2CAN080803, Request for Relief VRR-ANO2-2008-1 Frequency of Leak Rate Testing of the Service Water Boundary Isolation Valves
| ML082380146 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/21/2008 |
| From: | James D Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2CAN080803 | |
| Download: ML082380146 (8) | |
Text
Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4619 Dale E. James Manager, Licensing Arkansas Nuclear One 2CAN080803 August 21, 2008 U. S. Nuclear Regulatory Commission Attn.: Document Control Desk Washington, DC 20555-0001
SUBJECT:
Request for Relief VRR-ANO2-2008-1 Frequency of Leak Rate Testing of the Service Water Boundary Isolation Valves Arkansas Nuclear One, Unit 2 Docket No. 50-368 License No. NPF-6
Dear Sir or Madam:
Pursuant to 10 CFR 50.55a(a)(3)(ii), Entergy Operations, Inc. (Entergy) requests an alternative for the Inservice Testing Program. The proposed alternative is requested when using the requirements of ASME/ANSI OMa-1988, Part 10 (OM-10), pertaining to the frequency of the leak rate test for two service water boundary isolation valves at Arkansas Nuclear One, Unit 2 (ANO-2). OM-10, Section 4.2.2.3(a) requires that Category A valves, which perform a function other than containment isolation, shall be seat leakage tested to verify their leak-tight integrity and that the tests shall be conducted at least once every 2 years.
The proposed test frequency is to perform the test at least once every three (3) years for these valves. This request impacts only these two valves and would allow ANO-2 to test one valve per refueling outage instead of both valves in the same outage. The proposed alternate testing frequency provides adequate assurance of the valves leak tightness and minimizes the vulnerability of the unit during refueling outages. Request for Relief VRR-ANO2-2008-1 is provided as the attachment to this letter.
This letter contains no new commitments.
Entergy requests approval of the proposed request for alternative by September 1, 2009, in order to support the fall 2009 refueling outage for ANO-2. Although this request is neither exigent nor emergency, your prompt review is requested.
2CAN080803 Page 2 of 2 If you have any questions or require additional information, please contact me.
Sincerely, DEJ/rwc
Attachment:
Request for Relief VRR-ANO2-2008-1 cc: Mr. Elmo E. Collins Regional Administrator U. S. Nuclear Regulatory Commission Region IV 612 Lamar Blvd., Suite 400 Arlington, TX 76011-4125 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 U.S. Nuclear Regulatory Commission Attn: Mr. Alan B. Wang MS O-7 D1 Washington, DC 20555-0001 Mr. Bernard R. Bevill Director Division of Radiation Control and Emergency Management Arkansas Department of Health & Human Services P.O. Box 1437 Slot H-30 Little Rock, AR 72203-1437
ATTACHMENT TO 2CAN080803 REQUEST FOR RELIEF VRR-ANO2-2008-1
Attachment to 2CAN080803 Page 1 of 5 10 CFR 50.55a Request Number VRR-ANO2-2008-1 Proposed Alternative in Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request
Title:
Frequency of Leak Rate Testing of the SW Boundary Isolation Valves PLANT/UNIT: Arkansas Nuclear One, Unit 2, Docket No. 50-368, License No. NPF-6 INTERVAL: Third 120-Month Inservice Testing Interval COMPONENTS Valves: 2CV-1541-1 and 2CV-1560-2 AFFECTED:
System: Service Water (SW)
Valves 2CV-1541-1 and 2CV-1560-2 have an active open safety function on a Main Steam Isolation Signal (MSIS) or a Safety Injection Actuation Signal (SIAS) to direct the SW return flow from Return Header #1 or #2, respectively, to the Emergency Cooling Pond (ECP). These valves have an active closed safety function to isolate a ruptured SW header to ensure the long-term cooling capability is maintained. These valves serve as a SW boundary isolation valves and their leakage has been determined to be consequential.
(The above valves are ASME Code Class 3, OM Code Category A motor operated valves)
CODE EDITION AND ASME Section XI, 1989 Edition with no Addenda ADDENDA:
ASME/ANSI OM-1987 with OMa-1988 Addenda, Part 10 (OM-10)
REQUIREMENTS: The current code of record governing Inservice Testing (IST) for valves at Arkansas Nuclear One, Unit 2 (ANO-2), is the ASME Section XI, 1989 Edition with no Addenda, which requires the use of OM-10 for testing valves 2CV-1541-1 and 2CV-1560-2. OM-10 Section 4.2.2.3(a) requires that Category A valves, which perform a function other than containment isolation, shall be seat leakage tested to verify their leak-tight integrity and that the tests shall be conducted at least once every 2 years.
REASON FOR Pursuant to 10 CFR 50.55a, Codes and Standards, paragraph (a)(3)(ii), an RELIEF REQUEST: alternative is requested when using the requirements of OM-10 Section 4.2.2.3(a) pertaining to the frequency of the leak rate test for valves 2CV-1541-1 and 2CV-1560-2 (as listed above).
There are a total of 21 ANO-2 SW boundary isolation valves. These valves are leak tested to verify seat leakage does not exceed the leakage allowed based on maintaining the minimum volume of water in the ECP to meet the Design Basis Accident requirements.
Valves 2CV-1541-1 and 2CV-1560-2 are two of these 21 valves. They are normally closed motor-operated 18 Tricentric stainless steel butterfly stop
Attachment to 2CAN080803 Page 2 of 5 10 CFR 50.55a Request Number VRR-ANO2-2008-1 valves. As stated above, they have an active open safety function to direct the SW return flow to the ECP, an active closed safety function to isolate a ruptured SW header to ensure the long-term cooling capability is maintained, and serve as a SW boundary isolation valves.
Provided below is a description of how performing the leak rate test on both of the subject valves in the same outage causes unnecessary challenges to safety systems on both units.
These valves can only be tested when the unit is shutdown in Modes 5 or 6 and with the associated SW loop out of service one at a time. Normally these valves are tested during refueling outages. The entire loop of service water is required to be removed from service and drained empty to perform this test. In doing this, all the loads on that particular service water loop are declared inoperable including the associated emergency control room chiller, the associated emergency diesel generator, the backup SW train for cooling the spent fuel pool, and the standby shutdown cooling train. In declaring the emergency control room chillers inoperable requires ANO-1 to enter into Technical Specification action statements since this equipment is used for cooling both ANO control rooms.
Most importantly, the removal of a SW loop from operations reduces the defense in depth for loss of decay heat removal events by removing its cooling water from service and its emergency diesel generator. The emergency diesel generator also supplies a backup power supply to the standby shutdown cooling train. Removal of the SW loop from operation also removes the backup cooling water train from the spent fuel pool during outage conditions when the spent fuel pool heat load is the highest. This unnecessarily increases the risk and vulnerability of ANO-2 during a refueling outage.
These actions and vulnerabilities are repeated when the other valve is tested during the same outage.
The above discussion is specifically directed at those outages in which the only reason a loop of service water was removed from service was to leak rate test the appropriate service water return valve.
NUREG-1482, Revision 1, Guidelines for Inservice Testing at Nuclear Power Plants was reviewed for a definition of hardship. Hardship is interpreted to mean a high degree of difficulty or an adverse impact on plant operation. The above hardships can be significantly reduced using the modified test frequency without decreasing the level of quality or safety.
(Note: Even though Revision 0 of NUREG-1482 is still valid for licensees using OM-10, Revision 1 of NUREG-1482 was considered the more appropriate revision to use for NRC considerations regarding hardship and relief request content and format.)
Attachment to 2CAN080803 Page 3 of 5 10 CFR 50.55a Request Number VRR-ANO2-2008-1 PROPOSED Entergy proposes an alternate test frequency for performing leak rate tests ALTERNATIVE AND for valves 2CV-1541-1 and 2CV-1560-2. Specifically, Entergy proposes to BASIS:
test one valve each refueling outage. This would alter the frequency to once every three (3) years.
Entergy believes the current requirement for leak rate testing the identified valves every two years (i.e., testing both valves every refueling outage) results in a hardship without a compensating increase in the level of quality or safety. Entergy also believes that the proposed alternative of performing the leak rate test once every three years (i.e., testing one valve each refueling outage) provides reasonable assurance that the valves described herein are periodically leak tested and maintained leak tight.
This request for relief is from the frequency of the leak rate test only. The full stroke test of these valves will continue to occur every three months. The acceptance criterion of the full stroke and the leak rate tests nor the required corrective actions if the acceptance criterion is violated is not changed. The test methods for the full stroke test and the leak rate test are not being changed due to this request.
The ECP is shared between ANO-1 and ANO-2. The design basis for the ECP is that it be capable of dissipating the heat from an accident in one unit, permit the concurrent safe shutdown and cooldown of the remaining unit and maintain both in a safe shutdown condition. The capacity of the ECP is to be sufficient to provide cooling both for the period of time needed to evaluate the situation and for the period of time needed to take corrective action.
The inventory analysis for the ECP assumes a total loss of 30 gallons per minute (gpm) from the boundary valves of both units combined. Currently, the analysis assumes the allowable leakage to be evenly distributed among the valves, or 2.5 gpm per valve. Even distribution of the allowed leakage is not a design requirement for operability of the individual valves, provided total leakage is being monitored and margin is being maintained from the allowable.
While it is acceptable for individual valve leakage limits to be greater than those calculated from even distribution of the total, the valve limits needs to be below the total ECP allowable to avoid masking and shadowing concerns. Total leakage from the valves on each system is monitored to ensure the limit assumed in the ECP inventory analysis is not exceeded.
Thus, the limit for operability for an individual valve also needs to be below the limit for the system. In addition, it is desired to establish a maintenance limit (Acceptable Normal Range) to initiate corrective maintenance at a leakage threshold above what would normally be expected for the valve and below the operability threshold.
The allowable leakage below which corrective maintenance is not required is
Attachment to 2CAN080803 Page 4 of 5 10 CFR 50.55a Request Number VRR-ANO2-2008-1 established to be less than 1.5 gpm. This is the Acceptable Normal Range.
The SW boundary isolation valves have been replaced in previous cycles with metal seats (or metal/graphite laminated layers) to reduce the potential for gross leakage from failure modes of soft seats (i.e., rubber lined butterfly valves) tearing away from the valve body. The performance history (recent history summarized in the table below) has been reviewed and the valves should be readily capable of performing with less than 1.5 gpm leakage.
2CV-1541-1 2CV-1560-2 Test Date Leak Rate Acceptable Leak Rate Acceptable (gpm) Normal (gpm) Normal (gpm) (gpm) 10/10/2003 0.25 1.5 0 1.5 04/07/2005 0 1.5 0 1.5 10/20/2006 0 1.5 0 1.5 04/04/2008 0 1.5 1.25 1.5 This threshold initiates corrective maintenance at leakage levels below the currently established 2.5 gpm limit. Corrective maintenance will typically be performed during the outage that leakage exceeding 1.5 gpm is detected.
However, it may be scheduled during the following outage to better align with train maintenance and other preventative maintenance schedules provided the Limiting Range of Operability is not exceeded and the as-left total system leakage can be maintained below the Acceptable Normal Range (< 10 gpm / system).
The valve operability threshold is greater than or equal to 9.0 gpm, or 30% of the assumed ECP inventory loss to SW boundary valves. This threshold, being only 30% of the total assumed inventory loss for the ECP, provides conservatism to the total allowed leakage for establishing a functional failure criterion for the ECP boundary isolation valves.
As is evident from the information above, these valves have a history of being leak-tight. There are no plans in the foreseeable future that would require these valves to be changed or replaced.
Based on the determination that compliance with the OM-10 Section 4.2.2.3(a) requirements results in a hardship without a compensating increase in the level of quality or safety, this proposed alternative should be granted pursuant to 10 CFR 50.55a(a)(3)(ii).
DURATION: This relief will be effective for the remainder of ANO-2s Third 120-month Inservice Testing Interval (March 26, 2000 through March 25, 2010 based on letter from NRCs Mr. R. A. Gramm to ANOs Mr. C. G. Anderson dated March 31, 2000).
PRECEDENTS: None
Attachment to 2CAN080803 Page 5 of 5 10 CFR 50.55a Request Number VRR-ANO2-2008-1
REFERENCES:
Revision 0 of NUREG-1482, Guidelines for Inservice Testing at Nuclear Power Plants, Published April 1995 Revision 1 of NUREG-1482, Guidelines for Inservice Testing at Nuclear Power Plants, Final Report, Published January 2005 Letter from NRCs Mr. R. A. Gramm to ANOs Mr. C. G. Anderson dated March 31, 2000 STATUS: Submitted for Nuclear Regulatory Commission review and approval by 2CAN080803.