ML020730271
| ML020730271 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/22/2002 |
| From: | Clifford J NRC/NRR/DLPM/LPD1 |
| To: | Price J, Danni Smith Dominion Nuclear Connecticut |
| Ennis R, NRR/DLPM, 415-1420 | |
| References | |
| TAC MB4039 | |
| Download: ML020730271 (11) | |
Text
March 22, 2002 Mr. J. A. Price Vice President - Nuclear Technical Services - Millstone Dominion Nuclear Connecticut, Inc.
c/o Mr. David A. Smith Rope Ferry Road Waterford, CT, 06385
SUBJECT:
SAFETY EVALUATION OF RELIEF REQUEST RR-89-35, TEMPORARY INSTALLATION OF MECHANICAL NOZZLE SEAL ASSEMBLIES ON PRESSURIZER HEATER PENETRATION NOZZLES, MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 (TAC NO. MB4039)
Dear Mr. Price:
By letter dated February 19, 2002, as supplemented February 28 and March 1, 2002, Dominion Nuclear Connecticut, Inc. submitted Relief Request RR-89-35 for Millstone Nuclear Power Station, Unit No. 2 (MP2). Your submittal requested approval to install Mechanical Nozzle Seal Assemblies (MNSAs) for two leaking pressurizer heater penetration nozzles as an alternative to certain requirements of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code). As discussed in your letter dated February 28, 2002, the use of the MNSAs was proposed as a temporary repair for a time period not to exceed two operating cycles (i.e., Refueling Outage (RFO) 14 through RFO 16).
The U.S. Nuclear Regulatory Commission staff has completed its review of the subject relief request. The staffs Safety Evaluation (SE) is enclosed. Our SE concludes that the proposed alternative to the ASME Code requirements described in Relief Request RR-89-35 will provide an acceptable level of quality and safety for repair of the two leaking pressurizer heater penetration nozzles at MP2 for a time period not to exceed two operating cycles. Therefore, the alternative is authorized pursuant to Section 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations through RFO 16.
Sincerely,
/RA/
James W. Clifford, Chief, Section 2 Project Directorate I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
Safety Evaluation cc w/encl: See next page
- See previous concurrence OFFICE PDI-2/PM PDI-2/LA EMEB/SC*
EMCB/SC*
OGC*
PDI-2/SC NAME RStarkey for REnnis TClark KManoly BElliot CMarco JClifford DATE 03/21/02 03/21/02 03/14/02 03/14/02 03 /21/02 03/21/02
Millstone Nuclear Power Station Unit 2 cc:
Ms. L. M. Cuoco Senior Nuclear Counsel Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385 Edward L. Wilds, Jr., Ph.D.
Director, Division of Radiation Department of Environmental Protection 79 Elm Street Hartford, CT 06106-5127 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 First Selectmen Town of Waterford 15 Rope Ferry Road Waterford, CT 06385 Charles Brinkman, Manager Washington Nuclear Operations ABB Combustion Engineering 12300 Twinbrook Pkwy, Suite 330 Rockville, MD 20852 Senior Resident Inspector Millstone Nuclear Power Station c/o U.S. Nuclear Regulatory Commission P.O. Box 513 Niantic, CT 06357 Mr. W. R. Matthews Vice President and Senior Nuclear Executive - Millstone Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385 Ernest C. Hadley, Esquire P.O. Box 1104 West Falmouth, MA 02574-1104 Mr. P. J. Parulis Manager - Nuclear Oversight Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385 Mr. D. A. Christian Senior Vice President - Nuclear Operations and Chief Nuclear Officer Innsbrook Technical Center - 2SW 5000 Dominion Boulevard Glen Allen, VA 23060 Mr. C. J. Schwarz Director - Nuclear Operations and Chemistry Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385 Mr. John Markowicz Co-Chair Nuclear Energy Advisory Council 9 Susan Terrace Waterford, CT 06385 Mr. Evan W. Woollacott Co-Chair Nuclear Energy Advisory Council 128 Terry's Plain Road Simsbury, CT 06070 Mr. D. A. Smith Manager - Regulatory Affairs Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385 Ms. Nancy Burton 147 Cross Highway Redding Ridge, CT 00870
Millstone Nuclear Power Station Unit 2 cc:
Mr. G. D. Hicks Director - Nuclear Training Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385 Mr. J. Alan Price Vice President - Nuclear Operations - Millstone c/o Mr. David A. Smith Dominion Nuclear Connecticut, Inc.
Rope Ferry Road Waterford, CT 06385
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST RR-89-35 FOR TEMPORARY INSTALLATION OF MECHANICAL NOZZLE SEAL ASSEMBLIES ON PRESSURIZER HEATER PENETRATION NOZZLES AT MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 DOMINION NUCLEAR CONNECTICUT, INC.
DOCKET NO. 50-336
1.0 INTRODUCTION
The inservice inspection (ISI) of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) Class 1, 2, and 3 components is to be performed in accordance with Section XI of the ASME Code and applicable edition and addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
Pursuant to 10 CFR 50.55a(a)(3), alternatives to the requirements of paragraph (g) may be used, when authorized by the U.S. Nuclear Regulatory Commission (NRC), if the licensee 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.
By letter dated February 19, 2002, as supplemented February 28 and March 1, 2002, Dominion Nuclear Connecticut, Inc. (DNC or the licensee) submitted Relief Request RR-89-35 for Millstone Nuclear Power Station, Unit No. 2 (MP2). Pursuant to the provisions of 10 CFR 50.55a(a)(3)(i), the licensees submittal requested approval to install Mechanical Nozzle Seal Assemblies (MNSAs) for two leaking pressurizer heater penetration nozzles as an alternative to certain requirements of Section XI of the ASME Code. As discussed in the licensees letter dated February 28, 2002, the use of the MNSAs was proposed as a temporary repair for a time period not to exceed two operating cycles (i.e., Refueling Outage (RFO) 14 through RFO 16).
MNSAs are mechanical devices that are designed to fit around ASME Code Class 1 Alloy 600 nozzles as a means of preventing leakage past the nozzles. The MNSA design consists of two split gasket/flange assemblies. A gasket made from Grafoil packing, a graphite compound, is compressed within the gasket assembly to prevent reactor coolant system (RCS) pressure boundary leakage past the nozzle. The gasket assembly is bolted in place into holes that are drilled and threaded on the outer surface of the RCS pressure boundary wall. A second assembly is bolted to the flanges which serves as the structural attachment of the nozzle to the wall. The flange assembly serves to carry the loads in lieu of the partial penetration J-groove welds used to adjoin the nozzles to the particular RCS pressure boundary vessel or piping component of interest.
2.0 BACKGROUND
2.1 Licensees Rationale for Relief Request Based on recent industry operating experience associated with Alloy 600 cracking, DNC elected to perform a visual ISI of the pressurizer heater penetrations during the current MP2 refueling outage (RFO14). Two penetrations were found to show indications of leakage with the presence of boron encircling the penetrations.
The pressurizer heater penetration nozzles consist of a sleeve welded to the pressurizer bottom head with an internal J-groove weld. The typical permanent repair of these sleeves consists of either installing a heater sleeve plug welded to a temper-bead pad or a half-sleeve replacement. The licensees submittal stated that the typical repair/replacement techniques may be difficult or impractical to implement in certain locations such as the bottom of the pressurizer. The submittal also stated that installation of the MNSAs will shorten the repair/replacement time significantly and thereby reduce radiation exposure to workers.
Pursuant to the provisions of 10 CFR 50.55a(a)(3)(i), DNC proposed to install MNSAs as a temporary alternative repair method to the ASME Code requirements for the two leaking pressurizer heater penetration nozzles. The licensees submittal stated that MNSAs have already been used in the industry as an NRC-approved alternative and that MNSAs have been demonstrated to provide an acceptable level and quality and safety for degraded or potentially degraded pressurizer heater penetration nozzles.
The NRC has not previously approved the use of MNSAs on any MP2 nozzles. A similar request for temporary repair of pressurizer heater sleeves using MNSAs at Palo Verde Nuclear Generating Station was approved by the NRC in a Safety Evaluation dated October 1, 2001.
2.2 Regulatory Framework Paragraph (g) of 10 CFR 50.55a requires, in part, that all inservice examinations and system pressure tests conducted during the first 10-year interval and subsequent intervals on ASME Code Class 1, 2, and 3 components comply with the requirements in the latest edition and addenda of Section XI incorporated by reference in 10 CFR 50.55a(b), on the date 12 months prior to the start of the 10-year interval. By reference to, and implementation of, ASME Code Section XI, paragraphs IWB-3132 or IWB-3142, 10 CFR 50.55a also requires that existing flaws in ASME Code Class components be removed by mechanical means, or the components be repaired or replaced to the extent necessary to meet the acceptance standards in ASME Code Section XI, Article IWB-3000. Detection of leaks in the structural portion of an ASME Code Class 1, 2, or 3 component is direct evidence of a flaw in the component.
Paragraph IWA-4170 of Section XI of the ASME Code requires that repairs and the installation of replacements to the RCS pressure boundary be performed and reconciled in accordance with the Owners Design Specifications and Original Code of Construction for the component or system. The MP2 RCS pressurizer was designed and constructed to the rules of ASME Section III, 1968 Edition with Addenda through Summer 1969.
Paragraph NB-3671.7 to Section III of the ASME Code, Sleeve Coupled and Other Patented Joints, requires that ASME Code Class 1 joints be designed to meet the following criteria:
(1) provisions must be made to prevent separation of the joint under all service loading conditions, (2) the joint must be designed to be accessible for maintenance, removal, and replacement activities, and (3) the joint must either be designed in accordance with the rules of ASME Code,Section III, Subarticle NB-3200, or be evaluated using a prototype of the joint that will be subjected to additional performance tests in order to determine the safety of the joint under simulated service conditions.
These criteria also apply to the design, installation, inspection, and maintenance of MNSAs.
3.0 EVALUATION The licensee requested the use of MNSAs pursuant to 10 CFR 50.55a(a)(3)(i), stating that this alternative provides an acceptable level of quality and safety. In order to determine if the MNSAs would provide an acceptable level of quality and safety, the staff compared the MNSA design and operational characteristics to the applicable ASME requirements, reviewed the MNSAs resistance to corrosion for the intended service period, and evaluated the licensees commitments associated with the use of the MNSAs.
The MNSAs are designed, fabricated, and constructed using approved ASME Code materials (except for the Grafoil gasket, which is a non-Code material), in accordance with the applicable rules of ASME Section III. The MNSAs are designed to prevent separation of the joint under all service loadings. This design is supported by manufacturer technical analysis and tests that meet the design criteria specified in the ASME Code Section III, Subsection NB, 1989 Edition, no Addenda. Appendix B to the licensees letter of April 1, 2001, ASME Construction Code Reconciliation Report documents the required ASME Section XI, IWA-4170(b), reconciliation of the construction codes for the use of a component built to a later edition of the Code, which the staff finds acceptable. Additionally, MNSA installations are accessible for maintenance, removal, and replacement. The provisions of NB-3671.7 are, therefore, nominally satisfied.
MNSAs have been approved for installation on a temporary basis at other nuclear plants (e. g.,
Palo Verde Nuclear Generating Station, San Onofre Nuclear Generating Station). The acceptance was based on industry experience which demonstrated that the structural integrity and leak tightness of the MNSAs, and the structural integrity of the components to which the MNSAs are attached, was maintained at least through one or two cycles. The staff has also reviewed calculations and tests performed by the manufacturer for installations at other plants that demonstrate the structural integrity of the MNSAs, and the conformance of the component fatigue calculations with the ASME Section III Class 1 design fatigue limit. Based on experience at other plants, the staff considers the probability of exceeding the ASME Code,Section III, Class 1 fatigue cumulative limit of 1.0 in the short-term operation of two cycles to be very low. Based on the preceding information, the staff finds the proposed alternative acceptable from a structural standpoint.
In its letter dated February 19, 2002, and the subsequent letter dated February 28, 2002, DNC also provided an evaluation to address potential corrosion of the nozzle bore holes, J-groove weld cracking, galvanic corrosion (Grafoil Seal to Low Alloy Steel), and stress corrosion cracking (SCC) of the MNSA components. The results of this evaluation are summarized as follows:
A through-wall crack in the nozzle could be a source of corrosion. However, the borated water will stagnate and will not replenish, the boric acid will be consumed. The pH level will decrease the corrosion rate, and eventually the process will be stopped.
Boric acid corrosion of the materials of construction for the MNSA has been addressed by use of corrosion resistant materials, testing, and analysis.
A history of galvanic corrosion problems in applications where low alloy steel is in contact with a Grafoil seal in an environment of an electrically conductive fluid (water) exists. This particular combination is used in other applications where the low alloy (or carbon steel) is frequently inspected (for example, steam generator secondary side manway and hand hole applications). The Grafoil seal, grade GTJ, is chemically resistant to attack from nearly all organic and inorganic fluids, and is very resistant to borated water. The MNSA application is similar (i.e., Grafoil material is in contact with low alloy steel and visual inspections will be conducted at each refueling outage to identify signs of leakage) and for these reasons significant galvanic corrosion is not expected. The licensee also noted that, in the absence of leakage past the Grafoil seal, the boric acid solution in the annulus region will become stagnant and will not allow replenishment of the boric acid or oxygen, thereby limiting the corrosion potential.
ASME Code,Section XI requirements applicable to the MNSA during each 10-year ISI interval include a system leak test at the end of each refueling outage and bolting examination based on the schedule of percentages required. For the MNSA installed on the pressurizer heater penetration nozzles, the Bolting B-G-2 examination requirements would allow the VT-1 examination to be performed as follows: (a) in place under tension; (b) when the connection is disassembled; (c) or when the bolting is removed. This examination is required once each 10-year interval. If the MNSA device leaks, the bolts may be exposed to borated water or steam under conditions in which deposits or slurries will develop. Under these conditions and at stress levels present in the MNSA application, the bolts will operate satisfactorily for at least one fuel cycle. A leaking MNSA will be discovered and repaired as part of the walk-down inspections performed in response to NRC Generic Letter 88-05, Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants. These walk-down inspections are performed prior to entering unit outages.
Therefore, the existence of leaking MNSA conditions would be limited to one cycle.
Based on the preceding evaluation of potential corrosion effects, the staff concludes that there are no significant corrosion issues associated with the application of the MNSAs to pressurizer heater penetration nozzles. The data indicates that corrosion of the nozzle hole will also be acceptable over the requested two-cycle period of use.
The licensees submittal provided the following information regarding the installation, inspection, and testing of the MNSAs:
(1)
The licensee has performed a visual examination of the leaking nozzles. An informational ultrasonic test has been performed to determine the thickness measurement near the nozzles. A comparison of the data will be made between the leaking and non-leaking penetrations to evaluate if any measurable corrosion damage is present around the leaking nozzles.
(2)
The licensees installation procedure for the MNSAs contains instructions/guidance to ensure that the surface of the pressurizer is in a condition such that the MNSA will seal correctly.
(3)
As required by IWA-4600, a VT-1 preservice inspection will be performed on all MNSA installations in accordance with IWB-2200.
(4)
During plant startup (Mode 3), after initial MNSA installation and during subsequent plant restarts following scheduled outages, the pressurizer heater penetration nozzle MNSAs will be pressure tested and inspected for leakage. To ensure quality of the installation and continued operation with the absence of leakage, a pressure test with VT-2 visual examination will be performed on each of the installed MNSAs with any insulation removed. The test will be performed as part of plant restart and will be conducted at normal operating pressure with the test temperature determined in accordance with the pressure and temperature limits as stated in the MP2 Technical Specifications. Additionally, VT-3 exams will be performed, along with the VT-2 exams, during subsequent plant restarts following a refueling outage.
The staff has reviewed the licensees submittal with respect to the installation, inspection, and testing of the MNSAs. The staff concludes that these actions are sufficient to ensure proper installation and operation of the MNSAs for their intended use for a period not to exceed two operating cycles.
4.0 CONCLUSION
Based on the preceding evaluation, the NRC staff concludes that the proposed alternative to the ASME Code requirements described in Relief Request RR-89-35 will provide an acceptable level of quality and safety for repair of the two leaking pressurizer heater penetration nozzles at MP2 for a time period not to exceed two operating cycles. Therefore, the alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) through RFO 16.
Principal Contributors: T. Bloomer M. Hartzman Date: March 22, 2002