ML063340516
| ML063340516 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 12/08/2006 |
| From: | Raghavan L NRC/NRR/ADRO/DORL/LPLIII-1 |
| To: | Nazar M Indiana Michigan Power Co |
| Tam P | |
| References | |
| TAC MD0939, TAC MD0940, TAC MD2498, TAC MD2499 | |
| Download: ML063340516 (10) | |
Text
December 8, 2006Mr. Mano K. NazarSenior Vice President and Chief Nuclear Officer Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106
SUBJECT:
DONALD C. COOK NUCLEAR PLANT, UNITS 1 AND 2 (DCCNP-1 ANDDCCNP-2) - RELIEF REQUEST REL-002 AND REL-021 FOR THE THIRD AND FOURTH INTERVAL INSERVICE TESTING PROGRAMS (TAC NOS. MD0939, MD0940, MD2498, AND MD2499)
Dear Mr. Nazar:
By letter dated December 28, 2005, Indiana Michigan Power Company (I&M), the licensee,submitted, among other requests, Relief Request REL-002 for its fourth 10-year inservice testing (IST) program interval at DCCNP-1 and DCCNP-2. In addition, by letter dated March 31, 2006, I&M submitted Relief Request REL-021 for its third 10-year IST program. On February 27, 2006, the Nuclear Regulatory Commission (NRC) requested I&M to submit additional information to support Relief Request REL-002. I&M responded by a letter dated June 2, 2006. The NRC made a further request for additional information on July 7, 2006. The licensee responded by submitting additional information to support both Relief Requests REL-002 and REL-021 on October 26, 2006. In Relief Request REL-002 and REL-021, I&M requested relief from certain IST requirements ofthe 2001 Edition through 2003 Addenda of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code). I&M also requested relief from certain requirements of ASME/American National Standards Institute (ANSI) OM-1987 Edition, including OMa-1988 Addenda, which is invoked by ASME Section XI. The NRC staff has completed its review of Relief Requests REL-002 and REL-021. Reliefrequests REL-002 and REL-021 are granted pursuant to 10 CFR 50.55a(f)(6)(i) based on the impracticality of performing testing in accordance with code requirements, and in consideration of the burden on I&M if the code requirements were imposed on the facility. This relief is granted for the third and fourth 10-year IST intervals for relief requests REL-021 and REL-002, respectively.Granting relief pursuant to 10 CFR 50.55a(f)(6)(i) is authorized by law and will not endanger lifeor property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
M. K. Nazar- 2 -Details of the NRC staff's review is set forth in the enclosed safety evaluation. If you have anyquestions, please contact the NRC Project Manager, Mr. Peter Tam, at 301-415-1451. Sincerely,/RA/L. Raghavan, ChiefPlant Licensing Branch III-1 Division of Operating Reactor Licensing Office of Nuclear Reactor RegulationDocket Nos. 50-315 and 50-316
Enclosure:
Safety Evaluationcc w/encl: See next page
ML063340516 OFFICENRR/LPL3-1/PMNRR/LPL3-1/LANRR/CPTB/BCOGCNRR/LPL3-1/BCNAMEPTamTHarrisSLeeTCampbellLRaghavanDATE12/5/0612/5/0611/21/06*12/7/0612/8/06*Safety evaluation transmitted by memo of 11/21/06.
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATIONRELATED TO THE INSERVICE TESTING (IST) PROGRAMINDIANA MICHIGAN POWER COMPANY, LLC (I&M)DONALD C. COOK NUCLEAR PLANT, UNITS 1 AND 2 (DCCNP-1 AND DCCNP-2) DOCKET NOS. 50-315 AND 50-31
61.0INTRODUCTION
By letter dated December 28, 2005 (Accession No. ML060060110), I&M (the licensee)submitted relief request REL-002 for the fourth 10-year inservice testing (IST) program interval at DCCNP-1 and DCCNP-2. By letter dated March 31, 2006 (Accession No. ML061020055),
the licensee also submitted a similar request, REL-021, for the third 10-year IST interval. The licensee requested relief in REL-002 from certain inservice test requirements of the 2001 Edition through 2003 Addenda of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code). The licensee also requested relief from certain requirements of ASME/American National Standards Institute (ANSI) OM-1987 Edition, including OMa-1988 Addenda, which was invoked by ASME Section XI, in REL-021. In response to the Nuclear Regulatory Commission (NRC) staff's requests for additional information (publicly available e-mails dated February 27 and July 7, 2006, Accession Nos. ML060590089 and ML061920110, respectively), the licensee submitted additional information by letters dated June 2, 2006 (Accession No. ML061640312), and October 26, 2006 (Accession No. ML063110583). The NRC staff's safety evaluation of relief requests REL-002 and REL-021 are contained herein.
2.0REGULATORY EVALUATION
Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a, requires that IST ofcertain ASME Code Class 1, 2, and 3 pumps and valves be performed at 120-month (10-year) program intervals in accordance with the specified ASME Code incorporated by reference in the regulations, except where relief has been requested by the licensee and granted by the NRC pursuant to paragraphs (a)(3)(i), (a)(3)(ii), or (f)(6)(i) of 10 CFR 50.55a, or when alternatives have been authorized by the NRC. In accordance with 10 CFR 50.55a(f)(4)(ii), licensees are required to comply with the requirements of the latest edition and addenda of the ASME Code incorporated by reference in the regulations 12 months prior to the start of each 120-month IST program interval. In accordance with 50.55a(f)(4)(iv), IST of pumps and valves may meet the requirements set forth in subsequent editions and addenda that are incorporated by reference in 10 CFR 50.55a(b), subject to NRC approval. Portions of editions or addenda may be used provided that all related requirements of the respective editions and addenda are met.
In proposing alternatives or requesting relief, the licensee must demonstrate that: (1) the proposed alternatives provide an acceptable level of quality and safety; (2) compliance would ENCLOSURE result in hardship or unusual difficulty without a compensating increase in the level of qualityand safety; or (3) conformance is impractical for the facility. Section 50.55a authorizes the NRC to approve alternatives and to grant relief from ASME Code requirements upon making necessary findings. NRC guidance contained in Generic Letter (GL) 89-04, "Guidance on Developing Acceptable Inservice Testing Programs," provides alternatives to Code requirements which are acceptable. Further guidance is given in GL 89-04, Supplement 1, and NUREG-1482, Revision 1, "Guidance for Inservice Testing at Nuclear Power Plants."The licensee stated that the third 10-year IST interval was scheduled to end on June 30, 2006. The third interval program was developed in accordance with the ASME/ANSI OM-1987 Edition, including OMa-1988 Addenda, which is invoked by ASME Section XI. The licensee stated that the fourth 10-year IST interval would commence on July 1, 2006. The program was developed in accordance with the 2001 Edition through 2003 Addenda of the ASME OM Code. By the December 28, 2005, letter, the licensee requested relief (REL-002) from certain requirements of the OM Code for the fourth 10-year IST interval. In addition, by the March 31, 2006, letter, the licensee requested relief (REL-021) from related requirements of the Code for the third 10-year IST interval.
3.0 TECHNICAL EVALUATION
The licensee's Relief Requests, REL-002 and REL-021, relate to identical code requirements,and propose the same alternative testing. Therefore, a single evaluation will be provided for both relief requests. The code of record for DCCNP-1 and DCCNP-2 third 10-year interval IST program for pumps and valves is the 1989 Edition of the ASME Boiler and Pressure Vessel (BPV) Code,Section XI. The 1989 ASME BPV Code,Section XI, invokes ASME/ANSI OMa-1988, Part 10 for the IST of valves. The code of record for the DCCNP-1 and DCCNP-2, fourth 10-year interval IST program for pumps and valves is the 2001 Edition through 2003 Addenda of the ASME OM Code. 3.1 Valve Relief Requests REL-002 and REL-0213.1.1 Code RequirementsFor the Third 10-year Interval (REL-021), OMa-1988, Part 10, Paragraph 4.2.2.3(b),"Differential Test Pressure," requires that valve seat leakage tests shall be made with the pressure differential in the same direction as when the valve is performing its function.For the fourth 10-year Interval (REL-002), ISTC-3630(b), "Differential Test Pressure," requiresthat valve seat leakage tests shall be made with the pressure differential in the same direction as when the valve is performing its function.3.1.2 Licensee's Basis for Requesting ReliefThe licensee's requests for relief apply to the following valves:
1-IMO-261Refueling Water Storage Tank (RWST) Supply to Safety Injection (SI) PumpsShutoff Valve, Unit 11-IMO-910RWST to Chemical and Volume Control System (CVCS) Charging PumpsSuction Header Train "A" Shutoff Valve, Unit 1 1-IMO-911RWST to CVCS Charging Pumps Suction Header Train "B" Shutoff Valve, Unit 12-IMO-261RWST Supply to SI Pumps Shutoff Valve, Unit 2 2-IMO-910RWST to CVCS Charging Pumps Suction Header Train "A" Shutoff Valve, Unit 2 2-IMO-911RWST to CVCS Charging Pumps Suction Header Train "B" Shutoff Valve, Unit 2In its March 31 and June 2, 2006, letters, the licensee stated:These valves were reclassified as Category A valves (valves requiring a seat-leakage test) based on the concern raised in Information Notice 91-56, "Potential Radioactive Leakage to Tank Vented to Atmosphere," and reevaluation of the category definitions. Originally, the valves were categorized as Category B valves. Category B valves are valves that require full stroke exercising but whose "...seat leakage in the closed position is inconsequential for fulfillment oftheir required function(s)... ." I&M has determined that these valves, becausethey have a seat leakage requirement, should be categorized as Category A valves. The Category A classification requires that the valves be leak tested in accordance with the code requirements.[DCCNP-1 and DCCNP-2], were constructed and licensed prior to the concernabout back-leakage to the RWST being identified. As a result, the system in which these valves are located is not designed and constructed to allow accident-direction testing. Accident-direction testing is where the pressure differential exists in the same direction as when the valve is performing its isolation function. There are no isolation valves between these valves and the RWST.
As can be seen, there is not a practical means to measure seat leakage with pressure applied in the accident direction. Attempting to quantify leakage through these valves by monitoring the RWST level is not an accurate means of measuring seat leakage.
Additionally, system configuration does not allow leakage determination using the "test-volume makeup" method. This method also would not yield accurate results. There is presently no practical means of leak testing these valves in accordance withthe code requirements. Compliance with the code requirements would require a system modification to allow isolation of the RWST.The valves are 8-inch, 150-pound flex wedge gate valves. The seat seal for thesevalves is created by a combination of internal pressure and mechanical wedging force.
At line pressures under approximately 100 pounds per square inch (psi), the pressure force alone is not sufficient to create a seal, and the mechanical force resulting from the disc being wedged between the seat rings provides the additional force necessary to provide a seal. Testing these valves in the reverse direction tests the valves' leak tightness when the line pressure is below 100 psi, and provides evidence of any leakage past the valves.As can be seen in the Attachment 2 system schematic, Valve IMO-261 is in series withcheck valve SI-101, and valves IMO-910 and IMO-911 are in series with check valve SI-185. The check valves are Category A valves and are leak tested in compliance with the code, providing additional assurance that the back leakage to the RWST from these flow paths will meet system requirements. It is I&M's opinion that the proposed testing of the gate valves, combined with theleakage testing of the check valves in series with them, provides reasonable assurance that the system leakage requirements will be met under accident conditions.The licensee states that system modifications to allow for leakage determination tests thatwould meet code provisions would involve installing a minimum of one 8-inch isolation valve and a test/vent connection in order to test 1(2)-IMO-261 and an 8-inch isolation valve for the 1(2)-IMO-910 and 911 leakage tests. Another option would require addition of a 24-inch isolation valve on the RWST outlet header which would shut off flow to all of the Emergency Core Cooling System (ECCS) pump suctions from the RWST. 3.1.3 Licensee's Proposed Alternative TestingThe licensee proposes to test the valves in the reverse direction (the test pressure differential isopposite to the pressure differential that would exist when the valve is performing its isolation function) using the static head from the RWST. Although the accident conditions have a higher differential pressure than that used for the proposed leakage measurement test, the leakage measured during the leakage test would be corrected to the higher pressure.3.1.4 NRC Staff EvaluationThe code requirement to perform seat leakage testing for Category A valves is intended toverify the operational readiness of individual components. Failure of a valve to meet an acceptance criteria indicates that the valve is potentially degraded and may be incapable of performing its safety function. However, the leakage rate limits assigned to individual RWST isolation valves are artificially derived values because the critical leakage limit for these valves is the limit for overall leakage to the RWST. If one valve exceeds its leakage rate limit, the valve has not seated tightly and may be degraded. However, exceeding an individual leakage rate limit does not necessarily indicate that the group of all RWST isolation valves cannot meet their leak-tight safety function unless the total leakage limit to the RWST is exceeded.
The subject valves are in series with Category A check valves in these specific leakage paths tothe RWST. Excessive leakage of any one valve in the leakage pathways does not necessarily indicate that overall RWST in-leakage limits would be exceeded. Excessive seat leakage through two valves in series would be required to cause leakage to the RWST through any one of the pathways to exceed limits.The code requires that seat leakage test be made with the differential pressure applied in thesame direction as when the valve is performing its leak-tight safety function. In the case of the RWST outlet valves, existing system design does not allow a means of pressurizing the valve from the side opposite the RWST to conduct the seat leakage test. System modifications to allow testing in the accident direction would involve the addition of an 8-inch isolation valve and test/vent connection in each of the suction flow paths to the charging pumps and safety injection pumps, or the addition of a 24-inch isolation valve in the common supply line from the RWST to all of the ECCS pumps. Implementing modifications to the ECCS pump suction lines would involve extended out-of-service time for ECCS and residual heat removal equipment.
These options involve significant burden to implement and would result in a non-standard system configuration. The introduction of additional isolation valves would also increase the probability of inadvertently isolating an ECCS pump suction flow path by valve mispositioning.
Use of the "test volume makeup" method or observation of RWST level change to detect leakage while testing in the accident direction would not yield meaningful results due to thelarge system volumes involved and difficulty in positively identifying which test boundary isolation valve was contributing to the observed leakage. Therefore, the NRC staff agrees that it is impractical for the licensee to comply with the Code requirement to conduct leakage tests for the subject valves in the accident direction. A leakage test in the reverse direction to the accident conditions using the head of water in theRWST as the driving force must provide equivalent or more conservative results than a test in the accident direction to be considered adequate. In evaluating the adequacy of the licensee's proposed test, the physical construction and arrangement of the valve seat and disc, as well as the pressure forces acting in the attached piping, must be considered. The licensee stated that the subject valves are 8-inch 150-pound flex wedge gate valves. The design of the valve disc and seating surfaces is a symmetrical arrangement where thrust applied by the valve's motor operator will tend to seat each wedge face equally. Additionally, the flexible wedge design is robust and will not exhibit significant deformation at the relatively low line pressures (less than 200 psig) encountered in the accident scenario. These design features provide a degree of confidence that both faces of the valve wedge will seat equally to limit overall seat leakage through the valve. Pressure applied in a seat leakage test will tend to unseat the face of the valve disc closest to the pressure source, and seat the downstream face. Since both faces will be equally seated by actuator thrust, a seat leakage test in either direction will provide some indication of overall degradation of the seating surfaces. The licensee stated that at line pressures below 100 psig, the pressure force alone is not sufficient to create a seal.
Adequate leak tightness is ensured by the mechanical wedging force provided by the actuator.
The licensee has adjusted the valves under its GL 89-10 program to close against the estimated differential pressure that would exist during the transition from the loss-of-coolant accident (LOCA) injection phase to the LOCA recirculation phase. The seat load on the valves is specifically designed to ensure both seats of the flex wedge are fully seated to remain leak tight under the postulated system conditions. Testing the wedge at low line pressures (12-17 psid) using static head of the RWST will mainly test the seal created by the mechanical wedging force alone, thus providing an indication of the degree of degradation of the seating surfaces. The increased line pressure under accident conditions (122 psid for IMO-910 and IMO-911, 195 psid for IMO-261) will act to further seat the sealing face closest to the RWST, so the proposed test at lower pressure in the opposite direction will test this seating surface without the additional service pressure that would tend to diminish leakage by pressing the disconto the seat with greater force. Therefore, the proposed seat leakage test provides reasonable assurance of the operational readiness of the valves to isolate the RWST from back leakage during the LOCA recirculation phase.
4.0CONCLUSION
Based on the above evaluation, the NRC staff concludes that relief is granted pursuant to10 CFR 50.55a(f)(6)(i) based on the impracticality of performing testing in accordance with code requirements, and in consideration of the burden on the licensee if the code requirements were imposed on the facility. The licensee's proposed alternative to perform seat leakage tests with pressure applied in a direction that is opposite that encountered under accident conditions, using static head of the RWST and correcting leakage measured to the higher accident pressure, provides reasonable assurance of the operational readiness of the subject valves.
This relief is granted for the third and fourth 10-year IST intervals for relief requests REL-021 and REL-002, respectively. Granting relief pursuant to 10 CFR 50.55a(f)(6)(i) is authorized by law and will not endanger lifeor property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.Principal Contributor: J. McHale Date: December 8, 2006 Donald C. Cook Nuclear Plant, Units 1 and 2 cc:Regional Administrator, Region IIIU.S. Nuclear Regulatory Commission Suite 210 2443 Warrenville Road Lisle, IL 60532-4351Attorney GeneralDepartment of Attorney General 525 West Ottawa Street Lansing, MI 48913Township SupervisorLake Township Hall P.O. Box 818 Bridgman, MI 49106U.S. Nuclear Regulatory CommissionResident Inspector's Office 7700 Red Arrow Highway Stevensville, MI 49127Kimberly Harshaw, EsquireIndiana Michigan Power Company One Cook Place Bridgman, MI 49106Mayor, City of BridgmanP.O. Box 366 Bridgman, MI 49106Special Assistant to the GovernorRoom 1 - State Capitol Lansing, MI 48909Susan D. SimpsonRegulatory Affairs Manager Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106Michigan Department of Environmental Quality Waste and Hazardous Materials Div.
Hazardous Waste & Radiological Protection Section Nuclear Facilities Unit Constitution Hall, Lower-Level North 525 West Allegan Street P. O. Box 30241 Lansing, MI 48909-7741Lawrence J. Weber, Plant ManagerIndiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106Mark A. Peifer, Site Vice President Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106