U-602078, Forwards Response to Unresolved Item Noted in Insp Rept 50-461/92-20 Re Potential Radiological Releases Following Offgas Charcoal Bed Fire

Forwards Response to Unresolved Item Noted in Insp Rept 50-461/92-20 Re Potential Radiological Releases Following Offgas Charcoal Bed Fire

ML20128E661
Person / Time
Site:	Clinton
Issue date:	02/05/1993
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-602078, NUDOCS 9302100538
Download: ML20128E661 (2)

Text

l U 602078 L42 93 (02-05)-LP_.

4F.1 0 Illincas ower Company -

Chnton Power Staten P.O. Box 678 -

Chnton. IL 61727 Tel 217 935 8881 PGWER February 5. 1993 Docket No. 50 461 Document-Control Desk Nuclear Regulatory Commission Washington,-D.C.

20555

Subject:

Response to Unresolved Item 461/92020-01(DRP),

Potential Radiological Releases Following_an Offfas Charcoal Bed Fire

Dear Sir:

The cover letter to NRC Inspection Report No. 50 461/92020(DRP)-

requested that Illinois Power Company (IP) provide a written evaluation concerning potential radiological releases following an offgas charcoal:

bed fire. The attachment to this letter provides the IP responso to this request.

The-contents of this response have been discussed with Mr. P. G.

Brochman, Clinton Power Station (CPS) NRC Senior. Resident Inspector.

-Sincerely yours.:

q h.

c' by

-F. A. Spange org, II Manager, Licensing nd Safet MAR /mfm Attachment NRC Clinton' Licensing 1 Project Manager e ec:

NRC Resident Office, V-690 Regional _ Administrator,, Region III,lUSNRC-Illinois Department of Nuclear. Safety 090023

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9302100538 930205' 1 -

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4 Attechment.

Pegs 1 of 1 to U 602078

-r Paragraph 2.b of NRC Inspection Report-No. 50-461/92020(DRP) expressed concerti that the Clinton Power Station (CPS) Updated Safety Analysis Report (USAR) did not accurately address the possibility that a fire in the Offgas Treatment System charcoal adsorbers could resultiin the release of fission products to the environment.

Section 15.7.1.1.1.1.of the CPS USAR lists four events which conceivably could cause a gross failure in the offgas treatment system.

This list includes a fire in the filter (charcoal adsorber). assemblies. Of the four events listed, a seismic event is considered to be the only_

credible event which could result in the release of significant radioactivity to the environment. A charcoal fire in~a charcoal adsorber bed is a probable event, but one that would not conceivabl/

i causa a significant radioactivity release resulting in offsite radiation doces outside of the limits of 10CFR100, " Reactor Site Criteria."

~

The primary method used to extinguish a charcoal fire in an offgas charcoal adsorber bed is to establish a nitrogen gas (Ng) purge through the-affected bed.

In order to maintain the purge an outlet path must be available. This outlet is provided_through the offgar discharge inolation valve (IN66-F060)-and ultimately to the environment via the-station heating, ventilation, and cooling (HVAC) stack.

In the event a fire degraded the effectiveness of the charcoal in a charcoal adsorber bed, resulting in elevated releases of radioactivity, the effluent radiation monitors downstream of_the charcoal adsorber_ beds are designed to initiate a signal to shut the offgaa discharge isolation valve on high radiation level, thereby limiting a radioactive release below release limits.

In this: scenario, tJun charcoal adsorber beds would be-isolated in order to prevent further delivery of air to the. fire. The fire would burn itself out upon lack of air.

Because of the ability to monitor releases of radioactivity to the environment caused by charcoal fires in charcoal adsorber beds and to isolate these releases prior to exceeding radioactivity release limits, an analysis of such an event was not included in the CPS U'SAR.

The radiological consequences of a seismic occurrence-as identified in USAR Section 15.7.1.1.1.1 bound the radiclogical consequences of a charcoal fire in an offgas charcoal adsorber bed.

T 2

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