ML20206R733

Submits Addl Info Re Spurious Equipment Actuation Resulting from Control Room Fire,Per NRC Fire Protection Insp During Wks of 851209 & 860305 & Util 860530 Commitment.Emergency Procedure Emp 3.10 Revised to Eliminate Potential Problem

ML20206R733
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	07/01/1986
From:	Berry K CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8607070212
Download: ML20206R733 (3)

Text

Cl -t

@ Consumers messars amassess Kenneth W Berry b lear Lkensing Genera. offices 1945 West Parnall Road. Jackson. MI 49201 . (517) 788-1636 July 1, 1986 Director, Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT -

FIRE PROTECTION - ADDITIONAL CLARIFYING INFORMATION REGARDING SPURIOUS EQUIPMENT ACTUATION RESULTING FROM A CONTROL ROOM FIRE Consumers Power Company letter dated May 30, 1986 committed to submit, by July 1, 1986, additional clarifying information regarding spurious equipment actuation due to a fire in the Plant Control Room. The additional information provided by this letter pertains specifically to spurious actuation (or maloperation) of two trains of core spray valves, the two emergency condenser inlet valves, and one channel of the Reactor Depressurization System (RDS),

ie, actuation of one RDS isolation valve and its associated blowdown valve.

The need to supplement the associated circuit / spurious action information provided by our letter dated September 28, 1982 was identified as a result of the NRC fire protection inspection conducted at the Big Rock Point Plant.

This inspection took place during the weeks of December 9, 1985 and March 5, 1986, and associated meetings were held between Consumers Power Company and the NRC on March 31, 1986 and May 8, 1986. Accordingly, the additional clarifying information presented in this letter will show conclusively that spurious actuation of equipment needed to safely shut down the Plant due to a Control Room fire has been adequately analyzed and that spurious actuation is not a concern because of the equipment design or because of operator actions specified in Plant procedures. Furtheracre, the following restrictions will be imposed on the use of flammable and combustible liquid inside the Control Room.

. Storage of flanz:able and combustible liquids inside the Control Room shall be prohibited.

. Flammable and combustible liquids used inside the Control Room shall be limited to the smallest amount practical for such use and removed promptly following completion of the activity.

8607070212 860701 PDR ADOCK 05000155 ii q

phg OC0686-U100-NLU4 '

II

o -

Director, Nuclear Reactor Regulation 2 Big Rock Point Plant Fire Protection - Add'l Information - Control Room July 1, 1986 fcurious Actuation of One Train of the Resctor Depressurization System (RDS)

Due to a Control Room Fire For the reasons described below, spurious actuation of a single train of the RDS due to a fire in the Control Room was found to be not credible.

The RDS control panel is a relatively small metal enclosed vertical control panel located in the southeast corner of the Control Room. The RDS control panel contains no other control / power circuitry and is about four and one-half feet from the main control panel and about six feet from the main control console.

The RDS is designed such that the automatic sequence, which is controlled by computers located in a room separate from the Control Room, is started by low steam drum level. This starts a two minute timer that delays actuation of the RDS valves while a containment evacuation alarm sounds. A low reactor water level signal and fire pump pressure "available" signal in addition to the low steam drum level will cause RDS actuation as soon as the two-minute timer times out. This timer can, however, be reset to prevent actuation. The RDS can also be manually actuated from the RDS control panel in the Control Roem.

The manual actuation circuits are designed such that pressing two pushbuttons on the control panel vill actuate one train of RDS valves. (There are four trains of RDS valves, each controlled by a separate actuation channel. To manually actuate each train of RDS valves requires pressing the two pushbuttons on each actuation channel.) Each pushbutton is constructed such that when pushed one set of contacts close and, at the same time, another set of contacts open. The closed contacts complete a circuit that connects a relay coil in the actuation cabinet in the RDS computer room to 120 VAC, thereby closing a normally open contact in a trip circuit. The opened contacts de-energize a relay in the RDS computer room that is normally energized, thereby closing a different contact in the same trip circuit. The closing of these two contacts causes a trip on one subchannel associated with one train of RDS valves. In order for that train of RDS valves to actuate, the contacts in the other subchannel must also be closed. For a train of RDS valves to spuriously actuate two concurrent hot shorts and two concurrent open circuits must occur in the proper circuits.

The RDS control panel is separated into four compartments, one for each channel of the RDS, with a partial fire resistant metal barrier between each compartment. The two subchannel pushbuttons are located next to each other in each compartment, and are mounted to the front of the panel about four feet above the floor. The back of the panel is virtually free of combustibles as l only the wires, which are enclosed in metal conduit, leading to the contacts l are in the immediate area. Accordingly, there are few energized wires in a compartment to provide a source for a hot short. Finally, we have concluded that due to the mechanical construction of the subchannel pushbuttons, as ,

opposed to hand switches, fire damage would not result in the closing of one l set of contacts and concurrently open another set of contacts on the same trip circuit. j OC0686-0100-NLO4

o s Director, Nuclear Reactor Regulation 3 Big Rock Point Plant Fire Protection - Add'1 Information - Control Room July 1, 1986 Spurious Action or Maloperation of the Core Spray Valves and the Emergency Condenser Inlet Valves Due to a Control Room Fire-For the reasons described below, the effect of spurious actuation /maloperation of the core spray valves and the emergency condenser inlet valves on safe shutdown has been eliminated.

The hand switches for the two sets of core spray valves and the two emergency condenser inlet valves are located on the main control console and the main control panel. The control console is a metal-enclosure bena.h console which occupies the center of the Control Room, and the main control panel is a metal-walled vertical panel covering most of the back half of the Control Room. The two emergency condenser inlet valve handswitches and one sat of the redundant core spray valve handswitches are located near the west end of the main control console. The second set of core spray handswitches is located on the front on the main control pa'ael near the west end of the panel. Since the main control console and control panel are separated by three feet of clear space, the-possibility a fire which causes loss of control of both sets of core spray valves and the emergency condenser inlet valves was addressed. The ability to safely shut down the Plant would be compromised if, due to a fire in the Control Room, neither set of core spray valves could be opened due to fire induced open circuits, and both emergency condenser inlet valves closed due to fire induced hot shorts.

We have determined that this potential problem can be eliminated if, in the event of a Control Room panel fire, power is removed from the emergency condenser inlet valve motor-operators. Such operator action would preclude the possibility of both of these valves spuriously closing. Therefore, at '.

least one emergency condenser tube will remain available to safely shut the Plant down. (Note: Safe shutdown is assured under these conditions with one emergency condenser tube bundle in operation.) Accordingly, a step has been added to the appropriate emergency procedure (EMP 3.10) directing Plant operators to remove power to both the emergency condenser inlet valve motor-operators in the event of a fully involved cable fire in the main control console or panel. This procedure revision was reviewed in accordance with the-provisions of 10CFR50.59 and the Plant Revf;r ugpvittee determined that this change did not constitute an unreviewed safety question.

fb O Kenneth W Berry Director, Nuclear Licensing CC Administrator, Region III, USNRC NRC Resident Inspector - Big Rock Point OC0686-0100-NLO4 L