ML073450032
| ML073450032 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 12/19/2007 |
| From: | Stang J NRC/NRR/ADRO/DORL/LPLII-1 |
| To: | Gordon Peterson Duke Power Co |
| Stang J, NRR/DORL, 415-1345 | |
| References | |
| GL-04-002 | |
| Download: ML073450032 (5) | |
Text
December 19, 2007 Mr. G. R. Peterson Vice President McGuire Nuclear Station Duke Power Company LLC 12700 Hagers Ferry Road Huntersville, NC 28078
SUBJECT:
MCGUIRE NUCLEAR STATION, UNIT 2 - GENERIC LETTER 2004-02, APOTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS,@
EXTENSION REQUEST APPROVAL
Dear Mr. Peterson:
By letter dated February 9, 2007, Duke Power Company LLC (the licensee), requested an extension to the December 31, 2007, completion deadline for Generic Letter 2004-02, APotential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors,@ corrective actions for sump clogging issues at McGuire Nuclear Station, Unit 2 (McGuire 2). The Nuclear Regulatory Commission (NRC) staff has reviewed the licensees request. Based on the review, the NRC staff has concluded it is acceptable to extend the completion date for the installation of the replacement screens and strainer for McGuire 2 until the completion of the upcoming spring 2008 refueling outage scheduled to begin on March 1, 2008. Enclosed is the NRC staffs safety evaluation.
Sincerely,
/RA/
John Stang, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-370
Enclosure:
Safety Evaluation cc w/encl: See next page
December 19, 2007 Mr. G. R. Peterson Vice President McGuire Nuclear Station Duke Power Company LLC 12700 Hagers Ferry Road Huntersville, NC 28078
SUBJECT:
MCGUIRE NUCLEAR STATION, UNIT 2 - GENERIC LETTER 2004-02, APOTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS,@
EXTENSION REQUEST APPROVAL
Dear Mr. Peterson:
By letter dated February 9, 2007, Duke Power Company LLC (the licensee), requested an extension to the December 31, 2007, completion deadline for Generic Letter 2004-02, APotential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors,@ corrective actions for sump clogging issues at McGuire Nuclear Station, Unit 2 (McGuire 2). The Nuclear Regulatory Commission (NRC) staff has reviewed the licensees request. Based on the review, the NRC staff has concluded it is acceptable to extend the completion date for the installation of the replacement screens and strainer for McGuire 2 until the completion of the upcoming spring 2008 refueling outage scheduled to begin on March 1, 2008. Enclosed is the NRC staffs safety evaluation.
Sincerely,
/RA/
John Stang, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-370
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION: Public RidsAcrsAcnwMailCenter LPL2-1 R/F RidsNrrDorlLpl2-1 (EMarinos)
RidsNrrPMJStang (hard copy)
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RidsNrrLAMO=Brien (hard copy)
RidsNrrDorlDpr RidsNrrDssSsib (SSmith)
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RidsOgcRp Accession Number ML073450032
- SE by memo dated OFFICE NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/SSIB/BC NRR/LPLC/BC NAME JStang MO=Brien MScott*
EMarinos DATE 12/19 /07 12/19 /07 05/ 23 /07 12/19/07 OFFICIAL RECORD COPY
McGuire Nuclear Station, Units 1 & 2 cc:
Vice President McGuire Nuclear Station Duke Power Company, LLC 12700 Hagers Ferry Road Huntersville, NC 28078 Associate General Counsel and Managing Attorney Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, North Carolina 28202 County Manager of Mecklenburg County 720 E. Fourth St.
Charlotte, NC 28202 Regulatory Compliance Manager Duke Energy Corporation McGuire Nuclear Site 12700 Hagers Ferry Road Huntersville, NC 28078 Senior Resident Inspector U.S. Nuclear Regulatory Commission 12700 Hagers Ferry Road Huntersville, NC 28078 Mecklenburg County Department of Environmental Protection 700 N. Tryon St Charlotte, NC 28202 Vice President Customer Relations and Sales Westinghouse Electric Company 6000 Fairview Road, 12th Floor Charlotte, NC 28210 NCEM REP Program Manager 4713 Mail Service Center Raleigh, NC 27699-4713 Assistant Attorney General NC Department of Justice P.O. Box 629 Raleigh, NC 27602 Manager Nuclear Regulatory Issues &
Industry Affairs Duke Energy Corporation 526 S. Church St.
Mail Stop EC05P Charlotte, NC 28202 Division of Radiation Protection NC Dept of Environment, Health & Natural Resources 3825 Barrett Dr.
Raleigh, NC 27609-7721 Owners Group (NCEMC)
Duke Energy Corporation 4800 Concord Road York, SC 29745 Group Vice President, Nuclear Generation
& Chief Nuclear Officer P.O. Box 1006-EC07H Charlotte, NC 28201-1006 Senior Counsel Duke Energy Carolinas, LLC 526 South Church Street - EC07H Charlotte, NC 28202
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO EVALUATION OF EXTENSION FOR THE COMPLETION OF ISSUES ASSOCIATED WITH GENERIC LETTER 2004-02 DUKE POWER COMPANY LLC MCGUIRE NUCLEAR STATION, UNIT 2 DOCKET NO. 50-370 By letter dated February 9, 2007 (Agencywide Documents Access and Management System Accession No. ML070520392), Duke Power Company LLC (the licensee), requested corrective actions associated with Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors," dated September 13, 2004, be extended for McGuire Nuclear Station, Unit 2 (McGuire 2) from December 31, 2007, until the spring 2008, refueling outage (designated 2EOC18). This outage is scheduled to start on March 1, 2008.
The licensee stated in its February 9, 2007, letter, that in 2006, during the McGuire 2 fall refueling outage (RFO), it had already replaced the Unit 2 sump screen with a significantly larger one of new design having approximately 1045 square feet of surface area. This replaced the old strainer, which had only 135 square feet of surface area. In addition to the work on the strainer, the licensee replaced 12 panels of Microtherm insulation that had been installed on the reactor head, with reflective metal insulation (RMI). The licensee also stated that the insulation replacement eliminated the worst type of debris associated with potential sump strainer blockage.
Further, the licensee stated in its February 9, 2007, letter, that the vendor design of the strainer had weaknesses identified during the modification review process in 2006. Due to the small size of the plant=s containment, accessibility to some areas is overly restricted by the original design.
Thus, a redesign was required. The redesign required resizing the final strainer area from about 2000 square feet to 1640 square feet. About 595 square feet of strainer are to be installed during the spring 2008 RFO. This will supplement the 1045-square-foot strainer that was already installed at McGuire 2. In addition, the licensee wants to ensure that current uncertainties in the nuclear industry concerning the magnitude of chemical effects are addressed in the final design. The licensee desired to account for these remaining issues in the design prior to installing the final modification. The final design of the final sump strainer was completed in October 2007.
In its February 9, 2007, letter, the licensee described the following mitigative measures accomplished at McGuire 2:
Twelve panels of Microtherm insulation were removed from the reactor head and replaced with reflective metal insulation to reduce particulate loading on the sump strainer; and A 1045-square-foot strainer was installed in place of the original 135-square-foot strainer.
This is a partial implementation of the final strainer of about 1640 square feet.
The licensee has performed a probabilistic risk assessment (PRA) that considered the effects of delaying the implementation of the sump strainer modification at McGuire 2 until its spring 2008 outage. The licensee stated that the PRA is conservative because it takes no credit for actual available net positive suction head (NPSH) margin that exists at the plant, gives only modest credit for operator mitigative actions in response to loss of emergency core cooling system (ECCS) during a loss-of-coolant accident, gives only modest credit for previous compensatory actions taken by the plant in response to GL 2004-02, and includes conservative assumptions regarding the potential for sump blockage. The results of the PRA indicate that the increase in core damage frequency of extending the modification until the spring 2008 RFO is less than 1E-6.
The licensee stated that it has already implemented the following compensatory measures:
Several actions have been implemented to ensure containment cleanliness. These actions include provisions for cleanliness during containment close-out following RFOs and for at-power entries into containment. The procedures require extensive cleaning of the lower levels of containment and localized wash downs in other areas. Other inspections identify foreign material inside containment and remove it as necessary.
Also, material accountability logs are maintained in MODES 1 through 4 for items taken into containment; The coating program maintains 80 percent of containment coatings as Service Level 1 (qualified); and Guidance is provided to operators for continuous monitoring of sump clogging problems during recirculation including appropriate response to both trains of ECCS and containment spray, (CS) being affected by the blockage. In addition, refueling water storage tank make-up is initiated following ECCS and CS transfer to recirculation. The step to secure a CS pump when it is no longer needed to mitigate an event was relocated to earlier in the procedure for event response. Most recently, the licensee implemented a procedure change to manually start a containment air return fan to enhance flow through the ice condenser.
Based on its review, the NRC staff concludes that the licensees plans for the sump modification will result in the installation that will provide acceptable strainer function with adequate margin for uncertainties. Further, the NRC staff has concluded that the licensee has put mitigation measures in place to adequately reduce the risk for the requested short extension period.
Therefore, the NRC staff finds it acceptable to extend the completion date for the corrective actions for the issues associated with GL 2004-02 until the completion of the McGuire 2 spring 2008 refueling outage, currently scheduled to begin on March 1, 2008. Should the licensee elect to begin the McGuire Unit 2 outage more than 30 days after March 1, 2008, the licensee will need to provide the NRC with additional justification for further delay in completing corrective actions associated GL 2004-02.
Principal Contributor: Steve Smith Date: December 19, 2007