ML20148M817

Repts on Analysis Which Indicates post-LOCA Hydrogen Production Due to Corrosion of Matl Inside Primary Containment May Not Have Been Adequately Considered in Eval of Combustible Gas Control Sys

ML20148M817
Person / Time
Site:	Yellow Creek
Issue date:	11/06/1978
From:	Ketchen E NRC OFFICE OF THE EXECUTIVE LEGAL DIRECTOR (OELD)
To:	Kornblith L, Paris O, Smith I Atomic Safety and Licensing Board Panel
Shared Package
ML20148M821	List: ML20148M817 ML20148M826
References
NUDOCS 7811220149
Download: ML20148M817 (2)

Text

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November 6,1978 KRC PUBLIC DOCUMENT ROOM Ivan W. Smith, Esq., C4 airman Dr. Oscar H. Paris Atomic Safety and Licelsing Board Atomic Safety and Licensing Board U.S. Nuclear Regulator / Commission U.S. Nuclear Regulatory Commission Washington, D. C. 20575 Washington, D. C. 20555 Mr. Lester Kornblith Atomic Safety and Licensing Board U.S. Nuclear Regulatory Commission @ '

7 Washington, D. C. 20555 # 'b In the Matter of 9/ e 4 TENNESSEE VALLEY AUTHORITY (Yellow Creek Nuclear Plant, Z

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7 Units 1 and 2) s'@A veh 4 Docket Nos. 50-566 & 50-567 e Gentlemen: N &

The results of recent cnalyses indicate that the post-LOCA hydrogen production due to corrosion of materials inside the primary containment (such as aluminun and zinc) and the thermal, chemical, and radiolytic decomposition of organic components in protective coating systems may not have been adequately considered in the evaluation of combustible gas -

control systems.

Following a LOCA in a light-water reactor nuclear power plant, hydrogen may accumulate inside the primary containment as a result of (1) metal-water reaction invo? ving the fuel rod cladding; (2) radiolytic decompo-sition of the water in the reactor core and containment sump; (3) corrosion of materials inside the primary containment, stch as aluminum and zinc (in the form of galvanized steel and metal-rich paints); and (4) thermal, chemical and radiolytic decomposition of organic components of protective coating systems. Although hydrogen sources are considered routinely by applicants in their determination of the required capacities of post-LOCA hydrogen control systems, such as hydrogen recombiners, and by the NRC Staff in our evaluation of the adequacy of such systems, there is reason to believe that certain hydrogen sources may not have been adequately considered. Although this may prove to be insignificant in that considerable margin is already provided in the capacities of post-LOCA hydrogen control systems, it may prove to be significant if it turns out that the capacities of the post-LOCA hydrogen control systems are such that the post-LOCA hydrogen concentrations cannot be maintained below their combustible limits.

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r i As indicated in Dr. Mattson's memorandum, (attached) because of the uncertainty in the hydrogen generation rates with respect to ce rosion .

of zinc in dry containments, calculations were performed to dets rmine r, the impact of the uncertainty on the recombiner systems for several PWR plants. The hydrogen generation rate increase for galvanized s eel was .

increased by a factor of 2.0 to bound the available experimental data for gal vanized steel . This increase in the corrosito rate woulc only ,,_e r result in a very slight increase in the hydrogen concentration but would yield a H2 concentration slightly in excess of 4% for Yellow Crtek. In most cases, the recombiner systems had the capability of maintaining the hydrogen concentration below the 41 flammable limit by actuatint earlier in the post-LOCA period.

• e In the analysis performed for the Yellow Creek plant, the hydrogen concen-tration would reach a peak value of about 4.13%; however, giving credit to the diluting effect of the steam in the containment atmosphere following a LOCA shows that the hydrogen concentration would not exceed the 4%

flammable limit. o Although it is our view that no s'afety concern is involved as a result of our using the updated hydrogen generation rates for zinc-rich cc atings, there is sufficient justification to warrant further Staff effort toward examining the generation of hydrogen from zinc-rich paints and crganic ma terial s. A more refined knowledge of the behavior of these materials would increase our confidence in this area of review. (L -

We find, however, the effects evaluated regarding post-LOCA generation of hydrogen in both BWR and PWR pressure suppression type containments do not lead to new significant safety concerns not already being considered in our current safety reviews, although this matter was not explicitly considered in reviews until recently. Accordingly, the Staff's conclusion that the design of the Yellow Creek facility is acceptable has not been al tered.

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Sincerely,

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Edward G. Ketchen T Counsel for NRC Staff Enclosure cc (w/ encl . ):

Memorandum for Roger S. Boyd from Roger J. Mattson dated October 17, 1978 w/ enclosures I ra L . Mye rs , M. D. Atomic Safety & Licensing Board Panel Herbert S. Sanger, Jr. , Esq. Atomic Safety & Licensing Appeal Panel Honorable A. F. Summer Docketing and Service Section Alton B. Cobb, M.D.

William B. Hubbard, Esq.

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