ML20135C453
| ML20135C453 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/03/1996 |
| From: | Mcdonald D NRC (Affiliation Not Assigned) |
| To: | Kenyon B NORTHEAST UTILITIES SERVICE CO. |
| References | |
| TAC-M96355, NUDOCS 9612060310 | |
| Download: ML20135C453 (6) | |
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k UNITED STATES s
j NUCLEAR REGULATORY COMMISSION r
WASHINGTON, D.C. so66M001 December 3, 1996 Mr. B. D. Kenyon President - Nuclear Group i
l Northeast Utilities Service Company l
c/o Mr. Terry L. Harpster Director - Nuclear Licensing Services l
P.O. Box 128 Waterford, CT 06385 l
SUBJECT:
10 CFR 50.46 LARGE BREAK LOSS-0F-COOLANT ACCIDENT EVALUATION MODEL l
FOR MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2, REQUEST FOR ADDITIONAL INFORMATION (TAC NO. M96355)
Dear Mr. Kenyon:
In our letter of October 11, 1996, we informed you about the problems that we l
had identified concerning changes in the large break loss-of-coolant accident (LBLOCA) evaluation model of Siemens Power Corporation (SPC) for pressurized water reactors (PWRs) to comply with 10 CFR 50.46. The changes to the 1986-approved LBLOCA evaiuation model were to correct an error of nonphysical l
behavior in the prediction of heat transfer coefficients during core reflood.
The range-of-concern for core reflood rates following the LBLOCA is for rates of 1 "/sec to 1.77 "/sec. The 1986 model predicted a peak in the heat transfer coefficients uithin this range, but then the nonphysical behavior of l
decreases coefficients with reficad rates increasing.
The SPC 1991 model, l
which was also discussed in the October 11, 1996, letter, is not an acceptable LBLOCA model.
We stated in the letter that the 1986 model had an unacceptable error and l
requested, in accordance with 10 CFR 50.46(a)(3)(ii), that you assess the impact of the model error and changes, and take whatever actions are required to assure compliance with 10 CFR 50.46 for the Millstone Nuclear Power Station, Unit No. 2.
You were also requested to attend a public meeting on October 16, 1996, at the Nuclear Regulatory Commission (NRC) headquarters to present the results of the assessment of the peak cladding temperature (PCT) for the LBLOCA and the corrective actions and compensatory measures that have been undertaken, both short-term and long-term, to demonstrate compliance with l
10 CFR 50.46. An acceptable short-term measure would be to use a demonstrably conservative reflood heat transfer coefficient model; an acceptable long-term measure must be to eliminate the nonphysical behavior from the model.
In both i
cases, the model must comply with Appendix K of 10 CFR Part 50. The summary of the October 16 meeting was issued on November 5,1996.
l You submitted a letter dated October 25, 1996, documenting Northeast i
Utilities' assessment of the PCT for the LBLOCA and the corrective actions l
that have been undertaken for both short-term and long-term, which you had previously presented at the October 16 meeting for Millstone Nuclear Power Station, Unit No. 2.
You stated in the letter that the PCT for the 1986 model without limiting the reflood heat transfer coefficients within the above range i
of concern is 1927'F and with the reflood heat transfer coefficients limited 9612060310 961203 PDR ADOCK 05000336 P
Mr. B. D. Kenyon,
to no greater than that corresponding to a reflood rate of 1.77 "/sec is 1950*F. Based on these values, you concluded that operation of the Millstone Nuclear Fower Station, Unit No. 2, would be in compliance with 10 CFR 50.45.
i You also indicated that we had requested, during the October 16 meeting, that you submit the data to justify the conservatism of the reflood heat transfer i
coefficients used in the 1986 model. You noted that the data would not be submitted in the near-term because the Millstone Nuclear Power Station, Unit No. 2, is currently in an extended plant shutdown, but further indicated that you would work with SPC and the NRC staff in order to resolve this issue.
You did not reference a conference call held on October 23, 1996, in your letter. During that conference call, SPC provided clarification on the conservatism in the 1986 model that it presented during the October 16 4
meeting. We were informed by SPC that the 1986 model was not as conservative,
~
4 with respect to the measured heat transfer coefficients, as SPC had presented at the October 16 meeting. During the meeting, the discussion was on the use of a " modified" 1986 model that, for the reflood range-of-concern, capped the heat transfer coefficients at the coefficient value of 1.77 "/sec to correct the error. Based on the data provided by SPC during the meeting, which indicated significant conservatism in the modified 1986 model, we determined that the licensees involved had taken those actions required by 10 CFR 50.46 to allow continued plant operation. However, we requested that the licensees submit all the data that shows the modified 1986 model is conservative over the entire range of reflood rates of concern so that we could review the data j
in determining an acceptable correction to the error in the 1986 model.
Based on the new information provided during the conference call, we have concluded that " capping" the reflood heat transfer coefficient in the range-of-concern at a value of 1.77 "/sec, the reflood rate has not been demonstrated to be conservative. The staff has informed SPC that the non-physical error in the 1986 model must be c?rrected using a method that is demonstrably conservative. SPC has indicated that it intends to submit this correction before the end of December 1996.
Because Millstone Nuclear Power Station, Unit 2, is currently in an extended shutdown, a revised LBLOCA model is not needed at this time to show compliance with 10 CFR 50.46; however, prior to power operation of the unit, Northeast Utilities must submit an analysis using an acceptable LBLOCA model of the heat 1
transfer coefficient correlation and data to justify that the LBLOCA model for the unit is conservative for the reflood range-of-concern. Therefore, prior i
to restart of Unit 2, we request that you (1) submit data to justify an LBLOCA evaluation model that is conservative for heat transfer coefficients over the entire range of reflood rates during an LBLOCA, including 1 "/sec to 1.77
"/sec, (2) reanalyze the LBLOCA for the unit using the evaluation model i
Mr. B. D. Kenyon '
2 proposed in item (1), and (3) provide us the information requested in the enclosure. We further request your commitment to provide this information to j
the staff at least one month before the restart of the Unit 2.
Sincerely, 4
e
- h.
Daniel G. Mcdonald, Senior Project Manager Special Projects Office - Licensing Office of Nuclear Reactor Regulation l
Docket No. 50-336
Enclosure:
Request for Additional Information cc w/ encl:
See next page i
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1 Mr. B. D. Kenyon December 3, 1996 proposed in ites (1), and (3) provide us the information requested in the enclosure. We further request your commitment to provide this information to I
the staff at least one month before the restart of the Unit 2.
Sincerely, Original signed by:
Daniel G. Mcdonald, Senior Project Manager
~ Special Projects Office - Licensing Office of Nuclear Reactor Regulation Docket No. 50-336 1
Enclosure:
Request for Additional Information i
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REQUEST FOR ADDITIONAL INFORMATION 10 CFR 50.46 LARGE BREAK LOSS-OF-COOLANT ACCIDENT (LBLOCA) EVALUATION MODEL NORTHEAST UTILITIES SYSTEM i
MILLSTONE UNIT 2 j
DOCKET NO. 50-336 It is requested that Northeast Utilities reanalyze the LBLOCA for Millstone, Unit 2, using an LBLOCA evaluation model that is conservative for heat
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transfer coefficients over the entire range of reflood rates during the LBLOCA, including 1 "/see to 1.77 "/sec, and provide the following information:
1.
Maximum linear heat generation rate 2.
Reflood rate as a function of time 3.
Core collapsed level as a function of time 4.
Quench time as a function of core height 5.
Core pressure as a function of time 6.
Core subcooling as a function of time 7.
Heat transfer coefficient for PCT location as a function of time 8.
Clad temperature for PCT location as a function of time
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c B. D. Kenyon Millstone Nuclear Power Station Northeast Utilities Service Company Unit 2 4
4 cc:
Lillian M. Cuoco, Esq.
Charles Brinkman, Manager Senior Nuclear Counsel Washington Nuclear Operations Northeast Utilities Service Company ABB Combustion Engineering P. O. Box 270 12300 Twinbrook Pkwy, Suite 330 Hartford, CT 06141-0270 Rockville, MD 20852 Mr. John Buckingham Mr. F. C. Rothen Department of Public Utility Control Vice President - Work Services Electric Unit Northeast Utilities Service Company 10 Liberty Square P. O. Box 128 New Britain, CT 06051 Waterford, CT 06385 i
Mr. Kevin T. A. McCarthy, Director Ernest C. Hadley, Esq.
Monitoring and Radiation Division 1040 B Main Street Department of Environmental Protection P.O. Box 549 79 Elm Street West Wareham, MA 02576 Hartford, CT 06106-5127 Mr. T. C. Feigenbaum 4
l Mr. All' Johanson, Assistant Director Executive Vice President and Office of Policy and Management Chief Nuclear Officer Policy Development and Planning Division Northeast Utilities Service Company 80 Washington Street P. O. Box 128 Hartford, CT 06106 Waterford, Connecticut 06385 4
Regional Administrator Mr. D. W. Goebel j
Region I Vice President - Nuclear Oversight U.S. Nuclear Regulatory Commission Northeast Utilities Service Company 475 Allendale Road P. O. Box 128 4
King of Prussia, PA 19406 Waterford, Connecticut 06385 First Selectmen Mr. M. L. Bowling, Jr.
l Town of Waterford Millstone Unit No. 2 Nuclear Hall of Records Racovery Officer i
200 Boston Post Road Northeast Utilities Service Company i
Waterford, CT 06385 P. O. Box 128 Waterford, Connecticut 06385 Mr. Wayne D. Lanning 4
Deputy Director for Inspections Mr. J. K. Thayer Millstone Neclear Power Station Recovery Officer, Nuclear Engineering c/o U.S. Nuclear Regulatory Commission and Support P.O. Box 513 Northeast Utilities Service Company
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Niantic, CT 06357 P. O. Box 128 Waterford, Connecticut 06385 4
Mr. P. M. Richardson, Nuclear Unit Director Millstone Unit No. 2 Northeast Nuclear Energy Company P. O. Box 128 Waterford, CT 06385