ML16342A899
| ML16342A899 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/20/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16342A900 | List: |
| References | |
| GL-96-05, NUDOCS 9909240006 | |
| Download: ML16342A899 (18) | |
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UNITED STATES NUCLEAR REGULATORY COIVIMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATIONBY THE OFFICE OF NUCLEAR REACTOR REGULATION LICENSEE RESPONSE TO GENERIC LETTER 96-05 "PERIODIC VERIFICATIONOF DESIGN-BASIS CAPABILITYOF SAFETY-RELATED MOTOR-OPERATED VALVES" PACIFIC GAS AND ELECTRIC COMPANY DIABLOCANYON POWER PLANT UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323 1.0.
INTRODUCTION Many fluid systems at nuclear power plants depend on the successful operation of motor-operated valves (MOVs) in performing their safety functions.
Several years ago, MOV operating experience and testing, and research programs sponsored by the nuclear industry and the U. S. Nuclear Regulatory Commission (NRC), revealed weaknesses in a wide range of
,activities (including design, qualification, testing, and maintenance) associated with the performance of MOVs in nuclear power plants.
For example, some engineering analyses used in sizing and setting MOVs did not adequately predict the thrust and torque required to operate valves under their design-basis conditions.
In addition, inservice tests of valve stroke time under zero differential-pressure and flow conditions did'not ensure that MOVs could perform their safety functions under design-basis conditions.
Upon identification of the weaknesses in MOVperformance, significant industry and regulatory activities were initiated to verify the design-basis capability of safety-related MOVs in nuclear power plants. After completion of these activities, nuclear power plant licensees began establishing long-term programs to maintain the design-basis capability of their safety-related MOVs. This safety evaluation (SE) addresses the program developed by Pacific Gas and Electric Company (licensee) to verify periodically the design-basis capability of safety-related MOVs at Diablo Canyon Power Plant, Units 1 and 2.
2.0 REGULATORY RE UIREMENTS The NRC regulations require that MOVs important to safety be treated in a manner that provides assurance of their intended performance.
Criterion 1 to Appendix A, "General Design Criteria for Nuclear Power Plants," to Part 50 of Title 10 of the Code ofFederal Regulafions (10 CFR Part 50) states, in part, that structures, systems, and components important to safety shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be performed.
The quality assurance program to be applied to safety-related components is described in Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10 CFR 9909240006 990920 PDR ADOCK 0S000275 P
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Part 50.
In Section 50.55a of 10 CFR Part 50, the NRC requires licensees to establish inservice testing (IST) programs in accordance with Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code.
In response to concerns regarding MOVperformance, on June 28, 1989, the NRC staff issued Generic Letter (GL) 89-10, "Safety-Related Motor-Operated Valve Testing and Surveillance,"
which requested that nuclear power plant licensees and construction permit holders ensure the capability of MOVs in safety-related systems to perform their intended functions by reviewing MOVdesign bases, verifying MOVswitch settings initiallyand periodically, testing MOVs under design-basis conditions where practicable, improving evaluations of MOVfailures and necessary corrective action, and trending MOV problems.
The staff requested that licensees complete the GL 89-10 program within approximately three refueling outages or five years from the issuance of the generic letter. Permit holders were requested to complete the GL 89-10 program before plant startup or in accordance with the above schedule, whichever was tater.
The NRC staff issued seven supplements to GL 89-10 that provided additional guidance and information on MOVprogram scope, design-basis reviews, switch settings, testing, periodic verification, trending, and schedule extensions.
GL 89-10 and its supplements provided only limited guidance regarding MOVperiodic verification and the measures appropriate to assure preservation of design-basis capability. Consequently, the staff determined that additional guidance on the periodic verification of MOVdesign-basis capability should be prepared.
On September 18, 1996, the NRC staff issued GL 96-05, "Periodic Verification of Design-Basis Capability of Safety-Related Motor-Operated Valves," requesting each licensee establish a program, or ensure the effectiveness of its current program, to verify on a periodic basis that safety-related MOVs continue to be capable of performing their safety functions within the current licensing bases of the facility. In GL 96-05, the NRC staff summarized several industry and regulatory activities and programs related to maintaining long-term capability of safety-related MOVs. For example, GL 96-05 discussed non-mandatory ASME Code Case OMN-1, "Alternative Rules for Preservice and Inservice Testing of Certain Electric Motor Operated Valve Assemblies in LWR Power Plants, OM Code 1995 Edition; Subsection ISTC,"
which allows the replacement of ASME Code requirements for MOVquarterly stroke-time testing with exercising of safety-related MOVs at least once per operating cycle and periodic MOVdiagnostic testing on a frequency to be determined on the basis of margin and degradation rate.
In GL 96-05, the NRC staff stated that the method in OMN-1 meets the intent of the generic letter with certain limitations. The NRC staff also noted in GL 96-05 that licensees remain bound by the requirements in their code of record regarding MOVstroke-time testing,.as supplemented by relief requests approved by the NRC staff.
In GL 96-05, licensees were requested to submit the following information to the NRC:
a.
within 60 days from the date of GL 96-05, a written response indicating whether or not the licensee would implement the requested actions; and b.
within 180 days from the date of GL 96-05, or upon notification to the NRC of completion of GL 89-10 (whichever is later), a written summary description of the licensee's MOVperiodic verification program.
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The NRC staff is preparing an SE on the response of each licensee to GL 96-05. The NRC staff intends to rely to a significant extent on an industry initiative to identify valve age-related degradation which could adversely affect the design-basis capability of safety-related MOVs (described in Section 3.0) where a licensee commits to implement that industry program.
The NRC staff willconduct inspections to verify the im'plementation of GL 96-05 programs at nuclear power plants as necessary.
3.0 JOINT OWNERS GROUP PROGRAM ON MOV PERIODIC VERIFICATION In response to GL 96-05, the Boiling Water Reactor Owners Group (BWROG), Westinghouse Owners Group (WOG), and Combustion Engineering Owners Group (GEOG) jointly developed an MOV periodic verification program to obtain benefits from the sharing of information between licensees.
The Joint Owners Group (JOG) program on MOVperiodic verification is described by the BWROG in its Licensing Topical Report NEDC-32719, "BWR Owners'roup Program on Motor-Operated Valve (MOV) Periodic Verification," and described by the WOG and the GEOG in their separately submitted Topical Report MPR-1807, "Joint BWR, Westinghouse and Combustion Engineering Owners'roup Program on Motor-Operated Valve (MOV) Periodic Verification." The stated objectives of the JOG program on MOVperiodic verification are (1) to provide an approach for licensees to use immediately in their GL 96-05 programs; (2) to develop a basis for addressing the potential age-related increase in required thrust or torque under dynamic conditions; and (3) to use the developed basis to confirm, or ifnecessary to modify, the applied approach.
The specific elements of the JOG program are (1) providing an "interim" MOVperiodic verification program for applicable licensees to use in response to GL 96-05; (2) conducting a dynamic testing program over the next five years to identify potential age-related increases in required thrust or torque to operate gate, globe, and butterfly valves under dynamic conditions; and (3) evaluating the information from the dynamic testing program to confirm or modify the interim program assumptions.
The JOG interim MOVperiodic verification program includes (1) continuation of MOV stroke-time testing required by the ASME Code IST program; and (2) performance of MOV static diagnostic testing on a frequency based on functional capability (age-related degradation margin over and above margin for GL 89-10 evaluated parameters) and safety significance.
In implementing the interim MOVstatic diagnostic test program, licensees will.rank MOVs within the scope of the JOG program according to their safety significance.
The JOG program specifies that licensees need to justify their approach for risk ranking MOVs. In Topical Report NEDC 32264, "Application of Probabilistic Safety Assessment to Generic Letter 89-10 Implementation," the BWROG described a methodology to rank MOVs in GL 89-10 programs with respect to their relative importance to core-damage frequency and other considerations to be added by an expert panel.
In an SE dated February 27, 1996, the NRC staff accepted the BWROG methodology for risk ranking MOVs in boiling water reactor nuclear plants with certain conditions and limitations.
In the SE (dated October 30, 1997) oh the JOG program on MOV periodic verification, the NRC staff indicated its view that the BWROG methodology for MOV risk ranking is appropriate for use in response to GL 96-05. With respect to Westinghouse-designed, pressurized water reactor nuclear plants, the WOG prepared Engineering Report V-EC-1658, "Risk Ranking Approach for Motor-Operated Valves in Response to Generic Letter 96-05." On April 14, 1998, the NRC staff issued an SE accepting with certain conditions
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and limitations, the WOG approach for ranking MOVs based on their risk significance.
Licensees of plants not applicable to the BWROG or WOG methodologies need to justify their MOV risk-ranking approach individually.
The objectives of the JOG dynamic test program are to determine degradation trends in dynamic thrust and torque, and to use dynamic test results to adjust the test frequency and method specified in the interim program ifwarranted.
The JOG dynamic testing program includes (1) identification of conditions and features which could potentially lead to MOV degradation; (2) definition and assignment of valves for dynamic testing; (3) testing valves three times over a 5-year interval with at least a 1-year interval between valve-specific tests according to a standard test specification; (4) evaluation of results of each test; and (5) evaluation of collective test results.
In the last phase of its program, the JOG willevaluate the test results to validate the assumptions in the interim program to establish a long-term MOVperiodic verification program to be implemented by licensees.
A feedback mechanism willbe established to ensure timely sharing of MOVtest results among licensees and to prompt individual licensees to adjust their own MOVperiodic verification program, as appropriate.
Following consideration of NRC staff comments, the BWROG submitted Licensing Topical Report NEDC-32719 (Revision 2) describing the JOG program on July 30, 1997.
Similarly, the CEOG and the WOG submitted Topical Report MPR-1807 (Revision 2) describing the JOG program on August 6 and 12, 1997, respectively.
On October 30, 1997, the NRC staff issued an SE accepting the JOG program with certain conditions and limitations as an acceptable industry-wide response to GL 96-05 for valve age-related degradation.
4.0 DIABLOCANYON GL 96-05 PROGRAM On November 18, 1996, Pacific Gas and Electric Company submitted a response to GL 96-05 notifying the NRC that it would implement the requested MOVperiodic verification program at Diablo Canyon.
The licensee also provided a summary description of the MOVperiodic verification program planned to be implemented at Diablo Canyon.
In a letter dated September 8, 1998, the licensee updated its commitment to GL 96-05. On March 25, 1999, the licensee provided a response to a request for additional information regarding GL 96-05 forwarded by the NRC staff on December 29, 1998.
In its letter dated November 18, 1996, the licensee stated that the MOVperiodic verification program developed under GL 89-10 would continue to be implemented at Diablo Canyon.
In its letter dated September 8, 1998, the licensee supplemented its previous response by committing to implement the JOG MOVperiodic verification program as described in Topical Report MPR-1807 (Revision 2). The licensee noted that the risk ranking of MOVs at Diablo Canyon was performed before preparation of WOG Engineering Report V-EC-1658-A, but that its MOVprogram complied with the WOG methodology.
In a telephone conference with the NRC staff on June 10, 1999, the licensee clarified certain aspects of its GL 96-05 program at Diablo Canyon.
5.0 NRC STAFF EVALUATION The NRC staff has reviewed the information provided in the licensee's letters describing the program to periodically verify the design-basis capability of safety-related MOVs at Diablo Canyon in response to GL 96-05. The staff also reviewed NRC Inspection Report
,50-275 and 323/95-01 (IR 95-01) which provided the results of inspections to evaluate the licensee's program to verify the design-basis capability of safety-related MOVs in response to GL 89-10.
In a letter dated August 3, 1995, the staff closed the review of the GL 89-10 program at Diablo Canyon based on the verification of the design-basis capability of safety-related MOVs as documented in IR 95-01, and additional information provided by the licensee in a letter dated May 5, 1995. The staff's evaluation of the licensee's response to GL 96-05 is described below.
5.1 MOVProgram Scope In GL 96-05, the NRC staff indicated that all safety-related MOVs covered by the GL 89-10 program should be considered in the development of the MOVperiodic verification program.
The staff noted that the program should consider safety-related MOVs that are assumed to be capable of returning to their safety position when placed in a position that prevents their safety system (or train) from performing its safety function; and the system (or train) is not declared inoperable when the MOVs are in their nonsafety position.
In IR 95-01, the NRC staff noted that Diablo Canyon included 155 MOVs in its GL 89-10 program, and no deviations from the guidance provided by GL 89-10 and its supplements were identified.
In its letter dated November 18, 1996, the licensee reported that the MOV program continues to include 155 MOVs, and did not take exception to the guidance in GL 96-05. The staff considers the licensee to have made adequate commitments regarding the scope of its MOV program.
The licensee will be responsible forjustifying any deviations from the recommended scope of GL 96-05 at Diablo Canyon.
5.2 MOVAssumptions and Methodologies The NRC staff expects licensees to maintain the assumptions and methodologies used in the development of its MOVprograms for the life of the plant (a concept commonly described as a "living program").
For example, the design basis of safety-related MOVs willneed to be maintained up-to-date, including consideration of any plant modifications or power uprate conditions.
In IR 95-01 and in the letter dated August 3, 1995, the NRC staff discussed the licensee's justification for the assumptions and methodologies used in the MOV program in response to GL 89-10 at Diablo Canyon.
With certain long-term items discussed in the following section, the staff determined that the licensee had adequately justified the assumptions and methodologies used in its MOV program. The licensee's letter dated March 25, 1999, indicated ongoing activities, such as review of motor actuator output, to update its MOVprogram assumptions and methodologies.
The staff considers the licensee to have adequate processes in place to maintain the assumptions and methodologies used in its MOVprogram, including the design basis of its safety-related MOVs.
fl 5.3 GL 89-10 Long-Term Items In its letter dated May 5, 1995, the licensee responded to issues identified in IR 95-01 and discussed actions to be taken over the long term.
In its letter dated March 25, 1999, the licensee reported on the status of those long-term GL 89-10 items.
For example, the licensee noted that it had completed the confirmation of thrust requirements for the feedwater isolation valves and the pressurizer power operated relief valve (PORV) block valves using the Electric Power Research Institute (EPRI) MOVperformance prediction methodology (PPM). The licensee had completed a review of valve grouping using guidelines consistent with GL 89-10, Supplement 6. The licensee had verified that assembling valves using Neolube did not affect valve performance.
The licensee had revised the plant document used to evaluate dynamic tests to include margin for valve degradation.
The NRC staff completed the review of the licensee's actions in response to GL 95-07, "Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," in an SE dated December 1, 1998.
In IR 95-01, the NRC staff discussed qualitative and quantitative aspects of the licensee's program for trending MOVperformance at Diablo Canyon, including computer-based trending to summarize information obtained from reviews of MOVmaintenance documents and test results.
The licensee periodically evaluates this information to identify and correct recurring problems, and to detect potential MOVfailures.
I In a letter dated August 3, 1995, the NRC staff concluded that the licensee had demonstrated the design-basis capability of its safety-related MOVs at Diablo Canyon.
With the licensee's ongoing MOVactivities and trending program, no outstanding issues regarding the licensee's GL 89-10 program remain at Diablo Canyon.
5.4 JOG Program on MOV Periodic Verification In its letter dated September 8, 1998, the licensee committed to implement the JOG program on MOV periodic verification as described in Topical Report MPR-1807 (Revision 2). The NRC staff accepted the JOG program on MOVperiodic verification with certain conditions and limitations in the SE dated October 30, 1997. The JOG program includes (1) the JOG interim static diagnostic test program; (2) the JOG 5-year dynamic test program; and (3) the JOG long-term periodic test program.
The. NRC staff considers the commitments by the licensee to implement the JOG program at Diablo Canyon to be an acceptable response to GL 96-05 for valve age-related degradation.
The licensee will be responsible for addressing the conditions and limitations specified in the SE dated October 30, 1997, on the JOG program.
The staff considers the licensee's commitment to include all three phases of the JOG program.
Ifthe licensee proposes to implement an approach at Diablo Canyon different from the JOG program, the NRC staff willevaluate the proposed alternative approach.
In its letter dated November 18, 1996, the licensee noted that the interim MOVstatic diagnostic test program would establish a test frequency based on the safety significance and functional capability of each GL 96-05 MOV. In its letter dated September 8, 1998, the licensee indicated that (1) MOVstatic diagnostic tests at Diablo Canyon are scheduled at least as frequent as the
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. JOG recommendations; (2) the test matrix uses two margin categories to represent high and low margin MOVs with low margin being less than 20 percent, except that MOVs evaluated using the EPRI MOV PPM are categorized as high margin ifpositive margin is available; and (3) the MOV ranking method used at Diablo Canyon complies with the methodology presented in the WOG Engineering Report V-EC-1658. When implementing the WOG MOVrisk-ranking methodology, the licensee will be expected to address the conditions and limitations in the SE dated April 14, 1998, which accepted WOG Engineering Report V-EC-1658. Further, the licensee will be expected to address the provisions in the JOG topical report to justify the high-margin categorization of MOVs evaluated using the EPRI MOV PPM.
The JOG program is intended to address most gate, globe and butterfly valves used in safety-related applications in the nuclear power plants of participating licensees.
The JOG indicates that each licensee is responsible for addressing any MOVs outside the scope of applicability of the JOG program.
In the SE dated October 30, 1997, the NRC staff specifies that licensees implementing the JOG program must determine any MOVs outside the scope of the JOG program (including service conditions) and justify a separate program for periodic verification of the design-basis capability of those MOVs. The staff recognizes that the JOG has selected a broad range of MOVs and conditions for the dynamic testing program.
Consequently, the NRC staff expects significant information to be obtained on the performance and potential degradation of safety-related MOVs during the interim static diagnostic test program and the JOG dynamic test program. As the test results are evaluated, the JOG might include or exclude additional MOVs with respect to the scope of its program.
Although the test information from the MOVs in the JOG dynamic test program might not be adequate to establish a long-term periodic verification program for each MOVoutside the scope of the JOG program, sufficient information should be obtained from the JOG dynamic test program to identify any immediate safety concern for potential valve age-related degradation during the interim period of the JOG program.
Therefore, the NRC staff considers it acceptable for the licensee to apply its interim static diagnostic test program to GL 96-05 MOVs that currently might be outside the scope of the JOG program with'the feedback of information from the JOG dynamic test program to those MOVs. Upon completion of the JOG dynamic test program and development of the JOG long-term MOVperiodic verification criteria, the licensee willbe expected to establish a long-term MOVperiodic verification program for those MOVs outside the scope of the JOG program by applying information from the JOG program or additional
'ynamic tests, as necessary.
5.5 Motor Actuator Output The JOG program focuses on the potential age-related increase in the thrust or torque required to operate valves under their design-basis conditions.
In the SE dated October 30, 1997, on the JOG program, the NRC staff specifies that licensees are responsible for addressing the thrust or torque delivered by the MOVmotor actuator and its potential degradation.
Although the JOG does not plan to evaluate degradation of motor actuator output, significant information on the output of motor actuators willbe obtained through the interim MOVstatic diagnostic test program and the JOG dynamic test program.
ln its letter dated March 25, 1999, the licensee described the elements of its MOVprogram for monitoring the thrust or torque delivered by the motor actuator and the potential for degradation.
In particular, the licensee stated that it (1) performs an inspection of each
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I actuator once every fuel cycle (2 years); (2) overhauls actuators based on operating environment, maintenance experience, or condition monitoring; (3) calculates thrust or torque required to operate each valve using the latest maximum design-basis condition and applicable vendor information; (4) identifies structural weak links and maximum actuator thrust and torque; (5) evaluates motor actuator capability for design-basis degraded voltage conditions; (6) trends MOVfailures and performance; and (7) performs the periodic verification program to detect degradation.
In IR 95-01, the NRC staff reported that the licensee was monitoring stem friction coefficient, comparing data to existing assumptions, and making adjustments as necessary.
In the telephone conference on June 10, 1999, the licensee stated that it is continuing to monitor stem friction coefficient during periodic as-found and as-left diagnostic testing. The staff notes that several parameters can be obtained during MOVstatic and dynamic testing to help identify motor actuator output degradation when opening and closing the valve including, as applicable, capability margin, thrust and torque at control switch trip, stem friction coefficient, load sensitive behavior, and motor current.
In Technical Update 98-01 and its Supplement 1, Limitorque Corporation provided updated guidance for predicting the torque output of its ac-powered motor actuators.
In its letter dated March 25, 1999, the licensee reported that this information had been incorporated into the MOV sizing calculations at Diablo Canyon.
The licensee did not identify any deficiencies affecting MOV operability during its evaluations.
The NRC staff notes that the licensee is responsible for resolving any MOVoperability concerns in accordance with regulatory and plant-specific requirements.
In its letter dated July 17, 1998, forwarding Technical Update 98-01, Limitorque indicates that a future technical update will be issued to address the application of dc-powered MOVs. During the telephone conference on June 10, 1999, the licensee indicated that it is aware of the industry effort to evaluate the performance of dc-powered MOVs. In the interim, the licensee has verified the capability of its two safety-related dc-powered MOVs at Diablo Canyon (one MOVin the auxiliary feedwater system in each reactor unit) using nameplate motor torque, pullout efficiency, and a 0.9 application factor. The licensee plans to review any new guidance on dc-powered motor actuator output (including consideration of ambient temperature and heat-up during operation) when available and take appropriate actions based on the results.
The NRC staff considers the licensee to be establishing sufficient means to monitor MOV motor actuator output and its potential degradation.
6.0 CONCLUSION
On the basis of this evaluation, the NRC staff finds that the licensee has established an acceptable program to verify periodically the design-basis capability of the safety-related MOVs at Diablo Canyon.
Therefore, the staff concludes that the licensee has adequately addressed the actions requested in GL 96-05. The NRC staff may conduct inspections to verify the
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9 implementation of the VOVperiodic verification program is in accordance with the licensee's commitments; this SE; the SE dated October 30, 1997, on the JOG program on MOVperiodic verification; and the SE dated April 14, 1998, on the WOG methodology for ranking MOVs by their safety significance.
Principal Contributors:
T. Scarbrough, NRR S. Tingen, NRR Date:
September 20, 1999
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