ML070790231
| ML070790231 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/02/2007 |
| From: | Chernoff H Plant Licensing Branch III-2 |
| To: | Christian D Dominion Nuclear Connecticut |
| nerses V, NRR//DORL, 415-1484 | |
| References | |
| EA-03-009, TAC MD1735 | |
| Download: ML070790231 (12) | |
Text
May 2, 2007 Mr. David A. Christian Sr. Vice President and Chief Nuclear Officer Dominion Nuclear Connecticut, Inc.
Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711
SUBJECT:
MILLSTONE POWER STATION, UNIT NO. 3 REQUEST FOR RELAXATION OF THE REQUIREMENTS OF ORDER EA-03-009 REGARDING REACTOR PRESSURE VESSEL HEAD INSPECTIONS (TAC NO. MD1735)
Dear Mr. Christian:
By letter dated May 16, 2006, as supplemented by letters dated December 14, 2006 and February 23, 2007, Dominion Nuclear Connecticut (DNC), the licensee for Millstone Power Station, Unit No. 3 (MPS3), requested approval to relax the requirements to Section IV.C(5)b of the Nuclear Regulatory Commissions (NRC) Order EA-03-009 (Order), issued on February 20, 2004 [ADAMS accession number ML040220181]. The Order establishes inspection requirements for the reactor pressure vessel head. DNC states that it is unable to perform ultrasonic testing to the extent required by the Order at the bottom of five core exit thermocouple nozzles during the next refueling outage in the spring of 2007.
DNC made its request pursuant to the provisions of the Order,Section IV.F(2), regarding relaxation requirements, which states that requests for relaxation associated with specific penetration nozzles will be evaluated by the NRC using its procedure for evaluating proposed alternatives to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code in accordance the requirements of Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(a)(3).
The licensees proposed alternative inspection to perform the ultrasonic testing of five penetration nozzles at MPS3 to the maximum extent practical below the J-groove weld with a minimum inspection distance of 0.2-inch and as conditioned, provides reasonable assurance of the structural integrity of the RPV upper head and would provide an acceptable level of quality and safety.
D. Christian 2
In addition, compliance with Section IV.C.(5)b of the Order would result in hardship to the licensee without a compensating increase in quality and safety. Therefore, the NRC staff grants the licensees request for relaxation of Section IV.C(5)b of the Order, with the condition as noted in the NRC staffs enclosed safety evaluation. If you have any questions, please contact the project manager, John Hughey at (301) 415-3204.
Sincerely,
/ra/
Harold K. Chernoff, Acting Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-423
Enclosure:
as stated cc: See next page
DORL/DIR NAME VNerses CSola JHughey TChan
- GMLongo for BJones HChernoff (Acting)
DATE 4/09/2007 3/30/2007 04/24/07 3/19/2007 4/12/2007 5/2/07
Millstone Power Station, Unit No. 3 cc:
Lillilan M. Cuoco, Esquire Senior Counsel Dominion Resources Services, Inc.
Building 475, 5th Floor 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 Mr. J. W. "Bill" Sheehan Co-Chair NEAC 19 Laurel Crest Drive Waterford, CT 06385 Mr. Evan W. Woollacott Co-Chair Nuclear Energy Advisory Council 128 Terry's Plain Road Simsbury, CT 06070 Senior Resident Inspector Millstone Power Station c/o U.S. Nuclear Regulatory Commission P. O. Box 513 Niantic, CT 06357 Ms. Nancy Burton 147 Cross Highway Redding Ridge, CT 00870 Mr. Joseph Roy, Director of Operations Massachusetts Municipal Wholesale Electric Company Moody Street P.O. Box 426 Ludlow, MA 01056 Mr. J. Alan Price Site Vice President Dominion Nuclear Connecticut, Inc.
Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Mr. Chris Funderburk Director, Nuclear Licensing and Operations Support Dominion Resources Services, Inc.
5000 Dominion Boulevard Glen Allen, VA 23060-6711 Mr. David W. Dodson Licensing Supervisor Dominion Nuclear Connecticut, Inc.
Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ORDER EA-03-009 RELAXATION REQUEST, ALTERNATE EXAMINATION COVERAGE FOR REACTOR PRESSURE VESSEL HEAD PENETRATION NOZZLES MILLSTONE POWER STATION, UNIT 3 DOMINION NUCLEAR CONNECTICUT, INC.
DOCKET NUMBER 50-423
1.0 INTRODUCTION
The First Revised Nuclear Regulatory Commission (NRC) Order EA-03-009 (Order), issued on February 20, 2004, requires specific examinations of the reactor pressure vessel (RPV) head and vessel head penetration nozzles of all pressurized water reactor plants.Section IV.F of the Order states that requests for relaxation of the Order associated with specific penetration nozzles will be evaluated by the NRC staff using the procedure for evaluating proposed alternatives to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) in accordance with Title 10 of the Code of Federal Regulations 50.55a(a)(3).
Section IV.F of the 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 Order for specific nozzles would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. By letter dated May 16, 2006, [Agency Documents Access and Management System (ADAMS) accession number ML061370133] as supplemented by letters dated December 14, 2006 [ADAMS accession number ML063490057]
and February 23, 2007, [ADAMS accession number ML070650457] Dominion Nuclear Connecticut, Inc. (DNC, licensee) requested relaxation from certain requirements of the Order.
2.0 REGULATORY BACKGROUND The licensee calculated that the Millstone Power Station, Unit No. 3 (MPS3), RPV head will have accrued less than 3 effective degradation years in accordance with Section IV.A of the Order. Therefore, pursuant to Section IV.B of the Order, MPS3 is categorized as having a low susceptibility to primary water stress corrosion cracking (PWSCC). For MPS3, and similar plants determined to have a low susceptibility to PWSCC in accordance with Sections IV.A, IV.B, and IV.C.(3) of the Order, the following inspection is required to be performed by February 11, 2008, in accordance with Section IV.C.(5)(b) of the Order:
(b)
For each penetration, perform a nonvisual nondestructive examination (NDE) in accordance with either (i), (ii), or (iii):
(i)
Ultrasonic testing 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); 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. 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); 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 one 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.
(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 and inside diameter surfaces of the nozzle must be examined.
2.
On nozzle material above the J-groove weld, surface examination of the inside diameter surface of the nozzle is permitted provided examination of the J-groove weld is also performed.
By letter dated May 16, 2006, and supplemented by letters dated December 14, 2006 and February 23, 2007, the licensee requested relaxation to implement an alternative to the requirements of Section IV.C.(5)(b) of the Order for RPV head penetration nozzles at MPS3.
3.0 TECHNICAL EVALUATION
- ORDER RELAXATION REQUEST FOR EXAMINATION COVERAGE FOR REACTOR PRESSURE VESSEL HEAD PENETRATION NOZZLES 3.1 Order Requirements for Which Relaxation is Requested Section IV.C of the Order requires, in part, that inspections of Section IV.C.(5)(b) of the Order be performed by February 11, 2008, for low susceptibility plants similar to MPS3.
The licensee has requested relaxation from Section IV.C.(5)(b) of the Order. The specific relaxation requested is identified below.
3.2 Licensees Proposed Alternative The licensee seeks relaxation from the Order to revise the minimum volumetric inspection coverage requirement below the J-groove weld for five penetration nozzles, specifically five core exit thermocouples (CET) at MPS3, to the lowest elevation that can be practically inspected. The licensee identified a limitation to complete ultrasonic examination coverage to meet the requirements of the Order, but found that determination of the extent of volumetric coverage possible below the J-groove weld can only be quantified by performance of the examination during the refueling outage. The licensee further proposed to substitute a surface examination for the lower portion of the nozzle where a volumetric examination in compliance with the Order is not practical.
Through supplemental letters dated December 14, 2006 and February 23, 2007, in response to NRC staff requests for additional information, the licensee has calculated a minimum volumetric and surface inspection necessary to provide an acceptable level of quality and safety. The licensees proposed alternative is examination of five CET (penetration nozzle numbers 74 through 78) to the lowest elevation that can be practically inspected including a minimum distance of 0.2-inch below the toe of the J-groove weld volumetrically and 0.32-inch below the toe of the J-groove weld through a surface examination of the inside diameter of the penetration nozzle.
3.3 Licensees Basis for Proposed Alternative It is the licensees relaxation request to perform the volumetric examination required by the Order to the lowest elevation that can be practically inspected for five CET (penetration nozzle numbers 74 through 78). The licensee will utilize inspection option (b)(iii) and will achieve volumetric and surface coverage two inches above the J-groove weld down to the lowest elevation that can be practically inspected on each of these penetration nozzles, with a minimum volumetric distance of 0.2-inch below the J-groove weld volumetrically and 0.32-inch below the toe of the J-groove weld through a surface examination of the inside diameter for five CET (penetration nozzle numbers 74 through 78).
The licensee states that the bottom of each RPV upper head penetration nozzle includes a threaded region approximately 0.75-inch long on the outside diameter along with a chamfered area at the inside diameter which extends approximately 0.75-inch from the bottom of the penetration nozzle. The chamfered surface is machined at a 20 degree angle. In addition to the presence of the threaded and chamfered regions on all penetration nozzles, four penetration nozzles also have a threaded guide cone attached to the bottom of the penetration nozzle via the threaded connection along with a welded set screw and two tack welds. Each of these items invoke physical restraints on full effective coverage of the Order required volumetric inspection area with ultrasonic examination probes.
The licensee notes that while the Order allows provisions for dye penetrant inspection, it would require extensive work under and around the RPV upper head. The licensee estimates the general area to be a high radiation work area incurring significant radiological dose for personnel required to perform an extended surface examination. In addition, the threaded region of the penetration nozzles would make a dye penetrant inspection impractical.
Therefore, the licensee concludes, that additional manual inspection of the uninspected regions of each penetration nozzle for which full Order coverage could not be met would result in significant radiation exposure to personnel without a compensating increase in the level of quality or safety.
The licensee further states that testing of portions of the nozzle significantly below the J-groove weld is not significant to the phenomena of concern. The phenomena that are of concern are leakage through the J-groove weld and circumferential cracking in the nozzle above the J-groove weld. The nozzle is essentially an open-ended tube, and the nozzle wall below the J-groove weld is not part of the reactor coolant system (RCS) pressure boundary. The licensee believes the proposed inspection coverage does not preclude full UT examination coverage of the portions of these nozzles that are of primary interest.
The licensee contracted for a structural integrity evaluation for MPS3, penetration nozzles of an angle consistent with the 5 CET (penetration nozzle numbers 74 through 78). A series of crack growth calculations were performed presuming a flaw where the lower extremity of this initial through-wall flaw is conservatively postulated to be located on the penetration nozzle where either the inside or outside surface hoop stress drops below 0 ksi. The calculation was performed to demonstrate that more time in effective full power years (EFPY) of operation would elapse before a postulated flaw in the unexamined area of the penetration nozzle would propagate into the pressure boundary formed by the J-groove weld. MPS3, is in the low susceptibility category, therefore, in accordance with the Order, nonvisual NDE will be performed once every four refueling outages or within seven calendar years whichever is less.
The methodology and the technical basis of the crack growth calculation, which was based on the hoop stress distribution and the PWSCC crack growth rate recommended in MRP-55 Revision 1, were provided in the licensees letter dated February 23, 2007. The calculation demonstrates that for 5 CET (penetration nozzle numbers 74 through 78) the minimum time for a flaw to propagate from 0.2-inch below the J-groove weld to the bottom of the J-groove weld would be at least 6.9 EFPY. This is an EFPY value greater than four refueling outages of operation for MPS3. The results of the conservative flaw propagation calculation indicate that, even if a flaw were to occur in the region of the penetration nozzle not being inspected, there would be adequate opportunity for detection prior to the crack reaching the RCS pressure boundary. The results demonstrate that the extent of the proposed inspection coverage would provide reasonable assurance of the structural integrity of 5 CET (penetration nozzle numbers 74 through 78) under the inspection frequency of the Order.
In their December 14, 2006, letter, the licensee stated the following in response to an NRC staff request for additional information:
should the structural evaluation of the MPS3 [Millstone, Unit 3] vessel head nozzles indicate that operating stress levels (including all residual and normal operating stresses) are 20 ksi in tension or greater in the area of the bottom of CET nozzles that are not volumetrically examined, a supplemental surface examination of the inner diameter tapered region of the CET nozzles will be performed.
The calculation provided in the licensees letter dated February 23, 2007, identified operating stress levels of greater than 20 ksi in tension at a distance of 0.32-inch below the toe of the J-groove weld.
As the crack growth rate formula used in the structural integrity evaluation for MPS3, is the same as the PWSCC crack growth rate recommended in MRP-55, Revision 1, the licensee states the following:
If the NRC staff finds the crack-growth formula in MRP-55 is unacceptable, DNC
[the licensee] will revise its analysis that justifies the relaxation of the Order within 30 days from the date that the NRC informs DNC of an NRC-approved crack-growth rate formula. If the revised analysis shows that the crack-growth acceptance criteria are exceeded prior to the end of the current operating cycle, this relaxation request will be rescinded and DNC will, 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 a written justification for continued operation. If the revised analysis shows that the crack-growth acceptance criteria are to be exceeded during the subsequent operating cycle, DNC will, within 30 days, submit the revised analysis for NRC review. If the revised analysis shows that the crack-growth acceptance criteria are not exceeded during either the current operating cycle or the subsequent operating cycle, DNC will, within 30 days, submit a letter to the NRC confirming that its analysis has been revised.
3.4
NRC Staff Evaluation
The NRC staffs review of this request was based on criterion (2) of Section IV.F 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.
Full inspection coverage is not achievable at MPS3, for five CET penetration nozzles, because of nozzle end geometry. Specifically, the bottom end of these nozzles are externally threaded, or internally tapered, or both. Thus, the geometry of the nozzle ends makes inspection in accordance with the Order difficult and would involve a hardship including increased personnel radiation dose due to possible surface examination options. This evaluation focuses on the issue of whether there is a compensating increase in the level of quality and safety such that these nozzles should be inspected in accordance with the Order despite this hardship.
The alternative inspection proposed by the licensee for five CET penetration nozzles is to volumetrically examine each nozzle from two inches above the weld down to the maximum extent practical with a minimum required inspection distance of 0.2-inch below the J-groove weld. Further, if the ultrasonic examination of the penetration nozzle does not extend to 0.32-inch below the toe of the J-groove weld, a surface examination would be performed of the inside diameter of the penetration nozzle to cover the missed surface area. Previous Order inspections at MPS3, including bare metal visual inspection above the RPV head, indicate no evidence of head material wastage or leaking penetrations. The NRC staffs review of the evaluations and analyses performed by the licensee in support of this request is described below.
The stress profile, based on the finite element analysis provided in the licensees letter dated February 23, 2007, of the representative CET penetration nozzle at MPS3, shows that most residual stresses decrease significantly at short distances below the J-groove weld. The residual hoop stress falls to less than 20 ksi at a distance of 0.32-inch from the downhill side (the most limiting) of the penetration nozzle. Since the stress level at the unexamined area is low, initiation of a crack is very unlikely. Operating experience also indicates that locations with this low stress level have been much less susceptible to cracking.
The licensees analysis used the methodology described in footnote 1 of the Order and conservative criteria to set the necessary height of the examination. The analysis assumed a minimum volumetric inspection distance of 0.2-inch below the toe of the J-groove weld.
Further, it postulated a through-wall crack in the unexamined area and showed that it would take the crack more than 6.9 EFPY to reach the J-groove weld. The staffs assessment of the licensees conclusion is based on data analysis of the supporting figures of the crack growth predictions for various nozzle angles, as provided in the licensees February 23, 2007, letter.
NRC staff performed an independent crack growth calculation, the results of which support the licensees analysis. Therefore, NRC staff concurs with the licensees conclusion, that a crack located beyond 0.2-inch below the J-groove weld would take more than 6.9 EFPY to reach the J-groove weld.
As MPS3 is in the low susceptibility category, nonvisual NDE will be performed every four refueling outages or 7 calender years whichever is less. The NRC staff finds the licensees estimate of less than 6.9 EFPY of operation in-between Order required examination periods is conservative. Therefore, an inspection frequency based on the licensees crack growth assessment above provides a reasonable basis for the proposed alternative inspection.
However, this analysis as provided in the licensees letter dated February 23, 2007 incorporates a crack growth formula from the "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 completed a preliminary review of the crack growth formula, but has not yet made a final assessment regarding the acceptability of the report.
Therefore, a condition has been included regarding the approval of the proposed relaxations.
The condition was agreed to by the licensee in their December 14, 2006, letter to the NRC, and is as follows:
If the NRC staff finds the crack-growth formula in MRP-55 is unacceptable, DNC
[the licensee] will revise its analysis that justifies the relaxation of the Order within 30 days from the date that the NRC informs DNC of an NRC-approved crack-growth rate formula. If the revised analysis shows that the crack-growth acceptance criteria are exceeded prior to the end of the current operating cycle, this relaxation request will be rescinded and DNC will, 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 a written justification for continued operation. If the revised analysis shows that the crack-growth acceptance criteria are to be exceeded during the subsequent operating cycle, DNC will, within 30 days, submit the revised analysis for NRC review. If the revised analysis shows that the crack-growth acceptance criteria are not exceeded during either the current operating cycle or the subsequent operating cycle, DNC will, within 30 days, submit a letter to the NRC confirming that its analysis has been revised.
The safety issues that are addressed by the Order are degradation (corrosion) of the low-alloy steel RPV upper head, reactor coolant pressure boundary integrity and ejection of the RPV upper head penetration nozzle due to circumferential cracking of the nozzle above the J-groove weld. The licensees proposed alternative inspection, to perform the UT examination below the J-groove weld for five CET penetration nozzles to the maximum extent practical with a minimum inspection distance of 0.2-inch below the J-groove weld and as conditioned, provides reasonable assurance that these safety issues are addressed at MPS3. The additional surface examination on the inside diameter only of the penetration nozzle from a depth of 0.2-inch to 0.32-inch is not necessary to provide this reasonable assurance.
The licensee has noted that additional surface examination could be performed of the remaining surface area of the penetration nozzle to increase the inspection coverage to the full Order requirement, however, these additional inspections would require extensive work in very high radiation fields. The staff finds that performing these additional surface examinations would result in hardship through significant radiation exposure without a compensating increase in the level or quality or safety.
3.5 Summary Based upon the information above, the staff finds that the licensees proposed alternative examination would provide an acceptable level of quality and safety as it provides reasonable assurance of the structural integrity of the RPV upper head, associated penetration nozzles and J-groove welds. Further inspections to comply with the Order requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Therefore, the licensee has demonstrated good cause for relaxation from the requirements of the Order.
4.0 CONCLUSION
The staff concludes that the licensees proposed alternative inspection, to perform the ultrasonic testing of five CET (penetration nozzle numbers 74 through 78) at MPS3, to the maximum extent practical below the J-groove weld, with a minimum inspection distance of 0.2-inch and as conditioned would provide an acceptable level of quality and safety as it provides reasonable assurance of the structural integrity of the RPV upper head, associated penetration nozzles and J-groove welds. Further inspections of these penetration nozzles in accordance with Section IV.C.(5)(b), of the Order, would result in hardship without a compensating increase in the level of quality and safety. Therefore, the licensee has demonstrated good cause for relaxation, and pursuant to Section IV.F, of the Order, the staff authorizes the proposed alternative inspection as stated above at MPS3, until the Order is replaced or rescinded, subject to the following condition:
If the NRC staff finds the crack-growth formula in MRP-55 is unacceptable, DNC
[the licensee] will revise its analysis that justifies the relaxation of the Order within 30 days from the date that the NRC informs DNC of an NRC-approved crack-growth rate formula. If the revised analysis shows that the crack-growth acceptance criteria are exceeded prior to the end of the current operating cycle, this relaxation request will be rescinded and DNC will, 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 a written justification for continued operation. If the revised analysis shows that the crack-growth acceptance criteria are to be exceeded during the subsequent operating cycle, DNC will, within 30 days, submit the revised analysis for NRC review. If the revised analysis shows that the crack-growth acceptance criteria are not exceeded during either the current operating cycle or the subsequent operating cycle, DNC will, within 30 days, submit a letter to the NRC confirming that its analysis has been revised.
Principal Contributor: J. Collins Date: May 2, 2007