ML20203N380: Difference between revisions

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* o                            UNITED STATES g
[g 5 .*      ,  .p g                NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 k' v ,/
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SAFETY EVALUATION RY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO GENERIC LETTER 84-09 ON HYDROGEN RECOMBINER CAPARILITY PILGRIM NUCLEAR POWER STATION, UNIT 1 DOCKET NO. 50-293 1.0 INTPODUCTION Ry letters dated June 25, 1984; December 4, 1984; December 6, 1984; May 21, 1985; and October 11, 1985; the Boston Edison Company (licensee) provided information to support its conclusion that the Pilgrim Station does not reouire hydrogen recombiners to control combustible gases inside containment after a desian basis Loss of Coolant Accident (LOCA) as suggested in Generic Letter 84-09, 2.0 EVALUATION In order to iustify that recombiners are unnecessary the licensee provided an assessment indicating that the only post-LOCA oxycen generation would be due to radiolysis of reactor coolant, and that such radiolysis would not produce sufficient oxycen to provide a combustible mixture inside containment. The post-LOCA oxyaen concentration would be maintained below the combustible limit by the following measures taken by the licensee:
a.) The Technical Specifications have been amended to reouire the plant to shutdown within 24 hours of the containment oxygen concentration reaching 4 percent; b.) Nitrogen is used in all containment pneumatic control systems.
Although instrument air is used as a backup to the Nitrogen Supply System, the increasino of the containment oxygen concentration due to contributions from the instrument air system is prevented by the following plant features:
1). The instrument air system is only used when the Nitrogen Supply System is unavailable. After a 24 hour period without the Nitrogen Supply System the plant must be shutdown or an alternate supply of nitrogen must be made available.
2). The Instrument Air System is isolated from the nitrogen system by a locked closed valve; 8605050346 860430 PDR ADOCK 05000293 P                    PDR
~                                                                                _        _.
 
r 3). During the daily surveillarce tour the operator will verify that the Instrument Air System is properly isolated from the nitroaen system by reading pressure gauges on each system.    (The Instrument Air Systen is properly isolated from the Nitrocen Supply System as long as the pressure of the Nitrogen Supply System is higher than the pressure of the Instrument Air System.);
4). The volume of air that could be stored inside of the containment in piping, valves, instruments and accumulators is minute when compared to the drywell volume. Therefore, any contribution from this potential source to the drywell oxygen concentration is negliable; 5). The plant has two alarm settings for drywell oxycen concentration.
One set ooint is at the 3 percent concentration, and the other is at the 4 percent concentration limit.
CONCLUSTON Based on our review of the licensee's submittals, we conclude that the Pilgrim Station does not reouire recombiner capability to control combustible mixtures inside of the containment after a design basis LOCA. This, in part,.is based on the staff's understanding that the licensee will continue to maintain the safety grade puroe/repressurization system in conformance with the general requirements of Criteria 41, 42 and 43 of Appendix A of 10 CFR Part 50. Thus, a decision on recombiner capability does not affect the requirements of 50.44 (f1 and 50.44 (9) for the " safety grade" purge /repressurization system. The basis for this conclusion is that the " safety grade" purge /repressurization system is still necessary to control combustible gas mixtures for a narrow range of accident scenarios which have the potential to aenerate hydrogen and oxygen at rates that are comparable to the radiolysis rates described in Regulatory Guide 1.7.
Principal Contributor:    P. Hearn Dated:  April 30, 1986.
                                                                                          ,}}

Latest revision as of 05:13, 31 December 2020

Safety Evaluation Supporting Util 840625,1204,06,850521 & 1011 Responses to Generic Ltr 86-04 Concerning Recombiner Capability Requirements of 10CFR50.44(c)(3)(ii).Facility Does Not Require Recombiner Capability
ML20203N380
Person / Time
Site: Pilgrim
Issue date: 04/30/1986
From:
Office of Nuclear Reactor Regulation
To:
Shared Package
ML20203N376 List:
References
GL-84-09, GL-84-9, NUDOCS 8605050346
Download: ML20203N380 (2)
v • d • e


Text

r

  • o UNITED STATES g

[g 5 .* , .p g NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 k' v ,/

  • ...+

SAFETY EVALUATION RY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO GENERIC LETTER 84-09 ON HYDROGEN RECOMBINER CAPARILITY PILGRIM NUCLEAR POWER STATION, UNIT 1 DOCKET NO. 50-293 1.0 INTPODUCTION Ry letters dated June 25, 1984; December 4, 1984; December 6, 1984; May 21, 1985; and October 11, 1985; the Boston Edison Company (licensee) provided information to support its conclusion that the Pilgrim Station does not reouire hydrogen recombiners to control combustible gases inside containment after a desian basis Loss of Coolant Accident (LOCA) as suggested in Generic Letter 84-09, 2.0 EVALUATION In order to iustify that recombiners are unnecessary the licensee provided an assessment indicating that the only post-LOCA oxycen generation would be due to radiolysis of reactor coolant, and that such radiolysis would not produce sufficient oxycen to provide a combustible mixture inside containment. The post-LOCA oxyaen concentration would be maintained below the combustible limit by the following measures taken by the licensee:

a.) The Technical Specifications have been amended to reouire the plant to shutdown within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of the containment oxygen concentration reaching 4 percent; b.) Nitrogen is used in all containment pneumatic control systems.

Although instrument air is used as a backup to the Nitrogen Supply System, the increasino of the containment oxygen concentration due to contributions from the instrument air system is prevented by the following plant features:

1). The instrument air system is only used when the Nitrogen Supply System is unavailable. After a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period without the Nitrogen Supply System the plant must be shutdown or an alternate supply of nitrogen must be made available.

2). The Instrument Air System is isolated from the nitrogen system by a locked closed valve; 8605050346 860430 PDR ADOCK 05000293 P PDR

~ _ _.

r 3). During the daily surveillarce tour the operator will verify that the Instrument Air System is properly isolated from the nitroaen system by reading pressure gauges on each system. (The Instrument Air Systen is properly isolated from the Nitrocen Supply System as long as the pressure of the Nitrogen Supply System is higher than the pressure of the Instrument Air System.);

4). The volume of air that could be stored inside of the containment in piping, valves, instruments and accumulators is minute when compared to the drywell volume. Therefore, any contribution from this potential source to the drywell oxygen concentration is negliable; 5). The plant has two alarm settings for drywell oxycen concentration.

One set ooint is at the 3 percent concentration, and the other is at the 4 percent concentration limit.

CONCLUSTON Based on our review of the licensee's submittals, we conclude that the Pilgrim Station does not reouire recombiner capability to control combustible mixtures inside of the containment after a design basis LOCA. This, in part,.is based on the staff's understanding that the licensee will continue to maintain the safety grade puroe/repressurization system in conformance with the general requirements of Criteria 41, 42 and 43 of Appendix A of 10 CFR Part 50. Thus, a decision on recombiner capability does not affect the requirements of 50.44 (f1 and 50.44 (9) for the " safety grade" purge /repressurization system. The basis for this conclusion is that the " safety grade" purge /repressurization system is still necessary to control combustible gas mixtures for a narrow range of accident scenarios which have the potential to aenerate hydrogen and oxygen at rates that are comparable to the radiolysis rates described in Regulatory Guide 1.7.

Principal Contributor: P. Hearn Dated: April 30, 1986.

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