ML20199C140

SER Accepting Request to Integrate Reactor Vessel Weld Metal Surveillance Program for Byron,Units 1 & 2 & Braidwood,Units 1 & 2 Per 10CFR50

ML20199C140
Person / Time
Site:	Byron, Braidwood
Issue date:	01/16/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20199C112	List: ML20199C109 ML20199C140
References
NUDOCS 9801290142
Download: ML20199C140 (3)

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3* 4 . UNITED STATES y NUCLEAR REGULATORY COMMISSION

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO INTEGRATION OF REACTOP PRESSURE VESSEL SURVEILLANCE PROQBAM COMMONWEALTl! EDISON COMPANY BYRON AND BRAIDWOOD STATIONS. UNITS i AND 2 DOCKET NOS. STN 50-454 STN 50-455. STN 50-456. AND STN 50-457

1.0 INTRODUCTION

By letter dated May 6,1997, as supplemented by letter of May 6,19g7, Commonwealth Edison Company (Comed), *he licensee for Byron and Braidwood Stations, submitted a request to integrate the reactor pressure vessel (RPV) weld metal surveillance programs for several plants pursuant to Title 10 of the Code of Federal Reaulations, Par 150 (10 CFR Part 50),

Appendix H,Section Ill.C. The request, if approved, would result in the integration of the RPV weld metal surveillance program for Braidwood, Units 1 and 2, and it would also result in the integration of the Byron, Units 1 and 2, RPV weld metal surveillance programs.

In an integrated surveillance program, the representative materials chosen for surveillance for a reactor are irradiated in one or more other reactors that have similar design and operating foetures. Integrated surveillance programs must be approved by the Director, Office of Nuclear Reactor Regulation on a case by-case basis. Several of the criteria which must be met to obtain approval for an integratsd program are detailed in 10 CFR Part 50, Appendix H. These criteria are discussed below.

2.0 SACKGROUND The purpose of a RPV material surveillance program is to monitor changes in the fracture toughness properties of ferritic materials in the RPV beltline region of light water nuclear power reactors which result from exposure of these materials to neutron irradiation and the thermal environment. Under the RPV surveillance program, fracture toughness test data are obtained from material specimens exposed in surveillance capsulet, which are periodically withdrawn from the RPV, The data obtained from the survel.1ance program are used as described in 10 CFR Part 50, Appendix G (fracture toughness requirements) and 10 CFR 50.61 (fracture toughness requirements for protection against pressurized thermal shock).

As discussed in 10 CFR Part 50, Appendix H, several of the criteria for approving the integration of RPV surveillance programs include:

1, The reactor in which the materials will be irradiated and the reactor for which the materials are being irradiated must have sufficiently similar design and operating features to permit accutate comparisons of the predicted amount of radiation damage.

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2. Each reador must have an rigt dosimetry program.  ;

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3. There must be i;M ammgement for data shadng between plants. l'

4. There must be a contingency plan to assure that the survoiNance program for each reactor l

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wel not be jeopardized by operation at a reduced power level or by an extended outage of another reactor from which data are expected.

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6. There must be substantisi advantages to be gained such as reduced power outages or reduced personnel exposure to radiation, as a diroot result of not requiring surveillerwe

capsules in all reactors in the set.

6. No reduction in the requirements for number of matedals to be irradiated, specimen types, or number of spoolmens po' reactor is permitted.

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The surveillance programs at Byron and Braidwood, Units 1 and 2, are currently independent.- l

, The licensee is requesting to integrate the wold metal surveillance programs of Byron, Units 1 and 2 (both surveillance wolds were fabricated using weld wire heat number 442002) and to ,

integrate the weld metal surveillance programs of Braidwood, Units 1 and 2 (both surveillance welds were fabricated using weld wire heat number 442011). The surveillance material for the i limhing base metal materials for these unho are unique to each reactor vessel (Brandwood, Unit 1  !

host number 4gD867/4gC8131 1; Braidwood, Unit 2 heat number 500102/50Cg71 1; Byron, Unit i heat number 5P.5g33; Byron, Unit 2 heat number 4gD330/4gC2g61 1). As a result, each remotor vessel will still retain a completely independent surveillance program for these materials.

3.0 EVALUATION l To support their request to integrate the wold metal surveillance programs for Braidwood, Units 1 and 2, and for Byron, Units 1 and 2 Comed addressed the criteria within the regulations for an integratoo surveillance program, as discussed below. The staffs conclusion are provided in i

Section 4.0 of this evaluationi To dem enstrate that the reactor in which the materials will be irradiated and the reactor for which the materials are being irradiated are sufficisntly similar in design and operating features to 3 t

permh accurate comparisons of the predicted amount of radiation damage, Comed assessed the simMarity in RPV design and operating features between Byron, Units 1 and 2, and between Braidwood, Units 1 and 2. This assessment evaluated, !n part, the weld wire heat, vessei

- fabricator, fabrication data, type of fuel, fuel loading pattom, fluences at end-of-license, capsule  :

locations and lead factors, vessel inlet temperatures, vessel dimension and geometry, damage rate, spectral balance, gamma heating, and irradiation temperature. Based on this asseparnent, Comed concluded that the RPV design and operating features are sufficiently similar to warrant  ;

integrating the weld metal surveillance programs orBraidwood, Units 1 and 2, and Byron, Units 1 t and 2. l To demonstrate that the reactor has an adequate dosimetry program, Comed stated that their ,

dosimetry program is consistent with the requirements of Draft Regulatory Guide DG 1053,  !

" Calculation and Dosimetry Methods for Detstmining Pressure Vessel Neutron Fluence." Comed noted, however, that previously determined fluence values for Braidwood and Byron, Units 1 and

- 2, were not determined with the more recently approved neutron cross-section libraries

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! (i.e., ENDF/B VI). However, Comed indicated that the use of the previously determined fluence values is justified based on the relatively small change anticipated from updating the neutron fluence evaluations to ENDF/B VI as a result, in part, of implementing low leakage fuel .

management. Comed stated that an update to the ENDF/li VI cross sections wiu be made by ,

Comed at the next scheduled capsule withdrawal for each set of unNs (capsule W for Byron, Unit '

1, et outage B1R08 in November 1997 and capsule W for Braidwood, UnN 1 at outage A1R07 in )

September 1998).

Since Comed owns both Byron, UnHs 1 and 2, Comed indicated that there is an adequate arrangement for data shar6ng between the plards. The identical sMustion exists for Braidwood, ,

1 Units 1 and 2.

j To demonstrate that the surveillance program for each reactor will not be jeopardized by operation at reduced power level or by an extended outage of another reactor from which data are expected, Comed indicated that all originally planned surveillance capsules will still be e tested; thereby retaining a completely independent surveillance program that will not depend on the other vessel for data, in addition, Comed indicated that no reduction in the number of materials to be irradiated, specimen types, or number of specimens per reactor was requested. l As a resuh, the surveillance program for each reactor will not be jeopardized by operation at ,

reduced power level or by an extended outage of another reactor from which the data will be '

integrated.

Comed did not request a reduction in the number of surveillance capsules in each reactor nor did  ;

it request a reduction in the number of materials to be irradiated, specimen types, or number of specimens per reactor.

In addition to the Appendix H r:quirements for integrating the surveillance program, Comed also addressed the credibility criteria for the integrated surveillance data discussed in 10 CFR 50.61.

4.0 CONCLUSION

s. As discussed above, Comed's request basically involves com*o ining the weld metal surveillance data from the two units at a site (i.e., combine Byron, Units 1 and 2 data and combine Braidwood, UnNs1 and 2 data) to assess the embrittlement trends for the RPV in both units (rather than just using the surveillance data from Unit 1 to assess the RPV in UnN 1 and the data -

from UnN 2 to assess the RPV in UnN 2). The staff concludes that this general approach is acceptable and notes that it is consistent with 10 CFR 50.61(c)(2) which indicates that licensees ,

should consider information from related surveillance programs in assessing the embrittlement of their vessel.

The analysis performed by the licensee is intended to demonstrate, in part, that the design and .

operating features for the units for which the surveillance programs are to be integrated are sufficiently similar. Based on the information provided by Comed, the staff concludes that the -

Braidwood, Units 1 and 2, weld metal surveillance data can be integrated and the Byron, Units 1 and 2, weld metal surveillance data can be integrated. The staff, however, notes the following:  ;

. this conclusion is based on the operating characteristics (i.e., irradiation environment) 1

- between the units remaining sufficiently similar. This limitation is being considered as part of the NRC-approved methodology for the Pressure Temperature Lim!ts Report (PTLR), which

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- i is currenth under staff review Therefore, this limMation does not invalidate the conclusion l that the surveillance programs can be inlograted.

the oroditety (as defined in 10 CFR 50.61) of the surveillance data was not considered in determining the acceptatety of the proposal. The creditety of the surveillance data is being considered as part of the NRC approved methodology for the PTLR, which is currenty under i staff review. Therefore, this does not invalidate the conclusion that the surveillance .

programs can be integrated. i there is a significant difference between the unirradiated reference temperature for the  !

surveillar.co wold metal (host 442002) at Byron Units 1 and UnN 2 (i.e., RTag = 30'F for

+10'F for Byron, Unit 2). As discussed in a meeting with the ,

Dyron, industry onUnN 1, and12,1 November RTag =997 (" Meeting Summary for November 12,1997, Meeting

-l Owners Group Representatives and NEl Regardir g Review of Responses to Generic Letter 92-01, Revision 1, Supplemord 1. Responses" dated November 19,1997), the staff identified ,

this as a potential issue which may resuN in rule changes; however, this finding does not j invalidate the conclusion that the surveillance programs can be integrated. e Principal Contributor: K. Karwoski l i

Date: January 16, 1998 j 9

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