ML20206P048

Safety Evaluation Concluding That NPP Established Acceptable Program to Verify Periodically design-basis Capability of safety-related MOVs at CNS & Adequately Addressed Actions Requested in GL 96-05

ML20206P048
Person / Time
Site:	Cooper
Issue date:	05/12/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20206P022	List: ML20206P017 ML20206P048
References
GL-96-05, GL-96-5, NUDOCS 9905180129
Download: ML20206P048 (9)

Text

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putt p 1 UNITED STATES

, g j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30606-0001 1

i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l i

NEBRASKA PUBLIC POWER DISTRICT RESPONSE TO GENERIC LETTER 96-05.

'" PERIODIC VERIFICATION OF DESIGN-BASIS CAPABILITY l

OF SAFETY-RELATED MOTOR OPERATED VALVES" l COOPER NUCLEAR STATION DOCKET NO. 50-298

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 operat!ng 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 i 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 MOV performance, significant industry and regulatory l activities were initiated to verify the design-basis capability of safety-related MOVs in nuclear power plants. After compiction 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 addresses the program developed by Nebraska Public Power  !

District (the licensee) to verify periodically the design-basis capability of safety-related MOVs at the Cooper Nuclear Station (CNS).

1 2.0 REGULATORY REQUIREMENTS 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 of Federal Regulations (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 ,

ENCLOSURE

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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 q Part 50. In Section 50.55a of 10 CFR Part 50, the NRC requires licensees to establish inservice testing programs in accordance with Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, in response to concerns regarding MOV performance, the NRC staff issued Generic Letter

- (GL) 8910 (June 28,1989), " Safety-Related Motor-Operated Valve Testing and Surveillance,'  !

which requested that nuclear power plant licensees and construction permit holders ensure the j capability of MOVs in safety-related systems to perform their intended functions by reviewing 1 MOV design bases, verifying MOV switch settings initially and periodically, testing MOVs under f design-basis conditions where practicable, improving evaluations of MOV failures and j necessary corrective action, and trending MOV problems. The staff requested that licensees complete the GL 89-10 program within approximately threc refueling outages or 5 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 later.

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The NRC staff issued seven supplements to GL 89-10 that provided additional guidan and information on the MOV program scope, design basis reviews, switch settings, testin . rsrlodic verification, trending, and schedule extensions. GL 89-10 and its supplements prov.' t only limited guidance regarding MOV periodic verification and the measu es appropriate tc. assure preservation of design-basis capability. Consequently, the staff determined that additional guidance on the periodic verification of MOV design-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 to 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 severalindustry 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,

'Altemative Rules for Preservice and inservice Testing of Certain Electric Motor Operated Valve Assemblies in LWR [ Light-Water Reactor) Power Plants, OM Code 1995 Edition; Subsection j ISTC," which allows the replacement of ASME Code requirements for MOV quarterly stroke- I time testing with exercising of safety-related MOVs at leest once per operating cycle and periodic MOV diagnost;c 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 MOV stroke time testing, as supplemented by relief requests approved by the NRC staff.

In GL 96-05, licensees were requested to submit the fol!owing information to the NRC:

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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 l

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b. within 180 days from the date of GL 96-05, or upon notification to the NRC of completion of GL 8910 (whichever is later), a written summary description of the licensee's MOV periodic verification program.

The NRC staff is preparing safety evaluations 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 will conduct inspections to verify the implementation 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 (CEOG) jointly developed an MOV periodic verification program to obtain benefits from the sharing of information between licensees. The Joint Owners Group (JOG) Program on MOV Periodic Verification is described by the BWROG in its Licensing Topical Report NEDC-32719, "BWR Owners' Group Program on Motor-Operated Valve (MOV) Periodic Verification," and described by the WOG and the CEOG in their separately submitted Topical Report MPR-1807, " Joint BWR, Westinghouse and Combustion Engineering Owners' Group Program on Motor-Operated Valve (MOV) Periodic Verification." The stated objectives of the JOG Program on MOV Periodic Verification are (1) to i 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 if necessary to modify, the applied approach. The specific elements of the JOG program are (1) providing an

" interim' MOV periodic verification program for applicable licensees to use in response to GL 96-05, (2) conducting a dynamic testing program over the next 5 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 MOV periodic 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 cver and above margin for GL 89-10 evaluated parameters) and safety significance, in implementing the interim MOV static 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 8910 programs with respect to their relative importance to core-damage frequency and other considerations to

. be added by an expert panel. In a safety evaluation 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 NRC safety evaluation (October 30,1997) on 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

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4 in Response to Generic Letter 96-05." On April 14,1998, the NRC staff issued a safely evaluation accepting with certain ecnditions 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 2 dynamic thrust and torque, and to use dynamic test results to adjust the test frequency and method specified in the interim program if warranted. 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. .

O in the last phase of its program, the JOG will evaluate the test results to validate the I assumptions in the interim program to establish a long-term MOV periodic verification program to be implemented by licensees. A feedback mechanism will be established to ensure timely sharing of MOV test results among licensees and to prompt individual licensees to adjust their own MOV periodic verification program, as appropriate. 1 Following consideration of NRC staff comments, on July 30,1997, the BWROG submitted Licensing Topical Report NEDC-32719 (Revision 2) describing the JOG program. Similarly on August 6 and 12,1997, respectively, the CEOG and the WOG submitted Topical Report j MPR 1807 (Revision 2) describing the JOG program. On October 30,1997, the NRC staff 4 issued a safety evaluation to the BWROG, CEOG, and WOG accepting the JOG program with  !

certain conditions and limitations as an acceptable industry-wide response to GL 96-05 for O valve age-related degradation.

4.0 COOPER GL 96-05 PROGRAM ,

On November 18,1996, Nebraska Public Power District submitted a 60-day response to GL 96-05 notifying the NRC that it would implement the requested MOV periodic verification program. On March 17,1997, the licensee submitted a 180-day response to GL 96-05 l providing a summary description of the MOV periodic verification program planned to be  ;

in,plemented at CNS. In a submittal dated May 4,1998, the licensee updated its commitment j to GL 96-05.: On February 22,1999, the licensee provided a response to a request for l additionalinformation regarding GL 96-05 forwarded by the NRC staff on October 28,1998. j i

in its submittal dated May 4,1998, the licensee committed to implement without deviation l Topical Report NEDC-32719 (Revision 2) describing the JOG program. In its letter dated i March 17,1997, the licensee described its MOV periodic verification program, including j planned testing, capability margin, and implementation of the JOG program at CNS. For  ;

example, the licensee indicated that the interim MOV static diagnostic test program at CNS  :

would begin during Refueling Outage 17 (spring of 1997) and applied the same MOV risk and 1 margin threshold values as identified in the JOG topical report. The licensee also stated that  ;

dynamic testing of selected MOVs under its MOV periodic verificat.'on program would begin  !

during Refueling Outage 18 (fall of 1998) During a telephone conference on April 15,1999, the licensee stated that its GL 96-05 prograrn was underway at CNS as planned.

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5.0 NRC STAFF EVALUATION The NRC staff has reviewed the information provided in the licensee's submittals describing the program to verify periodically the design-basis capability of safety-related MOVs at CNS in response to GL 96-05. The staff also reviewed NRC Inspection Report (IR) 50-298/96-10 which provided the results of an inspection to evaluate the licensee's program to verity the design-basis capability of safety-related MOVs in response to GL 89-10. In a letter dated November 5,1996, the NRC staff closed the review of the GL 8910 program at CNS based on IR 96-10 and a follow-up lettcr from the licensee dated August 6,1996. The NRC staff's i evaluation of the licensee's response to GL 96-05 is described below.

5.1 MOV Proaram 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 MOV periodic verification program. l Thq staff noted that the program should consider safety-related MOVs that are assumed to be i 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 96-10, the NRC staff reviewed the scope of the licensee's MOV program in response to GL 89-10 at CNS and found that the licensee omitted several MOVs from the program that ai'e stroked to their nonsafety position for surveillance or test activities although the licensee considered the system or train to continue to be operable, in IR 96-10, the NRC staff reported that the licensee had adequately demonstrated the capability of those MOVs to return to their safety position. In its letter dated February 22,1999, the licensee stated that it had not included test return valves, or other MOVs that are normally in their safety position, in the GL 89-10 or GL 96-05 program scope at CNS. The licensee indicated that capability calculations had been prepared for these MOVs. The licensee also stated that procedures referencing MOVs that are normally in their safety position but are stroked during surveillances were being reviewed to ensure that no credit is taken for system operability during the test. In its February 22 letter and during the telephone conference on April 15,1999, the licensee reported that three procedures j remain under review as part of its problem identification report process. In the interim, the I licensee stated that special attention is being provided for the MOVs covered by these three j procedures and that completion of the procedure review will be achieved no later than Refueling j Outage 19 (scheduled for March 2000). l l

With these provisions, the NRC staff considers the licensee to have made adequate commitments regarding the scope of its MOV program under GL 96-05, i

5.2 MOV Assumotions and Methodoloaies The NRC staff expects licensees to maintain the assumptions and methodologies used in the development of its MOV programs for the life of the plant (a concept commonly described as a j

- '1iving program"). For example, the design basis of safety-related MOVs will need to be I maintained up to date, including consideration of any plant modifications or power uprate l conditions.

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6 In IR 96-10, the NRC staff reviewed the licensee's justification for the assumptions and methodologies used in the MOV program in response to GL 8910 at CNS. With certain long-term aspects discussed in the following section, the staff determined that the licensee had adequately justified the assumptions and methodologies used in its MOV program, in its letter dated February 22,1999, the licensee discussed ongoing activities, such as review of motor actuator output, to update its MOV program assumptions and methodologies. The NRC staff considers the licensee to have adequate processes in place to maintain the assumptions and I methodologies used in its MOV program, including the design basis of its safety-related MOVs.

f 5.3 GL 89-10 Lona-Term items When evaluating the GL 89-10 program at CNS, the NRC staff discussed in IR 96-10 several aspects of the licensee's MOV program to be addressed over the long term. In its letter dated 1 February 22,1999, the licensee reported on the status of those long term GL 89-10 aspects.

For example, the licensee revised its valve factor assumptions for certain valve groups to {

include results provided by the Electric Power Reseerch Institute (EPRI) MOV Performance  !

Prediction Methodology (PPM). In addition, the licensee is using the EPRI MOV PPM to 4 confirm settings for selected Crane and WKM gate valves. The licensee took actions that formalized several aspects of CNS's MOV program. The licensee resolved potential j unpredictable behavior concerns for several valves that may experience blowdown flow l conditions by replacing or machining valve internals. In its February 22 letter, the licensee also {

indicated that two valves (RCIC MO-MO15/16) were under review and any modification found to  !

be required upon completion of the EPRI MOV PPM calculations would be conducted during Refueling Outage 19. During the telephone conference on April 15,1999, the licensee stated that the EPRI MOV PPM calculations for RCIC-MOV MO15/16 had determined that modifications to these two valves were not necessary because their performance would be predictable assuming worst-case internal dimensions and edges. The licensee noted that it would consider modifying these two valves during any future internal maintenance work to optimize their performance. l I

in its letter dated February 22,1999, the licensee noted that past operability of the core spray valves and their pressure locking concerns were the subject of a Notice of Violation (NOV) received from the NRC on September 20,1996. The licensee indicated that it had responded to this NOV in a letter dated October 18,1996, and had described the actions taken to prevent pressure locking of these valves. The licensee's actions in response to GL 95-07, " Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," are being addressed by the NRC staff under a separate safety evaluation.

in IR 96-10, the NRC staff discussed the licensee's program for trending MOV performance at CNS by qualitative and quantitative methods. For example, the licensee trends diagnostic test parameters and diagnostic trace anomalies. The licensee periodically evaluates this information to identify and correct recurring problems, and to detect potential MOV failures before they occur.

In the letter dated November 5,1996, the staff concluded that the licensee had demonstrated the design-basis capability of its safety related MOVs at CNS. With the licensee's ongoing MOV activities and trending program, no outstanding issues regarding the licensee's GL 89-10 l progmm remain at CNS. '

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7 5.4 JOG Proaram on MOV Periodic Verification in its letter dated May 4,1998, the licensee updated its commitment to implement the JOG Program on MOV Periodic Verification as described in Topical Report NEDC-32719 (Revision 2) without deviation. In a safety evaluation dated October 30,1997, the NRC staff accepted the JOG program as an industry-wide response to GL 96-05 with certain conditions and limitations. The licensee's commitment to implement the JOG program includes (1) the JOG interim static diagnostic test program, (2) the JOG 5-year dynamic test program, and (3) l the JOG long term periodic test program. The NRC staff considers the commitments by the licensee to implement the JOG program at CNS to be an acceptable response to GL 96-05 for valve age related degradation. The licensee is responsible for reviewing and implementing the limitations and conditions discussed in the NRC safety evaluation dated October 30,1997, in applying the JOG program at CNS. This includes the coordination and feedback of test information obtained from the JOG dynamic testing program. Where the licensee proposes to implement an approach at CNS that is different from the JOG program, the staff anticipates that the licensee would notify the NRC of the alternative approach.

In its letter dated March 17,1997, the licensee noted that the interim MOV static diagnostic testing under the JOG program would be performed on a test frequency based on the safety significance and functional margin of each GL 96 05 MOV. In its letter dated February 22, 1999, the licensee indicated that MOV rankings were assigned based on CNS Engineering Study PAS ES010, that was consistent with the MOV risk-ranking methodology presented iri the BWROG Topical Report NEDC 32264. In the telephone conference on April 15,1999, the licensee stated that it had reviewed the NRC safety evaluation dated February 27,1996, accepting the BWROG MOV risk-ranking methodology. The licensee reported that the MOV risk-ranking approach at CNS is consistent with the BWROG methodology and the limitations and conditions in the NRC safety evaluation, including review of the sample list of risk significant MOVs provided by the BWROG and justification for their applicable ranking at CNS. The licensee indicated that it is updating its model at CNS to incorporate the latest information on probabilistic' risk assessment. Based on the licensee's summary, the staff considers the licensee's methodology for risk ranking MOVs at CNS to be reasonable.

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 NRC safety evaluation 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 lustify a separate program for periodic verification of the design-basis capability of those MOVs. The NRC staff recognizes that the JOG has selected a broad range of MOVs and conditions for the dynamic j 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. l Although the test information from the MOVs in the JOG dynamic test program might not be l adequate to establish a long term periodic verification program for each MOV outside the scope of the JOG program, sufficient information should be obtained from the JOG dynamic test program to identify any immediate safety concem for potential valve age-related degradation i

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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 MOV periodic verification criteria, the licensee will be expected to establish a long-term MOV periodic verification program for those MOVs outside the scope of the JOG program by applying information from the JOG program or additional dynamic tests, as necessary.

5.5 Motor Actuator Outout 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 NRC safety evaluation 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 MOV motor 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 will be obtained through the interim MOV static diagnostic test program and the JOG dynamic test program.

In its letter dated February 22,1999, the licensee indicated that it applies specific margins to account for age-related stem lubricant degradation, load sensitive behavior, and spring pack relaxation. Actuator output capability is routinely updated based on plant-wide stem friction coefficient studies to assure adequate actuator output capability for safety related MOVs at CNS to perform their design-basis functions, in IR 9610, the NRC staff indicated that the licensee had performed a limited amount of as found testing to monitor stem lubricant degradation. The NRC staff notes that several parameters can be obtained during MOV static 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. Plant specific and JOG test information can provide support for the licensee's plan for monitoring MOV motor actuator output and its potential degradation.

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 February 22,1999, the licensee reported that it was applying a methodology developed by Commonwealth Edison Company (Comed) to justify motor torque capability for ac-powered  ;

motors manufactured by Reliance Electric Company. As noted in NRC irs, the NRC staff has I accepted the use of the Comed methodology for estimating MOV motor-actuator output capability, based on test data obtained by Comed. The licensee indicated that the output capability of ac-powered motors from other motor manufacturers were evaluaiad using the provisions of Limitorque Technical Update 98-01. The licensee reported that it had performed  ;

motor upgrades to resolve capability concerns resulting from its evaluation of the updated '

guidance with one remaining motor upgrade scheduled for Refueling Outage 19. The NRC staff notes that the licensee is responsible for resolving any MOV operability concerns in accordance with regulatory and plant-specific requirements. Further, the licensee will be i expected to incorporate any changes in the Comed methodology that might result from the '

Limitorque guidance.

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In Technical Update 98-01 and its Supplement 1, Limitorque reported that it will issue a future i technical update to address de-powered MOV applications. During the telephone conference on April 15,1999, the licensee stated that it assumes pullout efficiency and a 0.9 application factor with the intent of obtaining conservative predictions of de-powered MOV output. The licensee also indicated that it is participating in the BWROG program underway to assess the performance of de-powered MOVs in response to a recent NRC-sponsored study.

l 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 CNS. Therefore, the staff concludes that the licensee has adequately addressed the actions requested in GL 91-05. The NRC staff may conduct inspections to verify the implementation of the MOV periodic verification program is in accordance with the licensee's commitments; this NRC safety evaluation; the NRC safety evaluation dated October 30,1997, on the JOG Program on MOV Periodic Verification; and the NRC safety evaluation dated February 27, 1996, on the BWROG methodology for ranking MOVs by their safety significance.

Principal Contributor: T. Scarbrough, NRR Date: May 12, 1999 1

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