ML20059M506
| ML20059M506 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/18/1993 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| References | |
| OLA-2-A-021, OLA-2-A-21, NUDOCS 9311190130 | |
| Download: ML20059M506 (3) | |
Text
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Onsite Safety Review Group (OSRG)
February 1993 Monthly Report l
93 001 28 P 6 :,z_/
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SUMMARY
l The following items summarize the OSRG's observations and concerns from the meetings for this month. A more detailed description follows, and all items'that were reviewed are listed in Attachment 1.
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The OSRG revisited unresolved precursor events outlined in the January minutes. Several potential corrective actions to prevent recurrence were proposed.
2.
The OSRG reviewed the design for a manual isolation valve on the discharge of the positive displacement charging pump (PDP) relief valve.
The administrative controls also were reviewed to ensure that the isolation valve is open whenever the PDP is operating or available for service.
The design was referred to QA for follow-up regarding compliance with applicable codes and standards.
l
_3.
The OSRG reviewed the current compensatory action of maintaining one containment fan cooler unit (CFCU) out of service (005) in each of DCPP Units 1 & 2.
The choice of CFCUs 1-3 and 2-3 was concurred with.
It was noted that CFCUs 1-2 and 2-2 might be slightly better than the current choices, from a redundancy standpoint.
4.
The ASW pump 4kV feeder cable failures were reviewed with regard to the high failure rate. The TRG seemed to be addressing all nuclear safety aspects adequately.
5.
In reviewing a recent NOV, the OSRG identified a potential generic concern with inappropriate painting.
The NOV involved painting over the blue dots used for locating vibration test points on plant equipment.
DESCRIPTION The following items were discussed by the OSRG.
Generally, where concerns exist, they have been discussed with the appropriate TRG Chairman or responsible department head and an AR has been initiated, if applicable.
j 1.
OSRG Surveillance 92-061:
Inadequate Corrective Actions for Precursors to Recent NCRs and QEs CONCERN:
The OSRG identified a concern in its January 1993 minutes regarding inadequate response to certain precursor events.
The precursor events did not receive adequate corrective actions.
Therefore, they recurred later in a form serious enough to warrant an NCR or QE.
The items that were cited included 9311190130 930818 PDR ADOCK 05000275 g
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OSRG Surveillance 93-003: CFCUs 1-3 and 2-3 Removed From Service OBSERVATION: The OSRG reviewed the CFCU configuration that currently is in We concur with CFCUs 1-3 and 2-3 being kept out of service.
Also, it use.
was noted that it might be slightly better if CFCUs 1-2 and 2-2 were removed from service rather than 1-3 and 2-3.
This was based on redundancy of components.
DISCUSSION:
CFCUs 1-3 and 2-3 have been removed from service as a temporary compensatory measure for Operability Evaluation 93-02. The purpose is to preclude a hypothesized overheating of the CCW system during a design basis large break LOCA.
The OSRG reviewed the current configuration for redundancy. A matrix was developed for the CFCUs in relation to their associated SSPS train, CCW vital header, and electrical bus (see below).
From this matrix it apptared that if a failure of CCW header B were to occur, in the current configuration, only one CFCU would remain operable. The FSAR analysis assumes two CFCUs remain operable.
The OSRG engineer then analyzed if there was a credible failure of CCW header B.
Nothing credible could be hypothesized.
Therefore, the OSRG had no objection to the current practice.
CFCU 1
2 3
4 l
5 SSPS A (K608)
A (K609)
A (K609)
B (K608) 8 (K609)
B (K609)
CCW A
A HDR B
B B
BUS F
F G
H G
Note:
Remoying CFCU 1-2/2-2 from service would retain th,e_
greatest degree of redundancy.
4.
DCl-92-EM-N054:
High Potential (Hi-pot) Test on ASW Pump Motor 1-2 4kV Failed Cable CONCERN: The OSRG reviewed earlier concerns (November 1992 Honthly Report) regarding the higher-than-expected failure rate of ASW pump 4kV motor cables during Hi-pot testing. The failure mechanism, potential reportability and operability were discussed.
RESOLt1 TION: The OSRG concluded that, to date, the TRG was addressing generic issues adequately.
In addition, the issues have a high degree of management attention in the form of an Integrated Problem Response Team (IPRT). The OSRG will continue to monitor further PG&E investigations into the cable failures.
DISCUSSION: ASW pump 1-2 was removed from service for repairs. When returning the ASW pump to service, a direct current Hi-pot test was conducted.
l During the test, the insulation broke down. All three phases of cable were replaced between the 12kV switchgear room and the discharge structure.
While replacing the three power cables, water was discovered in an ASW 1-2 pull box.
It is speculated that a storm a few days before the Hi-pot test was the source of the water. The DCPP cables are not designed for continuous submergenc-These ASW pump cables may have been pulled through conduit several times.
Both this failure and an earlier failure on Unit 2 occurred at approximately the same location in the conduit runs. Therefore, there could be an installation-related failure mechanism.
As investigative actions, PG&E will have the following tests performed:
1.
partial discharge 15kV corona testing 2.
power factor testing 3.
ac/dc withstand testing 4.
insulation resistance testing 5.
ac breakdown testing 6.
physical testing (tensile and elongation) 7.
dissection of the area with the fault Initial inspections of the cable by PG&E showed that the overall physical and electrical condition was good.
There was no obvious sign of a failure mechanism.
The exact failure mechanism for the earlier 1989 ASW pump motor cable also -
could not be determined. The failure was not considered generic to the cable manufacturing processes used in 1972 by Okonite.
Per Okonite, the neoprene jacket on the cable that failed in 1989 had aged as expected. All other properties met specifications. There were no significant differences between the cables tested and the properties reported in the 1972 test reports other than the neoprene jacket.
Examination of the conductors showed that there was no significant amount of moisture in the conductor for any appreciable length of time.
Each length was subjected to factory electrical tests. All lengths passed.
Okonite stated that electrically and physically the insulation was in "as new" condition.
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