ML20196A945
| ML20196A945 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 11/24/1998 |
| From: | Hannon J NRC (Affiliation Not Assigned) |
| To: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| References | |
| GL-97-04, GL-97-4, TAC-M99978, NUDOCS 9811300199 | |
| Download: ML20196A945 (8) | |
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l Mr. G. R. Horn November 24, 1998 Sr. Vice Pr:sid:nt of En:rgy Supply 3
Nebraska Public Power District 141415th Street Columbus, NE 68601
SUBJECT:
COOPER NUCLEAR STATION RESPONSE TO REQUEST FOR INFORMATION PERTAINING TO GENERIC LETTER 97-04, " ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS"(TAC NO.
M99978)
Dear Mr. Horn:
By letter dated August 14,1998, the Nuclear Regulatory Commission (NRC) requested additional information pertaining to the Cooper Nuclear Station Generic Letter (GL) 97-04 response. Specifically, we requested that the Nebraska Public Power District (NPPD)" provide a response within 30 days discussing how the NPPD response to GL 97-04 related to containment overpressure compares with your current licensing basis."
NPPD responded by letter dated September 22,1998. We have reviewed the NPPD letter and supporting documentation as referenced in the enclosed evaluation. Based on our review, we do not agree with the NPPD's conclusion that Cooper Nuclear Station remains within the licensing basis with regards to the current use of containment overpressure. In accordance with 10 CFR Part 50, Appendix B, Section XIV, NPPD should take prompt corrective action to address this issue. It is requested that NPPD inform the NRC within 30 days as to the course of action you plan to take and the schedule.
If there are any questions on this matter, please contact David Wigginton at (301) 41501301.
Sincerely, ORIGINAL'. SIGNED BY:
J. Hall for John N. Hannon, Director h$ b obh o$00$298 Project Directorate IV-1 p
PDR Division of Reactor Projects lil/IV Office of Nuclear Reactor Regulation
Enclosure:
As stated cc w/ encl: See next page DISTRIBUTION:
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i UNITED STATES s
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066 4001 k, n November 24, 1998 Mr. G. R. Horn Sr. Vice President of Energy Supply Nebraska Public Power District 141415th Street Columbus, NE 68601
SUBJECT:
COOPER NUCLEAR STATION RESPONSE TO REQUEST FOR INFORMATION PERTAINING TO GENERIC LETTER 97-04, " ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS * (TAC NO.
M99978)
Dear Mr. Horn:
By letter dated August 14,1998, the Nuclear Regulatory Commission (NRC) requested additional information pertaining to the Cooper Nuclear Station Generic Letter (GL) 97-04 response. Specifically, we requested that the Nebraska Public Power District (NPPD)" provide a response within 30 days discussing how the NPPD response to GL 97-04 related to containment overpressure compares with your current licensing basis."
NPPD responded by letter dated September 22,1998. We have reviewed the NPPD letter and supporting documentation as referenced in the enclosed evaluation. Based on our review, we do not agree with the NPPD's conclusion that Cooper Nuclear Station remains within the licensing basis with regards to the current use of containment overpressure. In accordance with 10 CFR Part 50, Appendix B, Section XIV, NPPD should take prompt corrective action to address this issue. It is requested that NPPD inform the NRC within 30 days as to the course of action you plan to take and the schedule.
If there are any questions on this matter, please contact David Wigginton at (301) 415-1301.
Sincerely, WM 41 hn N. Hannon, Director Project Directorate IV-1 Division of Reactor Projects Ill/IV Office of Nuclear Reactor Regulation Docket No. 50-298
Enclosure:
As stated cc w/ encl: See next page
l Mr. G. R. Hsrn l
Nebraska Public Power District Cooper Nuclear Station l
cc:
Mr. John R McPhail, General Counsel Lincoln Electric System Nebraska Public Power District ATTN: Mr. Ron Stoddard P. O. Box 499 1040 0 Street Columbus, NE 68602-0499 Box 80869 Lincoln, NE 68501 Nebraska Public Power District j
ATTN: Mr. J. H. Swailes MidAmerican Energy l
Vice President of Nuclear Energy ATTN: Dr. William D. Leech, Manager-Nuclear l
P. O. Box 98 907 Walnut Street Brownville, NE 68321 P. O. Box 657 l
Des Moines, IA 50303-0657 Randolph Wood, Director Nebraska Department of Environmental Nebraska Public Power District Control ATTN: Mr. B. L. Houston, Nuclear i
P. O. Box 98922 Licensing & Safety Manager Lincoln, NE 68509-8922 P. O. Box 98 l
Brownville, NE 68321 l
Mr. Larry Bohlken, Chairman l
Nemaha County Board of Commissioners Nemaha County Courthouse 1824 N Street Auburn, NE 68305 Senior Resident inspector U.S. Nuclear Regulaton/ Commission P. O. Box 218 Brownville, NE 68321 Regional Administrator, Region IV l
U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington,TX 76011 Lis. Cheryl Rogers, LLRW Program Manager Division of Radiological Health Nabraska Department of Health l
301 Centennial Mall, South j
P. O. Box 95007 Lincoln, NE 68509-5007 Mr. Ronald A. Kucera, Department Director i
of Intergovemmental Cooperation Department of Natural Resources P.O. Box 176 Jefferson City, MO 65102
., _. _ _ _ _ _ _. _ _ _ _ _ _ _ _. ~. _ _ _ _ _.. _. _ _ _ _ _ _ _.. _.... _
ASSESSMENT OF COOPER NUCLEAR STATION CONTAINMENT OVERPRESSURE CREDIT FOR NPSH ANALYSES
1.0 BACKGROUND
By !atter dated January 5,1998 (Reference 1), Nebraska Public Power District (District), the licensee, responded to Generic Letter (GL) 97-04 (Reference 2), " Assurance Of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps."
By letter dated August 14,1998 (Reference 3), the NRC staff requested that the District 4
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' provide a response within 30 days discussing how your response to GL 97-04 related to l
containment overpressure compares with your current I; censing basis," for Cooper Nuclear Station (CNS).
By letter dated September 22,1998 (Reference 4), the District responded to the staff's request for additional information (RAI). In their letter, the licensee stated that it was their conclusion that CNS is operating within its licensing basis related to the issue of NPSH for the ECCS pumps. This conclusion was based on the original Atomic Energy Commission (AEC) Safety Evaluation Report (SER) which noted that the CNS did not fully comply with the requirements of Safety Guide 1 (Reference 5). The Reactor Systems Branch (SRXB) does not agree with the District that CNS is still within its licensing basis since the amount of containment overpressure credit relied upon to ensure adequate NPSH has increased since the issuance of the original AEC SER (Reference 6).
2.0 QlSCUSSION in the original AEC SER dated February 4,1973, the staff made the following conclusion with regards to adequate NPSH for the ECCS pumps:
l The applicant analyzed, in Amendment 11, the availability of adequate net positive suction head (NPSH) for all ECCS pumps in conformance with Safety Guide No.1 which requires that there be no reliance on calculatedincreases in containment pressure. The most limiting case occurs during the long term transient following the design basis LOCA when one core spray and one RHR pump will be running continuously. The analysis shows that at least a 3 psimargin exists between the minimum containment pressure and the pressure required for minimum NPSH at the RHR pump and a 6 psi margin for the core spray pump. The analysis is conservative in assumptions ofinitial temperature, service water temperatures, equipment performance, leakage rates, and heat losses, resulting in a maximum suppression pool temperature of 152 *F (sic - typographical error-value should have been 192 *F). Although the design does not fully meet the guidelines of Safety Guide No.1, we have concluded that the applicant's analysis is conservative and that there should be adequate NPSH to the ECCS pumps even in the unlikely event of a LOCA.
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ENCLOSURE i
2-As described in the AEC SER, the staff found the small amount of containment overpressure that CNS was crediting acceptable based on the analysis presented in Amendment 11 (Reference 7) to the CNS Final Safety Analysis Report (FSAR). FSAR Amendment 11 responded to question 6.4 from the staff which requested the licensee to show the margin in required NPSH (NPSHR) in terms of overpressure and the time that will be available to the core standby cooling system pumps for the various amounts of equipment assumed to be operable.
The analysis provided in Amendment 11 was based on a maximum suppression pool temperature of 192 degrees Fahrenheit and a maximum service water temperature of 85 degrees Fahrenheit. However, the actual results of the analysis were provided in graphical form, and as such, the actual containment overpressure required for the RHR pumps was not discussed in the AEC SER. Amendment 11 provided the following information:
The most limiting of all the various modes occurs during the long term transient following j
a design basis loss of coolant accident when one core spray and one RHR pump will be running continuously. Figure 6.4.1 is a plot of both the minimum containment pressure required in order that the core spray and RHR pumps have adequate NPSH and a plot of the minimum containment pressure that would actually occur. At all times there.
would be atleast a 3 psimargin.
The staff notes that Figure 6.4-1 provides the NPSHR for the RHR and core spray pumps 2
starting at time greater than 10 seconds, i.e., short term requirements were not evaluated. As shown on the figure, the amount of containment overpressure required for the RHR pumps appears to be on the order of 1 psi (slightly greater than 15 psia) with no containment overpressure requirement for the core spray pumps. Although the exact amount of
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containment overpressure required for the RHR pumps was not discussed in the AEC SER nor the licensee's Amendment 11 submittal, Figure 6.4-1 did provide the amount of containment overpressure required for the RHR pumps. Therefore, CNS was licensed to credit the amount of containment overpressure depicted on Figure 6.4-1 for the RHR pumps, i.e., on the order of 1 psi, during the long term post LOCA, i.e., greater than 108 seconds.
CNS Amendment 82 (Reference 8), revised Section 3.7.A/4.7.A of the CNS Technical Specifications. Specifically, the revision increased the suppression pool temperature limit during normal operation from 90 degrees Fahrenheit to 95 degrees Fahrenheit. The staff found this change acceptable based on the General Electric (GE) analyses which demonstrated that the suppression pool local temperature will not txceed the post-accident limit of 200 degrees Fahrenheit, as specified in NUREG-0661, ' Safety Evaluation Report Mark 1 Containment Long-Term Program." The supporting GE analyses (Reference 9) used the following assumptions for the design basis accident pool temperature:
Power level = 104 percent t.1ermal power (2486 MW)
May-Witt decay heat curve Service water temperature of 84 degrees Fahrenheit RHR heat exchanger capability of 228.9 BTU /sec *F per loop Initial suppression pool temperature of 95 degrees Fahrenheit The GE analysis stated that "the results show a primary peak pool temperature of 137'F at the end of the reactor blowdown (vessel pressure = 0 psid), which is below the design basis limit of
. 170'F. The pool temperature rises to a long-term peak temperature of 184*F at - 24,000 seconds." :The staff notes that the maximum suppression pool temperature calculated by GE is less than the maximum pool temperature at the time of licensing. Additionally, in the staff SER, the staff did not evaluate the effect of the 5 degree increase in. suppression pool temperature on the NPSH requirements of the RHR and core spray pumps, but compared the events, assumptions, and results of the GE analysis to the criteria in NUREG 0783.
The CNS Updated Safety Analysis Report (USAR) discusses the current NPSH analyses for the RHR and core spray pumps in Section 5.2.6, CSCS Pumps NPSH. The current design basis suppression pool temperature analysis uses the following assumptions:
1 Power level = 102 percent thermal power ANS 5.1 decay heat model Service water temperature of 90 degrees Fahrenheit RHR heat exchanger capability of 177 BTU /sec 'F per loop initial suppression pool temperature of 95 degrees Fahrenheit
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. The maximum suppression pool temperature calculated in the current analysis is 195.9 degrees l
Fahrenheit. The results of these analyses are presented in Figure VI-5-15 of the CNS USAR.
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- The staff notes that Figure VI-5-15 provides the NPSHR for the RHR and core spray pumps, the pool temperature, and the minimum containment pressure starting at time greater than 108 seconds post LOCA. The staff notes that both the original and current NPSH analyses did not l
' evaluate the short term post LOCA, i.e., less than 103 seconds. According to the CNS GL 97-l 04 response, the current containment overpressure credit required is 3.89 psi for the RHR l
pumps and 1.11 psi for the core spray pumps at the maximum suppression pool temperature.
l This amount of containment overpressure credit is greater than the approximately 1 psi to which Cooper was originally licensed.
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There also appear to be differences in the assumptions and calculational methods used in the l
Cooper analyses from Amendment 82 to the current USAR. As discussed above, the -
1 Amendment 82 analyses assumed 104 percent thermal power, the May-Witt decay heat curve, l
service water temperature of 84 degrees Fahrenheit, and a higher RHR heat exchanger capacity, while the current analyses assume 102 percent thermal power, ANS 5.1 decay heat L
model (without a 2 sigma adder), and service water temperature of 90 degrees Fahrenheit.
The staff notes that the maximum suppression pool temperature in Amendment 82 was 184 degrees Fahrenheit while the current maximum suppression pool temperature is 195.9 degrees o
Fahrenheit. The staff believes that these differences are indicative of different containment l
'models being used to analyze the maximum suppression pool temperature. This would be l
considered to be a change in methodology.
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Based on the above discussion, the staff has concluded that Cooper is outside their licensing basis with respect to the amount of containment overpressure c,redited for the long term l
analyses of NPSH for the RHR and core spray pumps. Specifically, the staff believes that when ll Cooper was licensed, it was licensed to credit the amount of containment overpressure l
presented in Figure 6.4-1 of Amendment 11 of the Cooper FSAR. This credit was
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approximately 1 psi for the RHR pumps. Since initial licensing of the plant, Cooper has j
increased their reliance on containment overpressure. The staff defines ' increased reliance on
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. containment overpressure
- as an increase in the absolute amount of containment overpressure required to ensure adequate NPSH. The current amount of containment overpressure credited for the RHR and core spray pumps has not been reviewed and approved by the staff. The staff also believes that the plant design assumptions evaluated in the original AEC SER and Amendment 82 may not reflect the current design assumptions of the plant due to the use of new calculations and methodologies, it is on these bases that the staff concludes that Cooper's current use of containment overpressure goes beyond the licensing basis for the facility.
3.0 CONCLUSION
The staff has reviewed Cooper's GL 97-04 and RAI responses. The staff does not agree with the District's conclusions that Cooper remains within their licensing basis with regards to the current use of containment overpressure. The staff believes that when Cooper was licensed, it l
was licensed to credit the amount of containment overpressure presented in Figure 6.4-1 of Amendment 11 of the Cooper FSAR. The staff has concluded that the licensee's reliance on containment overpressure to ensure adequate NPSH for the ECCS pumps has increased in the amount credited and has not been reviewed and approved by the staff. In accordance with 10 CFR Part 50, Appendix B, Section XVI, the staff expects that the District will take prompt corrective action to restore the facility to a condition consistent with the licensing basis or to change the licensing basis.
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4.0 REFERENCES
1.
Hom, G.R., Nebraska Public Power District, to USNRC, " Response to NRC Generic Letter 97-04 Cooper Nuclear Station, NRC Docket 50-298, DPR-46," January 5,1998.
l 2.
USNRC Generic Letter 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps," October 7,1997.
3.
Hal!, J.R., USNRC, to G.R Hom, Nebraska Public Power District, " Request for l
Additional Information Related to Generic Letter 97 Cooper Nuclear Station (TAC l
No. M99978)," August 14,1998.
4.
Peckham, M.F., Nebraska Public Power District, to USNRC, " Response to NRC Generic l
Letter 97-04 Request for Additional Information Cooper Nuclear Station, NRC Docket 50-298, DPR-46," September 22,1998.
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' 5.
USNRC Safety Guide 1, " Net Positive Suction Head for Emergency Core Cooling and l
Containment Heat Removal System Pumps," November 2,1970.
6.
US Atomic Energy Commission, ' Safety Evaluation of the Cooper Nuclear Station,"
February 14,1973.
7.
Cooper Nuclear Station FSAR Question 6.4 Amendment 11 4
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' 8.
' Houston, R., USNRC, to G. Lainas, USNRC, " Proposed Change to the Technical
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Specifications for Cooper Nuclear Station Re: Suppressicn Pool Temperature Limit (TAC 48523)," April 8,1983, 9.
NEDC-24360-P, " Cooper Nuc'sar Station Suppression Pool Temperature P.esponse,"
Gener.at Electric Company, August 1981.
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