ML20044G680
| ML20044G680 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/24/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20044G679 | List: |
| References | |
| NUDOCS 9306040089 | |
| Download: ML20044G680 (3) | |
Text
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ENCLOSURE t
UNITED STATES
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j NUCLEAR REGULATORY COMMISSION C
WASHINGTON, D.C. 20555-0001
+...+
h SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RESPONSE TO THE 1991 PRESSURIZED THERMAL SHOCK RULE. 10 CFR 50.61 BALTIM0RE GAS AND ELECTRIC COMPANY CALVERT CLIFFS NUCLEAR POWER PLANT. UNIT NO 2 DOCKET NO. 50-318
1.0 BACKGROUND
By letters dated December 13, 1991, and May 22, 1992, Baltimore Gas and Electric Company (the licensee), remonded to the requirements of the
~
pressurized thermal shock (PTS) rule,10 CFR 50.61, " Fracture Toughness-Requirements for Protection Against Pressurized Thermal Shock Events."
In a -
letter to the licensee dated July 15, 1992, the staff provided a safety
evaluation (SE) on the licensee's compliance with the PTS rule.
In the staff's previous SE, the staff evaluated the chemical composition of the welds and plates, surveillance material test results, irradiation temperature, and fast neutron fluence. The staff concluded that the fluence estimates are acceptable and the methodology in the PTS rule is applicable to the Calvert Cliffs Nos. I and 2 reactor vessels.
In addition, the staff concluded that Calvert Cliffs Unit No. I with a flux reduction of 50 percent beginning with Cycle 11 would reach the PTS screening criteria la 2005 and additional information on the chemical composition of welds was needed to complete the review for Calvert Cliffs 2.
In a letter dated February 16, 1993, the licensee provided additional information on the chemical composition of the welds in the Calvert Cliffs 2 reactor vessel.
2.0 EVALUATION The PTS rule establishes a screening criterion that is a measure of a limiting 6
level of embrittlement beyond which operation cannot continue without further plant-specific evaluation.
The amount of embrittlement is dependent upon the amounts of cooper and nickel in the material and neutron fluence.
The PTS rule was amended on May 15, 1991.
Paragraph (b)(2)(iv) in the amended PTS rule states, "...WT-% copper and WT-% nickel are the best-estimate values for the materials, which will normally be the mean of measured values for a plate or forging or weld samples made with the weld wire heat number that matches the critical weld.
If these values are not available, the upper limiting values given in the materials specification to which the vessel was built may be used.
If not available, conservative estimates (mean plus one standard deviation) based on generic data may be used if justification is provided." Genericdataisdefinedasdaya rom reactor vessels fabricated to the same material specification, in the sim]e ? shop and in the same time period as the vessel being evaluated.
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- 1 In our previous SE the staff determined that the licensee has sufficient information on all its welds and plates, except for weld seams 2-203-A,B,&C in the reactor vessel of Calvert Cliffs 2, to determine the amount of copper and nickel in each material. Weld seams 2-203-A,B,&C were fabricated using weld wire heat number A8746. The licensee previously reported only one heat-specific value for the amount of copper and no value for the amount of nickel.
In the latest submittal, the licensee's best estimate of the amount of copper in weld seams 2-203-A,B,&C is 0.16%, which is the sum of the heat-specific measurement and a generic standard deviation for the amount of copper. The standard deviation was determined from welds that were fabricated using weld wire from the same supplier as the weld wire used to fabricate weld seams 2-203-A,B,&C.
The welds used to determine the standard deviation were welded in the same shop and in the same time frame as the Calvert Cliffs 2 vessel.
The licensee's best estimate of the amount of nickel in weld seams 2-203-A,B,&C is 0.10%, which is the sum of a generic mean value and a generic standard deviation for the amount of nickel. The mean value and the standard deviation were determined from welds that were fabricated using the same material specification, in the same shop, and in the same time frame as the Calvert Cliffs 2 vessel.
Based on the licensee's best estimates for the amounts of cepper and nickel, weld seams 2-203-A,B,&C will be below the PTS screening criteria 20-years after the expiration of Calvert Cliffs 2 current 40-year operating license.
3.0 CONCLUSION
S a.
Although weld seams 2-203-A,B,&C have only one heat-specific value reported for the amount of copper and none for the amount of nickel, the licensee has provided sufficient information from welds that are similar to weld seams 2-203-A,B,&C to determine the best estimate values for the amount of copper and nickel in these welds. The best estimate for the amount of copper is 0.16% and the best estimate for the amount of nickel is 0.10%.
t b.
Based on the currently reported material chemistry, irradiation temperature, and neutron fluence, the Calvert Cliffs 2 reactor vessel i
will be below the PTS screening criteria 20-year after the expiration of the current 40-year operating license.
Principal Contributor:
B. Ellict Date:
May 24, 1993
Mr. Robert E. Denton May 24, 1993 r
Unit No. 2, indicates that the reactor vessel will remain below the PTS screening criteria for a period exceeding 20 years beyond its current 40-year operating license.
This completes our action related to the subject TAC number for Unit No. 2.
Sincerely,
~I original signed by:
Daniel G. Mcdonald,' Senior Project Manager Project Directorate I-1 Division of Reactor Projects - I/II Office of Huclear Reactor Regulation Enclcsure:
Safety Evaluation cc w/ enclosure:
See next page Distribution:
Docket File CVogan NRC & Local PDRs DMcDonald PDI-1 Reading OGC SVarga ACRS (10)
CMiller, Acting AD CCowgill RACapra JStrosnider, 7/D/4 BElliot, 7/D/4 n
KWichman, 7/D/4 LA:PDI-1 PM:PDI-l h k D:PDI-1 CVogan 04 DMcDonald:smm RACapra 5 14 /93 of/S$93 5 /?,9 93
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OFFICIAL RECORD COPY FILENAME: CC282505.LTR a