ML100640446
| ML100640446 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/12/2010 |
| From: | Chernoff H Plant Licensing Branch 1 |
| To: | Heacock D Dominion Nuclear Connecticut |
| sanders c | |
| References | |
| TAC ME1261, FOIA/PA-2011-0115 | |
| Download: ML100640446 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 12, 2010 Mr. David A. Heacock President and Chief Nuclear Officer Dominion Nuclear Connecticut, Inc.
Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711
SUBJECT:
MILLSTONE POWER STATION, UNIT NO.3-ISSUANCE OF RELIEF REQUEST IR-3-09 REGARDING USE OF AMERICAN SOCIETY OF MECHANICAL ENGINEERING CODE, SECTION XI, 2004 EDITION (TAC NO.
ME1261)
Dear Mr. Heacock:
By letter dated April 28, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML091310666), Dominion Nuclear Connecticut, Inc. (DNC or the licensee) submitted relief requests for the third 1O-year in-service inspection (lSI) interval at Millstone Power Station, Unit NO.3 (MPS3). The licensee requested the use of alternatives to certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, 2004 Edition, no addenda requirements. IR-3-09, proposes alternate pressure testing criteria during performance of the end-of-interval system leakage test for the Class 1 piping segments in the reactor coolant system for the pressurizer auxiliary spray, low pressure and high pressure safety injection, residual heat removal, and reactor coolant vents and drain piping. The remaining relief requests submitted by the April 28, 2009, letter are being reviewed separately.
The results of the Nuclear Regulatory Commission (NRC) staff's review, as contained in the enclosed Safety Evaluation, conclude that DNC's compliance with ASME Code-required end-of interval leakage test for Class 1 piping segments in the reactor coolant system for the pressurizer auxiliary spray, low pressure and high pressure safety injection, residual heat removal, and reactor coolant vents and drain piping would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The NRC staff also concludes that the proposed system leakage tests in Relief Request IR-03-09, as an alternative to the ASME Code required test, is acceptable because it provides reasonable assurance of the structural integrity of the piping.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the NRC staff authorizes the proposed alternatives in Relief Request IR-3-09 for MPS3 for the remainder of the third 10-year lSI interval. The third 10-year lSI interval for MPS3 began on April 23, 2009, and is scheduled to be completed on April 22, 2019.
D. Heacock -2 All other ASME Code,Section XI requirements for which relief has not been specifically requested and approved remain applicable, including a third party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.
Sincerely,
~
- lliS Harold Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-423
Enclosure:
As stated cc wI encl: Distribution via Listserv
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST IR-3-09 FOR THE THIRD 10-YEAR INSERVICE INSPECTION INTERVAL DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION, UNIT NO.3 DOCKET NUMBER 50-423
1.0 INTRODUCTION
By letter dated April 28, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML091310666), Dominion Nuclear Connecticut, Inc. (DNC or the licensee) submitted relief requests for the third 1O-year in-service inspection (lSI) interval at Millstone Power Station, Unit NO.3 (MPS3). The licensee requested the use of alternatives to certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, 2004 Edition, no addenda requirements. IR-3-09, proposes alternate pressure testing criteria during performance of the end-of-interval system leakage test for the Class 1 piping segments in the reactor coolant system for the pressurizer auxiliary spray, low pressure and high pressure safety injection, residual heat removal, and reactor coolant vents and drain piping.
DNC requests relief from performing the ASME Code,Section XI required pressure testing criteria for the system leakage test conducted at or near the end of the inspection interval on Class I piping. The ASIVIE Code requirement, at or near the end of the interval, is to extend the pressure test to all Class 1 pressure retaining components within the system boundary. As an alternative to the ASME Code requirements, DNC proposes to pressurize up to the inboard isolation valve for vents and drains which would exclude a segment of the Class 1 pressure boundary from attaining test pressure and/or conduct the test at a reduced pressure for other systems. The visual examination during the pressure test would include all components within the system boundary.
2.0 REGULATORY REQUIREMENTS 10 CFR Section 50.55a(g) specifies that lSI of nuclear power plant components shall be performed in accordance with the requirements of the ASME Code,Section XI, except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
Section 50.55a(a)(3) of 10 CFR states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would Enclosure
-2 result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that lSI of components and system pressure tests conducted during the first 1O-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The lSI Code of Record for the third 10-year lSI interval for the MPS3 is the 2004 Edition of the ASME Code,Section XI, no addenda. The third 10-year lSI interval for MPS3 began on April 23, 2009, and is scheduled to be completed on April 22, 2019.
3.0 TECHNICAL EVALUATION
3.1 System/ComponenHs) for Which Relief is Requested
- Pressurizer Auxiliary Spray
- Reactor Head Vent
- Reactor Coolant Drains
- Low Pressure Safety Injection (LPSI)
- High Pressure Safety Injection (HPSI)
There are 41 Reactor Coolant Pressure Boundary (RCPB) piping segments primarily consisting of 2" nominal pipe size (NPS) or smaller piping vents, drains, and branch (VTDB) lines and connections. Additional segments are portions of larger diameter piping, 6", 8", 10", and 12" NPS, located between check valves which are required to be isolated during operation, but are statically pressurized.
3.2 ASME Code Requirements IWB-2500, Table IWB-2500-1, "Examination Categories," Item Number B15.10, requires that all Class 1 pressure retaining components be VT-2 visually examined each refueling outage. The required system pressure test can be either a system hydrostatic test or a system leakage test.
The system leakage test is performed at a pressure not less than the pressure corresponding to 100% rated reactor power.
-3 Per IWB-5222(a), the pressure retaining boundary during the system leakage test shall correspond to the reactor coolant boundary with all valves in the position required for normal reactor operation startup. The visual examination shall, however, extend to and include the second closed valve at the boundary extremity.
Per IWB-5222(b), the pressure retaining boundary during the system leakage test conducted at or near the end of each inspection interval shall be extended to all Class 1 pressure retaining components within the system boundary.
3.3 Licensee's Basis for Requesting Relief Reactor coolant system vents, drains and branch piping Each VTOB line and connection is equipped with two isolation valves to provide double isolation of the RCPB. These valves are generally maintained closed during normal operation. The piping outboard of the first isolation valve is not normally pressurized. Under normal operating conditions, these VTOB lines and connections, except for the LPSI VrOB lines and connections, are subject to reactor coolant system (RCS) pressure and temperature only if leakage through the inboard valves occurs. For the LPSI VTOB lines and connections, leakage at inboard valves will only result in pressures associated with the pressure of the safety injection tanks.
Because these VTOB lines and connections typically do not have test connections that would allow them to be individually pressure tested without design modifications, it will be necessary to open the inboard valves to pressurize these VTOB lines and connections to perform the ASME Code-required pressure test. Pressurization by this method defeats the double isolation feature and presents significant safety concerns for the personnel performing the test on the valves that are at normal RCS pressure and temperature.
Performing this test with the inboard isolation valves open requires several man-hours to position or cycle these valves for the test and restore the valves after the test is complete. Most of these valves are located in close proximity to the RCS loop piping and thus, require personnel entry into high radiation areas within the containment. The estimated radiation exposure associated with valve alignment and realignment is an additional 1.9 man-Rem to test personnel.
LPSI header pipe segments The LPSI header pipe segments are continuously pressurized to safety injection tank pressure.
In order to perform the Code-required pressure test of these piping segments, it would be necessary to connect jumpers (temporary piping) circumventing the inboard check valve boundaries from the RCS. This is a personnel safety concern that would result in an estimated additional 0.2 man-Rem of personnel radiation exposure.
Safety Injection to RCS Cold and Hot Legs The safety injection to RCS cold and hot legs pipe segments are part of the HPSI and LPSI systems. The pipe segments are in portions of piping between check valves that are not normally pressurized during plant operation. In order to perform the Code-required pressure
-4 test of these piping segments, it would be necessary to connect jumpers circumventing the inboard check valve boundaries from the RCS. This is a personnel safety concern that would result in an estimated additional 0.375 man-Rem of personnel radiation exposure.
RHR Suction The pipe segment in the RHR suction lines are not pressurized during normal plant operation.
In order to perform the Code-required pressure test of these piping segments, it would be necessary to open the isolation valves in both trains of RHR. These isolation valves are required to be closed, as described in the MPS3 Final Safety Analysis Report, Section 5.4.7.1, when the plant is in Modes 1, 2, and 3. Alternatively, temporary high pressure hoses with a hydrostatic pump would need to be installed to pressurize these segments during a refueling outage. This installation would introduce a significant personnel hazard if the connection or hose fails in the presence of inspection personnel.
Auxiliary Pressurizer Spray The auxiliary pressurizer spray line is not normally pressurized. In order to perform the ASIV1E Code-required pressure test of these piping segments, it would be necessary to open the normally closed upstream isolation valve. Water in this line is supplied from the charging system with an operating pressure greater than the RCS normal operating pressure. Opening this valve would allow water in the auxiliary pressurizer spray line, which is at containment ambient temperature, to pass through a check valve into the main spray header and through the spray nozzle into the pressurizer. With the RCS at normal operating temperature, this test would create a thermal shock transient to the spray nozzle, which has been evaluated to be in excess of 320 degrees F.
3.4 Licensee's Proposed Alternative Reactor coolant system vents, drains and branch piping The non-isolable portion of the RCPB VTDB lines and connections will be pressurized and will be visually examined as required. Only the isolable portion of these small diameter VTDB lines and connections will not be pressurized, but a VT-2 examination will still be performed.
LPSI header pipe segments The licensee proposes to use Code Case N-731, Alternative Class 1 System Leakage Test Pressure RequirementsSection XI, Division 1, as an alternative to the ASME pressure test requirements for the LPSI header pipe segments. Code Case N-731 allows for "portions of Class 1 safety injection systems that are continuously pressurized during an operating cycle, the pressure associated with statically-pressurized passive safety injection system of a pressurized water reactor may be used."
The LPSI header pipe segments fall into the scope of Code Case N-731 and are continuously pressurized and monitored for loss of pressure.
-5 Safety Injection to RCS Cold and Hot Legs The safety injection to RCS cold and hot legs pipe segments are located between check valves and will be pressure tested at a reduced pressure during the full flow check valve tests of these segments when the RCS is depressurized during the refueling outage.
RHR Suction The RHR suction pipe segments will be pressure tested at a reduced pressure corresponding to system operation prior to the closure of the isolation valves in the normal preparation for mode change during startup.
Auxiliary Pressurizer Spray The pipe segment will be pressure tested at a reduced pressure when pressurizer spray is initiated for normal plant cooldown in accordance with plant operating procedures.
4.0 STAFF EVALUATION ASME Code,Section XI requires that all Class 1 components within the reactor coolant system boundary undergo a system leakage test at or near the end of each inspection interval. The system leakage test is required to be performed at a test pressure not less than the nominal operating pressure of the RCS corresponding to 100% rated reactor power and shall include all Class 1 components within the RCS boundary. ONC proposes an alternate pressure testing criteria during performance of the end of interval system leakage test for the Class 1 piping segments in the RCS for the pressurizer auxiliary spray, low pressure and high pressure safety injection, residual heat removal, and reactor coolant vents and drain piping.
The line configuration provides double-isolation of the RCS. Under normal plant operating conditions, the subject pipe segments would see RCS temperature and pressure only if leakage through an inboard isolation valve occurs. With the inboard isolation valve closed during the system leakage test, the segment of piping between an inboard and an outboard isolation valve would not get pressurized to the required test pressure during a system leakage test. In order to perform the ASME Code-required test, it would be necessary to manually open each inboard isolation valve to pressurize the corresponding pipe segment. Pressurization by this method would preclude double valve isolation of the RCS and may cause safety concerns for the personnel performing the examination. Alternatively, the line segments between the isolation valves could be separately pressurized to the required test pressure by a hydrostatic pump, however, there are typically no test connections between the isolation valves to attach a pump.
Reactor coolant system vents, drains and branch piping The isolation valves in the RCPS VTOS lines are located inside the containment in the proximity of high temperature and high radiation areas. Any manual actuation (opening and closing) of these valves or system modification to connect jumpers circumventing the inboard check valve boundaries from the RCS, would expose plant personnel to safety hazard and undue radiation exposure during conduct of such activities. The NRC staff concurs with the licensee's finding that compliance with the ASME Code requirement would result in hardship without a
-6 compensating increase in the level of quality and safety. ONC will visually examine (VT-2) for leaks in the isolated portion of the subject segments of piping with the inboard and outboard isolation valves in the normally closed position. Any evidence of past leakage during the operating cycle as well as any active leakage due to the inboard isolation valves leaking will be detected during this test.
LPSI header pipe segments MPS3 is a pressurized water reactor. The LPSI header pipe segments are part of the statically pressurized passive safety injection system. They are continuously pressurized during operation because they are in the flow path of the safety injection tanks. Therefore, the LPSI header pipe segments fall into the scope of Code Case N-731.
The request to use Code Case N-731 is no longer necessary because Code Case N-731 was endorsed by the NRC, without conditions, in Regulatory Guide (RG) 1.147, Revision 16, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," dated January 2010.
Safety Injection to RCS Cold and Hot Legs, RHR Suction, and Auxiliary Pressurizer Spray The segments of Class 1 pressure boundary between the inboard and outboard isolation valves in the RHR suction and the safety injection to RCS cold and hot legs systems would not be tested to the Code-required test pressure. Instead these sections would be pressure tested at a reduced pressure. The RHR suction and safety injection systems would be pressure tested during the full flow check valve tests, for the respective piping segments, when the RCS is depressurized during the refueling outage. Likewise, for auxiliary pressurizer system, the pipe segment would be pressure tested at a reduced pressure when pressurizer spray is initiated for normal plant cooldown in accordance with plant operating procedures.
The NRC staff finds that there is reasonable assurance that a system pressure test for the safety injection to RCS cold and hot legs, RHR suction, and auxiliary pressuirzer spray systems conducted at a reduced pressure (operating pressure) will effectively detect leakage at a lower leak rate and initiate further corrective action. Also, there is no known degradation mechanism, such as intergranular stress corrosion cracking, primary water stress corrosion cracking, or thermal fatigue, that is likely to affect the welds in the subject segments.
Sased on the above considerations, the NRC staff concludes that the licensee's proposed alternatives in IR-3-09 will provide reasonable assurance of structural integrity for the RCPS VTOS lines and the piping segments in safety injection to RCS cold and hot legs, RHR suction, and auxiliary pressurizer spray systems between an inboard and an outboard isolation valve while maintaining personnel radiation exposure to as low as reasonably achievable.
5.0 CONCLUSION
On the basis of the above review, the NRC staff concludes that a system leakage test of the isolable RCPS VTOS lines, and the piping segments in safety injection to RCS cold and hot legs, RHR, and auxiliary pressurizer spray systems between an inboard and an outboard isolation valve at the Code-required test pressure corresponding to 100% rated reactor power
-7 would result in a hardship to the licensee without a compensating increase in the level of quality and safety. The NRC staff also concludes that the proposed system leakage tests in Relief Request IR-03-09, as an alternative to the ASME Code required test, is acceptable because it provides reasonable assurance of the structural integrity of the piping. Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the NRC staff authorizes the proposed alternatives in Relief Request IR-3-09 for MPS3 for the remainder of the third 10-year lSI interval.
All other ASME Code,Section XI requirements for which relief has not been specifically requested and approved remain applicable, including a third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: P. Patnaik Date: March 12, 2010
D. Heacock -2 All other ASME Code,Section XI requirements for which relief has not been specifically requested and approved remain applicable, including a third party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.
Sincerely, REnnis for Harold Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-423
Enclosure:
As stated cc w/ encl: Distribution via Listserv Distribution:
PUBLIC Branch Reading RidsAcrsAcnw_MailCTR Resource RidsN rrDorl Lp11-2 Resource RidsNrrDciCsgbResource RidsNrrLAABaxter Resource RidsNrrPMMilistone Resource RidsOgcRp Resource RidsRgn1 MailCenter Resource LTrocine, EDO R-1 PPatnaik, NRR D. Naujock, NRR ADAMS Accession N 0: ML100640446 *Bsv Memo Daet d OFFICE LPL 1-2/PM LPL 1-2/LA DCIICSGB LPL 1-2/BC NAME CSanders ABaxter RTaylor* HChernoff (REnnis for)
DATE 03/11/2010 03/11/2010 12/03/2009 03/12/2010 OFFICAL RECORD COPY