ML20126F119
| ML20126F119 | |
| Person / Time | |
|---|---|
| Issue date: | 12/08/1992 |
| From: | Jordan E NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Murley T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20126F122 | List: |
| References | |
| AEOD-S92-07, AEOD-S92-7, IEIN-92-026, IEIN-92-26, NUDOCS 9212300115 | |
| Download: ML20126F119 (2) | |
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MEMORANDUM TOR:
Thcans E. Murley, Director Office of Nuclear Reactor Regulation FROM:
Edward L. Jordan, Director Office for Analysis and Evaluation of Operational Data
SUBJECT:
pRESSVRE LOCKING AND THERMAL BlHDING 0F GATE VALVES Enclosed is AE00 Special Study, 592-07, " Pressure Locking and Thermal Binding of Gate Valves." This study was initiated as a "last straw" response to yet another valve inoperability event due to pressure locking.
The event occurred in July 1991, at the FitzPatrick plant where a low pressure emergency core cooling system (ECCS) valv.' failed to operate during a special test.
The study shows that pressure locking and thermal binding causes may each be common mode among trains of a given system and not only prevent the valve operator from opening the valve on demand but may damage the motor windings or valve internals so that subsequent remote operation is lost.
While the possibility of pressure locking and thermal binding of these valves has been known many years and at least six documents have communicated various aspects to industry, the report frequency for these prcblems has not diminished. The two strongest communications of the six occurred in 1984 and 15 of the approximately 20 reported instances occurred since 1987, 3 years to 8 years after the industry was alerted.
As a part of this study AE00 staff reviewed the status of programs at six licensees in mid 1992 to obtain an understanding of industry preventive or corrective actions related to pressure locking and thermal binding. The results were disappointing because prior to the visit most licensees did not believe the problem was ap)licable to them, hence, little action had been initiated in response to tio prior communications.
An idea of the risk associated with this common mode failure mechanism may be drawn from the accident sequence precursor evaluation of the July 1991 FitzPatrick event wpich estimated the conditional core damage probability as approximately 4x10' if all four ECCS valves failed to open.
Aside from Information Notice IN 92-26 issued in April 1992, to promptly convey NRC concerns, we are unaware of any further NRC or industry action to address this issue. A relatively simple valve modification is effective in diminishing the likelihood of pressure locking. While thermal binding of wedging components is not as amenable to control with a simple physical-I change, the affect can be reduced through appropriate operating procedures or e
use of a different type valve.
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Thomas E. Murley 2
i Although difficult to quantify, I believe this problem warrants priority attention by NRC and Industry, f
I propose that a Bulletin or Generic Letter be prepared.
I further propose that this issue be the subject of an NRC/ Industry workshop in order to adequately communicate with the proper licensee technical managers.
The meeting would serve as an opportunity to obtain industry feedback on the most effective way to resolve this problem. As we have discussed, AE00 is prepared to actively participate in these efforts, j
OrNnai Signed by:
Ddwood F. RODS Edward L. Jordan, Director ~
Office for Analysis and Evaluation of Operational Data
Enclosure:
As stated Distribution:
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