ML041550552
| ML041550552 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 06/04/2004 |
| From: | Ruland W NRC/NRR/DLPM/LPD3 |
| To: | Vanmiddlesworth G Nuclear Management Co |
| Chernoff, H, NRR/DLPM, 301-415-4018 | |
| References | |
| EA-03-009, FOIA/PA-2004-0282, TAC MC2532 | |
| Download: ML041550552 (11) | |
Text
June 4, 2004 Gary D. Van Middlesworth Site Vice President Point Beach Nuclear Plant Nuclear Management Company, LLC 6610 Nuclear Road Two Rivers, WI 54241
SUBJECT:
POINT BEACH NUCLEAR PLANT, UNIT 1 - RELAXATION OF THE REQUIREMENTS OF FIRST REVISED ORDER (EA-03-009) REGARDING REACTOR PRESSURE VESSEL HEAD INSPECTIONS DATED FEBRUARY 20, 2004 (TAC NO. MC2532)
Dear Mr. Van Middlesworth:
The U. S. Nuclear Regulatory Commission (NRC) has approved your request for relaxation of certain requirements of the First Revised Order Modifying Licenses (Order) EA-03-009, dated February 20, 2004. The Revised Order EA-03-009 superseded the original Order Modifying Licenses (Effective Immediately) EA-03-009, dated February 11, 2003. The Order imposes requirements for pressurized-water reactor licensees to inspect reactor pressure vessel (RPV) heads and associated penetration nozzles as stated in Section IV.C.(5), (a) and (b).
Section IV.C.(5)(b)(i), (ii) and (iii) mandate requirements for nondestructive examination of each penetration.Section IV.F of the Order states that requests for relaxation associated with specific penetration nozzles will be evaluated by the NRC staff using its procedure for evaluating proposed alternatives to the American Society of Mechanical Engineers Code in accordance with 10 CFR 50.55a(a)(3).
By letter dated March 30, 2004, as supplemented by letters dated May 14, May 15, and May 21, 2004, the Nuclear Management Company, LLC (the licensee), submitted a request for relaxation from certain nondestructive examination requirements of the Order for the Point Beach Nuclear Plant (PBNP), Unit 1, reactor vessel head penetration nozzles. Specifically, the licensee requested relaxation for: 1) the examination distance below the J-groove weld for 17 nozzles; and 2) the examination of a radial arc of 60 degrees on nozzle 33 from the J-groove weld upward through the full length of the Order-required examination area.
G. D. Van Middlesworth As documented in the supplement dated May 21, 2004, the licensee performed additional actions to obtain the Order-required examination coverage for nozzle 33 and withdrew the related portion (Item 2 in the previous paragraph) of its request for relaxation of the Order. In this supplement, the licensee also stated that the requested Order relaxation applied only to the current PBNP, Unit 1, operating cycle. The licensee plans to replace the PBNP, Unit 1, reactor vessel head at the end of the current operating cycle.
The NRC staff has completed its review and concludes, as documented in the enclosed safety evaluation, that the licensee has demonstrated that compliance with the Order for the RPV nozzles specified would have resulted in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The NRC staff has found the licensees request for relaxation of the Order acceptable, with a condition. Therefore, pursuant to Section IV, Paragraph F, of the Order, the NRC staff finds there is good cause shown to relax the Order and authorizes the proposed relaxation of the examination area for the specified 17 nozzles, subject to the following condition:
If the NRC staff finds that the crack-growth formula in industry report MRP-55 is unacceptable, the licensee shall revise its analysis that justifies relaxation of the Order within 30 days after the NRC informs the licensee of an NRC-approved crack growth formula. If the licensees revised analysis shows that the crack growth acceptance criteria are exceeded prior to the end of the current operating cycle, this relaxation is rescinded and the licensee shall, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, submit to the NRC written justification for continued operation. If the revised analysis shows that the crack growth acceptance criteria are not exceeded during the current operating cycle, the licensee shall, within 30 days, submit a letter to the NRC confirming that its analysis has been revised. Any future crack-growth analyses performed for this cycle for RPV head penetrations must be based on an acceptable crack growth rate formula.
The NRC staff based its evaluation on the licensee's deterministic evaluations based on the methodology in WCAP-14000, Revision 1, "Structural Integrity Evaluation of Reactor Vessel Head Penetrations to Support Continued Operation: Point Beach Units 1 & 2." The NRC staff did not use the Structural Integrity Associates Report SIR-04-032, Revision 0, "Probabilistic Fracture Mechanics Analysis of CRDM Inspection Alternatives at Point Beach Unit 1,"
(Enclosure 2 of letter dated March 30, 2004) as part of its evaluation.
In several conference calls which were conducted from April 29 through May 14, 2004, the NRC staff requested additional technical information necessary to support the review of the proposed relaxation of the Order. Your staff agreed to provide this information. Your May 14, 2004, supplement did not provide the requested information. Several additional requests by the NRC staff were required before your staff supplied the information necessary to support the review.
G. D. Van Middlesworth If you have any questions concerning this matter, please contact Mr. Harold Chernoff at (301) 415-4018.
Sincerely,
/RA/
William H. Ruland, Director Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-266
Enclosure:
Safety Evaluation cc w/encl: See next page
- RBouling 6/4/04 - Changes only OFFICE PDIII-1/PM PDIII-1/LA*
EMEB/SC PDIII-1/SC OGC PDIII/D NAME HChernoff THarris TChan JLamb for LRaghavan GLongo WRuland DATE 06/04/04 06/03/04 06/04/04 06/04/04 06/04/04 06/04/04
Point Beach Nuclear Plant, Units 1 and 2 cc:
Mr. 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 Mr. John Paul Cowan Executive Vice President
& Chief Nuclear Officer Nuclear Management Company, LLC 700 First Street Hudson, WI 54016 Mr. 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 FIRST REVISED ORDER MODIFYING LICENSES (EA-03-009) RELAXATION REQUEST ALTERNATE EXAMINATION COVERAGE FOR REACTOR PRESSURE VESSEL HEAD PENETRATION NOZZLES NUCLEAR MANAGEMENT COMPANY, LLC POINT BEACH NUCLEAR PLANT, UNIT 1 DOCKET NO. 50-266
1.0 INTRODUCTION
By letter dated March 30, 2004, as supplemented by letters dated May 14, May 15 and May 21, 2004, the Nuclear Management Company, LLC (the licensee), submitted a request for relaxation from certain nondestructive examination requirements of the Order for the Point Beach Nuclear Plant, Unit 1 (PBNP, Unit 1), reactor pressure vessel (RPV) head penetration nozzles.
The First Revised Order Modifying Licenses, EA-03-009 (hereinafter referred to as Order),
issued on February 20, 2004, requires specific examinations of the RPV head and vessel head penetration (VHP) nozzles of all pressurized-water reactor plants.Section IV, Paragraph F, of the Order states that requests for relaxation of the First Revised Order associated with specific penetration nozzles will be evaluated by the Nuclear Regulatory Commission (NRC) staff using the procedure for evaluating proposed alternatives to the American Society of Mechanical Engineers Code in accordance with 10 CFR 50.55a(a)(3).Section IV, Paragraph F, of the First Revised Order states that a request for relaxation regarding inspection of specific nozzles shall address the following criteria: (1) the proposed alternative(s) for inspection of specific nozzles will provide an acceptable level of quality and safety, or (2) compliance with this First Revised Order for specific nozzles would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
For PBNP, Unit 1, and similar plants determined to have a high susceptibility to primary water stress corrosion cracking (PWSCC) in accordance with Section IV, paragraphs A and B of the Order, the following inspections are required to be performed every refueling outage in accordance with Section IV, paragraph C.(5)(a) and paragraph C.(5)(b) of the Order:
(a)
Bare metal visual examination of 100 percent of the RPV head surface (including 360
around each RPV head penetration nozzle). For RPV heads with the surface obscured by support structure interferences which are located at RPV head elevations downslope from the outermost RPV head penetration, a bare metal visual inspection of no less than 95 percent of the RPV head surface may be performed provided that the examination shall include those areas of the RPV head upslope and downslope from the support structure interference to identify any evidence of boron or corrosive product. Should any evidence of boron or corrosive product be identified, the licensee shall examine the RPV head surface under the support structure to ensure that the RPV head is not degraded.
(b)
For each penetration, perform a nonvisual nondestructive examination (NDE) in accordance with either (i), (ii), or (iii):
(i)
Ultrasonic testing (UT) of the RPV head penetration nozzle volume (i.e., nozzle base material) from 2 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 2 inches below the lowest point at the toe of the J-groove weld on a horizontal plane perpendicular to the nozzle axis (or the bottom of the nozzle if less than 2 inches
[see Figure IV-1]); OR from 2 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 1.0-inch below the lowest point at the toe of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) and including all RPV head penetration nozzle surfaces below the J-groove weld that have an operating stress level (including all residual and normal operation stresses) of 20 ksi tension and greater (see Figure IV-2 of the Order). In addition, an assessment shall be made to determine if leakage has occurred into the annulus between the RPV head penetration nozzle and the RPV head low-alloy steel.
(ii)
Eddy current testing or dye penetrant testing of the entire wetted surface of the J-groove weld and the wetted surface of the RPV head penetration nozzle base material from at least 2 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 2 inches below the lowest point at the toe of the J-groove weld on a horizontal plane perpendicular to the nozzle axis (or the bottom of the nozzle if less than 2 inches
[see Figure IV-3]); OR from 2 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 1.0-inch below the lowest point at the toe of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) and including all RPV head penetration nozzle surfaces below the J-groove weld have an operating stress level (including all residual and normal operation stresses) of 20 ksi tension and greater (see Figure IV-4 of the Order).
(iii)
A combination of (i) and (ii) to cover equivalent volumes, surfaces, and leak paths of the RPV head penetration nozzle base material and J-groove weld as described in (i) and (ii). Substitution of a portion of a volumetric exam on a nozzle with a surface examination may be performed with the following requirements:
- 1.
On nozzle material below the J-groove weld, both the outside diameter (OD) and inside diameter (ID) surfaces of the nozzle must be examined.
- 2.
On nozzle material above the J-groove weld, surface examination of the ID surface of the nozzle is permitted provided a surface examination of the J-groove weld is also performed.
Footnote 3 of the Order provides specific criteria for examination of repaired VHP nozzles.
2.0 ORDER RELAXATION REQUEST FOR EXAMINATION COVERAGE FOR REACTOR PRESSURE VESSEL HEAD PENETRATION NOZZLES 2.1 Order Requirements for Which Relaxation is Requested The licensee requested relaxation to implement an alternative to the requirements of Section IV, paragraphs C.(5)(b)(i) and C.(5)(b)(ii) of the Order for RPV head penetration nozzles at PBNP, Unit 1. Specifically, the licensee requested relaxation on the examination distance below the weld.
2.2 Licensees Proposed Alternative The licensee seeks relaxation of the Order, where inspection coverage is limited on 17 reactor VHP nozzles with respect to NDE, specifically UT below the J-groove weld.
The licensee was able to meet the Order requirements of Section IV, paragraph C.(5)(b)(i) for 32 of the 49 RPV nozzles and the 1 vent line penetration. The examination distances below the J-groove weld for the other 17 RPV nozzles are listed below in Table 1.
TABLE 1 Nozzle Number Nozzle Angle Minimum ID distance below weld on down-hill side as measured (inches)
Minimum OD distance below weld on down-hill side as measured (inches)
Minimum OD distance below weld on the down-hill side less 0.03" instrument uncertainty (inches) 4 19.4 1.394 1.0 0.97 11 28.1 1.394 1.0 0.97 12 28.1 1.074 0.68 0.65 13 28.1 1.124 0.73 0.70 15 31.8 1.394 1.000 0.970 16 31.8 0.974 0.58 0.55 18 29.9 1.394 1.0 0.970 19 29.9 1.394 1.0 0.97 Nozzle Number Nozzle Angle Minimum ID distance below weld on down-hill side as measured (inches)
Minimum OD distance below weld on down-hill side as measured (inches)
Minimum OD distance below weld on the down-hill side less 0.03" instrument uncertainty (inches) 20 29.9 0.834 0.44 0.41 22 31.8 1.404 1.01 0.98 24 31.8 1.074 0.680 0.65 25 31.8 1.394 1.0 0.97 27 36.9 1.344 0.95 0.92 28 36.9 0.924 0.53 0.5 29 36.9 1.164 0.77 0.74 30 36.9 1.174 0.78 0.75 31 36.9 1.134 0.740 0.71 2.3 Licensees Basis for Relaxation The Order requires that ultrasonic or surface examination extend to two inches below the J-groove weld or one inch below the J-groove weld and including all VHP nozzle surfaces below the J-groove weld that have an operating stress level (including residual and normal operation stresses) of 20 ksi tension and greater or to the bottom of the nozzle.
The licensee identified seventeen nozzles which could not be examined to the nozzle end on the OD surface due to the blind zone. This distance was less than 1 inch below the toe of the J-groove weld. The amount of unscanned area is a function of the Areva blade tool and the distance the nozzles extend beyond the toe of the weld. The Areva blade tool has a blind zone at the nozzle end. The blind zone has a height of 0.4 inches on the OD of the nozzle. The ID of the nozzle can be scanned to the nozzle end.
For the subject 17 nozzles, the licensee volumetrically examined the full distance on the ID of the nozzle, but not the OD below the J-groove weld. The licensee used deterministic fracture mechanics to justify that a flaw would not grow to the toe of the weld in one cycle of operation for the limiting nozzle (nozzle 20).
The licensee determined the time for a worst-case flaw to grow to the toe of the weld would be approximately 2.5 effective full-power years (EFPYs). PBNP, Unit 1, operates on an 18-month cycle and will be replacing the RPV head during the next refueling outage scheduled for fall 2006.
2.4 Evaluation The NRC staffs review of this request was based on criterion (2) of paragraph F of Section IV of the Order, which states:
Compliance with this Order for specific nozzles would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Within the context of the licensees proposed alternative examination of the RPV head penetration nozzles, the licensee has demonstrated the hardship that would result from implementing examinations to the bottom end of these nozzles on the OD (approximately 0.4 inches). Performing a surface examination, such as a penetrant examination, would incur unnecessary radiation dose to employees and would not provide significant information due to the short examination distance.
The phenomenon of concern is PWSCC, which typically initiates in the areas of highest stress.
The area of Control Rod Drive Mechanism penetrations that has the highest residual stress is the area adjacent to the J-groove attachment weld. Therefore, it is most likely that PWSCC will initiate in an area adjacent to the J-groove attachment weld. The staff used the stress profiles, based on the licensee's finite element analysis of the VHP nozzles at PBNP, Unit 1, and estimated that the stresses decrease to 20 ksi or less at the examination distances obtained for 11 out of the 17 VHP nozzles with limited examination coverage below the J-groove weld. Of the six VHP nozzles to which the ID and OD stresses were not less then 20 ksi at the examination distance, (nozzle numbers 16, 20, 28, 29, 30, and 31) the limiting nozzle (nozzle number 20) decreased to approximately 20 ksi on the ID of the weld and was less than 30 ksi on the OD of the weld at the distance examined (the staff used the data supplied in the May 14, 2004, submittal for hoop stresses on the 28.2 and 43.5 degree nozzles for its estimates). The nominal yield strength of the VHP nozzles at PBNP, Unit 1, varies from 40.5 ksi to 60 ksi. The stress level of 20 ksi is a conservative value below which PWSCC initiation is unlikely and is referenced in the Order. Crack initiation would be more likely to occur at the weld region where the stresses are higher. These regions were examined by the licensee for the subject 17 nozzles. In addition, the staff finds that the higher stress (30 ksi) on the OD of nozzle number 20 at a distance of 0.41 inch below the weld is less than the yield stress and, therefore, the likelihood of crack initiation at that location is low.
The 0.41 inch inspection distance of the limiting nozzle base material below the attachment weld is supported by the licensees crack growth analysis. The results of the licensee's analysis shows that a postulated flaw located at or below 0.41 inch below the J-groove weld would not propagate to the toe of the J-groove weld within the next operating period. The licensees flaw evaluation was performed by postulating an axial through-wall flaw in the assumed area of missed coverage below the weld. The methodology was described in WCAP-14000, Rev. 1, Structural Integrity Evaluation of Reactor Vessel Upper Head Penetrations to Support Continued Operation: Point Beach Units 1 and 2." The licensee's deterministic flaw tolerance evaluation showed that the assumed through-wall flaw would take over 2.5 EFPY to reach the J-groove weld.
The licensees analysis used the crack growth formula in Electric Power Research Institute (EPRI) Report Material Reliability Program (MRP) report MRP-55, Material Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick Wall Alloy 600 Material (MRP-55), Revision 1. The NRC staff has performed a preliminary assessment of the crack growth rate, but has not yet made a final determination on the acceptability of the subject industry report. Should the NRC staff determine the crack growth formula used by the licensee to be unacceptable, the licensee committed to revise its analysis to incorporate an acceptable crack growth formula as described below in its letter dated May 21, 2004:
If the NRC staff finds that the crack-growth formula in industry report MRP-55 is unacceptable, the licensee shall revise its analysis that justifies relaxation of the Order within 30 days after the NRC informs the licensee of an NRC-approved crack growth formula. If the licensees revised analysis shows that the crack growth acceptance criteria are exceeded prior to the end of the current operating cycle, this relaxation is rescinded and the licensee shall, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, submit to the NRC written justification for continued operation. If the revised analysis shows that the crack growth acceptance criteria are not exceeded during the current operating cycle, the licensee shall, within 30 days, submit a letter to the NRC confirming that its analysis has been revised. Any future crack-growth analyses performed for this cycle for RPV head penetrations must be based on an acceptable crack growth rate formula.
The licensee inspected all penetrations using a volumetric UT examination including a UT leak path assessment. The UT examination covered the area from 2 inches above the J-groove weld down to the nozzle end.
No supplemental examinations were performed on the OD surface of the VHP nozzles to cover the small unexamined region (0.4 inches) that was not covered by UT examination. The staff finds that additional examination on the OD surface would be a hardship without a compensating increase in the level of quality or safety.
Based upon the information above, the NRC staff finds that the licensees examinations to the extent described above is acceptable as it provides reasonable assurance of the structural integrity of the RPV head, VHP nozzles and welds. Further inspections of the OD surface on the bottom of the nozzles (0.4 inch) to comply with the Order requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The NRC staff's evaluation is based on the licensee's deterministic evaluations using the methodology in WCAP-14000, Revision 1, "Structural Integrity Evaluation of Reactor Vessel Head Penetrations to Support Continued Operation: Point Beach Units 1 & 2." The NRC staff did not use the Structural Integrity Associates Report SIR-04-032, Revision 0, "Probabilistic Fracture Mechanics Analysis of CRDM Inspection Alternatives at Point Beach Unit 1,"
(Enclosure 2 of letter dated March 30, 2004) as part of this safety evaluation.
3.0 CONCLUSION
The NRC staff concludes that the licensees examinations of the subject 17 VHP nozzles at PBNP, Unit 1, from 2 inches above the J-groove weld to the level below the weld as identified in Table 1 provides reasonable assurance of the structural integrity of the RPV head, VHP nozzles and welds at PBNP, Unit 1. Further inspections of these VHP nozzles in accordance with Section IV, Paragraph C.(5)(b), of the First Revised NRC Order EA-03-009 dated February 20, 2004, would result in hardship without a compensating increase in the level of quality and safety. Therefore, for good cause shown, and pursuant to Section IV, Paragraph F, of the Order, the NRC staff authorizes the proposed alternative inspection for the subject 17 VHP nozzles at PBNP, Unit 1, subject to the following condition:
If the NRC staff finds that the crack-growth formula in industry report MRP-55 is unacceptable, the licensee shall revise its analysis that justifies relaxation of the Order within 30 days after the NRC informs the licensee of an NRC-approved crack growth formula. If the licensees revised analysis shows that the crack growth acceptance criteria are exceeded prior to the end of the current operating cycle, this relaxation is rescinded and the licensee shall, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, submit to the NRC written justification for continued operation. If the revised analysis shows that the crack growth acceptance criteria are not exceeded during the current operating cycle, the licensee shall, within 30 days, submit a letter to the NRC confirming that its analysis has been revised. Any future crack-growth analyses performed for this cycle for RPV head penetrations must be based on an acceptable crack growth rate formula.
In the licensee's request for additional information response dated May 21, 2004, the licensee agreed to comply with the condition language as stated above should the crack growth formula be found unacceptable to the NRC staff. In this supplement, the licensee also stated that the requested Order relaxation applied only to the current PBNP, Unit 1, operating cycle. The licensee plans to replace the PBNP, Unit 1, reactor vessel head at the end of the current operating cycle.
Principal Contributor: A. Keim Date: June 4, 2004