ML20209J524

Provides Clarification of Util Intentions Re Disposition of Systems for Which Exemption & TS Changes Were Requested in Licensee .Deferment of Action Re Hydrogen Monitors,Encl

ML20209J524
Person / Time
Site:	San Onofre
Issue date:	07/19/1999
From:	Nunn D SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9907210221
Download: ML20209J524 (6)

Text

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Dwight E. Nunn Vice President An LDISON INTERNATIONAL *' Company July 19, 1999 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Docket Nos. 50-361 and 50-362 Request for Exemption on Hydrogen Control, Proposed Technical Specification Change 496 San Onofre Nuclear Generating Station Units 2 and 3

Reference:

Letter, D. E. Nunn to U.S. Nuclear Regulatory Commission, Proposed Technical Specification Change 496, dated September 10,1998 Gentlemen:

This letter is to clarify Southern California Edison's intentions regarding the disposition of the systems for which the exemption and Technical Specification changes were requested in the reference letter, and request the NRC defer action regarding hydrogen monitors.

The reference letter requested an exemption to the requirements for hydrogen control systems in 10 CFR 50.44,10 CFR 50. Appendix A, General Design Criterion 41, and 10 j CFR 50, Appendix E Section VI. The purpose of the exemption request is to remove requirements for hydrogen control systems from the SONGS 2 and 3 design basis. In addition, the reference letter requested a license amendment to remove the hydrogen control systems from the plant licenses and Technical Specifications.

Since submittal of this request, Southern California Edison is participating in a joint effort with the Combustion Engineering Owr an Group to remove Post Accident l Sampling System requirements. Because ti,_ ..ydrogen monitors are involved in that l

application, Southern California Edison ls hereby requesting that the NRC defer action on the aspects of the reference letter related to the hydrogen monitors. This includes the exemption from 10 CFR 50 Appendix E, Section VI, the change to License Conditions 2.C(19)i for Unit 2 and 2.C(17)d for Unit 3, and the changes to Technical Specification 3.3.11. A revised "No Significant Hazards Consideration" is enclosed.

On the other hand, Southern California Edison will request relief similar to that recently l granted to Arkansas Nuclear One regarding the timing of the availability of these f monitors.

9907210221 990719 l l PDR ADOCK 05000361 -.

P PDR A j U_h3 l l P. O. fios 128 San Clemente. CA 92674-0128 949 368-1480 Fax 949-368-i490

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- Document Control Desk -2 July 19, 1999 I l

l The other hydrogen control systems which are the subject of Southern California Edison's request in the reference letter are the hydrogen recombiners and the hydrogen purge system. As to these systems, it is Southern California Edison's intention that, upon NRC approval of Southern California Edison's request, which

- includes removal of the recombiners from Technical Specification 3.6.7, we would remove the description of these systems from our Updated Final Safety Analysis Report and from the Emergency Operating Instructions to ensure it is clear these systems no longer perform a safety related function and no credit is taken for their operation for l-design basis event mitigation. 'In addition, the dose consequences related to operation of the hydrogen purge system would no longer be considered in design basis post-

! accident dose calculations. Furthermore, Southern California Edison would be free to reclassify these systems as non safety related where and to the extent it elects to do so.

Despite the above, it is currently Southern California Edison's intention to continue to

- maintain these systems to the extent that it remains prudent and practical. It is also our l intention that this equipment will continue to be included in our Severe Accident '

l: Management Guidelines, but with the notation "if available." If at some future time  :

equipment becomes inoperable and Southern California Edison decides to permanently cease repair efforts, Southern Califomia Edison will then inform the NRC of that decision.

If you have any questions in this regard, feel free to contact me or Mr. Jack Rainsberry at (949) 368-7420.

Sincerely, j N 7 ,

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3 State of California County of San Diego ,

On 7 [ h h before me, OlNlOM/ 1E S b . personally appeared bldi A h-

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E LL AJ . personally known to me to be the person whose name is subscribed to the within instrument and acknowledged to me that he executed the same in his authorized capacity, and that by his signature on the instrument the person, or the entity upon behalf of which the person acted, executed the instrument.

WITNESS my hand and official seal. -------------

q MARIANE SANCHEI C w .. M >#119 H 82

[ O NoteryPuerc l Collfa O son om county Signatur W $ [  ! _ _ _ _%T_?_".

t Enclosure cc: E. W. Merschoff, Regional Administrator, NRC Region IV L. Raghavan NRC Project Mar.ager, San Onofre Units 2 and 3 J. A. Sloan, NRC Senior Resident inspector, San Onofre Units 2 & 3 1

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SAN ONOFRE NUCLEAR GENERATING STATi: '"

UNITS 2 AND 3 Amendment Application Nos.180 and 166 REVISED "NO SIGNIFICANT HAZARDS CONSIDERATIONS"

NO SIGNIFICANT IIAZARDS CONSIDERATIONS The Commission has provided standards for determining whether a significant hazards consideration exists as stated in 10CFR50.92. A proposed amendment to an operating license for a facility involves no significant hazards consideration if operation of the facility in accordance with a proposed amendment would not: (1) involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety. A discussion of these standards as they relate to this change request follows.

1. Will operation of the facility in accordance with this proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No The containment hydrogen control system is currently classified as an engineered safety feature that serves as the combustible gas control system in the containment. The hydrogen control system is composed of a hydrogen recombiner subsystem and a hydrogen purge subsystem. Hydrogen control subsystem components are not considered to be accident initiators. Therefore, this change does not increase the probability of an accident previously evaluated.

The hydrogen control system is provided to ensure that the hydrogen concentration is maintained below the flammability limit of 4% so that containment integrity is not challenged following a design basis Loss Of Coolant Accident (LOCA). Existing analysis show that the hydrogen concentration will not reach the flammability limit of 4% for at least 13.5 days afler a design basis LOCA. The time available will be extended to over 30 days using more realistic hydrogen generation rates. The containment peak pressure will remain below the San Onofre Nuclear Generating Station Units 2 and 3 (SONGS 2 & 3) containment design pressure of 60 psig during this time. Beyond 30 days, hydrogen concentration may reach the flammability limit. However, containment failure due to hydrogen combustion is unlikely based on the results of the SONGS 2 & 3 IPE study.

The detailed SONGS 2 & 3-specific containment integrity analysis indicates that containment rupture pressure is approximately 139 psig with 95% confidence. Therefore, this change does not increase the consequences of accidents previously evaluated.

Removal of the existing requirements for hydrogen control will eliminate the Emergency Operating Instruction (EOI) steps for hydrogen control and hence simplify the EOls. This would have a positive impact on public health risk by reducing the probability of operator error during potential accidents and hence reduce the core damage frequency. As l proposed in this change request, these changes will allow the operators to address all j hydrogen controlissues as part of the proposed Accident Management Guidelines which cover operator actions at long time frames following accidents. )

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Removal of the existing requirements for hydrogen control will eliminate the EOl steps to initiate the containment hydrogen purge. This will result in a lower probability of a failed open containment purge valve. Consequently, the offsite doses would be reduced due to the reduction of the probability of a failed-open containment purge valve. The changes described in this request result in a " risk positive" change.

Therefore, this change does not involve a significant increase in the probability or consequences of any accident previously evaluated. 1

2. Will operation of the facility in accordance with this proposed change create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No This proposed change does not change the design or configuration of the plant beyond the i hydrogen control synem. Hydrogen generation following a design basis LOCA has been evaluated in accordh._ with regulatory requirements. Deletion of the hydrogen control system from the Technical Specifications does not alter the hydrogen generation processes post-LOCA. The consideration of hydrogen generation will no longer be included in the design basis of SONGS 2 & 3. Therefore, this change does not create the possibility of a new or different kind of accident from any previously evaluated.

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3. Will operation of the facility in accordance with this proposed change involve a significant reduction in a margin of safety?

Response: No l

The changes described in this change request result in a " risk positive" change. Removal i of the existing requirement for a hydrogen control system will, by eliminating the EOI steps for hydrogen control, result in lower operator error probabilities. Elimination of the EOl steps to initiate the containment hydrogen purge will result in a lower probability of a failed-open containment purge valve, resulting in lower large early release probabilities. l Therefore, this change involves an increase in safety, not a reduction in a margin of safety.

Based on the negative responses to these three criteria, Southern California Edison has concluded that the proposed change involves no significant hazards consideration.