ML20212D383

Safety Evaluation Supporting Proposed Rev to Withdrawal Schedule for First & Third Surveillance Capsules for BFN-3 RPV

ML20212D383
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Site:	Browns Ferry
Issue date:	09/20/1999
From:	NRC (Affiliation Not Assigned)
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NUDOCS 9909230109
Download: ML20212D383 (4)

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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30666 4001

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%g. . . . . ,f l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST TO REVISE THE REACTOR VESSEL SURVEILLANCE CAPSULE WITHDRAWAL SCHEDULE FOR BROWNS FERRY NUCLEAR PLANT. UNIT 3 DOCKET NO. 50-296

1.0 INTRODUCTION

By letter dated April 30,1999, the Tennessee Valley Authority (TVA, the licensee) submitted, for U.S. Nuclear Regulatory Commission (NRC) approval, a proposed revision to the reactor vessel material surveillance capsule withdrawal schedule for the Browns Ferry Nuclear Plant, Unit 3 (BFN-3). The purpose of the proposed change was to account for the low fluence projection of the first capsule.

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2.0 BACKGROUND

The reactor vessel material surveillance program for BFN-3 was implemented to monitor the radiation-induced changes in the mechanical and impact properties of the pressure vessel materials. This surveillance program is discussed in the Updated Safety Analysis Report and in the NEDO-10115 Report, " Mechanical Property Surveillance of General Electric BWR i Vessels." It was established in accordance with Title 10, Code of Federal Reaulations '

(10 CFR), Part 50, Appendix H.

Appendix H to 10 CFR Part 50, " Reactor Vessel Material Surveillance Program Requirements,"

requires licensees of light water nuclear power reactors to monitor changes in the fracture I toughness properties of ferritic materials in the reactor vessel beltline reg'on. Appendix H states that the design of the surveillance program and the withdrawal schedule must meet the {

q requirements of the edition of American Society for Testing and Materials (ASTM) E 185 that is current on the itsue date of the American Society of Mechanical Engineers (ASME) Code to {

which the reactor vessel was purchased. Later editions of ASTM E 185 may be used  ;

including those editions through 1982.

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The number of surveillance capsules installed in the BFN-3 reactor pressure vessel (RPV) surveillance program is three. This number was based on ASTM E 185-66, which was the ,

edition of the ASTM standard that was in effect on the issue date of Section til of the ASME 1 Boiler and Pressure Vessel Code (1968), to which the BFN-3 reactor vessel was purchased. }

The licensee later updated the BFN-3 surveillance capsule withdrawal schedule to the 1970 i Revision of the Code (ASTM E 185 70). The NRC staff found this acceptable, since ASTM E 185-70 was a ! ster edition of the ASTM standard that was in effect on the issue date of the ASME Code, to which the BFN-3 reactor vessel was purchased. By the safety evaluation dated May 15,1989, the NRC approved TVA's request to update the withdrawal schedule, for the first capsule of the BFN-3 RPV surveillancs program, to the ASTM E 185-82 Code. The staff also found this to be acceptable because ASTM E 185-82 is also a later edition of the f

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r ASTM standard that was in effect on the issue date of the ASME Code to which the BFN-3 reactor vessel was purchased.

The surveillance capsule withdrawal schedule and testing criteria for ASTM E 185-82 depend on the range of the predicted transition temperature shift at vesselinside surface. A first case is recommended to be used when the predicted transition temperature shift at vessel inside surface is 100*F or less. A second case is mcommended to be used when the predicted transition temperature shift at vessel inside surface is less than er equal to 200 'F. Finally, a third case is recommended for use when the predicted transition temperature shift at vessel inside surface is greater than 200*F.

The first case 8s applicable to BFN-3. The first case recommends a minimum of three capsules in the surveillance program. Of those three capsules, two are recommended to be withdrawn and tested ant', the third capsule is recommended to serve as a standby capsule. The withdrawal sc'wdule for this case includes the following criterion: (1) the first capsule is recommende d to be withdrawn and tested at 6 EFPYs, or at the time when the accumulated neutron fluence of the capsule exceeds 5 x 10"n/cm 2, or at the time when the highest l predicted shift in transition temperature of all encapsulated materials is approximately 50'F, {

whichever comes first, (2) the second capsule is recommended to be withdrawn and tested at J 15 EFPYs, or at the time when the accumulated neutron fluence of the capsule corresponds to the approximate end of life (EOL) fluence at the reactor vessel inner wall location, whichev'er comes first, and (3) the third capsule is recommended to be withdrawn at not less than once or greater than twice the peak EOL vessel fluence; however, this may be modified on tne basis of previous tests, and this capsule may be held without testing following withdrawal.

4 As required by the current surveillance program, the first capsule was removed during the BFN 3 Cycle 8 refueling outage, which was completed in the fall of 1998. However, TVA has not performed the analysis of the specimens in the removed capsule, because they have ,

determined that there may not be a sufficient amount of neutron fluence to monitor the amount '

of radiation embrittlement of the surveillance materials in this capsule. Therefore, TVA has proposed a revised surveillance withdrawal schedule, as discussed below. ,

1 3.0 EVALUATION The licensee has opted to use the ASTM E 185-82 standard in determining the number of capsules to be withdrawn and the schedule of withdrawing and testing the capsules of the BFN 3 RPV surveillance program. ASTM E 185-82 recommends that three capsules be withdrawn and tested, if the predicted transition temperature shift at vesselinside surface is less than 100*F, which is applicable to BFN 3.

The estimated peak EOL fluence for BFN-3 is 0.11 x 10" n/cm2 . To date, the licensee has withdrawn one capsula for BFN-3, as stated above. The first capsule was removed from the vessel at 8 EFPYs, as specified in their current schedule. However, TVA has, since then, determined that if the current withdrawal and testing schedule of the first capsule is used, the '

measured data may not be useful, since the expected shift in RT, (predicted to be 13 'F) may not be large enough to be differentiated from the data scatter, because the predicted fluence of the capsule at 8 EFPYs (1.85 x 10" n/cm 2) is low, and the amount of copper (0.11%) in the BFN-3 capsule weld materialis low. Thus, the data obtained may not be useful for predicting material behavior, since it may be indistinguishable from the unirradiated data. 1 Accordingly, TVA has proposed to reinsert the first capsule and withdraw and test the m_

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" previous" second capsule at 18 EFPYs, which will be approximately when the accumulated neutron fluence of the capsule exceeds 5 X 10 "n/cm2and when the mean shift in RT for the weld metal is projected to be 13"F. TVA also proposed that the " previous" second capsule

- will take the place of the first capsule to be withdrawn and tested as recommended by the ASTM E 185-82 Code. TVA proposed that the " previous" third capsule will serve as the second capsule. ASTM E 185-82 recommends that the second capsule be withdrawn and tested at 15 EFPYs, or at the time when the accumulated neutron fluence of the capsule corresponds to the approximate EOL fluence at the reactor vessel inner wall location, whichever comes first. Presently, the licensee has not determined a specific withdrawal and testing schedule of the second capsule. Instead, TVA has indicated that the schedule for the second capsule will be determined after analyzing the test results of the first capsule. Finally, the licensee proposed that the " previous" first capsule, which will be reinserted, will serve as the third capsule, and therefore serve as the standby capsule, which also meets the

- recommendations of ASTM E 185-82 for the third capsule.

The staff has verified that the proposed capsule withdrawal and testing schedule for the first and third capsules of the BFN-3 RPV surveillance program are in accordance with the recommendations of ASTM E 185-82 and thus with the. requirements of 10 CFR Part 50, Appendix H. WA must submit a withdrawal schedule for the second capsule, based on the test results from the first capsule, when the result of the analysis of the first capsule becomes available, if the licensee determines that the second capsule will be withdrawn in accordance with the withdrawal and testing recommendations of the ASTM E 185-82 Code, further staff approvalis not required.

4.0 ' CONCLUSION Based on the staff's review of the TVA submittal, the staff found that the revised withdrawal schedule for the first and third surveillance capsules of the BFN-3 RPV satisfies the I

requirements of Appendix H to10 CFR Part 50, and is therefore acceptable to the staff. As indicated above, TVA is requested to provide a withdrawal and testing schedule for the second capsule. If it is determined that the second capsule will be withdrawn in accordance with the withdrawal and testing recommendations of the ASTM E 185-82 Code, staff approvalis not required.

Principal Contributor: Meena K. Khanna, NRR Date: September 20, 1999 l

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5.0 REFERENCES

1. Letter from Mr. T. E. Abney (TVA) to NRC Document Control Desk, " Browns Feny Nuclear Plant - Unit 3, License No. DPR-68, Proposed Revision to the Unit 3 Reactor Pressure Vessel Material Surveillance Program," dated April 30,1999.

2. Code of Federal Regulations, Title 10 Part 50, Appendix H, " Reactor Vessel Material Surveillance Program Requirements," dated January 1998.

3. American Society for Testing and Materials, " Standard Recommended Practice for Surveillance Tests for Nuclear Reactor Vessels," ASTM E 185-82.

4. NUREG-1511, " Reactor Pressure Vessel Status Report," dated December 1994.

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