ML093570237
| ML093570237 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/26/2010 |
| From: | Chernoff H Plant Licensing Branch 1 |
| To: | Heacock D Dominion Nuclear Connecticut |
| Sandeers, Carleen, NRR/DORL, 415-1603 | |
| References | |
| RR-89-67, TAC ME2296, FOIA/PA-2011-0115 | |
| Download: ML093570237 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 26, 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 SUB~IECT:
MILLSTONE POWER STATION, UNIT NO.2-ISSUANCE OF RELIEF REQUEST RR-89-67 REGARDING THE REPAIR OF REACTOR COOLANT PUMP SEAL COOLER RETURN TUBING AND WELD (TAC NO. IVIE2296)
Dear Mr. Heacock:
By letter dated September 22, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML092710151), Dominion Nuclear Connecticut, Inc. (DNC or the licensee), submitted an alternative for the repair examination requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI.
In July 2009, the licensee repaired a degraded partial penetration weld and the base metal of the P40A reactor coolant pump (RCP) seal cooler return line at Millstone Power Station, Unit NO.2. As a result of the repair, Relief Request RR-89-67 was submitted as an alternative to some of the examination requirements in ASIVIE Code,Section XI.
The Nuclear Regulatory Commission (NRC) staff finds that requiring radiographic testing and hydrostatic test for the repair of weld RCPA-RC-95-W-4 in the subject cooler return line would result in hardship without a compensating increase in the level of quality and safety. The NRC staff concludes that the proposed alternative in Relief Request RR-89-67 is acceptable because it provides reasonable assurance of structural integrity of weld RCPA-RC-95-W-4. Therefore, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(a)(3)(ii), the NRC authorizes the use of Relief Request RR-89-67 for the repair of the reactor coolant pump seal cooler return line.
On November 10, 2009, the NRC staff verbally authorized the use of Relief Request RR-89-67 during a teleconference with DNC. A summary of the teleconference, dated November 17, 2009, is available in ADAMS (Accession No. ML093140625).
The NRC staff's safety evaluation is enclosed.
D. Heacock
- 2 If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.
Sincerely, L~rnOff' Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
As stated cc wi encl: Distribution via Listserv
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION RELIEF REQUEST RR-89-67 REACTOR COOLANT PUMP SEAL COOLER RETURN TUBING DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION, UNIT NO.2 DOCKET NUMBER 50-336
1.0 INTRODUCTION
By letter dated September 22, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML092710151), Dominion Nuclear Connecticut, Inc. (DNC or the licensee), submitted an alternative for the repair examination requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI.
In July 2009, the licensee repaired a degraded partial penetration weld and the base metal of the P40A reactor coolant pump (RCP) seal cooler return line at Millstone Power Station, Unit No.2 (MPS2). As a result of the repair, Relief Request RR-89-67 was submitted as an alternative to some of the examination requirements in ASME Code,Section XI.
On November 10, 2009, the Nuclear Regulatory Commission (NRC) staff verbally authorized the use of Relief Request RR-89-67 during a teleconference with DNC. A summary of the teleconference, dated November 17, 2009, is available in ADAMS (Accession No. ML093140625).
2.0 REGULATORY EVALUATION
Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(g) specifies that in-service inspection (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 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 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 Enclosure
- 2 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 Code of Record for the third 1O-year lSI program and its evaluation at MPS2 is the ASME Code,Section XI, 1998 Edition with no Addenda.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Components Affected
The component affected is 1~-inch ASME Class 1 tubing located on the seal cooler return side of the P40A RCP. The weld of the tubing is now designated as RCPA-C-95-W-4 and is part of the risk-informed lSI program designated as Category R-A and Item No. R1.12.
3.2
Applicable Code Requirement
ASME Code,Section XI, IWA-4421, Construction Code and Owners Requirements, states in part:
(a) Welding, brazing, defect removal, and installation activities shall be performed in accordance with the Owner's requirements and the Construction Code of the component or system, except as provided in (b) and (c) below. The requirements of IWA-4460 shall be used in lieu of Construction Code requirements for mechanical and thermal metal removal. The requirements of IWA-4422 shall be used in lieu of Construction Code requirements for examination of defect removal areas.
IWA-4422.2.2, Defect Removal Followed by Welding or Brazing, refers to IWA-4520, Examination.
Paragraph (a) of IWA-4520 states:
Welding or brazing areas and welded joints made for installation of items shall be examined in accordance with the Construction Code identified in the Repair/Replacement plan.
The Construction Code identified in the repair/replacement plan for MPS2 is the 1968 Edition with the Winter 1970 Addenda of ASME Section III. This Code has two requirements that apply to the repair.
N-462.4(d), Attachment of Connections Using Partial Penetration Welds, requires a progressive liquid penetrant test (PT) at the lesser of one-third the thickness of the joint or each ~ inch of thickness for the weld material. Requirements for a weld of this thickness are to PT the root and final layer.
- 3 N-324.9, Repair of Tubular Products by Welding, states in part:
(g) The repaired area is examined by radiography in accordance with N-324.7 and by a second method of examination which is selected so as to be applicable to the material being inspected.
This alternative request proposes relief from the requirement in paragraph N-324.9(g) to radiographic test (RT) the repair area of the tube.
The ASME Code,Section XI, IWA-4540, Pressure Testing of Class 1, 2 and 3 Items, states in part:
(a) Unless exempted by (b) below, repair/replacement activities performed by welding or brazing on a pressure retaining boundary shall include (a)(1) or (a)(2) below:
(1) A system hydrostatic test shall be performed in accordance with IWA-5000 prior to, or as part of, returning to service.
ONC wishes to invoke NRC approved Code Case N-416-3 Code Case N-416-3 allows for a system leakage test in lieu of a hydrostatic pressure test for welded or brazed repairs, subject to the following requirements:
(a) NOE [nondestructive examination] shall be performed on welded of brazed repairs and fabrication and installation joints in accordance with the methods and acceptance criteria of the applicable Subsection of the 1992 Edition of Section III.
(b) Prior to or immediately upon return to service, a visual examination (Vf-2) shall be performed on welded or brazed repairs, fabrication, and installation joints in conjunction with system leakage test, using the 1992 Edition of Section XI, in accordance with IWA 5000, at nominal operating pressure and temperature.
(c) Use of this Case shall be documented on an NIS-2 form.
The applicable Subsection of the 1992 Edition of Section III is NB-2500, Examination and Repair of Pressure Retaining Material, specifically NB-2539.4, Examination of Repair Welds, which requires a radiograph after the repair if the depth of the repair cavity exceeds the lesser of 1/8 inch of 10% of the section thickness.
This alternative request proposes relief from the requirement in paragraph NB-2539.4 to RT the repair area.
3.3 ONC's Reason For The Request On July 13, 2009, prior to start-up from a forced shutdown, with MPS2 in MOOE 3 (hot standby) at 0% reactor power, the licensee identified a Reactor Coolant System (RCS) pressure boundary leak in and around the "A" RCP seal cooler region at normal operating pressure and temperature. The leak was located at a weld location on the seal cooler return side of the 'A'
- 4 RCP. After excavation, the licensee was able to attribute the leak to a weld defect from original construction. ONC repaired the weld and base metal in accordance with the ASME Code Section XI. However, due to the close proximity of the repair area to surrounding obstructions and the component configuration, performance of a Code Radiography Test (RT) was not possible. Because of these restrictions, a best-effort RT examination was done. Also, because of these same restrictions, an Ultrasonic Test (UT) examination, as an alternative to the RT, was not possible.
At the time of the repair, ONC discussed the need for a verbal relief request with the NRC staff for the RT examination; however, ONC came to the conclusion that they did not need to complete an RT examination for this repair, and therefore did not need relief. After the repair had been performed and the equipment placed in service, ONC requested an interpretation from the ASME Code committee of the ASME Code as it applied to this type of repair. The ASME Code committee informed ONC that they would need to satisfy the Construction Code examination requirements for both the weld repair and the base metal repair. The Construction Code for MPS3 for base metal repairs requires an RT examination. The best-effort RT examination, which ONC had completed, is not in compliance with the image quality requirements of the MPS2 Construction Code. Since ONC had not been able to meet the image quality requirements for the RT examination, they were not in Code compliance for this repair.
Additionally, following repair welding, a hydrostatic test per IWA-5000 is required by the ASME Code,Section XI per IWA-4540(a). This Class 1 hydrostatic test would require pressurization at a pressure higher than that associated with normal startup and operations and would involve most of the RCS since there are no local isolation valves to limit the test area.
ONC invoked Code Case N-416-3, as an alternative of the required hydrostatic test.
Code Case N-416-3 allows a system leakage test in lieu of a hydrostatic test. As part of the system leakage test, the nondestructive examination methods and acceptance criteria must be done in accordance with ASME Code Section III, 1992 Edition with No Addenda. In ASME Section III, repair of defects in tubular products are to be examined in accordance with NB 2500, Examination and Repair of Pressure Retaining Material. NB-2539.4, Examination of Repair Welds, requires radiography of the repair area. The lack of access and configuration restrictions associated with the weld repair precludes the performance of an acceptable Code required RT, or an alternative UT examination. The best-effort RT examination, which ONe had completed, is not in compliance with the image quality requirements of the 1992 Edition of Section III. The licensee requests to use a best-effort RT in conjunction with progressive PT in lieu of the ASME Code-required RT for the Code Case N-416-3 system leakage test.
The licensee has determined that there is no way to comply with the RT requirements for this repair. An operability determination was performed because the repair was found to be in Code non-compliance. The operability determination concluded that the RCP seal cooler is operable, but not fully qualified with this repair. Oue to the close proximity of the repair area to surrounding obstructions and the component configuration, performance of a complete weld replacement is not possible. Replacement of the P40A RCP rotating element, includinq the P40A RCP Cover/Heat Exchanger Assembly, is the only way to restore full qualification of the component. However, the original welds that are on the replacement cooler did not receive RT examination during original fabrication and a replacement would not provide better assurance of structural integrity and safety than the cooler that is in place. A significant personnel radiation
- 5 exposure estimated at 17.630 person rem would result if a replacement was performed, and no increase in safety would be expected from such a replacement.
3.4 DNC's Proposed Alternative and Basis for Use DNC stated that the repair area had a progressive (i.e., after each weld pass) penetrate test (PT) performed and a best-effort RT. Due to the thin wall of the tubing being repaired, the PTs were comprised of a surface examination of the defect removal cavity, the root pass, the second layer, and the final layer with a best-effort RT of the final weld. The surface examinations and the best-effort RT were performed in accordance with the 1992 Edition of Section III.
DNC performed radiography in accordance with the 1992 Edition of the ASME Code,Section V, Article 2 requirements for the volumetric examination of the RCP seal cooler return tubing weld and tube repair to the extent possible to obtain the best possible image of the area of repair.
Complete ASME Code compliance could not be achieved based on access constraints of surrounding components and the configuration of the return tubing adjacent fittings, which restrict both source and film placement. The geometric unsharpness Code requirements were met. Only the Code sensitivity requirements were unable to be obtained. The configuration of the return tubing with the adjacent fittings does not provide adequate scan surface to apply UT examination techniques to perform volumetric examination of this area.
Additionally, the licensee performed a visual VT-2 examination on the repaired area during a Class 1 system leakage test prior to startup. This inservice leak test assured that there was no leak path and that the repair did not introduce major flaws.
DNC stated that the integrity of the repair is assured by the Code qualified and controlled welding process employed. In addition, the repaired weld and tube area received nondestructive examination as described above. The weld repair procedure included progressive PT examinations, similar to and exceeding those required by the Construction Code N-462.4(d)(1) and the 1992 Edition of Section III, for partial penetration welds.
The licensee stated that the multiple surface examinations performed provided additional assurance that no defects were introduced by the weld repair process. The original welds that are on the replacement cooler did not receive RT examination during original fabrication.
Therefore, the level of the quality of the repair weld is equal to or better than the original fabrication partial penetration weld immediately adjacent to it. Although the examination of the repair does not satisfy all Code requirements, the structural integrity of the weld repair is assured. In addition, the licensee has determined that the action taken is the only alternative to replacing the P40A RCP rotating element, including the P40A RCP Cover/Heat Exchanger Assembly which would create a hardship or unusual difficulty without a compensating increase in the level of quality or safety.
3.1.5 Duration of Proposed Alternative This proposed alternative to the ASME Code is applicable for the repair of weld RCPA-RC-95-W-4 in the P40A RCP seal cooler return line only and will remain in place for the life of the "A" RCP seal cooler.
- 6 4.0 Nuclear Regulatory Commission Staff Evaluation ONC asked relief from performing an RT on weld RCPA-RC-95-W-4.
When repairing the subject weld in July 2009, the licensee removed a portion of the base metal (i.e., the tube wall thickness) prior to depositing weld metal in the cavity. Because the base metal of the tube is affected, ONC must meet the ASME Code requirements for both the weld repair and the base metal repair. Paragraph N-462.4(d)(1) of the 1968 Edition with the Winter 1970 Addenda of the ASME Code Section III requires a progressive liquid penetrant test be performed on the weld passes. ONC was able to perform this test.
Also, paragraph N-324.7 of the ASME Code,Section III, requires an RT to be performed after the weld repair which ONC cannot perform because of obstructions and weld configuration.
Reviewing the photograph and drawing of weld RCPA-RC-95-W-4 provided in ONC's submittal, the NRC staff acknowledges that it is difficult to perform an ASME Code-qualified RT for the subject weld. The licensee stated that it is impossible to perform the required RT for the subject weld unless the entire RCP rotating element, including the RCP cover/heat exchanger assembly, is replaced with a new unit. Even if the new unit is installed, the weld in the replacement unit will not receive an RT because of the obstruction and weld configuration. The licensee demonstrated that should the RT requirement be followed, and a replacement unit installed, a hardship of significant personnel radiation exposure without an improvement in the corresponding level of safety and quality would occur. The NRC staff finds that hardship exists.
The licensee repaired the degraded weld per the welding requirements of ASME Code,Section XI and conducted progressive PT of the subject weld without detecting cracks. The NRC staff finds that progressive PT should be able to detect hot cracking in each weld layer. As compensatory measures, the licensee did perform a best-effort RT of the repaired weld. The licensee also performed a visual leakage test during a system leakage test and did not find any leakage.
As for the hydrostatic test requirement, the licensee invoked ASME Code,Section XI, Code Case N-416-3. Code Case N-416-3 allows a system leakage test to be performed in lieu of a hydrostatic test, provided that (a) NOE shall be performed on welded or brazed repairs and fabrication and installation joints in accordance with the methods and acceptance criteria of the applicable Subsection of the 1992 Edition of Section III, and (b) prior to or immediately upon return to service, a visual examination (VT-2) shall be performed on welded or brazed repairs, fabrication, and installation joints in conjunction with a system leakage test, using the 1992 Edition of Section XI, in accordance with IWA-5000, at nominal operating pressure and temperature. The NRC staff has approved Code Case N-416-3, without conditions, in Regulatory Guide 1.147, Revision 15.
ONC is not able to meet the system leakage radiography requirements for this repair. The NRC staff has determined that a combination of the progressive PT, visual examination, and informational RT is an acceptable alternative to the ASME Code required RT. Therefore, use of Code Case N-416-3, with an alternative to the RT requirements, instead of a hydrostatic test is acceptable.
- 7 The NRC staff finds that although the licensee was not able to perform the required RT, the progressive PT, a VT-2 examination, and the best-effort RT will provide reasonable assurance that the subject weld does not contain fabrication defects as a result of the weld repair. The NRC staff also finds that the system leakage test and VT-2 examination provide reasonable assurance of structural integrity such that there is no through wall leakage and the weld will be able to maintain the pressure boundary capability.
5.0 CONCLUSION
On the basis of the above review, the NRC staff finds that requiring compliance with the ASME Code RT requirements for the repair of weld RCPA-RC-95-W-4 in the P40A RCP seal cooler return line would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The NRC staff concludes that the proposed alternative in Request RR-89-67 is acceptable because it provides reasonable assurance of structural integrity of weld RCPA-RC-95-W-4. Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the NRC staff authorizes the use of Alternative Request RR-89-67 for the repair of weld RCPA-RC-95-W-4 for the remainder of the life of the "A" RCP seal cooler at MPS2.
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: J. Tsao Date: April 26, 2010
D. Heacock
- 2 If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.
Sincerely,
/raJ Harold Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
As stated cc w/ encl: Distribution via Listserv Distribution:
PUBLIC Branch Reading RidsAcrsAcnw_MailCTR Resource RidsNrrDorlLpl1-2 Resource RidsNrrDciCpnbResource RidsNrrLAABaxter Resource RidsNrrPMMillstone Resource RidsOgcRp Resource RidsRgn1 MailCenter Resource LTrocine, EDO R-1 JTsao, NRR ADAMS Accession No.: ML093570237
- Bsy Merno Dated OFFICE LPL1-2/PM LPL1-2/LA DCI/CPNB LPL1-2/BC NAME CSanders ABaxter TLupold*
HChernoff DATE 04/14/2010 02/25/2010 04/14/2010 04/26/2010 OFFICAL RECORD COPY