ML20137A994

Advises That Isolation Capability of Control Room Normal Ventilation Sys CB-2 Adequate.No Mods Required to Meet Intent of NUREG-0737,Action Item III.D.3.4, Control Room Habitability & GDC 19 Based on Listed Reasons

ML20137A994
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	11/21/1985
From:	Withers B PORTLAND GENERAL ELECTRIC CO.
To:	Butcher E Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-3.D.3.4, TASK-TM TAC-46486, NUDOCS 8511260159
Download: ML20137A994 (4)

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• M Pbitifulcih F_lectricCoir v enly Ebrt D. Wees Vce Presdent November 21, 1985 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulation ATTN: Mr. E. J. Butcher, Jr., Acting Chief Operating Reactors Branch No. 3 Division of Licensing U.S. Nuclear Regulatory Commission Washington DC 20555

Dear Mr. Butcher:

NUREG-0737 Action Item III.D.3.4 Control Room Habitability NUREG-0737 Action Item III.D.3.4, Control Room Habitability, required that all facilities that had not been reviewed for conformance with Standard Review Plan Sections 2.2.1,~ 2.2.2, 2.2.3, and 6.4 perform the necessary evaluations and recommend appropriate modifications to meet control room habitability requirements. The NRC Request for Information on this issue was transmitted to Portland General Electric Company (PGE) on October 31, 1980. On January 2, 1981, PGE transmitted its response to the NRC Information Request. The NRC Safety Evaluation Report on this item was transmitted to PCE on February 17, 1982.

The 1981 PGE evaluation of the ventilation systems criteria of Standard Review Plan Section 6.4 was limited to the control room cmergency ventila-tion system (CB-1). It has been subsequently determined that the evalua ._

tion did not include the isolation capability of the normal control room ventilation system (CB-2).

8511260159 B51121 (8 PDR ADOCK 05000344 g g PDR 121 S.W Salmon St eet Pomand. Oregon 97204

d' W M OOCiliCColT4MN1)f Mr. E. J. Butcher, Jr.

November 21, 1985 Page 2 An evaluation of the isolation capability of CB-2 has concluded that the system does not meet the single-failure criterion, as specified in Standard Review Plan Section 6.4, in the following areas:

. 1. The output signals from the redundant toxic gas detectors effect only a single outside air intake damper and outside air intake Fan VC-141; the redundant inner damper must be closed manually by control room operators (see Figure 1).

2. The safety injection and control room high radiation level signals, which close all dampers and shut off all fans in CB-2, are transmitted

.to a single solenoid-operated valve in the air supply system for CB-2 (see Figure 1). Therefore, failure of this solenoid-operated valve

. will result in failure of control room isolation.

CB-1 is designed for single failure.

Notwithstanding the above results, PGE believes that the current control room isclation capability meets the intent of 10 CFR 50, General Design Criteria.19, for the following reasons:

1. The toxic gas detectors are. redundant and provide an audible alarm in

-the control room. Plant Procedure ONI-54, Revision 2, requires that upon a toxic gas alarm, operators don self-contained breathing appara-tus (SCBA) as soon as possible. Control room operators are trained to 4

don SCBAs within 2 minutes. These actions provide operator protection in the event of control room isolation failure.

2. In a toxic gas event, VC-141 is shut down by the redundant toxic gas detectors but the other fans in CB-2 will continue to operate. The flow caused by VC-148 (CB-2 Recirculation Fan) will cause a positive pressure at the outlet of VC-141. This positive pressure will significantly minimize, if not prevent, toxic gas from entering through the outside air damper should it fail to close.

3. .The combination of events necessary to expose control room operators to high toxic gas levels is of very low probability. A sudden large-scale toxic gas release must occur close to the Plant with very stable meteorological conditions and the wind blowing directly from the acci-dent location toward the control room air intake. In addition, CB-2 isolation must fail and operators must fail to don SCBA gear in time.

.4. Control room isolation for radiological conditions (ie, safety injec-tion signal or control room high radiation alarm) is not required to be i accomplished in the short time (ie, minutes) required for toxic gas accidents. Therefore, ample time is available during radiological incidents for operators to manually isolate CB-2 if automatic isolation fails, i

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W Ge. M M W Mr. R. J. Butcher, Jr.

November 21, 1985 Page 3 Therefore, the isolation capability of the control room normal ventilation system (CB-2) is adequate and no modifications are required to meet the intent of NUREG-0737 Action Item III.D.3.4.

Sincerely, OP for Bart . Withers Vice President Nuclear Attachment c: Mr. Lynn Frank, Director State of Oregon Department of Energy l

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