 10 CFR 50.
Enclosed is a final report on this deficiency.
Very truly yours, j
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J. E. Gilleland Assistant to the Manager of Power i
Enclosure CC (Enclosure):
Mr. Norman C. Moscicy, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission
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Region II - Suite 818 230 Peachtree Street, hv.
Atlanta, Georgia 30303 I
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ROWNS FERRY !RICLEAR PLANT UNITS 2 AND 3 INVERTED ABSORBER TUBES IN CONT No RODS FINAL REPORT i
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Aaferences:
1.
Letter from J. E. Gilleland to Norman C. Moseley, AEC,
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Director of Region II.of the Directorate of Regulatory Operations, Final Report Concerning Inverted Control Rod Absorber Tubes for Browns Ferry Nuclear Plant Unit 1, dated August 13, 1973.
2.
Millstone Nuclear Power Stiltion, Unit 1, Special Report -
Reactor Control Blade Evaluation, dated July 23, 1973.
The init'ial report of the inverted absorber tubes in some of the control rods of units 2 and 3 at the Browns Ferry Nuclear Plant was made on August 21, 1973, by L. D. Weber to B.' J. Cochran, Principal AEC-DRO Region II Inspector for Browns Ferry Units 2 and 3, in c6mpliance with paragraph 50.55(c) of 10CFR50.
j An interim report was submitted on September 19, 1973.
Because 33 out of the 185 control rods in unit 1 of the Browns Ferry Plant contained inverted absorber tubes as reported in reference 1, the control rods of units 2 and 3 were suspected of having similar defect's. Likewise, similar conditions were reported for the control rods of unit 1 of the Inlistone Nuclear
'i Plant in July 1973 as described in reference 2.
This difficulty was caused by dtrrors in the control rod assembly operations.
All control rods for units 2 and 3 were x-ray inspected for proper tube orientation et the General Electric-Wilmington, N.C. plant. All control rods found with i
l; inverted tubes are being repaired by removing the tubes and reassembling rods
!)'I Properly. Correct re-assembly.is verified by x-ray inspection. This corrective
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cetion is planned to be completed by November 1,1973.
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$ x-ray inspection, radiographs were taken of cach control blade sheath
/the bottom end (velocity liniter end) cf each control rod. The presence of the steel wool packing used in cach absorber tube indicates that the tube is correctly installed.
If difficultics were experienced in positively determining the presence of steel wool and an identifying dimpic was not found 1-1/4 in, f rom the top end, a radiograph of the top end was taken, and the control rod assembly was accepted if steel wool was not observed tt the top and an identifying dimpic was found approximately 1-1/4 in. from the top.
It was found that any control rod assembly having inverted absorber tubes probably had a large fraction of its tubes inverted.
In fact, the assemblics with inverted tubes had an average of slightly more than 56 tubes inverted.
Each cssembly contains 84 tubes, with 21 in each wing of the cruciform. The data obtained during the inspection are given in the table below:
i Item Number Number of Control Rod Assceblics Inspected i
378 Number of Absorber Tubes Inspected 31,752 Number of Absorber Tubes Found Inverted 7,480 Percent of Absorber Tubes Found Inverted 24 Number of Control Rod Assemblics Found to Contain One or More Inverted Absorber Tubes 132 Absorber. tube inversion could possibly result in about a 15-inch settling of the contained B C level at the top of an inverted rod as discussed in reference 2.
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Reference 2 also' presents results of studies of reactivity cnges resulting from possibic B C settling in Millstone Point unit 1, and these results are 4
cpproximately applicabic to the Browns Ferry cores.
Substantial numbers of 1
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'rted tubes and concequent B C settling would have been detected during the 4
t ariodic tests which demonstrate compliance with the technicci :,pecification
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requirement for 0.38 percent A k shutdown margin with the strongest control rod i
fully withdrawn from the core and the reactor would have been kept shut down.
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