ML20206S978

Advises of Completion of Review of 840629 & s Discussing Rationale for Position That Hydrogen Recombiner Capability Not Required for Plant.Exemption from 10CFR50.44 Required to Depart from Generic Ltr 84-09 Guidance

ML20206S978
Person / Time
Site:	Cooper
Issue date:	07/01/1986
From:	Bernero R Office of Nuclear Reactor Regulation
To:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
References
GL-84-09, GL-84-9, NUDOCS 8607070464
Download: ML20206S978 (5)

Text

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Docket No. 50-298 Distribution

! Docket File 2 Mr. J. M. Pilant, Technical Staff Manager NRC PDR NThompson Nuclear Power Group -Local PDR BGrimes Nebraska Public Power District RBerrero JPartlow Post Office Box 499 RWHouston WLong Columbus, Nebraska 68601 Glainas SNorris OELD ACRS(10)

Dear Mr. Pilant:

EJordan Plant' File

SUBJECT:

MARK I CONTAINMENT COMBUSTIBLE GAS CONTROL FOR COOPER NUCLEAR STATION Your letters dated June 29, 1984 and July 17, 1985 provide the rationale for your position that hydrogen recombiner capability is not required for Cooper Station. We have reviewed the information provided in those letters. We have concluded that, to conform to 10 CFR 50.44 and Generic Letter 84-09, you must either (1) provide recombiners or, (2) provide a purge /nftrogen repressurization system meeting GDC 41, 42 and 43. In addition you must eliminate all potential sources of oxygen into the containment. The basis for our conclusion is discussed in the enclosure.

Should you conclude that you have sufficient basis for departure from the guidance of Generic Letter 84-09, you should seek an exemption from 10 CFR 50.44. An exemption to 10 CFR 50.44 would require a demonstration that the nitrogen inerting system provides means of combustible gas control equivalent to a nitrogen purge /repressurization system. Such a demonstration would have to take into consideration such factors as the historical reliability of the system, the mean time to repair / replenish the system, and the ability to improvise means of maintaining acceptable combustible gas concentrations under degraded-core conditions.

Please advise the NRR Project Manager within 30 days, of which alternative you intend to pursue.

Sincerely, Odginal W 4.

Gg Robert M. Bernero, Director Division of BWR Licensing Office of Nuclear Reactor Regulation

Enclosure:

As stated cc: w/ enclosure See next page

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OFFICIAL RECORD COPY 8607070464 860701 PDR ADOCK 05000298 El P PDR J _-_ , _ _ _ _ _

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l Docket No. 50-298 Mr. J. M. Pilant, Technical Staff Manager

{ Nuclear Power Group Nebraska Public Power District Post Office Box 499 i Columbus, Nebraska 68601 i

i

SUBJECT:

MARK I CONTAINMENT COMBUSTIBLE GAS CONTROL FOR COOPER NUCLEAR

STATION Your letters dated June 29, 1984 and July 17, 1985 provide the rationale for

, your position that hydrogen recombiner capability is not required for Cooper Station. We have reviewed the information provided in those letters. We have concluded that, to conform to 10 CFR 50.44 and Generic Letter 84-09, you must either (1) provide recombiners or, (2) provide a purge / nitrogen repressurization system meeting GDC 41, 42 and 43. In addition you must

, eliminate all potential sources of oxygen into the containment. The basis for our conclusion is discussed in the enclosure.

Should you conclude that you have sufficient basis for departure from the guidance of Generic Letter 84-09, you should seek an exemption from 10 CFR 4

50.44. An exemption to 10 CFR 50.44 would require a demonstration that the nitrogen inerting system provides means of combustible gas control equivalent to a nitrogen purge /repressurization system. Such a demonstration would have 4

to take into consideration such factors as the historical reliability of the system, the mean time to repair / replenish the system, and the ability to j improvise means of maintaining acceptable combustible gas concentrations under degraded-core conditions.

Please advise the NRR Project Manager within 30 days, of which alternative you

intend to pursue.

Sincerely, Robert M. Bernero, Director Division of BWR Licensing Office of Nuclear Reactor Regulation

Enclosure:

4 As stated 1

i cc: w/ enclosure

See next page 7

m _ . __ .

Mr. J. M. Pilant Nebraska Pt blic Power District Cooper Nuclear Station cc:

Mr. G. D. Watson, . General Counsel Nebraska Public Power District P. O. Box 4999 ~

Columbus, Nebraska 68601 Mr. Arthur C. Gehr, Attorney Snell & Wilmer 3100 Valley Center Phoenix, Arizona 85073

~

Cooper Nuclear Station ATTN: Mr. Paul Thomason, Division .

Manager of Nuclear Operations P. O. Box 98 Brownville, Nebraska 68321 Director fiebraska Department of Environmental Control P. O. Box 94877

. State House Station Lincoln, Nebraska 68509 Mr. William Siebert, Comissioner Nemaha County Board of Comissioners Nemaha County Courthouse l Auburn, Nebraska 68305

! Resident Inspector i U.S. Nuclear Regulatory Comission P. O. Box 218

{

Brownville, Nebraska 68321 Regional Administrator, Region IV

U.S. Nuclear Regulatory Comission i ton xa bl H. Ellis Simons, Director I'

Division of Radiological Health j Department of Health 301 Centennial Mall, South P. O. Box 95007 Lincoln, Nebraska 68509

,I '

i ENCLOSURE Acombustiblemixtureisconsideredtoesis{wh'enhydrogenconcentrationsare equal to or greater than 4%, and, at the same time, oxygen concentrations are equal to or greater than 5%. (Either condition alone does not constitute a combustible mixture.) Combustible gas control can thus be accomplished by  ;

maintaining 6ne or both gas concentrations below their respective ,

concentration limits. During pre-accident conditions both concentrations are i below their limits; no hydrogen is present, and oxygen has been reduced by I nitrogen inerting as required by 50.44(c)(3)(i) and the Technical l Specifications.  !

Following an accident resulting in degraded core conditions, hydrogen gas production may occur within containment as a result of: l

1. Metal-water reaction involving the zirconium fuel cladding and the reactor coolant;

2. Radiolytic decomposition of water; and,

3. Corrosion of metals by solutions used for emergency cooling or containment spray.

Oxygen may accumulate as a result of:

1. Compressed air connections to primary containment; and,

2. Radiolytic decomposition of water.

For inerted containments, the oxygen deficient atmosphere initially precludes a combustible mixture, assuming no other oxygen sources are present. The need for a combustible gas control system hinges on the question of oxygen and hydrogen concentrations produced by radiolysis, and oxygen entering the containment from other sources. Oxygen from other sources will be eliminated to show compliance with Generic Letter 84-09. Thus, assuming an inerted containment and elimination of possible sources of oxygen, the need for a combustible gas control system hinges on the effects of radiolysis.

Following adoption of the revised 10 CFR 50.44 on December 2, 1981, the Mark I Owners' Group and the staff undertook a substantial program to demonstrate that recombiners are not necessary in Mark I plants due to radiolysis. The Owners' Group study and the findings of the staff indicate that radiolysis source terms of Regulatory Guide 1.7 are very conservative for the large majority of accident sequences. Also, the source terms as proposed by the Owners' Group were sufficiently conservative for these sequences. In fact, an active combustible gas control system would not be required. Inerting would be sufficient since there would not be a sufficient amount of oxygen generated to create a flammable mixture during the first three days following an accident. It was as a result of this finding that relief from recombiner capability was allowed as indicated in Generic Letter 84-09.

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The staff, however, also noted that Regulatory Guide 1.7 was more appropriate for a narrow band of accident sequences. This conclusion was arrived at when one considered the uncertainties inherent with the Owners' Group methodology.

Among the parameters contributing to these uncertainties were the duration of boiling within the core, the degree of fuel rod damage and the effect of water contamination on the oxygen generation process.

For this narrow band of accidents, an active combustible gas control system would be needed to prevent a flammable mixture. It was in view of this finding that the staff indicated in Generic Letter 84-09 that a purge /repressurization capability was necessary to completely satisfy the criteria to obtain recombincr capability relief.

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