ML20206N755
| ML20206N755 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 05/13/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20206N753 | List: |
| References | |
| GL-95-07, GL-95-7, NUDOCS 9905180055 | |
| Download: ML20206N755 (3) | |
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UNITED STATES g
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WASHINGTON, D.C. 20066 4001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING LICENSEE RESPONSE TO GENERIC LETTER 95-07. " PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES" DUANE ARNOLD ENERGY CENTER DOCKET NO. 50-331
1.0 INTRODUCTION
Pressure locking and thermal binding 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 a wedge 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 thermal binding occurs 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 pressures and temperatures during various modes of plant operation. Operating experience indicates that these situations were not always considered in many plants as part of the design basis for valves.
2.0 REGULATORY REQUIREMENTS General Design Criteria 1 and 4 in Appendix A to 10 CFR Part 50 and plant licensing safety analyses require or commit (or both) that licensees design and test safety-related 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 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, " Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," to request that licensees take certain actions to ensure those safety-related power-operated gate valves that are susceptible to pressure locking or thermal binding are capable of performing their safety functions within the current licensing bases of the facility. GL 95-07 requested that each licensee, within 180 days Enclosure 9905190055 990513 l
PDR ADOCK 05000331 p
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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 actions (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 j
the date of issuance 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 dispositioning, for 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 inte compliance with the rules of the Commission referenced
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above.
In a letter of February 13,1996, IES Utilities submitted its 180-day response to GL 95-07 for Duane Amold Energy Center (DAEC). The NRC staff reviewed the licensee's submittal and requested additional information b a letter dated May 31,1996. In a letter of July 3,1996, the licensee provided the additional in'ormation. In a "NG-98-1927, Forwards Response to NRC 980923 RAI Re GL 96-05, Periodic Verification of Design-Basis Capability of SR Movs. List of Seventeen Valves Previously Removed from [[generic letter" contains a listed "[" character as part of the property label and has therefore been classified as invalid. Scope,Also Encl|letter dated November 20,1998]], the licensee supplemented its 180-day responss. The NRC staft requested additional information in a letter dated April 1,1999, and the licensee provided the additional information in a letter dated April 28,1999.
3.0 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 IES Utilities letters of February 13, and July 3,1996, November 20,1998, and April 28,1999, 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 fourid it complete and acceptable. 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 except in the instances when the system / train is declared inoperable in accordance with technical specifications. The criteria for determining the scope of power-operated valves for GL 95-07 are consistent with the NRC staffs 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, perfomt 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 modes of plant operation, including test configurations. The licensee's submittals discussed corrective actions to address potential pressure-locking and thermal-binding problems. The NRC staffs evaluation of the licensee's actions is discussed in the following paragraphs:
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a.
The licensee stated that the following valves were modified to eliminate the l
potential for pressure locking:
M01902 Loop B Drywell Spray MO1905 Low Pressure Coolant Injection Loop B Injection MO1913 Residual Heat Removal (RHR) B Pump Torus Suction 3
M01921 RHR D Pump Torus Suction MO2000 Loop A Drywell Spray M O2003 Low Pressure Coolant injection Loop A Injection MO2005 Loop A Torus Cooling / Spray MO2012 RHR A Pump Torus Suction MO2015 RHR C Pump Torus Suction MO2117 Core Spray Loop A Injection M O2137 Core Spray Loop B Injection MO2202 High Pressure Coolant Injection Turbine Steam Admission MO2312 High Pressure Coolant injection MO2512 Reactor Core Isolation Cooling Injection The NRC 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 axep'able.
b.
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 NRC staff concludes that the licensee's actions to address thermal binding of gate valves are acceptable.
4.0 CONCLUSION
On the basis of this 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 DAEC that are susceptible to pressurs locking or thermal binding. In addition, i
the NRC staff finds that the licensee has taken appropriate corrective actions to ensure that these valves are capable of performing their intended safety functions. Therefore, the NRC staff concludes that the licensee has adequately addressed the requested actions discussed in GL 95-07.
Principal Contributor: S. Tingen, EMEB Date: May 13, 1999 I