ML051360278
| ML051360278 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 06/16/2005 |
| From: | Uhle J NRC/NRR/DLPM |
| To: | Crane C Exelon Generation Co, Exelon Nuclear |
| Holden C | |
| References | |
| TAC MC6975, TAC MC6976 | |
| Download: ML051360278 (5) | |
Text
June 16, 2005 Mr. Christopher M. Crane President and Chief Nuclear Officer Exelon Nuclear Exelon Generation Company, LLC 200 Exelon Way, KSA 3-E Kennett Square, PA 19348
SUBJECT:
PEACH BOTTOM ATOMIC POWER STATION, UNITS 2 AND 3 - USE OF ALTERNATE SOURCE TERM (TAC NOS. MC6975 AND MC6976)
Dear Mr. Crane:
By letter dated July 14, 2003, as supplemented on March 15, April 23, May 20, December 8, and December 17, 2004, and again on January 21, 2005, you applied for an amendment to the Peach Bottom Atomic Power Station, Units 2 and 3 (Peach Bottom), Technical Specifications (TSs). The proposed changes would have reflected the use of an alternate source term (AST).
In a telephone call on April 29, 2005, we informed members of your staff that we would not be able to approve the requested amendment as justified by your application and its supplements.
As a result of this telephone call, you withdrew your amendment request by letter dated May 10, 2005. In your withdrawal letter you stated that you intend to submit another AST amendment request in the future. The purpose of this letter is to inform you of some of the problems we encountered with your first amendment request.
Your original proposed change would have revised Surveillance Requirement 3.6.1.3.14 to increase the allowable limit for the combined leakage rate for all main steam isolation valve (MSIV) leakage paths. The current allowable limit is less than or equal to 11.5 standard cubic feet per hour (scfh) for each MSIV when tested at greater than or equal to 25 pounds per square inch gauge. Your proposal would have increased this limit to less than or equal to 150 scfh for all four main steamlines and less than or equal to 75 scfh for any one main steamline.
Exelon supported these proposed changes by re-evaluating the design-basis loss-of-coolant accident (LOCA). During a design-basis LOCA, fission products are postulated to be released from the damaged core. For boiling-water reactors, the MSIVs have design leakage that may result in a radioactivity release. Regulatory Guide 1.183, Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors, Appendix A, Regulatory Position 6, provides methods acceptable to the NRC staff for modeling the MSIV leakage.
Regulatory Position 6 states that reduction of the amount of released radioactivity by deposition and plateout on steam system piping upstream of the outboard MSIVs may be credited, but the amount of reduction in concentration allowed will be evaluated on an individual case basis.
Generally, the model should be based on the assumption of well-mixed volumes, but other models, such as a slug flow model, may be used if justified. The Nuclear Regulatory Commission (NRC) staffs position is that the March 26, 1991, Letter Report entitled MSIV Leakage Iodine Transport Analysis, and NEDC-31858P, Revision 2, BWROG Report for Increasing MSIV Leakage Limits and Elimination of Leakage Control Systems, September 1993, provide guidance on acceptable models. The staff has also accepted a methodology
C. Crane based upon our Assessment of Radiological Consequences for the Perry Pilot Plant Application Using the Revised (NUREG-1465) Source Term, (AEB 98-03).
Peach Bottom proposed an aerosol deposition model based upon the well-mixed model in AEB 98-03, and an elemental iodine plateout model based upon the Cline Method. While the aerosol model that you proposed is based upon the AEB 98-03 model, it extends the AEB model in a nonconservative manner that is not acceptable to the NRC staff. Specifically, the NRC staff believes that the use of a single deposition velocity over almost the entire length of the main steamline piping overestimates the radioactive deposition in the piping. Aerosol deposition modeled in the main steamline piping is dominated by gravitational settling. In the AEB 98-03 model, the deposition in the pipe is dependent upon such factors as the area and volume of the well-mixed region, and the settling velocity. The AEB 98-03 model used an equation dependent upon parameters such as aerosol density and aerosol diameter to determine the settling velocity.
The AEB 98-03 study calculated the 50th percentile or median value and applied this value to three zones (segments of pipes) in two steamline pipes. The AEB 98-03 study modeled the two steam pipes in the following manner: (1) The first zone of the unbroken pipe is the length of pipe between the reactor vessel and the first MSIV, (2) The second zone in this pipe is the length of pipe between the first MSIV and the second MSIV, and (3) In the postulated broken pipe the single zone modeled is between the first and second MSIV.
The proposed Peach Bottom model also modeled two steam pipes, but added two additional zones. For the unbroken pipe, the added zone is outboard of the second MSIV. For the postulated broken pipe the added zone is also outboard of the second MSIV. Peach Bottom used the 50th percentile settling velocity from the AEB 98-03 study for all zones.
The settling velocity in the pipe is dependent upon aerosol density and aerosol diameter.
These aerosol characteristics change due to deposition along the pipe. The size distribution changes along the length of the pipe as the particle size becomes smaller in the downstream zones; thus, aerosol removal becomes more difficult as the more easily deposited particles are removed upstream and, as the aerosol is removed, the aerosol density decreases. Peach Bottom's two additional nodes, beyond those modeled in the AEB 98-03 study, and the use of a median deposition velocity constant does not adequately account for the changes in aerosol size and density. While the AEB 98-03 study also used a constant deposition velocity, using this velocity over three zones does not impose the error that using a constant velocity over five zones does. By adding the two nodes and not accounting for changes in aerosol size and density, the Peach Bottom deposition model is not conservative. Your application and its supplements did not provide adequate justification for the use of this model.
The NRC staff also had problems with other aspects of the Peach Bottom model. For example, Peach Bottom used average bulk temperatures in the drywell and wetwell to calculate the leak flow rate from the reactor to the first MSIV following a loss of coolant accident. The gas temperatures at the entrance of the steamline are higher than the average bulk temperature used. The ideal gas law shows that the volumetric leak rate will increase as temperature is increased; therefore, use of the average temperature non-conservatively underestimates the leak rate of the gas in the steamline. This underestimation of leak rate leads to an underestimation of on site and off site doses.
C. Crane We understand that you would like to meet with our technical staff to discuss your upcoming AST application. I encourage such a meeting. Please contact the Project Manager, George Wunder, at (301) 415-1494 to arrange this meeting.
Sincerely,
/RA/
Jennifer Uhle, Acting Director Project Directorate I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-277 and 50-278 cc: See next page
ML051360278 OFFICE PM/PD1-2 LA/PD1-2 SC/PD1-2 DLPM/DD D/PD1 (A)
NAME GWunder SLittle for MOBrien REnnis for DRoberts CHolden JUhle DATE 6/9/05 6/9/05 6/9/05 6/15/05 6/16/05 C. Crane Peach Bottom Atomic Power Station, Unit Nos. 2 and 3 cc:
Site Vice President Rich Janati, Chief Peach Bottom Atomic Power Station Division of Nuclear Safety Exelon Generation Company, LLC Bureau of Radiation Protection 1848 Lay Road Department of Environmental Protection Delta, PA 17314 Rachel Carson State Office Building P.O. Box 8469 Associate General Counsel Harrisburg, PA 17105-8469 Exelon Generation Company, LLC 4300 Winfield Road Board of Supervisors Warrenville, IL 60555 Peach Bottom Township 545 Broad Street Ext.
Plant Manager Delta, PA 17314-9203 Peach Bottom Atomic Power Station Exelon Generation Company, LLC Mr. Richard McLean 1848 Lay Road Power Plant and Environmental Delta, PA 17314 Review Division Department of Natural Resources Regulatory Assurance Manager B-3, Tawes State Office Building Peach Bottom Atomic Power Station Annapolis, MD 21401 Exelon Generation Company, LLC 1848 Lay Road Dr. Judith Johnsrud Delta, PA 17314 National Energy Committee Sierra Club Resident Inspector 433 Orlando Avenue U.S. Nuclear Regulatory Commission State College, PA 16803 Peach Bottom Atomic Power Station P.O. Box 399 Manager-Financial Control & Co-Owner Delta, PA 17314 Affairs Public Service Electric and Gas Company Regional Administrator, Region I P.O. Box 236 U.S. Nuclear Regulatory Commission Hancocks Bridge, NJ 08038-0236 475 Allendale Road King of Prussia, PA 19406 Manager Licensing-Peach Bottom Atomic Power Station Mr. Roland Fletcher Exelon Generation Company, LLC Department of Environment 200 Exelon Way, KSA -3E Radiological Health Program Kennett Square, PA 19348 2400 Broening Highway Baltimore, MD 21224 Correspondence Control Desk Exelon Generation Company, LLC P. O. Box 160 Kennett Square, PA 19348
C. Crane Peach Bottom Atomic Power Station, Unit Nos. 2 and 3 cc:
Vice President - Licensing and Regulatory Affairs Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Vice President-Operations Mid-Atlantic Exelon Generation Company, LLC 200 Exelon Way, KSA 3-N Kennett Square, PA 19348 Senior Vice President, Nuclear Services Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Director-Licensing and Regulatory Affairs Exelon Generation Company, LLC 200 Exelon Way, KSA 3-E Kennett Square, PA 19348