U-600850, Informs of Need to Modify Two Rooms Inside Containment Containing Mixing Compressors for Combustible Gas Control Sys.Rooms Do Not Meet Intended Function of Protecting Contained Equipment from post-accident Environ Conditions

Informs of Need to Modify Two Rooms Inside Containment Containing Mixing Compressors for Combustible Gas Control Sys.Rooms Do Not Meet Intended Function of Protecting Contained Equipment from post-accident Environ Conditions

ML20212P411
Person / Time
Site:	Clinton
Issue date:	03/11/1987
From:	Spangenberg F ILLINOIS POWER CO.
To:	Butler W Office of Nuclear Reactor Regulation
References
U-600850, NUDOCS 8703160100
Download: ML20212P411 (7)

Text

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U-600850 L30-87 (0 3L 11) 1A.120 ILLINDIS POWER COMPANY CLINTON POWER STATION, P.O. BOX 678 CLINToN, ILLINOIS 61727 March 11, 1987 Docket No. 50-461 Director of Nuclear Reactor Regulation Attention: Dr. W. R. Butler, Director BWR Project Directorate, No. 4 Division of BWR Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555 4

Subject:

Clinton Power Station

. Hydrogen Mixing Compressor Room Design

Dear Dr. Butler:

The purpose of this letter is to inform the NRC of the need to modify the two rooms inside containment which contain the mixing compressors for the Combustible Gas Control System. These rooms, as currently configured, do not meet their originally intended function of protecting the contained equipment from post-accident environmental conditions. Both of these rooms will be modified, and the environmental qualification packages for affected equipment will be upgraded to resolve this concern.

The hydrogen mixing system compressor rooms, located adjacent to the drywell on containment elevations 778'-0" and 803'-3", were originally intended to be sealed rooms isolated from the containment environment and protected from hydrogen intrusion. The concerns with this approach of protecting the enclosed equipment via sealed rooms are twofold:

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1) The doors of the sealed rooms, as currently configured, are capable of withstanding design basis accident pressure conditions, assuming reliance on pressure equalization via the non-safety related floor drain system or other unsealed penetrations. However, tightly sealing the rooms and assuming design basis accident conditions or assuming the pressure spike associated with the occurrence of a deflagration burn of hydrogen, as predicated by the CLASIX-3 computer code, cannot be accommodated. Failure of the doors could result in environmental conditions in excess of the current equipment qualification temperature limit, and in the potential accumulation of hydrogen in the rooms.

8703160100 870311 PDR ADOCK 05000461 P PDR el g i

. .- . _ . _ . ._ __ . . _ . _ - - ._ ~_

U- 600850 ,

L30-87(03- 11) 1A.120 2)' CPS FSAR Section 6.2.5.2.2.1.c describes the location criteria for the placement of hydrogen igniters in enclosed areas of the containment. This criteria specifies two igniters supplied by-ldifferent electrical divisions to be installed in all enclosed areas -

of.the containment.. Even though sealed rooms would prevent significant hydrogen intrusion from the general containment area, this criteria'is not satisfied for the hydrogen mixing compressor

1. rooms.

l In response to the'above concerns, IP has chosen to modify the compressor rooms such that they are open to.the containment atmosphere.

This modification will be accomplished by removal;of the doors and presumes credit for mixing of the room atmosphere to prevent hydrogen.

stratification via the room coolers. Such an approach will eliminate the concern of sealed. room response to rapid pressurization events and will eliminate the enclosed area status of the rooms, thus negating the need for igniters per the FSAR criteria..

t The equipment-in these rooms (e.g. mixing compressors, control l panels, drywell isolation valves and room coolers) is currently qualified.

to a temperature of 150*F. Opening'the roots will subject this equipment to a more harsh environment. Therefore, the environmental qualification

'i

- packages for this equipment will be upgraded to 185'F in order to withstand the post-LOCA temperature-of the containment general area.

Based upon. preliminary review of affected qualification packages, no hardware changes are-expected to be required to accommodate this revised l- qualification criteria. Removal of the doors will not occur until the '

j. qualification upgrade. process is completed in order to assure that currently established equipment qualification limits would not be exceeded

' if a design basis event occurred.

These rooms are equipped with safety-related room coolers which will start with the hydrogen mix'.ng compressors when the drywell or containment hydrogen concentration reaches 0.5%. .These units have a rated flow of approximately 1950 scfm; therefore, they will circulate the room's air 3,

- volume in less than one minute. The cooler suction is located high in the room near the open doorway. The discharge is located in the opposite end i

of.the room and directed in a downward manner.. With this configuration, thorough mixing of the room atmosphere will occur, and equalized hydrogen concentration between the room and the general containment area via the

' open doorway is expected. Figures 1 through 4 are attached to provide plan and section views of the rooms and coolers configuration.

IP will proceed to complete the above described work prior to commercial operation of the plant. The technical justification for the proposed implementation schedule is as follows:

!

• CPS complies, in all material aspects, with the requirements of 10CFR50.44 (Hydrogen Rule).

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U- 600850 L30-87 (03- 11)

-1A.120

2) CPS FSAR Section 6.2.5.2.2.1.c describes-the location criteria for the placement of hydrogen igniters in enclosed areas of the containment. This criteria specifies two igniters supplied by different electrical-divisions to be installed in all enclosed areas

.of.the containment. Even though sealed rooms would prevent significant hydrogen intrusion from the general containment area, this criteria is not satisfied for the hydrogen mixing compressor rooms.

4

'In response to the above concerns, IP has chosen to modify the compressor rooms such that they are open to the containment atmosphere.

This modification will be accomplished by removal of the doors and presumes credit for mixing of the room atmosphere to prevent hydrogen stratification via,the room coolers. Such an approach will eliminate the concern of sealed room response to rapid pressurization events and will eliminate the enclosed area status of the rooms, thus negating the need for igniters per the FSAR criteria.

The equipment in these rooms (e.g. mixing compressors, control

- panels, drywell isolation valves and room coolers) is currently qualified to a temperature of 150*F. Opening the rooms will subject this equipment to a more harsh environment. -Therefore, the environmental qualification packages ~for this equipment will be upgraded to 185*F in order to i withstand the post-LOCA temperature of the containment general area.

Based upon preliminary review of affected qualification packages, no hardware changes are expected to be required to accommodate this revised qualification criteria. Removal of the doors will not occur until the qualification upgrade process is completed in order to assure that currently established equipment qualification limits would not be exceeded if a design basis event occurred.

These rooms are equipped with safety-related room coolers which will start with the hydrogen mixing compressors when the drywell or containment hydrogen concentration reaches 0.5%. These units have a rated flow of approximately 1950 scfm; therefore, they will circulate the room's air volume in less than one minute. The cooler suction is located high in the room near the open doorway. The discharge is located in the opposite end l of the room and directed in a downward manner. With this configuration thorough mixing of the room atmosphere will occur, and equalized hydrogen concentration between the room and the general containment area via the

open doorway is expected. Figures 1 through 4 are attached to provide

! - plan and section views of the rooms and coolers configuration.

IP will proceed to complete the above described work prior to i commercial operation of the plant. The technical justification for the proposed implementation schedule is as follows:

CPS complies, in all material aspects, with the requirements of 10CFR50.44 (Hydrogen Rule).

l l

2

U- 600850 L30-87(0>1D 1A.120 During most of the power ascension program, fission product inventory necessary to produce significant decay heat quantities for hydrogen generation events will not be attained. In the latter stage of power ascension, the probability of a severe accident occurring in this time frame is sufficiently low.

Even if combustible concentrations of hydrogen is assumed, the likelihood of hydrogen accumulation in these rooms is small based on the following:

- Igniters are located in the immediate vicinity of these rooms inside containment.

- Leakage from components (e.g, mixing compressors and isolation valves) inside these rooms is calculated to be so small that combustible levels of hydrogen cannot be reached.

- CLASIX-3 computer code predicts that the hydrogen would burn in the wetwell region of the containment. Thus, hydrogen concentration outside these upper elevation rooms is expected to be low.

The as-installed configuration of these rooms is capable of withstanding the design basis accident pressure transient.

Therefore, resolution of this concern under the proposed modification plan / schedule is considered adequate.

The Clinton Power Station Final Safety Analysis Report will be revise (. during the next update to include the new equipment environmental qualification data for the affected components.

If you should have any questions on this matter, please contact me.

The Staff will be informed upon completion of the above work.

Sincerely yours, M

F. A. Spangenberg Manager - Licensing and Safety DLH/cke Attachments - 4

! cc: B. L. Siegel, NRC Clinton Licensing Project Manager NRC Resident Office Regional Administrator, Region III Office Illinois Department of Nuclear Safety i

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