ML16342A071
| ML16342A071 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 04/14/1993 |
| From: | Jun Lee Office of Nuclear Reactor Regulation |
| To: | George Minor, Sholly S MHB TECHNICAL ASSOCIATES |
| Shared Package | |
| ML16342A067 | List: |
| References | |
| NUDOCS 9304260252 | |
| Download: ML16342A071 (4) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 206664001 April 14, 1993 ENCLOSURE 1
Docket Nos. 50-275 and 50-323 Mr. Gregory C. Minor Vice-President MHB Technical Associates 1723 Hamilton Avenue - Suite K
San Jose, California 95125
Dear Gentlemen:
SUBJECT:
DIABLO CANYON CABLE DEGRADATION Mr. Steven Sholly Senior Consultant MHB Technical Consultants 1723 Hamilton Avenue - Suite K
San Jose, California 95125 Thank you for your letter and fax transmittal to Mr. Ashok Thadani, dated
.April 1 and 2, 1993, respectively, concerning the above subject.
The NRC was already aware of these cable failures and has been actively monitoring the licensee's follow up activities.
Our preliminary review indicates that there is no immediate safety concern at Diablo Canyon associated with the cable degradation issues you raised, for the reasons discussed below.
As discussed in your letter, a possible root cause of the cable failures is water submergence; however, this hypothesis is still being evaluated.
While the root cause is being investigated, the licensee has taken action to preclude the possibility of future cable failures attributable to moisture intrusion and migration.
For example, the licensee has implemented an electrical maintenance instruction to monitor the water level in the cable vaults immediately outside the turbine building 12kV cable spreading
- rooms, and to pump down the water level as necessary, following any significant rainfall.
In addition, the licensee is performing an engineering and chemical analysis of the degraded cable jackets and samples of fluid taken from cable vaults, pull boxes and associated conduits to determine and resolve root cause of the cable degradation.
The licensee also has continuous on-line electrical ground detection capability.
With regard to the three 4kV cable failures, only the first failure was an in-service failure of safety-related equipment occurring in October, 1989.
The second failure of a 4kV cable, which occurred in May 1992, was on a non-safety related bus feeder cable.
The third failure was on a safety-related
- cable, which was not in service, that failed during a periodic high potential test.
There have also been two in-service failures of non-safety-related 12kV cable.
The three 4kV cable failures did not exhibit the same jacket degradation as the two 12kV cable failures.
The 4kV cables that failed were removed and analyzed
- and, except for the fault, were found to be in good physical and electrical condition.
In addition, the 4kV cables experienced much lower levels of electrical stress and cable self-heating than the 12kV cables.
In all five cases of safety and non-safety related cable failures at. Diablo
- Canyon, the faulted portion of the circuit has been replaced.
Additionally, in March 1993, the licensee replaced a section of 4kV cable associated with 9304260252 9304i6 PDR 't ADOCK OS000275'DR
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Messrs.
Minor and Sholly the safety-related auxiliary salt water (ASW) pump, which had not previously experienced any cable failures.
This was done as part of the licensee's root cause efforts.
As a result, both trains of safety related cable to the 4kV ASW pumps have been replaced since October 1992, for that section of cable routing where the 12 kV cable degradation has been observed.
Concerns received in our office regarding the operation of a specific facility are normally forwarded to the NRC regional office responsible for inspection and enforcement activities for that facility.
Therefore, because there is no immediate safety concern, I have forwarded your concerns to our Region V
office in Walnut Creek, California.
Although our office will be assisting that office on this issue, the Region V office will address this matter and inform you of the results of the review.
Your point of contact at the Region V office is as follows:
Mr. Forrest Randall Huey Enforcement Officer U.S. Nuclear Regulatory Commission Region V
1450 Maria Lane Walnut Creek, California 94596-5368 (510) 975-0342 Sincerely, Je Lee Allegations Coordinator Office of Nuclear Reactor Regulation