ML050630528
| ML050630528 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/04/2005 |
| From: | Abney T Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML050630528 (11) | |
Text
March 4, 2005 10 CFR 50.55a(a)(3)(i)
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop: OWFN P1-35 Washington, D.C. 20555-001 Gentlemen:
In the Matter of ) Docket No. 50-259 Tennessee Valley Authority )
BROWNS FERRY NUCLEAR PLANT (BFN) - UNIT 1 - AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) SECTION XI AND AUGMENTED INSPECTIONS - REQUEST FOR RELIEF 1-ISI-19, REGARDING REACTOR PRESSURE VESSEL (RPV) CIRCUMFERENTIAL SHELL WELD EXAMINATIONS
- SUPPLEMENTAL INFORMATION Based on recent verbal communications with the NRC Staff, TVA is submitting this supplemental information to support BFN Unit 1 Relief Request 1-ISI-19, submitted to the NRC by letter dated May 12, 2004 (Reference 1). Relief Request 1-ISI-19 requests relief from the inservice inspection requirements of 10 CFR 50.55a(g) for the volumetric examination requirements of the reactor vessel circumferential shell welds.
As requested by the Staff, this letter documents the differences in the assumptions used to calculate vessel fluence in support of Relief Request 1-ISI-19 versus the assumptions used to support extension of the relief for the extended period of operation associated with BFN Unit 1 license renewal.
The Enclosure to this letter provides the background associated with BFN Unit 1 Relief Request 1-ISI-19 and a comparison and explanation of the assumptions used to support
U.S. Nuclear Regulatory Commission Page 2 March 4, 2005 this relief request versus those used to support extending the relief through the end of the license renewal period.
There are no new commitments contained in this letter. If you have any questions, please telephone me at (256) 729-2636.
Sincerely, Original signed by:
T. E. Abney Manager of Licensing and Industry Affairs
References:
- 1. TVA letter, T. E. Abney to NRC, Browns Ferry Nuclear Plant (BFN) - Unit 1 - American Society of Mechanical Engineers (ASME)Section XI and Augmented Inspections -
Request for Relief, 1-ISI-19, Regarding Reactor Pressure Vessel (RPV) Circumferential Shell Welds, dated May 12, 2004.
cc: See Page 3
U.S. Nuclear Regulatory Commission Page 3 March 4, 2005 Enclosure cc: (Enclosure)
(Via NRC Electronic Distribution)
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-3415 Mr. Stephen J. Cahill, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Senior Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, AL 35611-6970 Margaret Chernoff, Senior Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739
U.S. Nuclear Regulatory Commission Page 4 March 4, 2005 MJB:BAB
Enclosure:
cc (Enclosure):
A. S. Bhatnagar, LP 6A-C J. C. Fornicola, LP 6A-C D. F. Helms, BR 4T-C R. F. Marks, PAB 1C-BFN F. C. Mashburn, BR 4X -C N. M. Moon, LP 6A-C R. G. Jones, NAB 1A-BFN K. L. Krueger, POB 2C-BFN J. R. Rupert, NAB 1A-BFN K. W. Singer, LP 6A-C M. D. Skaggs, PAB 1E-BFN E. J. Vigluicci, ET 11A-K NSRB Support, LP 5M-C EDMS WT CA - K S:lic/submit/subs/BFN U1 Circ Weld RR Supplement 03-03-05.doc
E-1 ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)
UNIT 1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME)
SECTION XI, INSERVICE (ISI) AND AUGMENTED INSPECTION PROGRAM (FIRST TEN YEAR INSPECTION INTERVAL)
SUPPLEMENTAL INFORMATION REQUEST FOR RELIEF 1-ISI-19 INTRODUCTION The following discussion provides supplementary information to support NRC Staff review and approval of BFN Unit 1 Relief Request 1-ISI-19, which requests relief from the volumetric examination requirements of the reactor vessel circumferential shell welds required under 50.55a(g)(6)(ii)(A). As requested during recent verbal communications with the NRC Staff, this letter documents the differences in the assumptions used to calculate vessel fluence in support of Relief Request 1-ISI-19 versus the assumptions used to support extension of the relief for the extended period of operation associated with BFN Unit 1 license renewal.
BACKGROUND On May 12, 2004, TVA submitted BFN Unit 1 Relief Request 1-ISI-19, requesting relief from the requirement to perform examination of the reactor vessel circumferential shell welds (Reference 1). Relief Request 1-ISI-19 was based on the guidance contained in NRC Generic Letter 98-05 (Reference 2). That relief request was based, in part, on an assumed reactor vessel neutron exposure of 32 Effective Full Power Years (EFPY) at Extended Power Uprate (EPU) conditions (120% of current licensed thermal power). A vessel exposure of 32 EFPY was extremely conservative because BFN Unit 1 has been shut down since 1985 and is expected to receive less than 14 EFPY of vessel neutron exposure through the end of its current operating license, which expires December 20, 2013. However, since BFN Unit 1 fracture toughness analyses had already been performed assuming 32 EFPY at EPU conditions to support the BFN Unit 1 EPU license amendment application, TVA used these analyses already completed to support Relief Request 1-ISI-19, rather than perform a separate BFN Unit l calculation to remove unneeded conservatism.
On August 13, 2004, TVA submitted a response to an NRC Request for Additional Information on 1-ISI-19 (Reference 3). In that
E-2 response, TVA 1) provided information concerning past vessel shell weld exams, 2) indicated that it would perform exams on all axial shell welds prior to restart of BFN Unit 1, and 3) identified the methodology used to calculate vessel fluence, including key inputs and results of that calculation.
In an October, 2004 teleconference, the NRC Staff informed TVA that while TVA had based Relief Request 1-ISI-19 on a reactor vessel circumferential weld nil-ductility transition temperature (RTNDT) calculated at the reactor vessel 1/4 thickness (1/4T) depth, the Staff required a reactor vessel circumferential weld RTNDT calculated at the reactor vessel inside surface to review and approve the relief request.
On November 8, 2004, TVA submitted a revision to Relief Request 1-ISI-19, providing the reactor vessel circumferential weld RTNDT calculated at the vessel inside surface (Reference 4). In this revision, TVA changed the assumption for vessel exposure (for the end of the current license period) from 32 EFPY to 16 EFPY, which is still conservative, as discussed further below. This assumption was changed because use of a vessel fluence calculated using the extremely conservative assumptions of 32 EFPY of reactor vessel exposure at EPU conditions returned an inside vessel surface circumferential weld RTNDT value that would have slightly exceeded the value used as part of the Staffs acceptance criteria for approving this request.
In recent discussions with the NRC Staff, TVA was requested to explain the differences in assumptions used in BFN Unit 1 Relief Request 1-ISI-19 versus those used to support evaluation of this relief through the end of the twenty additional years of operation requested in the BFN license renewal application. The basis for evaluation of the reactor vessel circumferential weld examination relief through the license extension period was provided to the NRC in a January 31, 2005 TVA letter (Reference 5), responding to an NRC Staff request for additional information on the BFN license renewal application.
REGULATORY BASIS Generic Letter 98-05 states that the NRC will grant relief from examination of the reactor vessel circumferential welds if the following two criteria are met:
(1) at the expiration of their license, the circumferential welds will continue to satisfy the limiting conditional failure probability for circumferential welds in the staff's July 30, 1998, safety evaluation, and (2) licensees have implemented operator training and established procedures that limit the frequency of cold over-pressure
E-3 events to the amount specified in the staff's July 30, 1998, safety evaluation.
These criteria stem from the NRCs review and approval of the Boiling Water Reactors Vessel & Internals Project (BWRVIP) report BWRVIP-05, BWR Reactor Pressure Vessel Shell Weld Inspection Recommendations (Reference 6) documented in the NRCs July 28, 1998 Safety Evaluation (Reference 7).
In Reference 7, the NRC reported the results of the Staffs conditional failure probability evaluations performed for limiting (bounding) reactor vessels for each manufacturer. The bounding vessels were selected as that set of vessels (for each vessel manufacturer) with the worst-case material properties (i.e., highest RTNDT) for the selected time frames. Accordingly, the Staff used these RTNDT values as input into their calculation of limiting circumferential weld conditional failure probability for each vessel manufacturer.
The Staff performed evaluations at two separate fluence levels:
Table 2.6-4 of the July 28, 1998 Safety Evaluation reported conditional failure probabilities for fluence levels corresponding to an assumed 32 EFPY of operation. That table provides the acceptance criteria for demonstrating that the limiting conditional failure probability of the reactor vessel circumferential welds relief through the end of the current license; Table 2.6-5 of the July 28, 1998 Safety Evaluation reported conditional failure probabilities for fluence levels corresponding to an assumed 64 EFPY of operation. That table provides the results of the conditional failure probability analyses extended to evaluate the impact of operation beyond the original license term, and accordingly provide an acceptance criteria for relief over the extended period of operation associated with license renewal.
To demonstrate that criterion (1) above is met requires showing that the (conservatively) calculated reactor vessel circumferential weld RTNDT is less than that assumed in the Staffs evaluation for the given time frame.
BFN UNIT 1 BASIS BFN Unit 1 has been shut down since 1985. The vessel currently has only 6.15 EFPY of exposure. It is expected that through the end of its current license, BFN Unit 1 will accumulate less than 14 EFPY of vessel exposure, and through an extended operational period (license renewal) less than 32 EFPY of vessel exposure.
The vessel exposure assumed for BFN Unit 1 Relief Request 1-ISI-19 and for license renewal are as follows:
E-4 Relief Request 1-ISI-19 assumes an exposure of 16 EFPY for relief through the end of the current license; The BFN license renewal application (as documented in Reference 5) assumes 54 EFPY for evaluation of relief through the end of the renewal period.
These assumptions, as shown in Table 1, are both conservative for their purpose, and demonstrate that the Staffs acceptance criteria for each period (as documented in Tables 2.6-4 and 2.6-5 of the NRCs July 28, 1998 SER) are met. At issue is whether these assumptions are consistent. The following discussion provides TVAs basis for selecting the assumptions used in each case.
Current License Period As discussed in the background section above, in Reference 4, TVA revised BFN Unit 1 Relief Request 1-ISI-19 to base it on an assumed vessel exposure of 16 EFPY at EPU Conditions (120% of the original thermal power level, or 3952 MWt).
BFN Unit 1 has been shut down since 1985, with an accumulated vessel exposure of 6.15 EFPY at the original licensed thermal power level (3293 MWt). Restart of BFN Unit 1 is projected in 2007. The current license expiration date is December 20, 2013.
Assuming BFN Unit 1 re-commences operation on January 1, 2007, the maximum BFN Unit 1 reactor vessel exposure would be approximately 13.1 EFPY. If this exposure were normalized to account for the fact that BFN Unit 1 operated for the existing 6.15 EFPY at the original power level, then the effective maximum expected vessel exposure at the end of the current license period would be even lower, or approximately 12.1 EFPY at EPU conditions. Therefore, the assumption of 16 EFPY of reactor vessel exposure at EPU conditions through the end of the current license period is very conservative.
To support the revision to BFN Unit 1 Relief Request 1-ISI-19 (Reference 4), TVA assumed a vessel exposure of 16 EFPY at EPU conditions to:
- 1. Ensure that the NRCs acceptance criteria in Table 2.6-4 of Reference 7 was met;
- 2. Ensure that the bases for BFN Unit 1 Relief Request 1-ISI-19 was sufficiently conservative;
- 3. Make the basis consistent with the assumptions being used to revise the BFN Unit 1 reactor vessel Pressure-Temperature operating limit curves (P-T Curves) submitted in Reference 8;
- 4. Avert performing an additional fluence analysis for the first 6.15 EFPY of operation at the original license thermal power level using a methodology consistent with NRC Regulatory
E-5 Guide 1.190, and adding that result to the fluence analysis performed as part of the BFN Unit 1 Extended Power Uprate project, performed in accordance with NRC Regulatory Guide 1.190.
Accordingly, the vessel exposure assumption used for BFN Unit 1 Relief Request 1-ISI-19, as revised in Reference 4, demonstrates that the NRC criteria for granting reactor vessel circumferential weld examination relief is met, the assumption is conservative with respect to expected BFN Unit 1 operation, and the assumption is consistent with the basis used to support the revision to the BFN Unit 1 P-T curves.
Extended License Period As discussed above, in Reference 5, TVA responded to an NRC Request for Additional Information in regard to the BFN license renewal application currently under NRC review. TVAs response to Item 4.2.6-1 in Reference 5 provided an evaluation of the requested BFN Unit 1 reactor vessel circumferential weld examination relief through the twenty years of extended operation requested in its license renewal application.
The reactor vessel exposure assumed in the evaluation provided in the response to Item 4.2.6-1 of Reference 5 was 54 EFPY. TVA acknowledges, based on the low BFN Unit 1 exposure accumulated to date, that assuming 54 EFPY in this evaluation was extremely conservative. However, TVA chose to simply assume reactor vessel exposure through the extended period of operation associated with license renewal to be 60 years of operation at a 90% capacity factor (54 EFPY) to simplify the bases for these evaluations.
TVA could have used a more realistic (and less conservative) assumption for the license renewal period, but chose instead to simplify the evaluation basis for the purposes of license renewal. Even using this conservative basis, TVA was able to demonstrate that the acceptance criteria was met for evaluation of the circumferential weld relief through the extended period of operation as well as reactor vessel fracture toughness.
CONCLUSION The differences in basis for the reactor vessel exposure assumption used in BFN Unit 1 Relief Request 1-ISI-19 versus that used in evaluation of the relief through the extended period of operation associated with license renewal were selected for convenience and consistency with other pending applications. For each case, the assumptions used are conservative and appropriate for their intended purposes, and as shown in Table 1, the NRC acceptance criteria for granting the requested relief is met.
E-6 REFERENCES
- 1. TVA letter, T. E. Abney to NRC, Browns Ferry Nuclear Plant (BFN) - Unit 1 - American Society of Mechanical Engineers (ASME)Section XI and Augmented Inspections - Request for Relief, 1-ISI-19, Regarding Reactor Pressure Vessel (RPV)
Circumferential Shell Welds, dated May 12, 2004.
- 2. NRC Generic Letter 98-05, Boiling Water Reactor Licensees Use of the BWRVIP-05 Report to Request Relief From Augmented Examination Requirements on Reactor Pressure Vessel Circumferential Shell Welds, dated November 10, 1998.
- 3. TVA letter, T. E. Abney to NRC, Browns Ferry Nuclear Plant (BFN) - Unit 1 - American Society of Mechanical Engineers (ASME)Section XI and Augmented Inspections - Response to Request for Additional Information - Request for Relief, 1-ISI-19, Regarding Reactor Pressure Vessel (RPV)
Circumferential Shell Welds, dated August 13, 2004.
- 4. TVA letter, T. E. Abney to NRC, Browns Ferry Nuclear Plant (BFN) - Unit 1 - American Society of Mechanical Engineers (ASME)Section XI and Augmented Inspections - Revision to Request for Relief, 1-ISI-19, Regarding Reactor Pressure Vessel (RPV) Circumferential Shell Weld Examinations, dated November 8, 2004.
- 5. TVA letter, T. E. Abney to NRC, Browns Ferry Nuclear Plant (BFN) - Units 1, 2, And 3 - License Renewal Application -
Reactor Vessel and Internals Mechanical Systems Sections 3.1, 4.2, and B.2.1 - Response to NRC Request for Additional Information (RAI) (TAC Nos. MC1704, MC1705, and MC1706),
dated January 31, 2005.
- 6. EPRI Report 105697, BWR Vessel and Internals Project, BWR Reactor Pressure Vessel Shell Weld Inspection Recommendations (BWRVIP-05), dated September, 1995.
- 7. NRC Letter, G. C. Lainas (NRC) to C. Terry (BWRVIP), Final Safety Evaluation of the BWR Vessel and Internals Project BWRVIP-05 Report (TAC No. M93925), dated July 28, 1998.
- 8. TVA letter, T. E. Abney to NRC, Browns Ferry Nuclear Plant (BFN) Unit 1 - Technical Specifications (TS) Change TS 428 -
Update of Pressure-Temperature (P-T) Curves, dated December 6, 2004.
Table 1 BFN Unit 1 Circumferential Weld Examination Relief Request Inputs and Results Relief Request 1-ISI-19 Inputs &
Result 32 EFPY NRC BWRVIP-05 SER Inputs &
Acceptance Criteria for B&W Vessels1 License Renewal Relief Evaluation Inputs &
Result 64 EFPY NRC BWRVIP-05 SER Inputs &
Acceptance Criteria for B&W Vessels1 Manufacturer B&W B&W B&W B&W Vessel Exposure to Date2 6.15 EFPY N/A N/A N/A Expected Vessel Exposure3
<14 EFPY N/A
<32 EFPY N/A Vessel Exposure Assumed for Weld Exam Relief 16 EFPY 32 EFPY 54 EFPY 64 EFPY Cu%
0.27 0.31 0.27 0.31 Ni%
0.60 0.59 0.60 0.59 Chemistry Factor 184 196.7 184 196.7 Fluence at clad/weld interface (1019 n/cm2) 0.0578 0.095 0.2 0.19 RTNDT w/o margin 58.2 °F 79.8 °F 104 °F 109.4 °F Initial RTNDT 20 °F 20 °F 20 °F 20 °F BFN Calculated Mean RTNDT 78.2 °F N/A 124 °F N/A NRC Mean RTNDT Acceptance Criteria N/A 99.8 °F N/A 129.4 °F
- 1. Reference 7.
- 2. BFN Unit 1 has been shut down since 1985.
- 3. BFN Unit 1 current license expires December 20, 2013.