ML20057F829
| ML20057F829 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 10/12/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20057F419 | List: |
| References | |
| GL-89-04, GL-89-4, NUDOCS 9310190211 | |
| Download: ML20057F829 (8) | |
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NUCLEAR REGULATORY COMMISSION pv WASHINGTON, D.C. 205S5-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING RELIEF RE0 VESTS FOR INSERVICE TESTING PROGRAM
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REVISIONS 7 (UNIT 1) AND 4 (UNIT 2) f V0GTLE ELECTRIC GENERATING PLANT. UNITS 1 AND 2 DOCKET NOS 50-424 AND 50-425 l
1.0 INTRODUCTION
By letter dated April 15, 1993, Georgia Power Company (the licensee) submitted revisions to the inservice testing (IST) program for the Vogtle Electric Generating Plant (Vogtle), Units 1 and 2.
These revisions were Revision 7 for i
Unit 1 and Revision 4 for Unit 2.
The revisions included three valve relief requests (RR) identified as RR-14, RR-23, and RR-28; and a cold shutdown justification identified as CS-31.
The NRC staff's evaluation of these items follow.
2.0 BACKGROUND
The NRC staff's original Safety Evaluation for Vogtle Unit I was issued 1
March 1987 as part of Supplement 6 to NUREG-1137, " Safety Evaluation Report Related to the Operation of Vogtle Electric Generating Plant, Units I and 2."
Supplement 7 of NUREG-ll37, dated January 1988, indicated that based on a review of the differences in the Unit 2 program and the Unit 1 program, "the staff concludes that the proposed IST program for Unit 2 is acceptable for implementation." Supplement 8 of NUREG-ll37, dated February 1989, provided a summary table of the differences and whether they were acceptable.
Both the Unit 1 and Unit 2 IST Programs were established to the 1983 Edition, with Addenda through Summer 1983, of ASME Section XI which was incorporated into 10 CFR 50.55a(b) September 28, 1985, effective October 28, 1985.
The Code of Federal Regulations,10 CFR 50.55a, requires that inservice testing of certain ASME Code Class 1, 2, and 3 pumps and valves be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable addenda, except where relief has been requested and granted or proposed alternatives have been authorized by the Commission pursuant to 10 CFR 50.55a subparagraphs (f)(6)(i), (a)(3)(1), or (a)(3)(ii).
In order to obtain authorization or relief, the licensee must demonstrate that: (1) conformance is impractical for its facility; (2) the proposed alternative provides an acceptable level of quality and safety; or (3) compliance would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(f)(4)(iv),
inservice tests of pumps and valves may meet tu requirements set forth in subsequent editions and addenda that are incorporated by reference in paragraph (b) of 10 CFR 50.55a, subject to the limitations and modifications listed, and subject to Commission approval.
NRC guidance contained in 9310190211 931012 PDR ADOCK 05000424 P
e 4 Generic Letter (GL) 89-04, " Guidance on Developing Acceptable Inservice Testing Programs," provided alternatives to the Code requirements determined to be acceptable to the staff and authorized the use of the alternatives in Positions 1, 2, 6, 7, 9, and 10 provided the licensee follows the guidance delineated in the applicable position. When an alternative is proposed that is in accordance with the GL 89-04 guidance and is documented in the IST program, no further evaluation is required; however, implementation of the alternative is subject to NRC inspection.
Under 10 CFR 50.55a, the Commission has the authority to grant relief from ASME Code requirements or to approve proposed alternatives upon making the necessary findings. The NRC staff's findings with respect to granting or not granting the relief requested or authorizing the proposed alternative as part of the licensee's IST program are contained in this Safety Evaluation (SE).
After rulemaking on 10 CFR 50.55a, effective September 8,1992 (see 57 Federal Reaister 34666), the 1989 Edition of ASME Section XI was incorporated in paragraph (b) of 10 CFR 50.55a. The 1989 Edition provides that the rules for IST of pumps and valves shall meet the requirements set forth in ASME Operations and Maintenance Standards Part 6 (OM-6), " Inservice Testing of Pumps in Light-Water Reactor Power Plants," and Part 10 (OM-10), " Inservice Testing of Valves in Light-Water Reactor Power Plants." Pursuant to (f)(4)(iv), portions of editions or addenda may be used provided that all related requirements of the respective editions or addenda are met, and subject to Commission approval. Because the alternatives meet later editions of the Code, relief is not required for those inservice tests that are conducted in accordance with OM-6 and OM-10, or portions thereof, provided all related requirements are met. Whether all related requirements are met is subject to NRC inspection.
3.0 EVALUAT M 3.1 Relief Reouest RR-14 Valve Relief Request RR-14 was revised to change the frequency of disassembly and inspection of the containment spray system check valves 1/2-1206-06-015 and -016.
These Class 2 valves have the safety-related functions of opening to allow flow for containment spray and closing to perform a containment isolation function. The Code requirements of IWV-3522 specify that check 4
valves be exercised to the position required to fulfill their safety function quarterly, or during cold shutdown, if testing at power conditions is impractical.
3.1.1 Licensee's Basis for Relief The licensee states:
" Forward flow operability can be verified only by initiating flow through the valves into the containment structure. The initiation of containment spray into the containment would result in extensive damage to equipment inside containment.
The only method available to verify reverse flow closure is valve leak testing during Appendix J, Type C, testing at refueling."
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3.1.2 Alternative Testina The licensee proposes:
"One of these valves will be disassembled and manually stroked every other refueling on a staggered test basis.
If disassembly reveals that the valve is inoperable, the remaining valve will be disassembled.
In addition, reverse flow closure will be verified during Appendix J, Type C, testing at refueling.
This relief request complies with the alternative to full flow testing of check valves as described in Position 2 of NRC Generic letter 89-04.
The provisions for extending the disassembly frequency have been reviewed and extension to every other outage is justified."
3.1.3 Evaluation Generic Letter (GL) 89-04, Position 2, contains guidance on extending the frequency based on extreme hardships with disassembly and inspection each refueling outage. The position states that "in order to support extension of the valve disassembly / inspection intervals to longer than once every 6 years, licensees should develop the following information:
a.
Disassemble and inspect each valve in the valve grouping and document in detail the condition of each valve and the valve's capability to be full-stroked.
b.
A review of industry experience, for example, as documented in NPRDS, regarding the same type of valve used in similar service.
c.
A review of the installation of each valve addressing the "EPRI Applications Guidelines for Check Valves in Nuclear Power Plants" for problematic locations."
Further information is provided in response to Question 19 in the " Minutes of the Public Meetings on Generic Letter 89-04," dated October 25, 1989.
The question asked the NRC to define " extreme hardship." The response indicates that "the licensee should conduct a detailed evaluation of the various competing factors" (plant safety, maintenance history of the valves, and information on the reliability of the valves). Hardship examples included core off-load, mid-level reactor coolant loops operation, and radiation exposure that results from the disassembly and inspection in combination with the other factors.
Generic letter (GL) 89-04 approves the alternative of disassembly and inspection where it is not practical to perform flow testing or closure verification.
The staff does, however, encourage the use of nonintrusive techniques when these techniques can be applied. Due to the design of these valves, nonintrusive techniques may be impractical because the only flow path available would be into the containment, causing damage to equipment below the discharge of the containment spray. Therefore, the alternative meets the guidance for application of GL 89-04, Position 2.
Provided all the guidance is met, as verified by NRC inspection, no further evaluation by the NRC is required. As stated in response to Question 20 of the minutes reference above, the burden is on the licensee to demonstrate the extreme hardship
. necessary to comply with the identified sample disassembly / inspection schedule. The staff considers the sampling aspect of the position to provide assurance of the continued operability of the valves that are not inspected during any given outage. Therefore, the licensee should justify through the provisions listed in Position 2, any deviation from the stated schedule and include the justification in the IST program which is submitted to the NRC staff on a periodic basis.
3.1.4 Conclusion No further evaluation is required. The licensee has not included the basis for the extension of the disassembly and inspection in the program revision submittal. Therefore, the licensee should ensure that the basis is documented as part of the IST program, available for inspection in accordance with the guidance provided in GL 89-04 and the minutes of the public meetings, and included in the next periodic program submittal to the NRC.
3.2 Relief Reauest RR-23 Valve Relief Request RR-23 was revised to disassemble and inspect check valves on a staggered basis. The applicable components are Class 3 main steam valves 1301-U4-006 or -008.
These valves perform safety-related functions to open to allow steam to the auxiliary feedwater (AFW) pump turbine and to close to prevent reverse flow back into the steam system. The Code requirements of IWV-3522 specify that check valves be exercised to the position required to fulfill their safety function quarterly, or during cold shutdown if testing at power conditions is impractical.
3.2.1 Licensee's Basis for Relief The licensee states:
" Full-stroke exercising these valves during full power operation would require establishing full AFW pump flow into the steam generators. The introduction of cold water into the hot steam generators during full power operation results in a significant thermal shock to the feedwater nozzle.
Subjecting the feedwater nozzle to this thermal transient on a quarterly basis decreases the fatigue life of the nozzle and could possibly result in nozzle cracking. There are no system provisions for utilizing flow or pressure as an indication of reverse flow closure."
3.2.2 Alternative Testina The licensee proposes:
"These valves are partial-stroke exercised quarterly during the turbine-driven AFW pump test. These valves will be full-stroke exercised on a cold shutdown frequency by verifying that the AFW pump is delivering the required flow through valves 1302-U4-014,1302-U4-017, 1302-U4-020, 1302-U4-023, and 1302-U4-026 as discussed in [ cold shutdown justification] CS-19.
Reverse flow closure will be demonstrated by disassembly and manual full-stroke exercising on a staggered test basis at refueling. Valves will be exercised with flow after reassembly. This relief request complies with the alternative of full flow testing check valves as described in Position 2 of NRC Generic Letter 89-04."
c 3.2.3 Evaluation Generic Letter (GL) 89-04 approves the alternative described in Position 2 provided the licensee follows the guidance delineated in the position. Where the provisions of Position 2 for an alternate disassembly schedule are followed, no further evaluation is required for implementation. The implementation of the alternative is subject to NRC inspection as discussed in the minutes to the public meetings on GL 89-04 referenced previously.
3.2.4 Conclusion The alternative is approved in accordance with GL 89-04. The licensee should ensure that the program for disassembly and inspection of these check valves complies with the guidance delineated in Position 2 of GL 89-04. The implementation of the guidance is subject to NRC inspection.
3.3 Relief Reouest RR-28 Valve Relief Request RR-28 was added to the Vogtle IST Programs to address a recommendation by Westinghouse.
By Nuclear Safety Advisory Letter NSAL-92-012 on December 21, 1992, Westinghouse informed the licensee of a potential leak path outside of containment during a loss-of-coolant accident (LOCA) due to overpressurizing the charging or safety injection pump suction line.
Specifically, chemical r.nd volume control system (CVCS) check valves 1/2-1208-U6-124 are located downstream of the volume control tank (VCT), the two motor-operated isc!ation valves, and the seal return line.
If these check valves leak when the plant is in the recirculation mode with the residual heat removal (RHR) pumps feeding the charging pumps, flow would be dWted through the seal water heat exchanger. This could cause a CVCS relief vai<e (1/2-PSV-8123) to lift and relieve to the VCT.
Once the VCT fills, the overflow would go into the liquid hold-up tanks outside containment, resulting in a leakage of reactor coolant that bypasses containment. Thus, these CVCS check valves need to be tested for reverse flow closure which prevents flow diversion to the VCT.
These CVCS check valves have been added to the IST program. They are designated as having the safety-related function of closing to isolate the leakage path. They are categorized n Category C, Class 2 valves.
The Code requirements of IWV-3522 specify that check valves shall be exercised quarterly to the position required to fulfill their safety function, or during cold shutdown if testing at power conditions is impractical.
The requested relief would defer testing to refueling outages.
3.3.1 Licensee's Basis for Relief The licensee states:
" Testing this check valve [one per unit] requires that letdown and Reactor Coolant Pump (RCP) seal water return to the Volume Control Tank (VCT) be isolated, thus, removing the Chemical and Volume Control System (CVCS) from service. The CVCS is required to be in service during normal operation. Therefore, quarterly testing is not possible.
., Similarly, performir.g the test at cold shutdown would require isolating seal water to the RCPs.
RCP sesl water is typically only isolated during mid-loop operations when the Reactor Coolant System (RCS) level is below the RCP seals thus preventing crud intrusion into the seal packages. There have been numerous undesirable events throughout the industry which have resulted from mid-loop operations, e.g., vortexing/ cavitation of the RHR pumps due to improper RCS level indication. Mid-loop operation reduces RCS inventory which thereby reduces the plant's margin of safety. Therefore, the safety risks associated with testing this check valve during cold shutdowns are unwarranted."
3.3.2 Alternative Testina The licensee proposes:
" Reverse flow closure will be verified during each refueling outage by measuring a change in VCT level over time.
This test will be performed in conjunction with the Emergency Core Cooling Systems (ECCS) check valve flow tests when the RHR system is providing flow to the suction of the centrifugal charging pumps. This check valve must close to prevent flow diversion to the VCT. The proposed alternate testing method complies with Position 3 of NRC Generic Letter 89-04."
3.3.3 Evaluation Section XI of the ASME Code, Subsection IWV, Paragraph IWV-1400, " Owner's Responsibility," requires that each valve be categorized by the Owner.
The Code committee further clarified that the categorization of valves is the responsibility of the Owner (this clarification is found in the committee's reply to Code Inquiry XI-1-83-62, regarding whether check valves used in applications in which the valve disk must be in the closed position to fulfil i
the valve's safety-related function should be categorized as Category A/C and be leak rate tested).
By Information Notice 91-56, the NRC informed licensees that potential leak paths outside containment could result in releases of radioactivity to the atmosphere through a tank vent. The NRC also noted that valves with seat leakage limited to a specific amount should be Category A.
In its submittal the licensee referenced, but did not include, the Westinghouse advisory letter. Therefore, the staff could not review the adequacy of the licensee's determination to categorize these valves as Category C (check valves) rather than Category A/C (check valves with seat leakage limited to a specific amount). The licensee should ensure that there are no analyses that assume a maximum leakage limit for these valves.
If so, the valves should be Category A and are required to be leak tested in accordance with IWV-3420, " Valve Leak Rate Test." The categorization of these valves is subject to further review during NRC inspections.
Reverse flow testing these valves during power operation is not practical because they must be open to keep the CVCS in service.
CVCS is needed during normal operations to maintain the coolant volume and chemistry in the reactor coolant system.
Therefore, in accordance with IWV-3522, these check valves could be exercised during cold shutdown conditions rather than quarterly.
RCP seal water is supplied by the CVCS.
Unless the RCPs are shutdown, the CVCS is maintained in service during cold shutdown conditions.
Requiring the
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l licensee to take CVCS out of service would require stopping the RCPs and/or j
reducing the reactor coolant inventory to allow for mid-loop operations.
1 Stopping and restarting RCPs, or operating in mid-loop conditions, solely to j
perform testing of these valves, creates a hardship. Wear and stress on the RCPs and seals, cycles of plant equipment, and extension of the cold shutdown could result. Concerns relating to loss of RHR during mid-loop operations are described in Generic Letter 87-12, " Loss of Residual Heat Removal (RHR) While i
the Reactor Coolant System (RCS) is Partially Filled," and Generic Letter 88-17, " Loss of Decay Heat Removal." Therefore, establishing plant conditions solely to perform testing reduces the margin of safety for maintaining reactor coolant inventory.
The hardship and risks associated with performance of reverse flow testing of the CVCS check valves are not offset by an increased level of quality and safety in ensuring the capability of the valves to function.
Exercising the valves during each refueling outage provides an adequate level of safety as indicated by later Code editions. The 1989 Edition of Section XI references OM-10, as noted above in Section 2.0, for inservice testing of valves. 0M-10, Paragraph 4.3.2.2, specifies that check valve exercising may be limited to full-stroke during refueling outages if it is impractical to exercise the valves during plant operation or cold shutdowns.
Measuring a change in the VCT level to verify reverse closure meets the requirements of IWV-3522(a) for " confirmation that the disk is on the seat by a position indicating device, by observation of appropriate pressure indications in the system, or by other positive means." The requirements of IWV-3522(a) are restated in GL 89-04, Position 3, "Back Flow Testing of Check Valves."
3.3.4 Conclusion The proposed alternative to defer testing to refueling outages for the subject CVCS check valves (one per unit) is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) based on the hardship created by testing at the Code frequency and based on the determination that imposition of the Code requirements would not provide a compensating increase in the level of quality and safety for the plant.
3.4 Cold Shutdown Justification CS-31 The Category C, Class 3, main steam supaly check valve (1301-U4-404 - one per unit) to the auxiliary feedwater (AFW) pump turbine driver performs a safety-related function by opening to allow steam flow to the AFW turbine. The valve is partial-stroke exercised quarterly during the AFW pump inservice test.
Full-stroke exercising cannot be performed during power operation because the turbine-driven AFW pump is not delivering full-flow to the steam generators, Full-stroke exercising is verified during cold shutdown testing by ensuring that the turbine-driven AFW pump is delivering required flow. The test frequency is in accordance with the exercising provisions of IWV-3522.
i Because the test frequency is in accord with the Code, NRC approval is not required.
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> To ensure the valve inservice tests are documented, the licensee should include the full-stroke verification in the test procedure with acceptance criteria. The corrective actions should be specified in the test procedure for test data that indicates acceptance criteria are not met.
4.0 CONCLUSION
The staff has determined that the reliefs, granted in accordance with Generic letter 89-04, and approved pursuant to 10 CFR 50.55a(a)(3)(ii), are authorized by law and will not endanger life or property, or the common defense and security, and are otherwise in the public interest.
Principal Contributor:
P. Campbell Date:
October 12, 1993 m