ML20211N040

Exemption from 10CFR50.44(d) & (E) to Remove Hydrogen Control Requirements from SONGS Units 2 & 3 Design Basis. Exemption Also Allows Licensee to Modify Emergency Operating Instructions to Remove Operator Action Requirements

ML20211N040
Person / Time
Site:	San Onofre
Issue date:	09/03/1999
From:	Black S NRC (Affiliation Not Assigned)
To:	SOUTHERN CALIFORNIA EDISON CO.
Shared Package
ML20211N031	List: ML20211N026 ML20211N040 ML20211N051
References
NUDOCS 9909100033
Download: ML20211N040 (4)

Text

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i 7590-01-P UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION in the Matter of )

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SOUTHERN CALIFORNIA EDISGN ) Docket Nos. 50-361 and 50-362 COMPANY )

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(San Onofre Nuclear Generating Station, )

Units 2 and 3) )

EXEMPTION I

1.

Southern California Edison Company (SCE, or the licensee) is the holder of Facility Operating License Nos. NPF-10 and NPF-15, which authorize operation of the San Onofre Nuclear Generating Station (SONGS), Units 2 and 3. The licenses provide, among other things, that the licensee is subject to all rules, regulations, and orders of the Commission now or hereafter in effect.

These facilities consist of two pressurized-water reactors located at the licensee's site in San Diego County, California.

II.

Regulatory requirements for the hydrogen control system are specified in 10 CFR 50.44 j l

and 10 CFR Part 50, Appendix A, (General Design Criteria 41,42, and 43). Different j I

requirements apply to facilities according to the date of publication of the Notice of Hearing for the Construction Permit. With regard to hydrogen recombiner and purge-repressurization system requirements, SONGS Units 2 and 3 are subject to the requirements of 10 CFR 50.44(e) which states:

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l' For facilities whose notice of hearing on the application for a construction permit was published on or after November 5,1970, purging and/or repressurization shall not be the primary means for controlling combustible gases following a LOCA )

[ loss-of-coolant accident]. However, the capability for controlled purging shall be l provided. For these facilities, the primary means for controlling combustible gases l following a LOCA shall consist of a combustible gas control system, such as

! recombiners, that does not result in a significant release from containment.

SONGS Units 2 and 3 are also subject to 10 CFR 50.44(d) which states :

For facilities that are in compliance with [section] 50.46(b), the amount of hydrogen contributed by core metal-water reaction (percentage of fuel cladding that reacts with water), as a result of degradation, but not total failure, of emergency core cooling functioning shall be assumed either to be five times the totbl amount of hydrogen calculated in demonstrating compliance with [section] 50.O(b)D), or to be the amount that would result from reaction of all the metal in the outside surfaces of the cladding cylinders surrounding the fuel (excluding the cladding surrounding the plenum volume) to a depth of 0.00023 inch (0.0058 mm),

whichever amount is greater.

Ill.

The licensee proposed to remove hydrogen control requirements from the SONGS Units 2 and 3 design basis. The licensee stated that the hydrogen control requirements in the SONGS design basis are not required to provide assurance that the containment would not fail due to combustible gas accumulation and ignition during accidents where fission products would be present in the containment atmosphere. The licensee also proposed to modify emergency operating instructions to remove operator action requirements for monitoring and controlling hydrogen concentration in containment.

The licensee's proposed removal of the hydrogen control requirements from the SONGS Units 2 and 3 design basis requires an exemption from certain requirements of 10 CFR

' 50.44 (d) and (e). By its letter dated September 10,1998, as supplemented July 19,1999, the licensee submitted its exemption request.

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IV.

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. Section 50.12(a) of Title 10 of the Code of Federa/ Regulations Part 50 states that the Commission may, upon application by any interested person or upon its own initiative, grant I

exemptions from the requirements of the regulations of this part, which are (1) authorized by law, will not present an undue risk to the public health and safety, and are consistent with the common defense and security, and (2) the Commission will not consider granting an exemption unless special circumstances are present. ,

l- Section 50.12(a)(2)(ii) of 10 CFR Part 50 states that special circumstances are present when application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.

I V.

l The staff has evaluated the licensee's analysis and documented its evaluation in the enclosed safety evaluation. The staff's evaluation is summarized below, t ,

I The underlying purpose of 10 CFR 50.44 is to ensure that following a LOCA, an

!. uncontrolled hydrogen-oxygen recombination would not take place, or that the plant could withstand the consequencec of uncontrolled hydrogen-oxygen recombination without loss of safety function. The licensee demonstrated that the plant could withstand the consequences of uncontrolled hydrogen-oxygen recombination without loss of safety function without credit for the hydrogen recombiners or the hydrogen purge system for both the design-basis and the more limiting severe accident with up to 75 percent metal-water reaction that remains in-vessel scenario. Several risk studies, such as NUREG-1150," Severe Accident Risk: An Assessment for Five U.S. Nuclear Plants," and those performed by the licensee have shown that the relative importance of hydrogen combustion for large, dry containments with respect to containment failure to be quite low. The licensee also demonstrated that hydrogen recombiners are I

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4 insignificant from a large, dry containment integrity perspective and the radiological consequences remain unchanged with or without recombiners. Therefore, the requirements for hydrogen recombiners and the backup hydrogen purge capability for large, dry containments, such as SONGS Units 2 and 3, are not necessary. Accordingly, the Commission has determined that special circumstances are present as defined in 10 CFR 50.12(a)(2)(ii).

VI.

The Commission has determined that, pursuant to 10 CFR 50.12, the exemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security, and is otherwise in the public interest.

Therefore, the Commission hereby grants Southem California Edison Company an exemption from the requirements of 10 CFR 50.44(d) and (e) to remove hydrogen control requirements from the SONGS Units 2 and 3 design basis. The exemption also allows the licensee to modify its emergency operating instructions to remove operator action requirements for controlling hydrogen concentration in containment.

Pursuant to 10 CFR 51.32, the Commission has determined that the granting of this exemption will have no significant effect on the quality of the human environment (64 FR 48211).

This exemption is effective upon issuance.

FOR THE NUCLEAR REGULATORY COMMISSION l

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h wC.h(Eck Suzannd . Black, Acting Director Division of Licensing Project Management Office of Nuclear Reactor Regulation Dated at Rockville, Maryland, this 3rd day of September 1999