ML18059B094
| ML18059B094 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 07/12/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18059B092 | List: |
| References | |
| NUDOCS 9407180229 | |
| Download: ML18059B094 (4) | |
Text
ENCLOSURE UNITED STATES NUCLEAR REGULATORY COMMISSION WASHIN~TON, D.C. 20555--0001 INTERIM SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION CONSUMERS POWER COMPANY PALISADES NUCLEAR PLANT DOCKET NO. 50-255
1.0 BACKGROUND
Appendix G, 10 CFR Part 50, and 10 CFR 50.61 contain requirements to ensure reactor vessel integrity throughout the licensed term of operation of nuclear plants. Appendix G, 10 CFR Part 50, requires that reactor vessel beltline materials have Charpy upper-shelf energy (USE) of no less than 50 ft-lb throughout the life of the vessel unless it is demonstrated (in a manner approved by the Director, Office of Nuclear Reactor Regulation) that lower values of USE will provide margins of safety against fracture equivalent to those required by Appendix G, 10 CFR Part 50.
The pressurized thermal shock (PTS) rule, 10 CFR 50'.61, establishes screening criteria that is a measure of the limiting level of embrittlement beyond which operation can not continue without further plant-specific evaluation.
In a letter to G. B. Slade of the Consumers Power Company, dated April 10, 1992, the staff provided a PTS interim safety evaluation for the Palisades plant. This evaluation indicated that based on the reported material chemistry, irradiation temperature, and neutron fluence, the Palisades plant will not reach the PTS screening criteria until well after 1995.
In a letter from G. B. Slade of the Consumers Power Company, dated August 31, 1990, the licensee provided the staff its analysis of the Palisades reactor vessel beltline materials to demonstrate their compliance with the USE requirements of Appendix G, 10 CFR Part 50.
In a letter from D. W. Rogers of the Consumers Power Company, dated February 23, 1994, the licensee provided the staff an updated PTS analysis.
- 2. O EVALUATION 2.1 PTS Analysis In the licensee's 1992 PTS evaluation, the amounts of copper and nickel were determined from measurements of weld deposits fabricated using the same heat number of weld wire as used in the fabrication of the Palisades welds.
The licensee's best-estimate values for each weld, except for the axial welds fabricated;with heat number W-5214, were the average of the data.
The licensee'o/. best-estimate values of copper and nickel for the axial welds fabricatep with heat number W-5214 were the average of all data, except the H. B.
Ro~inson, Unit 2, surveillance data was excluded.
This resulted in best,esr'imate values of 0.178 percent copper and 1.06 percent nickel for the axial welds, which were projected to reach the PTS screening* criteria in the year 2010.
However, the limiting weld was the beltline girth weld, which was*
projected to reach the PTS screening criteria in the year 2008.
The February 23, 1994, PTS evaluation by. the 1 icensee changed the best-estimate copper and nickel for the axial welds fabricated with heat number W-.5214 weld wire. Subsequent to the issuance of the April 1992 staff, interim safety evaluation, the licensee reported th~t they were unable to trace the data from one weld deposit with a measured copper content of 0.20 percent and four copper and four nickel measurements from the Indian Point, Unit 2, surveillance weld.
In addition, a surveillance weld from Oyster Creek was.
discovered to be fabricated using W-5214 weld wire.
Th~ axial welds in the Palisades reactor pressure vessel were fabricated using tandem primary electrodes and a cold nickel wire.
The licensee's revised best-estimates for the amounts of copper and nickel for the axial welds fabricated with heat number W-5214 weld wire include the H. B. Robinson, Unit 2, and Oyster Creek surveillance welds and exclude the data that could not be traced.
The revised best-estimate for the amount of copper is a weighted average in which the amount of copper is weighted as one for welds fabricated with a single electrode and the amount of copper is weighted as two for welds fabricated with tandem electrodes.
The revised best-estimate for the amount of nickel is a simple average of the nickel values. These methods produce best-estimates because nickel was added to the weld from a single spool of nickel wire and copper is added to the weld from either single or tandem spools of copper coated steel filler metal. This results in best-estimate values of 0.20 percent copper and 1.02 percent nickel.
With these best-estimate values, the axial welds fabricated with heat number W-5214 weld wire is projected to exceed the PTS screening criteria in the year 2004, which is more limiting than the girth weld discussed earlier.
The licensee plans to provide additional chemical composition, unirradiated reference temperature, unirradiated USE and surveillance data for the axial welds in the Palisades beltline by removing weld material from its retired steam generators, which were fabricated using the same heat number of weld wire as used for the axial welds in the Palisades reactor vessel beltline.
The tests for providing the additional chemical composition, unirradiated reference temperature and USE data are scheduled to be completed in October 1994.
Two surveillance capsules containing specimens from the retired steam generator weld samples could be installed as early as the next refueling outage, which is scheduled for June 1995. These capsules would be placed in accelerated neutron fluence locations. The first capsule could then be removed during the refueling outage in 1997.
The second capsule could then be removed in 1998 and test results could be obtained six months later. These tests could change the date when the Palisades reactor vessel reaches the PTS screening criteria. The NRC staff will re-assess the licensee's PTS evaluation when the new chemistry data from the retired steam generator weld samples become available in late 1994 and when the results of any additional surveillance tests become available.
3 -.
2.2 Upper-She~f Energy Evaluation The limiting materials in the Palisades. b~ltline, with r~spect to USE, are plate materials, because the welds have higher unirradiated.USE values and lower amounts of copper than the limiting plates. Regulatory Guide {RG) 1.99, Revision 2, indicates that the reduction in the USE is dependent upon the.
amount of copper in the material and the neutron fluence.
This guide recommends two methods for determining the amount of drop in USE.
One method is used when surveillance data are available and the other method when surveillance data are not available.
When surveillance data are available, as in the case of Palisades, the rate of decrease in USE should be determined by plotting the. data on Figure 2 of the guide and fitting a line ~rawn parallel to the existing lines as the upper bound of all the surveillance data.
The plates with the greatest amount of copper {0.24 percent) are plates D-3803-1, D-3803-2 and D-3803-3.
Material from plate D-3803-3 is being irradiated in Palisades surveillance capsules.
To date, two capsules with longitudinally and transversely oriented plate specimens have been irradiated and tested.
The licensee determined the rate of decrease in the USE by plotting the data from the transversely oriented test specimens on Figure 2 of RG 1.99, Revision 2, and fitting a line drawn parallel to the existing lines as the upper bound of the data.
Specimen orientation affects the unirradiated USE, but does not effect the rate of change in USE {embrittlement).
- Hence, the licensee's determination of the rate of decrease in USE was incomplete because the licensee did not use the data from the longitudinally oriented specimens.
Using all the surveillance data and following the methodology in RG 1.99, Revision 2, results in a greater rate of embrittlement than reported in the licensee's analysis.
However, a staff evaluation using all of the data to determine the rate of decrease in the USE indicates that all three plates will have upper-shelf energies greater than 50 ft-lb at the expiration of the Palisades license in the year 2007.
There are three other plates in the beltline of Palisades.
Of these three plates, the plate with the greatest amount of copper (0.19 percent) and the lowest unirradiated USE (72 ft-lb) is plate D-3804-1.
Since it has the greatest amount of copper and lowest unirradiated USE, it is the limiting plate with respect to USE.
Using the methodology in RG 1.99, Revision 2, when surveillance data is not available, the staff has determined that plate D-3804-1 is projected to have 50 ft-lb of USE at the expiration of Palisades' license in the year 2007.
3.0 CONCLUSION
S
- 1.
The data provided by the licensee indicates that the Palisades reactor vessel will reach the PTS screening criteria in the year 2004.
- However, this conclusion could change when test results from weld material removed from the Palisades retired steam generators are completed in November 1994.
- e. :
- 2.
The licensee's determination of the rate of decrease in USE ~as unacceptable because the licensee did not utilize all the surveillance data.
However, when the rate of decrease in USE is determined using the
- methodologies recommended in RG 1.99, Revision 2, all the materials in the Palisades beltline are projected to have at least 50 ft-lb of USE at the expiration of Palisades' license in the year 2007.
Principal Contributor:
B. Elliot Date:
July 12, 1994