ML041760065
| ML041760065 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 07/16/2004 |
| From: | Chernoff H NRC/NRR/DLPM/LPD3 |
| To: | Koehl D Nuclear Management Co |
| Chernoff, H, NRR/DLPM, 301-415-4018 | |
| References | |
| MR 02-018-2, Rev 1, TAC MC3221 | |
| Download: ML041760065 (10) | |
Text
July 16, 2004 Dennis L. Koehl Site Vice-President Point Beach Nuclear Plant Nuclear Management Company, LLC 6590 Nuclear Road Two Rivers, WI 54241-9516
SUBJECT:
POINT BEACH NUCLEAR PLANT, UNIT 1 - REACTOR VESSEL CLOSURE HEAD PENETRATION FLAW CHARACTERIZATION RELIEF REQUEST MR 02-018-2, REVISION 1 (TAC NO. MC3221)
Dear Mr. Koehl:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated May 13, 2004, as supplemented by letters dated May 15, May 20, May 21, and May 25, 2004, the Nuclear Management Company, LLC (NMC, the licensee), submitted Relief Request MR 02-018-2, Revision 1. This request pertained to relief from the requirement to characterize flaws that may exist in the remnants of the control rod drive mechanism nozzle J-groove welds after the repair of a reactor vessel head penetration.
Relief Request MR 02-018-2 was originally approved on September 10, 2003. In its safety evaluation of the initial relief request, the NRC staff limited its approval to cases where there was no overlap of the new Alloy 52 weld material onto any portion of the remnant J-groove weld. MR 02-018-2, Revision 1, submitted on May 13, 2004, was intended by NMC to provide the technical basis for eliminating this restriction.
The NRC staff reviewed the proposed revision to MR 02-018-2 and provided verbal approval of this relief request to NMC during a telephone conference on May 26, 2004. The NRC staff concluded that your proposed alternative to operate with an Alloy 52 weld repair, which overlaps the remnant J-groove weld(s), for 1.5 effective full-power years before retiring the reactor vessel closure head from service, provides an acceptable level of quality and safety, and is authorized pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(a)(3)(i), for the remainder of the current operating cycle (the reactor vessel head is scheduled to be replaced during the next refueling outage) at Point Beach Nuclear Plant, Unit 1.
The NRC staffs safety evaluation is enclosed.
In performing its review, the NRC staff observed that during the period April 29 through May 14, several telephone discussions with your staff were necessary to obtain required additional information.
We understand that you are using your corrective action program to ensure that future submittals contain mutually agreed upon information without the need for iterative discussions.
Sincerely,
/RA/
Harold K. Chernoff, Project Manager, Section 1 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-266
Enclosure:
Safety Evaluation cc w/encl: See next page
ML041760065 NRR-028 OFFICE PDIII-1/PM PDIII-1/PM PDIII-1/LA EMCB:SC OGC PDIII-1/SC NAME MChawla HChernoff THarris TChan RHoefling LRaghavan DATE 06/25/04 06/25/04 06/25/04 06/28/04 7/14/04 7/16/04
Point Beach Nuclear Plant, Unit 1 cc:
Jonathan Rogoff, Esquire Vice President, Counsel & Secretary Nuclear Management Company, LLC 700 First Street Hudson, WI 54016 Mr. F. D. Kuester President & Chief Executive Officer WE Generation 231 West Michigan Street Milwaukee, WI 53201 Regulatory Affairs Manager Point Beach Nuclear Plant Nuclear Management Company, LLC 6610 Nuclear Road Two Rivers, WI 54241 Mr. Ken Duveneck Town Chairman Town of Two Creeks 13017 State Highway 42 Mishicot, WI 54228 Chairman Public Service Commission of Wisconsin P.O. Box 7854 Madison, WI 53707-7854 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532-4351 Resident Inspectors Office U.S. Nuclear Regulatory Commission 6612 Nuclear Road Two Rivers, WI 54241 Mr. Jeffery Kitsembel Electric Division Public Service Commission of Wisconsin P.O. Box 7854 Madison, WI 53707-7854 Nuclear Asset Manager Wisconsin Electric Power Company 231 West Michigan Street Milwaukee, WI 53201 John Paul Cowan Executive Vice President & Chief Nuclear Officer Nuclear Management Company, LLC 700 First Street Hudson, WI 54016 Douglas E. Cooper Senior Vice President - Group Operations Palisades Nuclear Plant Nuclear Management Company, LLC 27780 Blue Star Memorial Highway Covert, MI 49043 Site Director of Operations Nuclear Management Company, LLC 6610 Nuclear Road Two Rivers, WI 54241
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST MR 02-018-2, REVISION 1 POINT BEACH NUCLEAR STATION, UNIT 1 NUCLEAR MANAGEMENT COMPANY DOCKET NO. 50-266
1.0 INTRODUCTION
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated May 13, 2004, as supplemented by letters dated May 15, May 20, and May 25, 2004, the Nuclear Management Company, LLC (NMC, the licensee), submitted a revision to relief request MR 02-018-2, requesting relief from selected American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),Section XI, requirements related to the reactor pressure vessel control rod drive mechanism (CRDM) J-groove weld repairs that overlap remnant J-groove weld(s) at Point Beach Nuclear Plant (Point Beach), Unit 1. This revision was submitted by the licensee per the NRC staffs September 10, 2003, safety evaluation condition whereby the staff granted relief pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(g)(6)(i), for instances when the repair weld does not come into contact with the remnant J-groove weld pressure boundary. The NRC staff required additional technical justification if the repair weld came into contact and would overlap the remnant J-groove weld. The information submitted on May 13, 2004, was intended to provide the technical basis for eliminating this restriction.
The revision to the relief request would provide relief from the requirement to characterize flaws that may exist in the remnants of the CRDM nozzle J-groove weld after a weld repair where Alloy 52 weld metal would overlap the remnant J-groove weld due to the thickness and radius of the curvature of the reactor vessel closure head (RVCH). The licensees letter dated May 13, 2004, as supplemented by letters dated May 15, May 20, and May 25, 2004, addressed revision to relief requests MR 02-018-01, which addressed the gas tungsten arc welding temper bead weld repair alternative, and MR 02-018-02. This safety evaluation applies to Point Beach, Unit 1 for relief request MR 02-018-02. The proposed revision to relief request MR 02-018-01 for Unit 1 will be addressed under separate cover.
2.0 REGULATORY EVALUATION
Alternatives to requirements may be authorized or relief granted by the NRC pursuant to 10 CFR 50.55a(a)(3)(i), 10 CFR 50.55a(a)(3)(ii), or 10 CFR 50.55a(g)(6)(i). In proposing alternatives or requesting relief, the licensee must demonstrate that: (1) the proposed alternatives provide an acceptable level of safety; or (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for the facility. Pursuant to 10 CFR 50.55a(g)(4)(iv), inservice inspection of items may meet the requirements set forth in subsequent editions and addenda of the ASME Code that are incorporated by reference in 10 CFR 50.55a(b), subject to the limitations and modifications listed therein, and subject to Commission approval. Portions of editions or addenda may be used provided that all related requirements of the respective editions or addenda are met. In its letter dated May 13, 2004, pursuant to 10 CFR 50.55a(a)(3)(i), the licensee requested a revision to the relief granted by the staffs safety evaluation dated September 10, 2003, from the requirements of the 1998 Edition of ASME Code,Section XI, IWA-3300(b), IWB-3142.4, and IWB-3420, which require characterization of flaw(s) existing in the remnant of the J-groove weld(s) that will remain in service for Point Beach, Unit 1, RVCHs if a CRDM nozzle must be partially removed and a new pressure boundary deposited over a portion of the J-groove weld remnant.
3.0 TECHNICAL EVALUATION
3.1 Code Requirements for which Relief is Requested The licensee requested relief from the requirements of the 1998 Edition of ASME Code,Section XI, IWA-3300(b), IWB-3142.4, and IWB-3420. The licensee proposed alternatives to the following ASME Section XI requirements:
Item 1 - IWA-3300(b) requires that flaws shall be characterized in accordance with IWA-3310 through IWA-3390, as applicable.
Item 2 -IWB-3142.4 states in part that a component accepted for continued service based on an analytical evaluation shall be subsequently examined in accordance with IWB-2420(b) and (c).
Item 3 - IWB-3420 states in part that each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaws.
3.1.1 System/Component(s) for which Relief is Requested The requested relief from the flaw characterization requirements applies to pressure-retaining Alloy 52 repair welds to CRDM nozzles when the repair weld overlaps by direct contact with the remnant J-groove Alloy 82/182 weld in the RVCH.
3.2 Licensees Proposed Alternative and Bases Pursuant to the alternative provisions in 10 CFR 50.55a(a)(3)(i), the licensee proposed that the overlap condition(s) be acceptable by analytical evaluation for one cycle of operation then removed from service in conjunction with the planned replacement of the RVCH.
The licensee stated that the basis in its original relief request, dated April 10, 2003, remain applicable to this request. In addition, the licensee stated that the repairs on the uphill side of the penetrations in the outer ring of the RVCH such as penetration No. 26, cannot physically be performed without overlapping the new pressure boundary weld onto portions of the remnant J-groove weld due to the high curvature of the RVCH in this area. Westinghouse 2-loop plants have a higher head curvature than most plants due to the reactor vessel diameter being smaller (132 inches).
The licensee conservatively decided to remove several surface indications on the Unit 1 CRDM Nozzle No. 26 J-groove weld by repair of the nozzle rather than to remove the flaws by grinding in order to minimize dose to personnel. The small diameter RVCH resulted in an overlap condition where the new Alloy 52 pressure retaining boundary came into contact with the remnant J-groove weld. The licensee evaluated an alternative which involved separating the overlap condition via grinding. This alternative resulted in an accumulated dose of 15 man-rem due to the high degree of physical contact with irradiated components.
The licensee stated that an analytical evaluation using Alloy 600 crack growth rates as documented in EPRI MRP-55, Materials Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Material, showed that a worst-case flaw in an Alloy 82/182 weld would take in excess of 1.5 effective full power years (EFPY) to go through the remaining weld ligament of 0.26 inches.
Since the actual ligament is 0.5 inches at Point Beach, the plant-specific calculations demonstrated that the worst case flaw would require over two years to pass through the Alloy 52 heat-affected zone ligament using the crack growth rates specific to Alloy 600 material.
Finally, in its supplemental letter dated May 15, 2004, the licensee submitted revised calculations which used Alloy 82/182 crack growth rates, which were more conservative when compared to those of the Alloy 600 material. Those results showed that it would take 1.39 EFPY for an assumed 0.100-inch root defect located at the weld/head interface to propagate through the Alloy 52 weld. Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee stated that the analytical evaluation submitted shows the existing overlap condition provides an acceptable level of quality and safety.
3.3 Evaluation The Alloy 52 repair weld overlap on the Alloy 82/182 remnant J-groove weld condition noted by the licensee occurs due to the high radius of curvature for a Westinghouse two-loop design of the RVCH. Figure 1 below shows the condition which occurs on the uphill side of outer ring RVCH nozzles:
The licensee postulated that the remnant J-groove weld was completely cracked and that a 0.50-inch ligament of sound metal remained at the Alloy 52 weld overlap. The staff noted that the licensee had applied the Alloy 600 crack growth (MRP-55) rate to determine the amount of time before a postulated flaw in the remnant J-groove weld would grow through the ligament.
The NRC staffs conclusion is that using the MRP-55 model for this specific weld overlap configuration is not conservative, and that a more representative model will be gained by using an Alloy 82/182 crack growth rate.
In its supplemental letter dated May 15, 2004, in response to the NRC staffs request for additional information, the licensee provided an analytical evaluation of the same configuration using the crack growth rate for Alloy 82/182 as the basis for the model in determining the amount of time involved for the postulated flaw to grow through the Alloy 52 ligament. The NRC staff concludes that the use of the Alloy 82/182 crack growth rate is a more conservative representation for Alloy 52 since published information indicates that the crack growth rates are 5 to 6 times higher in Alloy 82 welds than in Alloy 600 nozzle materials. Secondly, since Alloy 52 and Alloy 82 are both coarse-grained austenitic welds, the 82/182 crack growth rate model is more representative than when compared to the rolled, annealed Alloy 600 material crack growth model. The subject calculation package, Point Beach Unit 1 CRDM Top Head Analysis, PBCH-09Q-302, used the following assumptions:
1.
Stress intensity factors at the interface of the new Alloy 52 repair weld and the original Alloy 82/182 J-groove weld were computed assuming the entire original J-groove weld to be cracked.
2.
The use of a crack growth law recommended by a panel of industry experts for Alloy 82/182 weld metals to calculate the time for the Alloy 52 diluted zone to crack through its full segment (proprietary information submitted by supplemental letter dated May 25, 2004).
3.
The PWSCC crack growth correlation was adjusted to the Point Beach head operating temperature of 592 F due to the lower operating temperature.
4.
The calculation assumed a 0.100-inch weld root defect was present in the triple point area of Alloy 52 and the RVCH ferritic material thereby using the remaining 0.400-inch ligament for the postulated flaw to grow through.
5.
The calculations assumed that the postulated flaw grew axially/radially since the applied plus residual stresses in the hoop direction are greater than those in the radial direction by a factor of two to four.
6.
Fatigue crack growth was considered and was estimated at approximately 0.0002 inch and, therefore, considered negligible when compared to PWSCC propagation.
The NRC staff notes that published data verifies the appropriateness of the licensees assumption that a 0.100-inch root defect may exist at the weld triple point of the Alloy 82, Alloy 600 and ferritic material of the RVCH head. The results of the analysis indicated that assuming a 0.100-inch root defect contacts the fully cracked remnant, the time required for the assumed flaw to propagate through the remaining ligament would be 1.39 EFPY of operation.
The NRC staff recognizes that this is less than remaining amount of time the plant may operate before retiring the RVCH from service at the end of this operating cycle. However, based on the conservative assumptions in the licensees revised calculations, the NRC staff concludes that it would take in excess of 1.5 EFPY for a flaw to propagate through the J-groove weld with an overlap condition.
When considering the conclusions in the NRC staffs safety evaluation dated September 10, 2003, compliance with the ASME Code requirements therein were predicated on the fact that a new Alloy 52 pressure retaining boundary was not coming into contact with the remnant, assumed cracked, J-groove weld. On that assumption, the NRC staff concluded that successive inspections in accordance with ASME Code,Section XI, IWB-3142 were not necessary. Under this configuration, since the licensee will be removing the head from service after one operating cycle (1.5 EFPY), the same successive inspections required by IWB-3142.4 do not apply and the alternative to remove the RVCH from service after one cycle of operation is therefore, acceptable to the NRC staff. Secondly, since the morphology and weld structure is the same for the non-overlap condition and the Alloy 52/82 overlap condition, the conclusions in the previous safety evaluation regarding impracticality of characterizing defects in the remnant J-groove weld still apply. The NRC staff concludes that the previously granted relief from the requirements of IWA-3300 and IWB-3640, remain in effect for this repair situation.
In its supplemental letter dated May 20, 2004, the licensee provided additional information supporting its dose estimate of 15 man-rem to separate the welds. The work involved with this evolution was listed as:
1.
Set up ladders and support equipment 2.
Install template 3.
Layout the grind location 4.
Inspect 5.
Grind, etch and measure - estimated 12 people to grind 6.
Quality Control measurement 7.
Swab nozzle to clean 8.
Clean the nozzle(s) ground area for liquid penetrant examination 9.
Perform liquid penetrant examination - requires four entries under head Based on the information provided by the licensee indicating that removal of the overlap condition will result in 15 man-rem of dose, the licensee has sufficiently justified the hardship involved with removing the overlap condition by grinding. The conservative assumptions in the revised calculations indicate that an actual flaw would require more than 1.39 EFPY to grow through the J-groove weld. Based on the analytical information provided by the licensee, the short time of operation (1.5 EFPY) prior to removal of the RVCH from service, and the NRC staffs conclusion that no safety concern exists for this configuration due to its short operating time, the staff finds the alternative provides an acceptable level of quality and safety.
4.0 CONCLUSION
The NRC staff has reviewed the licensees submittal and determined that in accordance with 10 CFR 50.55a(a)(3)(i), the proposed alternative to overlap a remnant J-groove weld with Alloy 52 and operate 1.5 EFPY before retiring the RVCH from service at the end of the current operating cycle, will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the licensees proposed alternative for 1.5 EFPY of operation as a revision to relief request MR 02-018-02, which was granted by the staff as documented by safety evaluation dated September 10, 2003, for Point Beach, Unit 1.
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: T. Steingass Date: July 16, 2004