ML20206J930
| ML20206J930 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 05/10/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20206J918 | List: |
| References | |
| GL-95-07, GL-95-7, NUDOCS 9905130018 | |
| Download: ML20206J930 (3) | |
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1 UNITED STATES g
j NUCLEAR REGULATORY COMMISSION
't WASHINGTON, D.C. 200e60001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO GENERIC LETTER 95-07. " PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES."
FOR FACILITY OPERATING LICENSE NO. NPF-43 DETROIT EDISON COMPANY FERMl 2 DOCKET NO. 50-341
1.0 INTRODUCTION
Pressure locking and thermal binding of power-operated gate valves represent potential common-cause failure mechanisms that can render redundant safety systems incapable of performing their safety functions. The identification of susceptible valves and the determination of when the phenomena might occur require a thorough knowledge of components, systems, and plant operations. Pressure locking occurs in flexible-wedge and double-disk gate valves when fluid becomes pressurized inside the valve bonnet and the actuator is not capable of overcoming the additional thrust requirements resulting from the differential pressure created across both valve disks by the pressurized fluid in the valve bonnet. Thermal binding is generally associated with n wedg6 gate valve that is closed while the system is hot and then is allowed to cool before an attempt is made to open the valve.
Pressure locking or the mal binding occur as a result of the valve design characteristics (wedge and valve body configuration, flexibility, and material thermal coefficients) when the valve is subjected to specific presuures and temperatures during various modes of plant operation.
Operating experience indicates that, in many plants, these situations were not always considered as part of the design basis for valves.
2.0 BEGULATORY REQUIREMENTS 10 CFR Part 50 (Appendix A, General Design Criteria 1 and 4) and plant licen:Ing safety analyses require or commit (or both) that licensees design and test safety-relateo' components and systems to provide adequate assurance that those systems can perform their safety functions. Other individual criteria in Appendix A to 10 CFR Part 50 apply to specific systems.
In accordance with those regulations and licensing commitments, and under the additional provisions of 10 CFR Part 50 (Appendix B, Criterion XVI), licensees are expected to act to ENCLOSURE 2 I
9905130018 990510 PDR ADOCK 05000341 P
2-ensure that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety functions.
On August 17,1995, the NRC issued Generic Letter (GL) 95-07 to request that licensees take certain actions to ensure that safety-related power-operated gate valves that are susceptible to pressure locking or thermal binding are capata of performing their safety functions within the current licensing bases of the facility. GL 95-07 requested that each licensee, within 180 days of the date of issuance of the generic letter; (1) evaluate the operational configurations of safety-related power-operated gate valves in its plant to identify valves that are susceptible to pressure locking or thermal binding, and (2) perform further analyses and take needed corrective dons (orjustify longer schedules) to ensure that the susceptible valves, identified in (1) above, are capable of performing their intended safety functions under all modes of plant operation, including test configurations. In addition, GL 95-07 requested that licensees, within 180 days of the date ofissuance of the generic letter, provide to the NRC a summary description of (1) the susceptibility evaluation used to determine that valves are or are not susceptible to pressure locking or thermal binding, (2) the results of the susceptibility evaluation, including a listing of the susceptible valves identified, and (3) the corrective actions or other methods used to disposition the valves identified as susceptible to pressure locking or thermal binding. The NRC issued GL 95-07 as a " compliance backfit" pursuant to 10 CFR 50.109(a)(4)(i) because modification may be necessary to bring facilities into compliance with the rules of the Commission referenced above, in a letter dated February 13,1996, Detroit Edison submitted its 180-day response to GL 95-07 for Fermi 2. The NRC staff reviewed the licensee's submittal and requested additional
- information in a letter dated July 8,1996. In a "NRC-96-0072, Responds to NRC RAI Re GL 95-07, Pressure Locking & [[Topic" contains a listed "[" character as part of the property label and has therefore been classified as invalid. of Safety-Related Power-Operated Gate Valves Response|letter dated August 7,1996]], the licensee provided the additionalinformation.
3.0 STAFF EVALUATION 3.1 Scope of Licensee's Review GL 95-07 requested that licensees evaluate the operational configurations of safety-related power-operated gate valves in their plants to identify valves that are susceptible to pressure locking or thermal binding. The Detroit Edison letters of February 13, and August 7,1996, described the scope of valves evaluated in response to GL 95-07. The NRC staff has reviewed the scope of the licensee's susceptibility evaluation performed in response to GL 95-07 and found it complete and acceptable. The licensee stated that normally open, safety-related power-operated gate valves which are closed for test or surveillance, but must return to the open position, were evaluated within the scope of GL 95-07 and that plant technical specifications for the train / system considered out of service were entered. The staff finds the criteria for determining the scope of power-operated valves for GL 95-07 are consistent with the staff's acceptance of the scope of motor-operated valves associated with GL 89-10,
" Safety-Related Motor-Operated Valve Testing and Surveillance."
3.2 Corrective Actions GL 95-07 requested that licensees, within 180 days, perform further analyses as appropriate, and take appropriate corrective actions (or justify longer schedules), to ensure that the susceptible valves identified are capable of performing their intended safety function under all 4'
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modes of plant operation, including test configurations. The licensee's submittals discussed proposed corrective actions to address potential pressure-locking and thermal-binding problems. The staff's evaluation of the licensee's actions is discussed in the following paragraphs; a.
. The licensee stated that the following valves have been modified to eliminate the potential for pressure locking:
E1150F015NB Low Pressure Coolant injection inboard Isolation E2150F005NB Low Pressure Core Spray Outboard Isolation E4150F006 High Pressure Coolant injection Discharge to Feedwater E5150F013 Reactor Core Isolation Cooling Discharge to Feedwater The staff finds that physical modification to valves susceptible to pressure locking is an appropriate corrective action to ensure operability of the valves and is thus, acceptable.
b.
The licensee stated that the high pressure coolant injection (HPCI) pump discharge outboard isolation valve, E4150F007, is susceptible to pressure locking if closed to isolate primary system leakage past E4150F006 and that procedures require that the HPCI system be declared inoperable when E4150F007 is closed. The staff finds that the licensee's procedural requirement j
to declare the HPCI system inoperable provides assurance that pressure-locking conditions are adequately identified, and is thus, acceptable.
c.
The licensee stated that all flexible and solid wedge gate valves in the scope of GL 95-07 were evaluated for thermal binding. When evaluating whether valves were susceptible to thermal binding, the licensee assumed that thermal binding would not occur below specific temperature thresholds. The screening criteria used by the licensee appear to provide a reasonable approach to identify those
- valves that might be susceptible to thermal binding. Until more definitive industry criteria are developed, the staff concludes that the licensee's actions to address thermal binding of gate valves are acceptable.
4.0 CONCLUSION
On the basis of its evaluation, the NRC staff finds that the licensee has performed appropriate evaluations of the operational configurations of safety-related power-operated gate valves to identify valves at Fermi 2 that are susceptible to pressure locking or thermal binding. In addition, the NRC staff finds that the licensee has taken appropriate corrective actions to ensure that these valves are capabt of performing their intended safety functions. Therefore, the staff concludes that the licerK las adequately addressed the requested actions discussed in GL 95-07.
PrincipalContributor: S.Tingen Date: May 10, 1999
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