ML20140F647
| ML20140F647 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/07/1997 |
| From: | Amy Cubbage NRC (Affiliation Not Assigned) |
| To: | Hernan R NRC (Affiliation Not Assigned) |
| Shared Package | |
| ML20140F623 | List: |
| References | |
| NUDOCS 9706130183 | |
| Download: ML20140F647 (2) | |
Text
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From:
Amy Cubbage Yo:
WNP3(RWH)
Date:
Sm97 3:56pm j
Subject:
SEQUOYAH PRESSURIZER DRAINDOWN -Forwarded -Forwarded -Reply
- Amy, Please review the attached comments from Paul Blanch. I think I hear saying the same thing you said in yesterday's prebriefing. The question is what should we be doing with/to licensee's to make them appreciate this phenomenon?
j Ron Heman
- Ron, The technical content of Blanch's e-mailis mostly correct. It is my understanding that TVA has identified the root cause of the loss of reference leg inventory as non-condensible gases coming out of solution during depressurization. This may not be stated in the same way the J
Blanch states it but it is the same root cause. Until this event, TVA was apparently not sensitive to this issue, but they seem to understand the phenomenon now. The Westinghouse i
notice he refers to was sent in 2/89 (not 1988) to Northeast utilities, and I don't remember if it was sent to all Westinghouse plant at the same time. To the best of my knowledge this particular notice was brought to our attention in 1992. The PWR level issue was raised to the NRC in 1991 via allegations and a Milistonc 3 LER. When he refers to the fact that he was given assurance that "every licensee corrected the problem," I assume that he is referring to the hardware modifications that were completed by all BWRs. PWRs were not required to make any hardware modifications.
FYI, see attached chronology of PWR levelinstrumentation concems. I have the documents that are mentioned if anyone needs more detail.
Amy Cubbage CC:
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4 PWR LEVEL INSTRUMENTATION CHRONOLOGY I
I 2/89 Westinghouse letter to Millstone discussed pressurizer level errors la 3/91 Allegations raised regarding Millstone and Haddam Neck pressurizer level j
4/91 Millstone 3 LER discusses pressurizer level errors 7/92 IN 92 54 issued - Discussed BWR and PWRs. For PWRs, informed licensees that the
. problem may affect. indication of PZR level. "The inaccuracies caused by rapid depressurization events in PWRs have limited safety significance because instrumentation other than PZR level is used by operators to determine appropriate manual actions." NOTE: only accident scenarios were considered here, it was not considered at the time that errors could occur during a normal plant j
depressurization.
1 l
10/92 Letters sent from NRC to WOG, CEOG, and B&WOG which requested an evaluation of the following:
i (1)
Automatic safety system response during all licensing basis transients and l
accidents; (2)
Operator short and long-term actions during and after alllicensing basis accidents and transients; t
j (3)
Operator actions prescribed in EOPs or other affected procedures not covered in (2).
2/93 Responses received from Owner's groups 1
3/94 Staff SERs issued for PWRs. "The staff determined that the impact on plant safety due to j
water level instrument inaccuracies in the pressurizer and steam generator is minimal due to l
the diverse indicators used for operator short-and long-term actions. In addition, automatic j
actuation of safety systems is not based on pressurizer level, steam generator level, or i
reactor vessellevel. Therefore, the staff has determined that water levelinstrument inaccuracies due to non-condensible gases are not a significant safety concern for Westinghouse NSSS." SERs for CEOG and B&WOG drew similar conclusions.
3/97 Sequoyah event -inadvertent draindown due to erroneous PZR level indication. Operators rely on 1 channel of non safety related PZR and no other indication for RCS draindown for refueling outage. Similar events at Sequoyah in 1993.
i NOTE: BWR nneric communications and resultant hardware modifications not included