ML083231064
| ML083231064 | |
| Person / Time | |
|---|---|
| Site: | Boiling Water Reactor Owners Group |
| Issue date: | 11/20/2008 |
| From: | Michelle Honcharik NRC/NRR/DPR/PSPB |
| To: | Coleman D Energy Northwest |
| Michelle Honcharik, 415-1774 | |
| References | |
| TAC MD8146 | |
| Download: ML083231064 (9) | |
Text
November 20, 2008 Mr. Doug Coleman Chair, BWROG Energy Northwest Columbia Generating Station Mail Drop PE20 P.O. Box 968 Richland, WA 99352-0968
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION RE: BOILING WATER REACTOR OWNERS= GROUP (BWROG) TOPICAL REPORT (TR)
NEDC-33347P, "CONTAINMENT OVERPRESSURE CREDIT FOR NET POSITIVE SUCTION HEAD (NPSH)" (TAC NO. MD8146)
Dear Mr. Bunt:
By letter dated February 15, 2008 (Agencywide Documents Access and Management System Accession Package No. ML080520268), the BWROG submitted for U.S. Nuclear Regulatory Commission (NRC) staff review TR NEDC-33347P, "Containment Overpressure Credit for Net Positive Suction Head (NPSH)." Upon review of the information provided, the NRC staff has determined that additional information is needed to complete the review. On November 19, 2008, Fred Emerson, BWROG Project Manager and I agreed that the NRC staff will receive your response to the enclosed Request for Additional Information (RAI) questions by January 30, 2009. If you have any questions regarding the enclosed RAI questions, please contact me at 301-415-1774.
Sincerely,
/RA Michelle C. Honcharik, Senior Project Manager Special Projects Branch Division of Policy and Rulemaking Office of Nuclear Reactor Regulation Project No. 691
Enclosure:
RAl questions cc w/encl: See next page
November 20, 2008 Mr. Doug Coleman Chair, BWROG Energy Northwest Columbia Generating Station Mail Drop PE20 P.O. Box 968 Richland, WA 99352-0968
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION RE: BOILING WATER REACTOR OWNERS= GROUP (BWROG) TOPICAL REPORT (TR)
NEDC-33347P, "CONTAINMENT OVERPRESSURE CREDIT FOR NET POSITIVE SUCTION HEAD (NPSH)" (TAC NO. MD8146)
Dear Mr. Bunt:
By letter dated February 15, 2008 (Agencywide Documents Access and Management System Accession Package No. ML080520268), the BWROG submitted for U.S. Nuclear Regulatory Commission (NRC) staff review TR NEDC-33347P, "Containment Overpressure Credit for Net Positive Suction Head (NPSH)." Upon review of the information provided, the NRC staff has determined that additional information is needed to complete the review. On November 19, 2008, Fred Emerson, BWROG Project Manager and I agreed that the NRC staff will receive your response to the enclosed Request for Additional Information (RAI) questions by January 30, 2009. If you have any questions regarding the enclosed RAI questions, please contact me at 301-415-1774.
Sincerely,
/RA/
Michelle C. Honcharik, Senior Project Manager Special Projects Branch Division of Policy and Rulemaking Office of Nuclear Reactor Regulation Project No. 691
Enclosure:
RAl questions cc w/encl: See next page DISTRIBUTION:
PUBLIC RidsNrrDpr RidsNrrDprPspb RidsNrrLADBaxley RidsNrrDss PSPB Reading RidsNrrPMMHoncharik RidsOgcMailCenter RidsAcrsAcnwMailCenter Ahsan Sallman RidsNrrDssScvb Richard Lobel ADAMS ACCESSION NO.: ML083231064 NRR-106 OFFICE PSPB/PM PSPB/LA SCVB/BC PSPB/BC NAME MHoncharik DBaxley RDennig SRosenberg DATE 11/20/08 11/20/08 11/19/08 11/20/08 OFFICIAL RECORD COPY
BWR Owners= Group Project No. 691 Mr. Richard Libra Executive Vice Chair, BWR Owners= Group Exelon Generation Co, LLC 200 Exelon Way Mail Code KSA 2-N Kennett Square, PA 19348 Rick.libra@exeloncorp.com Mr. Richard Anderson BWROG, Executive Chair FPL Energy (DAEC)
Duane Arnold Energy Center 3277 DAEC Road Palo, IA 52324 richard_l_anderson@fpl.com Mr. James F. Klapproth GE-Hitachi Nuclear Energy M/C A50 3901 Castle Hayne Road Wilmington, NC 28401 james.klapproth@ge.com Mr. Joseph E. Conen, Vice Chair Regulatory Response Group BWR Owners= Group DTE Energy-Fermi 2 200 TAC 6400 N. Dixie Highway Newport, MI 48166 conenj@dteenergy.com Dennis Madison, Hatch Vice President Southern Nuclear Operating Co.
11028 Hatch Parkway North Baxley, GA 31515-2010 drmadiso@southernco.com Frederick Emerson BWROG, Project Manager Frederick.emerson@ge.com Mr. Ken A. McCall, Program Manager GE-Hitachi Nuclear Energy M/C F12 3901 Castle Hayne Road Wilmington, NC 28401 kenneth.mccall@ge.com Oscar Limpias Entergy Nuclear Northeast 1340 Echelon Parkway.
Jackson, MS 39213-8202 olimpia@entergy.com Joe Donahue Progress Energy Inc.
410 S. Wilmington St.
PEB 6A Raleigh, NC 27601-1849 joe.w.donahue@pgnmail.com Paul J. Davison Hope Creek Generating Station P.O. Box 236 Hancocks Bridge, NJ 08038 paul.davison@pseg.com Mr. Ted Schiffley Vice Chairman, BWROG Exelon Generation Co., LLC.
Cornerstone II at Cantera 4300 Winfield Road Warrenville, IL 60555 frederick.schiffley@exeloncorp.com Mr. Randy C. Bunt, Chair Regulatory Response Group Southern Nuclear Operating Company 40 Inverness Center Parkway/Bin B057 Birmingham, AL 35242 rcbunt@southernco.com 8/6/08
ENCLOSURE REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION TOPICAL REPORT (TR) NEDC-33347P, "CONTAINMENT OVERPRESSURE CREDIT FOR NET POSITIVE SUCTION HEAD (NPSH)"
BOILING WATER REACTOR OWNERS= GROUP PROJECT NO. 691 General Comment The NRC staff does not intend to include a review of the following TR items:
(a)
Section 5.0, Other Evaluations Associated with NPSH. The NRC staff expects a plant-specific risk analysis for each proposed license amendment requesting use of containment accident pressure.
(b)
Appendix C, Alternate Methods to Containment Overpressure Credit. The methods discussed in this appendix would be reviewed on a plant-specific basis.
(c)
Appendix D, Containment Overpressure Credit. The methods discussed in this appendix would be reviewed on a plant-specific basis.
These items will be reviewed, if proposed, on a plant-specific basis.
Requests for Additional information
- 1.
Please describe how the proposed approach of TR NEDC-33347P is consistent with and where it varies from the methodology set forth in Section 2 of NUREG/CR-5249, Quantifying Reactor Safety Margins. Please address the 14 steps discussed in NUREG/CR 5249. In particular, Step 3, Phenomena Identification and Ranking, Step 7 (which addresses code uncertainty), and Steps 11 to 14.
- 2.
Deleted
- 3.
Deleted
- 4.
The TR does not appear to require that a licensee using this TR to support its license amendment request use the same containment response analysis model as used in the TR (i.e., the SHEX computer code). Is it intended that approval of the TR will be limited to only SHEX? If not, please describe the proposed steps to justify use of a different containment response model. The NRC staff suggests the appropriate steps of NUREG/CR 5249.
- 5.
Discuss the impact on the proposed statistical method if a change is made to a model or models in SHEX. How would such a change affect the proposed method? For example, would the model uncertainty be reevaluated? Would the version of SHEX used for this TR be frozen?
- 6.
The term overpressure has several definitions (pressure above atmospheric, pressure above saturation, etc.), if it is to be used, please define.
- 7.
For some boiling water reactors (BWRs), main steamline isolation valve (MSIV) leakage is considered separately from containment leakage (La). In these cases, how is MSIV leakage to be considered?
- 8.
Please define the terms nominal and realistic" as used in the TR. Are they synonymous? For example:
(Section 3.1.2) For the statistical approach with realistic assumptions (Section 4.3) It is expected that the deterministic approach utilizing nominal input values will be used to calculate NPSHa For those parameters which cannot be statistically defined, will nominal, realistic, or conservative values be used?
- 9.
Section 3.1 - Submittals to the NRC on this subject have shown that the design-basis accident (DBA) loss-of-coolant accident (LOCA) does not always produce the highest peak suppression pool temperature.
- 10.
For the variables that will be included in the statistical analysis, what type of statistical distribution will be used for each? Will this be determined on a plant-specific basis? What guidance or criteria, if any, are used to determine the statistical distribution?
- 11.
Section 2.3 - This section states that when evaluating whether containment overpressure (COP) is required, the most realistic NPSHr curve available should be used.
a)
What is meant by most realistic?
b)
Why is it not necessary to consider the NPSHr uncertainty?
- 12.
Section 3.1, Page 8 - The list of conservative assumptions lists nominal decay heat plus 2-sigma as a conservative assumption. Typically, the decay heat value used is the value predicted for the most conservative conditions during an operating cycle. Please clarify.
- 13.
Section 3.1.1, Page 9 - (a) Please provide a sensitivity study similar to that in Table 3-1 for (i) mixing efficiencies, (ii) containment leakage, (iii) drywell and wetwell volumes, and (b) for the example plant used in the TR, please provide the effect on NPSHa.
- 14.
Section 3.1 - For conservative input assumption Number 6, please define the RHR
[residual heat removal] heat exchanger heat transfer factor and how it is related to the RHR heat exchanger effectiveness and Number of Transfer Units (NTU).
- 15.
Section 3.1 - For conservative input assumption Number 11, please provide responses to the following:
(a)
How is mixing thermal efficiency defined?
(b)
How is the short term time domain defined?
(c)
How is the long term time domain defined?
(d)
Why is break flow temperature lower than the drywell temperature toward the end of the short term time domain?
(e)
Why is the break flow temperature higher than the drywell temperature for the long term time domain?
- 16.
Section 3.1 - For conservative input assumption Number 12, please explain why is it conservative to assume that the containment spray droplets are in thermal equilibrium with the containment airspace before falling to the bottom of the drywell or the suppression pool?
- 17.
Section 3.3.1 - Please explain how conservatism is introduced in the last four bulleted items, i.e., Water Properties, Manual calculations, Manual Hydraulic (Head Loss) calculation methodology, and Piping Systems modeling in software used for Hydraulic (Head loss) calculations.
- 18.
Section 3.1 - Please explain why initial drywell and wetwell gas space temperature is not included in the list of conservative assumptions. Please also note that Table A-1 does list the initial drywell temperature and does not list the initial wetwell gas space temperature.
- 19.
Section 4.4, Page 20 - Item 8 states that credit may be taken for operators throttling emergency core cooling system flow. How is this action included in the analyses since the timing of the action is not specified? For pumps injecting into the vessel, how is it ensured that the flow rate is equal to or greater than that assumed in the LOCA analysis?
- 20.
Section 4.3-The TR states that the proposed method for evaluation of special events will utilize nominal input values. It goes on to state that if this approach does not show that NPSHa - NPSHr 0 then the statistical approach using mean values will be used.
a)
How is the mean determined?
b)
If the statistical approach does not show acceptable results, what is the next step?
- 21.
Section 6.1 Step 2 - In order to be consistent with Step 3, should Step 2 state without COP included rather than with COP included in second line? If not, please explain why the statement is correct.
- 22.
Section 6.1 - Steps 1 through 6 are not clear as to which approach would be the licensing basis.
The NRC staffs understanding of these steps is as follows:
First a deterministic calculation without COP is performed in order to demonstrate that NPSHa is greater than NPSHr. If this requirement is not met, the licensee will perform a deterministic analysis with COP. If this analysis does not yield an acceptable result (NPSHa NPSHr) then a statistical analysis without COP is performed. If this analysis gives an acceptable result (NPSHa NPSHr), then the assumption is made that the deterministic analysis using COP is acceptable. If the statistical analysis without COP is not acceptable (NPSHa NPSHr) then a statistical analysis is done with COP. If this analysis is not acceptable, then plant-specific measures would be necessary based on alternative methods such as those of Sections 5.1 and 5.2 of NEDC-33347P.
Please confirm that the above description is consistent with the intent of the TR.
- 23.
Section 6.1 Item 1.a - The acceptance criterion for the deterministic calculation states that the calculated wetwell pressure should be greater than the wetwell pressure required for adequate (available) NPSH such that the wetwell pressure credit granted in the licensing basis minimizes the likelihood of having to seek additional ad hoc regulatory relief.
The NRC staff approach to this issue (used in recent extended power uprate (EPU) reviews and intended for future use) is that an analysis is acceptable if the pressure required for adequate available NPSH is less than the calculated accident pressure. No amount of wetwell pressure is granted. Therefore, the quoted words above are not needed. The LOCA calculation of accident pressure and the pressure required for adequate available NPSH should be calculated conservatively. The special events may be calculated with realistic input.
- 24.
Section 6.1 Item 1.b - Acceptance criterion b. states that a possible duration of the time that the wetwell pressure should be shown to be available may be the maximum coping time after which assured cooling sources other than the suppression pool will be available for core and containment cooling.
(a)
For the LOCA, which is a DBA, why should not only safety related water sources and systems be credited?
(b)
For the special events, the assumptions in the analysis about the use of other equipment must be consistent with emergency or abnormal operating procedures.
- 25.
Section 6.1 Item 3 a)
Why is this step used only to justify that the deterministic approach is acceptable?
b)
If NPSHa is greater than NPSHr using the statistical approach without COP included, why is this not the licensing basis?
c)
If use of the deterministic approach as the licensing basis depends on the results the statistical analysis, is not the statistical analysis included in the licensing basis?
d)
Why is not the 95/95 criterion stated?
- 26.
Section 6.2 Step 3 of Section 6.1 states that if NPSHa is greater than NPSHr using the statistical approach without COP included, then credit for deterministic COP from Step 1 is justified. In order to maintain this justification, do not Title 10 of the Code of Federal Regulations Part 50 Appendix B requirements have to apply? Therefore, is not configuration control still needed?
- 27.
Section 6.1 Item 4.a - The acceptance criterion states that the calculated 95/95 wetwell pressure (Pww) using the statistical method with COP included should be greater than the wetwell pressure required for adequate NPSH such that the wetwell pressure credit granted in the licensing basis minimizes the likelihood of having to seek additional ad hoc regulatory relief.
The NRC staff approach to this issue (used in recent EPU reviews and intended for future use) is that an analysis is acceptable if the pressure required for adequate available NPSH is less than the calculated accident pressure. No amount of wetwell pressure is granted. Therefore, the quoted words above are not needed.
- 28.
Section 6.1 Item 4.b - The acceptance criterion states that the calculated mean wetwell pressure (Pww) using the statistical method with COP included should be greater than the wetwell pressure required for adequate NPSH such that the wetwell pressure credit granted in the licensing basis minimizes the likelihood of having to seek additional ad hoc regulatory relief.
The NRC staff approach to this issue (used in recent EPU reviews and intended for future use) is that an analysis is acceptable if the pressure required for adequate available NPSH is less than the calculated accident pressure. No amount of wetwell pressure is granted. Therefore, the quoted words above are not needed.
- 29.
Section 6.1 Item 5 - Credit for acceptable operation of a pump in cavitation should comply with Positions 1.3.1.3 and 2.1.1.3 of Regulatory Guide 1.82 Revision 3 which discusses an approach acceptable to the NRC staff.
- 30.
Section 6.1 Item 6 - A risk assessment in support of using COP in determining the available NPSH of a pump should be plant-specific.
- 31.
Section 2.2, Page 5 states that the statistical analysis uses certain inputs, each based on randomly generated factor applied to their input exceedance probability.
a)
Please describe how these inputs were chosen and compare the method of selection with the phenomenon importance ranking table (PIRT) process described in NUREG/CR 5249 if not addressed in RAI 1.
b)
Explain why the exceedance probability is used.
- 32.
Section 2.3 lists the outputs from the Monte Carlo calculation. One of these is the time step distribution. Please explain the significance of this output. How is it used or interpreted?
- 33.
Section 3.1, Page 8 - Other conservative assumptions are typically included in deterministic analyses. These include minimum flow rates for service water and suppression pool water through the RHR heat exchangers, the worst single failure, wetwell (air space) volume maximized, passive heat sinks modeled to maximize heat transfer from the containment atmosphere to the heat sinks, etc. Is the list presented in the TR meant to be complete for an acceptable calculation? If so, would these other variables be realistic values?
- 34.
Section 2.3 states that when evaluating if COP is required, the most realistic NPSHr should be used. Does this mean the 3 percent value? If not, please explain what is meant by the realistic NPSHr value.
- 35.
Section 3.1, Page 8 - Other conservative assumptions are typically included in deterministic analyses. These include minimum flow rates for service water and suppression pool water through the RHR heat exchangers, the worst single failure, wetwell volume maximized, passive heat sinks modeled to maximize heat transfer from the containment atmosphere to the heat sinks, etc. Is the list presented in the TR meant to be complete for an acceptable calculation?
- 36.
Section 7.0. A discussion of the acceptability of NPSHr values used should be included in individual license amendment requests if based on other than 3 percent or 1 percent head drop values.