ML021000541
| ML021000541 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 04/22/2002 |
| From: | Raghavan L NRC/NRR/DLPM/LPD3 |
| To: | Forbes J Nuclear Management Co |
| References | |
| TAC MB3904 | |
| Download: ML021000541 (9) | |
Text
April 22, 2002 Mr. Jeffrey S. Forbes Site Vice President Monticello Nuclear Generating Plant Nuclear Management Company, LLC 2807 West County Road 75 Monticello, MN 55362-9637
SUBJECT:
MONTICELLO NUCLEAR GENERATING PLANT - THIRD 10-YEAR INTERVAL INSERVICE INSPECTION PROGRAM REQUEST FOR RELIEF FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE, SECTION XI REQUIREMENTS (TAC NO. MB3904)
Dear Mr. Forbes:
By letter dated January 11, 2002, Nuclear Management Company, LLC, (NMC), the licensee for Monticello Nuclear Generating Plant, submitted Relief Request No. 14 proposing an alternative to certain requirements of the ASME Code,Section XI and Code Case N-498-1 (Alternative Rules for 10-year System Hydrostatic Testing for Class 1, 2, and 3 Systems,Section XI, Division 1), which has been approved by the Nuclear Regulatory Commission. NMC has requested relief from the requirement of Code Case N-498-1 in regard to the 4-hour hold time for insulated systems prior to VT-2 visual examination during system pressure test of portions of the high pressure coolant injection (HPCI) line, including the HPCI turbine exhaust, vents and drains to the suppression chamber, for the third 10-year inservice inspection interval of Monticello Nuclear Generating Plant. NMC has proposed to perform the pressure test during a periodic HPCI surveillance test performed in accordance with the ASME Section XI Inservice Testing Program with a 60-minute hold time in lieu of the required 4-hour hold time due to operational limitations on the suppression chamber.
In this instance, the staff considers compliance with the 4-hour hold time, and certain other requirements of the applicable Code and Code Case N-498-1, to be a hardship without a compensating increase in the level of quality and safety. Therefore, the staff finds the licensees request, pursuant to 10 CFR 50.55a(a)(3)(ii), to be acceptable, and authorizes the licensees proposed alternative for the third 10-year inservice inspection interval of Monticello Nuclear Generating Plant. The staffs evaluation is enclosed.
Sincerely,
/RA/
L. Raghavan, Chief, Section 1 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-263
Enclosure:
Safety Evaluation cc w/encl: See next page
NAME SMiranda RBouling SBrock LRaghavan TChan DATE 04/11/02 04/11/02 04/15/02 04/22/02 04/02/02
Monticello Nuclear Generating Plant cc:
J. E. Silberg, Esquire Shaw, Pittman, Potts and Trowbridge 2300 N Street, N. W.
Washington, DC 20037 U.S. Nuclear Regulatory Commission Resident Inspectors Office 2807 W. County Road 75 Monticello, MN 55362 Site Licensing Manager Monticello Nuclear Generating Plant Nuclear Management Company, LLC 2807 West County Road 75 Monticello, MN 55362-9637 Robert Nelson, President Minnesota Environmental Control Citizens Association (MECCA) 1051 South McKnight Road St. Paul, MN 55119 Commissioner Minnesota Pollution Control Agency 520 Lafayette Road St. Paul, MN 55155-4194 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532-4351 Commissioner Minnesota Department of Health 717 Delaware Street, S. E.
Minneapolis, MN 55440 Douglas M. Gruber, Auditor/Treasurer Wright County Government Center 10 NW Second Street Buffalo, MN 55313 Commissioner Minnesota Department of Commerce 121 Seventh Place East Suite 200 St. Paul, MN 55101-2145 Adonis A. Neblett Assistant Attorney General Office of the Attorney General 445 Minnesota Street Suite 900 St. Paul, MN 55101-2127 Mr. Roy A. Anderson Executive Vice President and Chief Nuclear Officer Nuclear Management Company, LLC 700 First Street Hudson, WI 54016 Nuclear Asset Manager Xcel Energy, Inc.
414 Nicollet Mall Minneapolis, MN 55401 March 2002
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION THIRD 10-YEAR INTERVAL INSERVICE INSPECTION PROGRAM REQUEST FOR RELIEF FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE, SECTION XI REQUIREMENTS MONTICELLO NUCLEAR GENERATING PLANT NUCLEAR MANAGEMENT COMPANY, LLC DOCKET NO. 50-263
1.0 INTRODUCTION
Inservice inspection (ISI) of the ASME Code Class 1, 2, and 3 components is to be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code (Code) and applicable addenda as required by 10 CFR 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the Nuclear Regulatory Commission (NRC), if the applicant demonstrates that (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would 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 inservice examination of components and system pressure tests conducted during the first 10-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 applicable edition of the ASME Code,Section XI, for the third 10-year ISI interval of Monticello Nuclear Generating Plant, is the 1986 Edition.
By letter dated January 11, 2002, Nuclear Management Company, LLC, (NMC), the licensee for Monticello Nuclear Generating Plant, submitted Relief Request No. 14 proposing an alternative to certain requirements of the ASME Code,Section XI and Code Case N-498-1 (Alternative Rules for 10-year System Hydrostatic Testing for Class 1, 2, and 3 Systems,Section XI, Division 1), which has been approved by the NRC. NMC has requested relief from the requirement of Code Case N-498-1 in regard to the 4-hour hold time for insulated systems prior to VT-2 visual examination during system pressure test of portions of the high pressure coolant injection (HPCI) line, including the HPCI turbine exhaust, vents and drains to the suppression chamber, for the third 10-year ISI interval of Monticello Nuclear Generating Plant. NMC has proposed to perform the pressure test during a periodic HPCI surveillance test performed in accordance with the ASME Section XI Inservice Testing Program with a 60-minute hold time in lieu of the required 4-hour hold time due to operational limitations on the suppression chamber.
The staff has evaluated the licensees request for relief pursuant to 10 CFR 50.55a(a)(3)(ii) for the third 10-year ISI interval of Monticello Nuclear Generating Plant.
2.0 DISCUSSION (RELIEF REQUEST NO. 14)
Identification of Systems and Components Insulated Class 2 pressure retaining piping and components in the HPCI system include; but are not limited to: 1) the steam line, downstream of the HPCI steam admission valve (MO-2036) through the HPCI Turbine (S-201), up to and including Torus penetration X-221; 2) the insulated portion of the branched main process vacuum breaker line, downstream of the manual block valve (HPCI-82) in the steam exhaust line and up to and including Torus penetration X-217; 3) steam line drain lines including those attached and downstream of stop valve HO-7, up to and including Torus penetration X-222; and 4) a small section of gland seal condenser condensate pump return piping between check valve HPCI-20 and the cooling water return line.
Code Requirements ASME Code,Section XI, 1986 Edition, Table IWC-2500-1, Examination Category C-H requires a VT-2 visual examination during a system hydrostatic test once every 10-year ISI interval.
Subsection IWA-5213(d) requires a 4-hour hold time for insulated systems, and a 10-minute hold time for non-insulated systems or components after attaining the test pressure and temperature conditions prior to performing the VT-2 visual examination.
Code Case N-498-1 (Alternative Rules for 10-year System Hydrostatic Testing for Class 1, 2, and 3 Systems,Section XI, Division 1), approved for use by NRC in Regulatory Guide 1.147 Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1" Revision 12, allows performance of a system leakage test in lieu of the hydrostatic test, but also requires pressurization for a minimum of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> for insulated systems and 10 minutes for non-insulated systems at nominal operating pressure prior to performing the VT-2 visual examination.
Licensees Requested Relief Relief is requested from maintaining the 4-hour holding time at test pressure required by the Code in subsection IWA-5213(d) and also in Code Case N-498-1, step b(3) for the subject systems.
Licensees Proposed Alternative (as stated):
Monticello Nuclear Generating Plant will implement the inspection rules for 10 year hydrostatic testing per ASME Code Case N-498-1 with the following exception:
A system pressure test shall be performed in accordance with ASME Section XI, IWA-5211(b) for the subject system or a portion of the system not required to operate during normal reactor operation, but for which periodic system or component functional testing is performed to meet Owners requirements. This test shall consist of performing the required VT-2 examinations in conjunction with a periodic HPCI surveillance test performed in accordance with the ASME Section XI Inservice Testing Program. The test hold time for normally unpressurized, insulated components shall be a minimum of 60 minutes starting when the test flow and the pressure requirements have been met.
Use of Code Case N-498-1 with a 60 minute hold time for normally unpressurized, insulated components will provide acceptable detection of any leaks in the (mostly low pressure) portion of the system which is insulated.
Licensees Basis for Relief (as stated):
Operation of the HPCI system at the Code required pressure and temperature for the required 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> test condition hold time would result in undesirable Torus water temperature, thereby challenging compliance with the technical specification limits and reducing the suppression pool heat sink margin. Additionally, a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> test would unnecessarily challenge the operating personnel for a longer time than is needed to determine whether pressure boundary leakage exists in the insulated, normally unpressurized, portions of the system.
Not only will undesirable Torus water temperatures result from operating the HPCI system for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, there will also be a decrease in maneuvering tolerance for response to an actual transient should one occur simultaneously with the performance of the test. This challenge to operating personnel, and decrease in maneuvering tolerances would be without a compensating increase in safety. The proposed one hour hold time, as discussed in the proposed alternative examination, provides an acceptable level of quality and safety to ensure that pressure boundary leakage can be identified in accordance with Code requirements.
Additionally, this relief request only applies to those portions of the HPCI system that are insulated, normally unpressurized, and/or require turbine operation to be pressurized (e.g., the turbine exhaust line and steam line drains from the exhaust piping). The majority of the HPCI steam line is normally pressurized at reactor pressure. The normally pressurized lines may be inspected in conjunction with or at a time separate from this system examination.
Uninsulated piping, such as the water side piping of the HPCI system can be inspected following a hold time of 10 minutes per Code Case N-498-1. Other portions of system piping such as the steam lines upstream of the outboard isolation valve are inspected during other Code examinations.
3.0 EVALUATION Both the Code and Code Case N-498-1 specify pressure tests that require a 4-hour hold time prior to performing the VT-2 visual examination during the hydrostatic test of insulated systems.
The licensee has stated that compliance with the 4-hour hold time will result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The licensee has further stated that performance of the test with a 4-hour hold time could compromise plant safety.
Based on the review of information provided, the staff believes that in order to maintain suppression pool temperature within the technical specification limits, the pressure test and the 4-hour hold time for the subject system would require dedicated operation of the residual heat removal system in the suppression pool cooling mode while the reactor is at power.
Furthermore, due to exhaust of steam from the HPCI turbine into the suppression pool, the steam condensation capability of the suppression pool will be reduced. Therefore, should an actual plant emergency occur during the test, the ability to bring the plant to a safe shutdown condition could be diminished.
Within each 10-year inspection interval, a system functional test at operating pressure including a VT-2 visual examination is conducted on the system at 40-month intervals in accordance with the Code. At or near the end of each inspection interval, the Code requires a hydrostatic test, which by virtue of Code Case N-498-1, can be a system leakage test requiring pressurization to nominal operating pressure for at least 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> prior to the VT-2 visual examination. However, the licensees proposed alternative would allow performance of the pressure test during the ASME Section XI Inservice Test with pressurization for at least 60 minutes at nominal operating pressure without removal of the insulation in lieu of a 4-hour hold time at this pressure prior to the VT-2 visual examination.
The piping and components subject to the VT-2 visual examination contain steam. The staff believes that steam leaks are audible and, therefore, are more easily detectable than comparable water leaks from insulated components. Therefore, for these components, a reduced hold time for steam piping at nominal operating pressure without removal of the insulation prior to performing VT-2 visual examination is expected to permit detection of leakage. The piping included in this relief are the portions extending from the steam admission valve through the HPCI turbine and the turbine exhaust piping to the suppression pool along with the associated drains and vent lines. In an unlikely event of missing a very small leak during the system pressure test, the leak can be detected during maintenance activities requiring pump/turbine operation for post maintenance testing or the next system functional test. Further, assuming reasonable crack growth between consecutive tests for the portion of subject piping which is at system pressure during normal plant operation, the system will also remain functional in spite of a leak. Compliance with the Code requirement would require removal of insulation from the affected piping, conduct of the test and replacement of the insulation following the test. This would result in hardship to the licensee without a compensating increase in the level of quality and safety.
4.0 CONCLUSION
The staff concludes that for the HPCI turbine inlet and exhaust piping to the suppression pool and the associated drains and vents, maintaining a 4-hour hold time at nominal operating pressure prior to the VT-2 visual examination during a system pressure test could challenge the heat limitations of the suppression pool and thus, could create an operational safety concern. A system pressure test during the ASME Section XI Inservice Test at nominal operating pressure with a 60-minute hold time at pressure without removal of the insulation prior to performing the VT-2 visual examination will provide reasonable assurance of leak-tight integrity of the subject system. In addition, the staff considers the removal and subsequent reinstallation of insulation for the sole purpose of complying with the requirements of the applicable Code and Code Case N-498-1 to be a hardship without a compensating increase in the level of quality and safety.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the licensees proposed alternative is authorized for the third 10-year ISI interval of Monticello Nuclear Generating Plant.
Principal Contributor: P. Patnaik Date: April 22, 2002