ML071340120
| ML071340120 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/06/2007 |
| From: | Catherine Haney Plant Licensing Branch III-2 |
| To: | Spina J Constellation Energy Group |
| Pickett D, NRR/DORL, 415-1364 | |
| References | |
| TAC MD4139 | |
| Download: ML071340120 (4) | |
Text
June 6, 2007 Mr. J. A. Spina, Vice President Calvert Cliffs Nuclear Power Plant, Inc.
Constellation Generation Group, LLC 1650 Calvert Cliffs Parkway Lusby, MD 20657
SUBJECT:
CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NO. 1 - PRESSURIZER SURGE, SPRAY, SAFETY, AND RELIEF NOZZLE WELD SUSCEPTIBILITY TO PRIMARY WATER STRESS CORROSION CRACKING (TAC NO. MD4139)
Dear Mr. Spina:
This letter acknowledges the receipt of information from Calvert Cliffs Nuclear Power Plant, Inc.
pertaining to the pressurizer surge, spray, safety, and relief nozzle and safe end welds at the Calvert Cliffs Nuclear Power Plant (CCNPP), Unit No. 1.
The discovery, in October 2006, of five circumferential indications in three Alloy 82/182 dissimilar metal (DM) welds on the pressurizer at the Wolf Creek Generating Station (Wolf Creek) raised safety concerns based on the size and location of the indications. At Wolf Creek, three indications were in the pressurizer surge nozzle-to-safe end weld and two separate indications were in the safety and relief nozzle-to-safe end welds. These findings also indicated that significant concerns might exist with the inspection schedules for addressing the pressurizer weld concerns issued by the industry-sponsored Materials Reliability Program (MRP), in Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139).
The Nuclear Regulatory Commission (NRC) is concerned about the pressurizer surge nozzle-to-safe end weld indications, as this is the first time that multiple circumferential primary water stress-corrosion cracking (PWSCC) indications have been identified in a weld. This condition calls into question the degree of safety margin present in past structural integrity evaluations for flawed DM welds susceptible to PWSCC, since multiple stress-corrosion cracking flaws may grow independently and ultimately grow together, significantly reducing the time from flaw initiation to leakage or rupture.
Based on discussions with the NRC staff, licensees of plants susceptible to this condition have committed to enhanced inspection frequency and reactor coolant system leakage monitoring until actions to mitigate the potential of PWSCC in the affected welds have been completed.
In your letter dated January 30, 2007 (Agencywide Documents Access & Management System (ADAMS) Accession Number ML070320127), you stated that the pressurizer surge, spray, safety, and relief nozzle-to-safe end welds containing Alloy 82/182 material have been mitigated through stress improvement at CCNPP Unit No. 1. As a result, your response adequately addresses the concerns that the NRC has at this time regarding PWSCC susceptibility of these welds.
This completes the NRC staff efforts on TAC No. MD4139 for the review associated with this issue. If you have any questions regarding this matter, please contact the CCNPP Project Manager, Douglas Pickett, at 301-415-1364.
Sincerely,
/RA/
Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-317 cc: See next page
ML071340120 OFFICE LPL1-1/PE LPL1-1/LA LPL1-1/PM CPNB CPNB/BC LPL1-1/BC D/DORL NAME DWoodyatt SLittle DPickett TLupold TChan MKowal CHaney DATE 5/31/ 07 5/31/ 07 5/31 / 07 5/31/ 07 6/01/ 07 6/05/ 07 6/06/ 07
Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2 cc:
President Calvert County Board of Commissioners 175 Main Street Prince Frederick, MD 20678 Mr. Carey Fleming, Esquire Sr. Counsel - Nuclear Generation Constellation Generation Group, LLC 750 East Pratt Street, 17th floor Baltimore, MD 21202 Mr. Jay S. Gaines Director, Licensing Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657-4702 Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 287 St. Leonard, MD 20685 Mr. R. I. McLean, Manager Nuclear Programs Power Plant Research Program Maryland Department of Natural Resources 580 Taylor Avenue (B wing, 3rd floor)
Tawes State Office Building Annapolis, MD 21401 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Ms. Kristen A. Burger, Esquire Maryland People's Counsel 6 St. Paul Centre Suite 2102 Baltimore, MD 21202-1631 Ms. Patricia T. Birnie, Esquire Co-Director Maryland Safe Energy Coalition P.O. Box 33111 Baltimore, MD 21218 Mr. Roy Hickok NRC Technical Training Center 5700 Brainerd Road Chattanooga, TN 37411-4017