ML20084R943
| ML20084R943 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/02/1974 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML20084R941 | List: |
| References | |
| 712-74, AO-50-249-74-29, NUDOCS 8306160079 | |
| Download: ML20084R943 (3) | |
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Address Reply to: Post Omce Box 767 Chicago, liiinois 60690 BBS Ltr.#712-74 Dresden Nuclear Power Stat R. R. #1 M% /'
Morris, Illinois 60450 October 2, 1974
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U. S. Atomic Energy Comnission 799 Roosevelt Road Citj A gh Glen Ellyn, Illinois 60137 SUBJET: REPORT OF AENORMAL OCCURRDICE PER SECTION 6.6.A OF THE TT HNICAL SPECIPICATIONS.
THROUGH-WALL CRACK ON '1VRUS/DRYWu PURGE LI!!E, UNIT 3.
References:
- 1) Regulatory Guide 1.16 Rev.1 Appendix A
- 2) Notification of Region III of AEC Regulatory Operations Telephone Mr. P. Maura, 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> on September 24, 1974 Telegram: Mr. J. Keppler, 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> on September 24, 1974
- 3) Drawing Number: M-336 (S&L)
- 4) Attached copy of NDP Report on Unit 3 Torus /Drywell Purge Line Report Number 50-249/1974-29 Report Date: October 2, 1974 Occurrence Dates September 24, 1974 Facility: Dresden Nuclear Power Station, Morris, Illinois IDENTIFICATION OP OCCURRD;CE Through-wall crack on torua/drywoll purge line, Unit 3 CONDITIONS FRIOR TO OCCURRE!CE Unit 3 was locked in the shutdown mode, with the drywell open for repairs unrelated to this incident, at tho time of the occurrence.
DESCRIPTION OP OCCURRD:CE At about 1030 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91915e-4 months <br /> on September 24, 1974, a local leak rate test was being conducted on the boundary for:::cd by air-operated valves 1601-21,
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1601-22, 1601-55, 1601-56, and 8502-500 on the torus /drywell purge (See Reference 3).
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o Mr. James G. Keppler October 2, 1974 i
The test involved pressurizing the piping to 50 pais and noting pressure decay A rapid decay was noted and further investigation revealed a crack in the 18-inch 3-8506 torus /drywell purge line, extending completely through the pipe wall, for approximately 170 degrees of are around the lower half of the horizontally-mounted pipe, running through the weld joint for a 3/4-inch bushing that a rved as a flow test line connection. A similar bushing, located on the opposite side (180 degrees around), was plugged and unused.
The crack followed almost perfectly the are joining the two bushings.
DESIGNATION OF APPARENT CAUSE OF OCCURRENCE (Equipnent Failure)
The cause of the occurrence is unknown at this time. After investigation of the failed pipe section, a follow-up report on the apparent cause of the occurrence will be issued.
ANALYSIS OF OCCURRENCE The piping in which the crack was found is a redundant primary containment boundary, since it is isolated from the drywell by the 1601-21 valve, from the torus by the 1601-56 valvo, and from the reactor building atznosphere by the 1601-22 valve. All of these valves are nomally closed during operation.
In this case, while the reactor was shutdown and the drywell was open, 2
absolutely no danger to plant personnel or to the public existed.
Operation with this pipe segment cracked would have posed no in: mediate danger or threat. However, in the event of a serious accident involving drywell and torus pressurization, the statistical probability of a release into the accondary containment would have been increased due to lack of redundancy in the isolation valvo lineup.
4 CORRECTIVE ACTION Since the unit was shutdown, no immediate corrective action was re;uired.
i Nevertheless, repairs were promptly initiated.
A 15-inch-long segment containing the crack was cut out of the line. A i
new pipe segment was welded in place on September 25, and radiographic tests of the welds were performed on September 26.
In addition, 30 other welds on the same piping (3-8506, 18-inch) were magnetic particle checked and found to be sound. See Reference 4.
On Unit 2, the corresponding piping was visually checked and pressurized with air; no visible or audible leaks were detected, f
F Mr. James G. K2ppler October 2, 1974 A subsequent magnetic particle check of 34 welds, completed on September 27, produced no indications of cracking. (Three surface indications, which disappeared with filing, were noted).
Further preventive measures are dependent on the results of the analysis to determine the cause of the occurrence.
FAILURE DATA The 18-inch 3-8506 torus /drywell purge piping is of seamless, A106 Grade B steel of 3/8-inch wall thickness.
Sincerely,
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Ste enson Superinte dent BBS do c
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