ML20235E656
| ML20235E656 | |
| Person / Time | |
|---|---|
| Issue date: | 07/06/1988 |
| From: | Beckjord E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Jordan E Committee To Review Generic Requirements |
| Shared Package | |
| ML19318E953 | List: |
| References | |
| RTR-REGGD-01.106, RTR-REGGD-1.106 NUDOCS 8902210562 | |
| Download: ML20235E656 (2) | |
Text
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UNITED STATES 8
NUCLEAR REGULATORY COMMISSION O
WASHINGTON, D. C. 20555 sNL 6 158 p
MEMORANDUM FOR:
E. L. Jordan, Chairman j
Committee to Review Generic Requirements j
i FROM:
Eric S. Beckjord, Director Office of Nuclear Regulatory Research
SUBJECT:
CRGR REVIEW - PROPOSED REVISION 2 TO REGULATORY GUIDE 1.106, " THERMAL OVERLOAD PROTECTION FOR MOTOR-0PERATED VALVES FOR NUCLEAR POWER PLANTS" - COMMENT VERSION BACKGROUND:
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l Thermal overload devices protect valve operator motors from damage due to overheating by tripping and disconnecting the motors. However, a thermal overload protection device could trip and remove power from the motor before the safety function has been completed or even initiated.
In nuclear power I
plant applications, the criterion for establishing an overload trip setpoint should be to enable the motor to complete the safety function (e.g., drive the valve to its proper position to mitigate the effects of an accident) rather than merely to protect the motor from destructive heating. The regulatory positions in Regulatory Guide 1.106, Rev.1, dated March 1977, delineate such criteria.
An NRC AE0D study (AE0D/S503, dated September 1985) identifies more than 200 valve operator motor burnouts that had occurred within the past 5 years.
a What is especially disturbing about these events is that many have gone undetected for extended periods.
In retrospect, this circumstance follows
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from what the staff now perceives as a deficiency in Regulatory Guide j
1.106. Specifically, there is no provision to indicate or alann thermal overload device trip. Since burnouts, as well as many lesser motor overload conditions, would be accompanied by a properly sized thermal overload device trip, it seems essential that such tripping should be alarmed to warn of the potential or actual nonfunctioning condition of the valve operator. While the conditions that cause overload, such as faulty limit switches, excessive friction, and undersized valve operators, cannot be corrected by Regulatory Guide 1.106, the staff believes that thermal overload device trip alarm would make a contribution to safety by removing this observed class of undetected i
failures which has obvious common-cause failure, as well as random failure, i
implications. An appropriate Regulatory Position (C.1) has been added; and Regulatory Position C.1.(a) of Revision 1, which permitted continuous bypassing during normal operation, has been deleted to lessen the probability of motor l
burnout.
l STAFF COMMENTS AND RESOLUTION:
NRR concurred with the regulatory positions (Draft 1). AE0D provided comments k
by memorandum dated August 19, 1987, Novak to Arlotto (Enclosure 1) and in
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l subsequent meetings on April 15 and April 18, 1988. We believe that these J
f comments have been satisfactorily resolved.
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Concurrences.on this pack' age were obtained from the. Director'of NRR, and.the.
I Office of the General Counsel..
ACTION l
CRGR approval to issue Revision 2 to Regulatory Guide.1.106 (Enclosure 2) for.public comment is requested.
J
).A.,Jb Eric S. Beckjord irector Office of NuclearM egulatory Research q
Enclosures:
(15copieseach)
- 1. Memo dated August 19, 1987, Novak to Arlotto
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- 2. Proposed Revision 2 to'Regu-l latory Guide 1.106 l
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