B13225, Reiterates Util Position on 10CFR50.44(c)(3)(ii) & Provides Addl Info & Clarification Re Combustible Gas Control Issue. Calculations of Combustible Gas Generation Updated Following LOCA to Address Plans for Conversion to Zircaloy Cladding

Reiterates Util Position on 10CFR50.44(c)(3)(ii) & Provides Addl Info & Clarification Re Combustible Gas Control Issue. Calculations of Combustible Gas Generation Updated Following LOCA to Address Plans for Conversion to Zircaloy Cladding

ML20247J172
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	05/19/1989
From:	Mroczka E CONNECTICUT YANKEE ATOMIC POWER CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
B13225, NUDOCS 8906010061
Download: ML20247J172 (5)

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May 19, 1989 Docket No. 50-213 10.R?5 Re: 10CFR50.44 ISAP Topic No. 1.63 ISAP Topic No. 2.17 U.S. Nuclear Regulatory Commission I Attention: Document Control Desk ,

Washington,~DC 20555 b Gentlemen:

Haddam Neck Plant Combustible Gas Control Evaluation

.In a letter dated March 4, 1983,(1) Connecticut Yankee Atomic Power Company (CYAPC0) provided to the NRC Staff documentation of how the requirements of 10CFR50.44(c)(3)(ii) were being addressed at the Haddam Neck Plant. Included therein was a detailed technical discussion of a combustible gas control evaluation.of potential -flammable gas mixtures inside containment following a desig[2pasis LOCA at the Haddam Neck Plant. In a letter dated March 2, 1989, CYAPC0 provided a status summary of this project as part of the Integrated Safety Assessment Program (ISAP) update report. CYAPC0 stated that based on recent discussions with the NRC Staff, CYAPC0 was pursuing final resolution of this issue. The purpose of this letter is to reiterate CYAPC0's position regarding 10CFR50.44(c)(3)(ii) for the Haddam Neck Plant and provide additional information and clarification requested by the NRC Staff to support closeout of this issue by the NRC Staff. Due to the fact that the Haddam Neck

' Plant has stainless steel fuel cladding, we wish to emphasize that only 10CFR50.44(c)(3) needs to be considered for applicability to the Haddam Neck ,

Plant. l (1) W. G. Counsil letter to D. M. Crutchfield, "Haddam Neck Pl ant, Combustible Gas Control Evaluation," dated March 4,1983.

(2). E. J. Mroczka letter to the U.S. Nuclear Regulatory Commission, "Haddam Neck Plant, Integrated Safety Assessment Program," dated March 2,1989.

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'U.S. ' Nuclear Regulatory Commission B13225/Page 2 May 19, 1989 Backaround 10CFR50.44(c)(3)(ii) requires that by the end of the first scheduled outage beginning after July 5, 1982 and of sufficient duration to permit required modifications, each light-water nuclear power reactor that relies upon a purge /repressurization system as the primary means for controlling combustible gases following a design basis loss of coolant accident (LOCA) shall be provided with either an internal recombiner or the cap M11ty to install an external recombiner following the start of the accident.

As described in the evaluation documented in the March 4,1983 letter, CYAPC0 1 determined that a total of approximately 475 lbs. of hydrogen must be gener-ated or released from the reactor coolant system following a design basis LOCA to obtain flammable gas mixtures (i.e., 4% by volume concentration of hydro-gen) .inside containment. Potential sources of hydrogen following a design basis LOCA were then evaluated. Such sources include hydrogen initially dissolved in the primary coolant and contained in the pressurizer vapor space  ;

that could be released during a design basis LOCA, the short-term generation of hydrogen as a result of the oxidation of protective coatings inside containment, and the long-term generation of hydrogen as a result of radiol-ysis. Based upon this evaluation, CYAPC0 concluded that the hydrogen concen-tration inside containment would not reach the flammable limit until approxi-mately thirteen (13) months from the time of the design basis LOCA. Fl amma-bility can be essentially indefinitely postponed (i.e., greater than ten years) by pressurizing the containment with air. The fact that the ratio of the containment building volume to the reactor power for the Haddam Neck Plant is one of the largest of existing large power reactors is a key factor in achieving these favorable results.

The March 4,1983 letter outlined the substantial conservatism that charac-terized the combustible gas evaluation for the Haddam Neck Plant. Even considering these conservatism, CYAPC0 calculated that approximately thirteen (13) months would pass before a flammable concentration of hydrogen in containment was achieved. Clearly, a means of combustible gas control that adequately and conservatively maintains a nonflammable gas mixture inside containment for at least thirteen (13) months following a design basis LOCA is i the " primary" means of combustible gas control. Therefore, as outlined in the l March 4,1983 letter, the " primary" means of combustible gas control at the Haddam Neck Plant is simply the design of the containment building which represents a passive means of combustible gas control. CYAPC0 concluded that ,

due to the containment design, 10CFR50.44(c)(3)(ii) does not require that the Haddam Neck Plant be provided with hydrogen recombiner capability.

However, in the March 4,1983 letter, CYAPC0 also described that there were

" secondary" means of combustible gas control, independent of the requirements of 10CFR50.44, for the Haddam Neck Plant which included: (1) adding air to l

containment to dilute hydrogen, (2) installing external recombiners, and (3) purging of containment. The capability to either add air or purge already exists at the Haddam Neck Plant (see Items 15,16, and 23 of Attachment 1 to f

4 "U S. . Nuclear Regulatory Commission B13225/Page 3 May 19, 1989 the March 4, 1983 letter). The letter also stated that without the need for plant modifications, a " skid-mounted" external hydrogen recombiner could be installed within the time interval available following a design basis LOCA.

In addition, further pressurization of containment could extend the available time interval as necessary. As previously described to the NRC Staff, provi-sions are already in place (including containment penetrations) for availabil-ity of " secondary" means of combustible gas control at the Haddam Neck Plant.

In a letter dated November 17,1986,(3) CYAPC0 provided additional information to the NRC Staff on the following two concerns:

(1) that the combustible gas control evaluation did not provide suffi-cient basis for neglecting the effects of the oxidation of aluminum and zinc protective coatings as a source of hydrogen; and (2) that the evaluation did not include the effects of radiolysis of water in the containment sump.

The letter responded to these questions, concluding first, that " presuming a very pessimistic corrosion rate, the maximum contribution of hydrogen from these materials could reduce the time of formation of a critical hydrogen concentration in containment from approximately 13 months to 8.5 months."

Second, the letter concluded that the evaluation performed assumed that all fission products remain in the reactor region, and therefore the effects of radiolysis of water in the containment sump need not be considered. Accord-ingly, the letter concluded that based upon different corrosion rate assump-tions, a flammable concentration of hydrogen in the containment would not be reached until approximately 8.5 to 13 months subsequent to the beginning of a postulated design basis LOCA. Therefore, our initial position that the Haddam Neck Plant utilizes its containment as the primary means of combustible gas control remains valid. This conclusion reiterated in CYAPCO's November 13, 1987 ISAP report to the NRC Staff. y CYAPC0 has recently updated the calculations of combustible gas generation following a design basis LOCA at the Haddam Neck Plant to address the future plans for conversion to zircaloy fuel cladding. The original calculation had shown that the hydrogen concentration inside containment would not reach the (3) J. F. Opeka letter to C. I. Grimes, "Haddam Neck Plant, Integrated Safety Assessment Program," dated November 17, 1986.

(4) E. J. Mroczka letter to the U.S. Nuclear Regulatory Commission, "Haddam Neck Plant Integrated Safety Assessment Program," dated November 13, 1987.

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U.S. Nuclear Regulatory Commission B13225/Page 4 May 19, 1989 flammable limit until at least about 8 months (5) and possibly as long as 13 months from the time of a design basis LOCA for stainless steel fuel cladding. The calculation performed for zircaloy fuel cladding yielded a result of 7% months until the combustible limit was reached. It is the conclusion of CYAPC0 that the total amount of hydrogen generated for stainless steel and zircaloy cladding is essentially equivalent. Therefore, CYAPCO's previously established positions continue to be valid for both stainless steel and zircaloy cladding.

Summary and Conclusion It continues to be CYAPCO's position that the " primary" means of combustible gas control for the Haddam Neck Plant is the design of the containment build-ing which by itself maintains a nonflammable gas mixture inside containment for many months following a design basis LOCA (i.e., .a minimum of about 8 months for stainless steel and 7% months for zircaloy cladding). This represents a passive means of combustible gas control. Since the " primary" means of combustible gas centrol is not a purge /repressurization system, 10CFR50.44(c)(3)(ii) does not require that the Haddam Neck Plant be provided with hydrogen recombiner capability. This applies both for stainless steel and zircaloy cladding.

As a " secondary" means of addressing this issue independent of the require-ments of 10CFR50.44, CYAPC0 has identified containment penetrations that could l be used for hydrogen control. These would be available for purging or pres-l surizing containment and for use of an external hydrogen recombiner for both stainless steel and zircaloy cladding. There is sufficient time available to ensure that electrical power is configured for the recombiner. CYAPC0 wishes to stress that although analyses demonstrate that this would not be required nonetheless there is sufficient time to arrange for the use of an external hydrogen recombiner.

In the unlikely event of a design basis LOCA, CYAPC0 could carefully evaluate all of the above and any other existing options based upon the specific l circumstances associated with the incident before pursuing any specific course of action. However, it is most probable that CYAPC0 would not need to adopt any " secondary" means of combustible gas control, since more realistic hydro-l gen source terms would make the " primary" means of combustible gas control following a design basis LOCA the only necessary means.

Based on the above, CYAPC0 believes that the requirements of 10CFR50.44(c)(3)(ii) and an adequate means of combustible gas control have (5) The value of 8.5 months discussed in our November 17, 1986 letter resulted from an extrapolation of the curve submitted with that letter.

Recently, a more exacting calculation was performed which resulted in a specific value of about 8 months.

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U.S. Nuclear Regulatory Commission B13225/Page 5 May 19, 1989 been ~ addressed for the Haddam Neck Plant' for both stainless steel and zircaloy cladding., Since 10CFR50.44(c)(3)(iii) regarding. high point' vents has been previously addressed, NRC Staff concurrence with CYAPCO's position en 10CFR50.44(c)(3)(ii) will fully resolve CYAPCO's compliance with all current applicable . sections of 10CFR50.44. We believe such Staff concurrence needs to indicate that the " primary" means of combustible gas control is the design of the containment building. Upon conversion to zircaloy clad fuel, a larger :

portion of 10CFR50.44 would become applicable to the Hadd:s Neck Plant.

We trust that you will find this information adequate to address this issue.

Please contact us if you have any additional . questions.

Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY-w/

E. J. Mp6czka'~ /

Senior Vice President cc: W. T. Russell, Region I Administrator A. B. Wang, NRC Project Manager, Haddam Neck Plant J. T. Shedlosky, Senior Resident Inspector, Haddam Neck Plant

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