ML20028E428

Discusses NRC Position Re Hydrogen Ignition Sys,Per ACRS .Safety Benefits from Addl Power Supply for Igniters,Should Degraded Core Accident Occur W/Station Blackout,Do Not Warrant Addl Costs

ML20028E428
Person / Time
Site:	Sequoyah
Issue date:	01/14/1983
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Ray J Advisory Committee on Reactor Safeguards
Shared Package
ML20028B939	List: ML20028B938 ML20028E428
References
ACRS-GENERAL, NUDOCS 8301210343
Download: ML20028E428 (4)

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' Docket flos: 50-327' and 50-328 Mr. J. Ray, Chairman Advisory Cornittee on Reactor Safeguards Nuclear Regulatory Comission Washington, D. C.

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Dear 14r. Ray:

In your-letter of December 13,~1982, regarding the Sequoyah hydrogen inni-tion systen,. the ' ACRS recomended that t'ie staff give more consideration to the need for a backup power supply for the igniters should a degraded core accident occur in conjunction with a station blackout.

The staff's present views on this matter, which were presented at the ACRS neeting are as follows:

1) the probability of a recoverable severe accident occurring in conjunction with a station blackout is extrenely small. This is due to the very short tine window following onset of hydrogen generation, f.e., about 30-ninutes, wtin AC power must be restored to 4

preclude a core melt; 2) the plant-unique RSSt4AP study performed for the Seonoyah plant, flVREG/CR-1659, shows that severe accidents associated-with a total loss of AC Dower are not acong the dominant contributors to risk; and 3) the objective of the distributed ignition system is to accortnodate a substantial fraction, but not necessarily all, of the severe' accident sequences that are recoverable short of core celt. t!e, therefore, believe that pending conpletion of IISI TAP A-44 on station blackout, secuences that lead to severe accidents in conjunction with a station blackout should not be made a design basis scenario for the distributed ignition systen.

If the objective of this recoroendation of the ACKS is to delay containnent failure for core nelt sequences, then the back-up power supply will have to be large enough to power both the return air fans and the containment spray system, and not just the igniters. These mixing systems are extrenely helpful in assuring that the pressure consequences of the burn are within the pressure capacity of the containment.

Ve, therefore, believe pending completion of the staff's longer tern studies of severe accidents that the safety benefits from such an additional power supply do not warrant i

the associated costs.

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He will keep you infomed on the progress regardin' chose studies.

Sincerely, CriginiSW W l{. R. Denton Harold R. Denton, Director Office of' Nuclear Reactnr Regulation

Contact:

W. Butler, CSB:DSI X29412 DISTRIBUTION

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