ML042120199
| ML042120199 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/29/2004 |
| From: | Stephen Dembek NRC/NRR/DLPM/LPD4 |
| To: | Rueger G Pacific Gas & Electric Co |
| Shukla G, NRR/DLPM/LPDIV-2/415-8439 | |
| References | |
| TAC MC2092, TAC MC2093 | |
| Download: ML042120199 (6) | |
Text
July 29, 2004 Mr. Gregory M. Rueger Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P. O. Box 3 Avila Beach, CA 93424
SUBJECT:
DIABLO CANYON POWER PLANT, UNIT NOS. 1 AND 2 - REQUEST FOR RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) BOILER AND PRESSURE VESSEL CODE (CODE) CONCERNING THE USE OF NONSTANDARD HYDRAULIC NUTS (TAC NOS. MC2092 AND MC2093).
Dear Mr. Rueger:
By letters dated January 9 and February 12, 2004, Pacific Gas and Electric Company (the licensee) submitted an inservice inspection (ISI) Relief Request No. REP-1 for the use of alternatives to certain ASME Code Section XI requirements at its Diablo Canyon Power Plant (DCPP), Units 1 and 2.
The NRC staff granted verbal authorization to your ISI Relief Request No. REP-1, in accordance with 10 CFR 50.55a(a)(3)(i), by a telephone call on May 6, 2004. The NRC staff has completed its formal review of Relief Request No. REP-1 and the staffs safety evaluation is enclosed.
Sincerely,
/RA/
Stephen Dembek, Chief, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323
Enclosure:
Safety Evaluation cc w/encl: See next page
July 29, 2004 Mr. Gregory M. Rueger Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P. O. Box 3 Avila Beach, CA 93424
SUBJECT:
DIABLO CANYON POWER PLANT, UNIT NOS. 1 AND 2 - REQUEST FOR RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) BOILER AND PRESSURE VESSEL CODE (CODE) CONCERNING THE USE OF NONSTANDARD HYDRAULIC NUTS (TAC NOS. MC2092 AND MC2093).
Dear Mr. Rueger:
By letters dated January 9 and February 12, 2004, Pacific Gas and Electric Company (the licensee) submitted an inservice inspection (ISI) Relief Request No. REP-1 for the use of alternatives to certain ASME Code Section XI requirements at its Diablo Canyon Power Plant (DCPP), Units 1 and 2.
The NRC staff granted verbal authorization to your ISI Relief Request No. REP-1, in accordance with 10 CFR 50.55a(a)(3)(i), by a telephone call on May 6, 2004. The NRC staff has completed its formal review of Relief Request No. REP-1 and the staffs safety evaluation is enclosed.
Sincerely,
/RA/
Stephen Dembek, Chief, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION:
PUBLIC RidsOgcRp PDIV-2 Reading RidsAcrsAcnwMailCenter RidsNrrDlpmLpdiv (HBerkow)
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GGeorgiev RidsNrrPMGShukla TChan RidsNrrLAEPeyton Accession No. ML042120199 Nrr-028
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OFFICE PDIV-2/I PDIV-2/PM PDIV-2/LA EMCB/SC OGC PDIV-1/SC NAME GTaylor:mp GShukla EPeyton TChan TSmith SDembek DATE 7/29/04 7/29/04 7/29/04
- 6/22/2004 7/28/04 7/29/04 C:\\ORPCheckout\\FileNET\\ML042120199.wpd OFFICIAL RECORD COPY
Diablo Canyon Power Plant, Units 1 and 2 cc:
NRC Resident Inspector Diablo Canyon Power Plant c/o U.S. Nuclear Regulatory Commission P.O. Box 369 Avila Beach, CA 93424 Sierra Club San Lucia Chapter c/o Henriette Groot 1000 Montecito Road Cayucos, CA 93430 Ms. Nancy Culver San Luis Obispo Mothers for Peace P.O. Box 164 Pismo Beach, CA 93448 Chairman San Luis Obispo County Board of Supervisors Room 370 County Government Center San Luis Obispo, CA 93408 Mr. Truman Burns Mr. Robert Kinosian California Public Utilities Commission 505 Van Ness, Room 4102 San Francisco, CA 94102 Diablo Canyon Independent Safety Committee ATTN: Robert R. Wellington, Esq.
Legal Counsel 857 Cass Street, Suite D Monterey, CA 93940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 Richard F. Locke, Esq.
Pacific Gas & Electric Company P.O. Box 7442 San Francisco, CA 94120 Mr. David H. Oatley, Vice President and General Manager Diablo Canyon Power Plant P.O. Box 56 Avila Beach, CA 93424 City Editor The Tribune 3825 South Higuera Street P.O. Box 112 San Luis Obispo, CA 93406-0112 Mr. Ed Bailey, Chief Radiologic Health Branch State Department of Health Services P.O. Box 997414 (MS 7610)
Sacramento, CA 95899-7414 Mr. James D. Boyd, Commissioner California Energy Commission 1516 Ninth Street (MS 31)
Sacramento, CA 95814 Mr. James R. Becker, Vice President Diablo Canyon Operations and Station Director Diablo Canyon Power Plant P.O. Box 3 Avila Beach, CA 93424
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF ON THE USE OF NONSTANDARD HYDRAULIC NUTS PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323
1.0 INTRODUCTION
Section 50.55a(g) of Title 10 of the Code of Federal Regulations (10 CFR) specifies that inservice inspection (ISI) of nuclear power plant components shall be performed in accordance with the requirements of the American Society of Mechanical Engineers (ASME), Boiler and Pressure Vessel Code (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) 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 result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Section 50.55a(g)(5)(iii) states that if the licensee has determined that conformance with certain code requirements is impractical for its facility, the licensee shall notify the Commission and submit, as specified in 10 CFR 50.4, information to support the determinations.
By letters dated January 9 and February 12, 2004, Pacific Gas and Electric Company (PG&E),
requested pursuant to 10 CFR 50.55a(a)(3)(i), relief from the requirements of ASME Section III, Code Case N-579, "Use of Nonstandard Nuts, Class 1, 2, 3, MC, CS Components and Supports Construction Section III, Division 1." The licensee will use nonstandard hydraulic nuts to fasten the excess letdown heat exchanger flange at its Diablo Canyon Power Plant (DCPP),
Units 1 and 2. Specifically, the licensee requested to use SA-540 Grade B23 material instead of SA-194 material specified in Code Case N-579 and proposed to use proprietary thread designs instead of those specified in ASME B1.1. Also, the licensee is requesting relief from the Code requirements that the "Certificate Holder" assume overall responsibility for the use of nonstandard nuts. Code Case N-579 has been approved by the NRC staff and the approval is documented in Regulatory Guide 1.84, "Design, Fabrication, and Materials Code Case Acceptability, ASME Section III," Revision 32, dated June 2003.
2.0 REGULATORY EVALUATION
2.1 Licensees Evaluation System/Component for Which Relief is Requested Excess letdown heat exchanger flange replacement bolting (ASME Class 2).
ASME Section III Code Requirements Code Case N-579, "Use of Nonstandard Nuts, Class 1, 2, 3, MC, CS Components and Supports Construction Section III, Division 1," approval documented in Regulatory Guide 1.84, "Design, Fabrication, and Materials Code Case Acceptability, ASME Section III," Revision 32, dated June 2003.
Code Requirement from Which Relief is Requested Relief is requested from use of SA-194 material specified in Code Case N-579 for the nonstandard hydraulic nuts, conformance of thread configuration to ASME B1.1, and from involvement of a "Certificate Holder."
Basis for Relief Request The excess letdown heat exchanger flange is located in a locked high radiation area inside the regenerative heat exchanger compartment. The DCPP Unit 1 excess letdown heat exchanger flange has been a slow, but chronic source of boric acid leakage inside containment. The current joint design incorporates unusual tapered geometry and a series of spacer washers that are very difficult to maintain. Efforts to stop the leakage with gasket replacement and bolt torque adjustments have not been successful and have caused unnecessary radiation exposure to maintenance personnel. The joint is being redesigned to eliminate the tapered geometry and spacer washer configuration, and hydraulic nuts are specified to ensure consistent loading around the joint as well as to reduce personnel exposure by reducing maintenance time in the area. SA-540 Grade B23, which is referenced in Section III, paragraph NC-2128(a) as an acceptable material type for Class 2 bolting, has sufficient strength for the application and will be used instead of SA-194 for manufacture of the hydraulic nuts.
Code Case N-579 requires the screw threads of nonstandard nuts be manufactured to meet the requirements for threads in ASME B1.1. While the inside threads of the hydraulic nuts conform to ASME B1.1, the outside threads will have a proprietary thread design developed by the vendor, Nova-Technofast, which minimizes thread deflection between the nut and lock ring and thereby minimizes loss of pre-load.
Code Case N-579 also assigns responsibilities to a "Certificate Holder" to assume overall responsibility for the components or supports using the nonstandard nuts. In the case of the excess letdown heat exchanger, PG&E is the entity having overall responsibility in lieu of a "Certificate Holder" and registered professional engineers on the utility staff will perform these functions.
Proposed Alternative SA-540 Grade B23 material meeting the requirements for bolting material in Section III, paragraph NC-2128(a), will be used to fabricate the hydraulic nuts for the excess letdown heat exchanger flange instead of the SA-194 material specified in Code Case N-579. The hydraulic nuts will incorporate a proprietary outside thread design providing minimized thread deflection to maximize retained load and allow lower preload to be used in contrast to standard threads manufactured in accordance with ASME B1.1. PG&E registered professional engineers acting under the utility quality assurance program will assume the responsibilities assigned to the "Certificate Holder" in Code Case N-579.
Justification for Relief Use of SA-540 Grade B23 material as referenced by Section III, paragraph NC-2128(a) in lieu of the SA-194 material specified in Code Case N-579, will ensure adequate strength in the joint.
The special thread design of the outside threads of the hydraulic nut minimizes thread deflection and loss of preload. Use of these nonstandard nuts is expected to eliminate leakage from the joint while reducing radiation exposure to maintenance personnel. These advantages and performance of "Certificate Holder" responsibilities by PG&E registered professional engineers provide an equivalent level of quality and safety in accordance with 10 CFR 50.55a(a)(3)(i).
Implementation Schedule This relief request will be implemented during the DCPP Units 1 and 2 second ISI intervals.
This is a new request based on approved Code Case N-579.
2.2 Staff Evaluation The licensee stated that the excess letdown heat exchanger flange is located in a locked high radiation area inside the regenerative heat exchanger compartment. The current joint design incorporates unusual tapered geometry and a series of spacer washers that are very difficult to maintain. Therefore, the joint was redesigned to eliminate the tapered geometry and spacer washer configuration, and hydraulic nuts were specified to ensure consistent loading around the joint. SA-540 Grade B23 was used instead of SA-194 for the manufacture of the hydraulic nuts.
The licensee has determined that SA-540 Grade B23 material has sufficient strength for this application. The NRC staff finds that SA-540 Grade B23 is acceptable for this application because the material is listed as an acceptable material for Class 2 bolting in Section III of the Code.
Code Case N-579 requires the screw threads of nonstandard nuts be manufactured to meet the requirements for threads in ASME B1.1. The hydraulic nuts used by the licensee have a proprietary outside thread design developed by the nut manufacturer which minimizes thread deflection between the nut and lock ring and thereby minimizes loss of pre-load. The inside threads of the hydraulic nuts conform to ASME B1.1. The NRC staff finds the use of the proprietary outside thread design acceptable because the design minimizes thread deflection between the nut and lock ring and thus the loss of pre-load is minimized.
Code Case N-579 also assigns responsibilities to a "Certificate Holder" to assume overall responsibility for the components or supports using the nonstandard nuts. In this case since the licensee is not a "Certificate Holder" as defined by the ASME Code, the licensee is assuming the overall responsibility and has employed registered professional engineers on the utility staff to perform these functions. The NRC staff finds this approach acceptable because the licensee has assumed overall responsibility for the use of nonstandard hydraulic nuts at its facility and since licensed professional engineers are assigned to monitor and manage this activity. Therefore, the NRC staff finds that the use of hydraulic nonstandard nuts provides an equivalent level of quality and safety in accordance with 10 CFR 50.55a(a)(3)(i).
3.0 CONCLUSION
Based on the above evaluation, the NRC staff concludes that the proposed alternative as discussed in the licensees request for relief provides an acceptable level of quality and safety.
Therefore, the proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) for the second 10-year ISI interval at DCPP Units 1 and 2. All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: George Georgiev Date: July 29, 2004