ML20205H026
| ML20205H026 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/12/1986 |
| From: | Miraglia F Office of Nuclear Reactor Regulation |
| To: | Opeka J NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| GL-84-09, GL-84-9, NUDOCS 8608190679 | |
| Download: ML20205H026 (7) | |
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August 12, 1986 Docket No.: 50-245 Mr. John F. Opeka, Senior Vice President Nuclear Engineering and Operations Northeast Nuclear Energy Company Post Office Box 270 Hartford, Connecticut 06141-0270
Dear Mr. Opeka:
SUBJECT:
MARK I CONTAINMENT COMBUSTIBLE GAS CONTROL FOR MILLSTONE UNIT NO. 1 In letters dated August 6,1982 and July 17, 1984, you presented the rationale by which you concluded that hydrogen recombiner capability is not required for Millstone Unit 1.
The August 6, 1982 submittal included a detailed analysis of combustible gas evolution and recombination. Based on that analysis you implemented plant modifications to eliminate potential sources of oxygen leakage into the containment and the Commission issued Amendment No. 101 to the Millstone Unit I license to incorporate the containment inerting requirements as limiting conditions for plant operation.
In addition, your analysis was incorporated, in part, into the BWR Owners' Group evaluation from which the staff concluded that hydrogen recombiners would not be necessary for inerted Mark I containments, as described in Generic Letter 84-09.
With respect to the need for recombiner capability, the staff concluded that Millstone Unit 1 met the three criteria identified in GL 84-09 and, therefore, need not provide this added capability. This staff position was forwarded to you by letter dated November 1, 1984 which forwarded Amendment No. 101. What was not explicitly addressed was the need for an active combustible gas control system. The staff has 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. The basis for our conclusion is discussed in the enclosure.
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7 Mr. John F. Opeka Please advise the NRR Project Manager within 30 days, of your proposed course of action on this matter.
Sincerely, Y
Frank. Miraglia, Director Division of PWR Licensing - B Office of Nuclear Reactor Regulation
Enclosure:
As Stated cc w/ enclosure:
See Next Page
Mr. John F. Opeka Millstone Nuclear Power Station Northeast Nuclear Energy Company Unit No. I cc:
Gerald Garfield, Esquire Kevin McCarthy, Director Day, Berry & Howard Radiation Control Unit Counselors at Law Department of Environmental City Place Protection Hartford, Connecticut 06103-3499 State Office Building Hartford, Connecticut 06106 Edward J. Mroczka Vice President, Nuclear Operations Richard M. Kacich, Supervisor Northeast Utilities Service Company Operating Nuclear Plant Licensing Post Office Box 270 Northeast Utilities Service Company Hartford, Connecticut 06141-0270 Post Office Box 270 Hartford, Connecticut 06141-0270 State of Connecticut Office of Policy and Management ATTN: Under Secretary Energy Division 80 Washington Street Hartford, Connecticut 06106 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 Northeast Nuclear Energy Company ATTN: Superintendent Millstone Nuclear Power Station l
P. O. Box 128 l
Waterford, Connecticut 06385 i
Resident Inspector c/o U.S. NRC Millstone Nuclear Power Station P. O. Box 811 Niantic, Connecticut 06357 First Selectman of the Town of Waterford Hall of Records 200 Soston Post Road Waterford, Connecticut 06385 I
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ENCLOSURE A combustible mixture is considered to exist when hydrogen concentrations are 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 one or both gas concentrations below their respective concentration limits.
During pre-accident conditions both concentrations are below their limits; no hydrogen is present, and oxygen has been reduced by nitrogen inerting as required by 50.44(c)(3)(i) and the Technical Specifications.
Following an accident resulting in degraded core conditions, hydrogen gas production may occur within containment as a result of:
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 i
containment from other sources. Oxygen from other sources will be eliminated l
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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2-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 recombiner capability relief.
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August 12, 19gg Mr. John F. Opeka Please advise the NRR Project Manager within 30 days, of your proposed course of action on this matter.
Sincerely, Original signed by Frank J. Miraglia Frank J. Miraglia,_Diredtor Division of PWR Licensing - B Office of Nuclear Reactor Regulation
Enclosure:
As Stated cc w/ enclosure:
See Next Page
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p Mr. John F. Opeka Please advise the NRR Project Manager within 60 days, of which alternative you intend to pursue.
Sincerely, Robert M. Bernero, Director Division of BWR Licensing Office of Nuclear Reactor Regulation
Enclosure:
As Stated cc w/ enclosure:
See Next Page DI3TRIBUTION Docket File FMiraglia LHarmon WJones OPA ISAP Reading PAnderson EJordan EButcher LFMB NRC PDR JShea BGrimes NThompson MBoyle Local PDR CGrimes JPartlow WRegan RBernero NSIC OELD TBarnhart(4)
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