ML050840343
| ML050840343 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/01/2005 |
| From: | Banerjee M NRC/NRR/DLPM/LPD3 |
| To: | Crane C Exelon Generation Co |
| Banerjee M, NRR/ADPT, 415-2277 | |
| References | |
| TAC MC5018, TAC MC5019 | |
| Download: ML050840343 (4) | |
Text
April 1, 2005 Mr. Christopher M. Crane, President and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3 (TAC NOS. MC5018 AND MC5019)
Reference:
Letter from P. Simpson (Exelon Generation Company, LLC) to the U.S. Nuclear Regulatory Commission (NRC), Main Steam Safety Valve Setpoint Tolerances and Tolerance Uncertainty Treatment Methodology, dated October 29, 2004
Dear Mr. Crane:
In the referenced letter, Exelon Generation Company, LLC (Exelon) submitted for NRC approval a tolerance uncertainty treatment methodology applied to the main steam safety and safety/relief valve setpoint test data for the Dresden Nuclear Power Station. This submittal was made to comply with a condition added to the license with NRC approval of an amendment to the technical specification that increased the number of main steam safety valves from eight to nine. This condition was added to affect the resolution of the issue of the valve lift setpont drift beyond the current TS tolerance value. While reviewing the October 29, 2004 submittal, the NRC staff came up with some questions. A draft version of these questions was compiled in a request for additional information (RAI) and transmitted to Mr. Ken Nicely of your staff via e-mail on February 9, 2005. The e-mail also provided for an opportunity for a phone call with the NRC staff in case any clarifications were sought by Exelon. As no request for a phone call has been made, I am enclosing with this letter the final RAI, which is unchanged from the draft version. I request that Exelon provide a response to the enclosed RAI by April 15, 2005.
If you have any questions, please do not hesitate to contact me (301-415-2277 or e-mail:
mxb@nrc.gov).
Sincerely,
/RA/
Maitri Banerjee, Senior Project Manager, Section 2 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-237 and 50-249
Enclosure:
As stated above cc w/encls: See next page
April 1, 2005 Mr. Christopher M. Crane, President and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3 (TAC NOS. MC5018 AND MC5019)
Reference:
Letter from P. Simpson (Exelon Generation Company, LLC) to the U.S. Nuclear Regulatory Commission (NRC), Main Steam Safety Valve Setpoint Tolerances and Tolerance Uncertainty Treatment Methodology, dated October 29, 2004
Dear Mr. Crane:
In the referenced letter, Exelon Generation Company, LLC (Exelon) submitted for NRC approval a tolerance uncertainty treatment methodology applied to the main steam safety and safety/relief valve setpoint test data for the Dresden Nuclear Power Station. This submittal was made to comply with a condition added to the license with NRC approval of an amendment to the technical specification that increased the number of main steam safety valves from eight to nine. This condition was added to affect the resolution of the issue of the valve lift setpont drift beyond the current TS tolerance value. While reviewing the October 29, 2004 submittal, the NRC staff came up with some questions. A draft version of these questions was compiled in a request for additional information (RAI) and transmitted to Mr. Ken Nicely of your staff via e-mail on February 9, 2005. The e-mail also provided for an opportunity for a phone call with the NRC staff in case any clarifications were sought by Exelon. As no request for a phone call has been made, I am enclosing with this letter the final RAI, which is unchanged from the draft version. I request that Exelon provide a response to the enclosed RAI by April 15, 2005.
If you have any questions, please do not hesitate to contact me (301-415-2277 or e-mail:
mxb@nrc.gov).
Sincerely,
/RA/
Maitri Banerjee, Senior Project Manager, Section 2 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-237 and 50-249
Enclosure:
As stated above cc w/encls: See next page DISTRIBUTION:
PUBLIC CHammer FAkstulewicz PD3-2 R/F DTerao ZAbdullahi GSuh TFord WRuland MBanerjee GHill (4), T5C3 PCoates MRing, RIII ADAMS Accession Number: ML050840343 OFFICE PM:LPD3-2 LA:LPD3-2 EMEB SC:LPD3-2 NAME MBanerjee PCoates DTerao GSuh DATE 3/31/05 3/31/05 4/01/05 4/1/05 OFFICIAL RECORD COPY
Enclosure Dresden Nuclear Power Station Units 2 and 3 Exelon Submittal dated October 29, 2004 (TAC Nos. MC5018-9)
Request for Additional information
- 1. In the October 29, 2004, submittal, the licensee used a Monte Carlo analysis method to assess the main steam safety valve setpoint uncertainty effects on the plant overpressure protection analysis. The method uses a random sampling technique to assess the effects of setpoint variation. The setpoint values are sampled individually about the mean values using variances determined by the available test data. The setpoint values are considered to be independent of each other, such that a high setpoint on one MSSV does not bias any of the other MSSV setpoints. However, operational experience at several facilities has shown that in some cases, there have been safety valves which have drifted in the upward direction due to common cause effects (e.g., due to excessive friction or bonding). A review of the Dresden and Quad Cities MSSV setpoint test data indicates there is such a common cause effect.
Specifically, it is noted that when any one MSSV had drifted high by approximately +1.75% or greater, then all other MSSVs which were tested at that time, had also drifted in the high direction (reference data from tests performed in October 1999 for Dresden and in June 1994, April 1997, and September 2001 for Quad Cities). This indicates that the proposed Monte Carlo sampling should model a bias in the positive direction when any setpoints have drifted high, above a threshold value. Please provide an analysis of the effects of common causes on the MSSV setpoint modeling.
- 2. The Target Rock safety/relief valves are found to be susceptible to common cause vibration related wear that affects its setpoint. Please indicate how this finding affects the data distribution and the uncertainty treatment methodology. Please also provide an update of the final design change including when it will be implemented and if their schedule will support implementation of the proposed overpressure analysis method.
- 3. Given that some of the test data are reflective of pre-EPU operation, please provide assurance that a necessary penalty is being applied to the methodology to account for a possible post-EPU bias.
Dresden Nuclear Power Units 2 and 3 cc:
Site Vice President - Dresden Nuclear Power Station Exelon Generation Company, LLC 6500 N. Dresden Road Morris, IL 60450-9765 Dresden Nuclear Power Station Plant Manager Exelon Generation Company, LLC 6500 N. Dresden Road Morris, IL 60450-9765 Regulatory Assurance Manager - Dresden Exelon Generation Company, LLC 6500 N. Dresden Road Morris, IL 60450-9765 U.S. Nuclear Regulatory Commission Dresden Resident Inspectors Office 6500 N. Dresden Road Morris, IL 60450-9766 Chairman Grundy County Board Administration Building 1320 Union Street Morris, IL 60450 Regional Administrator U.S. NRC, Region III 801 Warrenville Road Lisle, IL 60532-4351 Illinois Emergency Management Agency Division of Disaster Assistance &
Preparedness 110 East Adams Street Springfield, IL 62701-1109 Document Control Desk - Licensing Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Senior Vice President, Nuclear Services Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Vice President of Operations - Mid-West Boiling Water Reactors Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Vice President - Licensing and Regulatory Affairs Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Director - Licensing and Regulatory Affairs Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Associate General Counsel Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Manager Licensing - Dresden, Quad Cities and Clinton Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555