ML25168A056

05-17-83 ACRS Subcommittee Report on Control Room Habitability

ML25168A056
Person / Time
Issue date:	05/17/1983
From:	Dircks W Advisory Committee on Reactor Safeguards
To:	Ebersole J NRC/Chairman
References
Download: ML25168A056 (1)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON. D. C. 20555 May 17, 1983 Mr. William J. Dircks Executive Director for Operations U.S. Nuclear Regulatory Commission Washington, D. C. 20555

SUBJECT:

ACRS SUBCOMMITTEE REPORT ON CONTROL ROOM HAlHTABILITY On April 28, 1983, the ACRS Subcommittee on Reactor Radiological Effects met with the NRC Staff for foll ow-up discussions on the subject of control room habitability. Serving as a basis for these discussions was the ACRS letter to Chairman Palladino of August 18, 1982, and your responses of September 17, 1982, and January 31, 1983.

On the basis of these discussions, the Subcommittee has summarized its comments and a copy is enclosed for your information.

We look forward to continuing discussions with the NRC Staff on this matter.

Sincerely yours, f.::c:.,:.~~,L Acting Chairman En closure:

"Response to NRC Staff CofTITlents on Control Room Habitability," Prepared by Subcommittee on Reactor Radiological Effects, ACRS, 4/30/83 2502

Response to NRC Staff Co111T1ents on Control Room Habitability Prepared by Subconmittee on Reactor Radiological Effects Advisory Committee on Reactor Safeguards April 30, 1983 This report represents a follow-up to the ACRS letter of August 18, 1982 on the subject of control room habitability.

On the basis of the responses of the NRC Staff and discussions held on April 28, 1983, the Subcommittee continues to be concerned about this matter.

If a control room becomes un-inhabitable, the NRC Staff assumes that the operators can retreat to the remote shutdown panel and manage the nuclear power plant from there.

Since the shutdown of a nuclear power plant on an emergency basis is a serious matter, we believe the preferred option is to increase the habitability of the main control room to permit the operators to remain at their normal posts.

To this extent, we believe that improvements in control room habit-ability are justified for safety reasons.

General Comments

l. The Subcommittee continues to be concerned that the reviews and evalu-ations by the NRC Staff of problems associated with control room habit-ability are not centralized.

No single NRC group has the responsibility for coordination and integration of such reviews and co1nmunications among the groups involved appear to need improvement.

We recommend that one of the groups involved be assigned the administrative and technical responsibilities for coordinating all reviews and evaluations on this subject.

2.

The NRC Staff members involved appear to be too ready to accept the responses of applicants and licensees on these matters, rather than assuring themselves on an independent basis that conditions are ac-ceptable.

Some of the models used by the licensees (for example, those for estimating the rate of temperature rise in a contra l room following the loss of the air cooling system) appear to be supported by insufficient experimental data.

The Subcommittee suggests a more aggressive approach by the NRC Staff in critically reviewing potential problems related to control room habitability.

3.

The Subcommittee al so recommends that the NRC Staff be more aggressive in seeking information on eciuipment failures that might affect control room habitability.

The NRC Regional Office staffs, for example, may 2503 be able to obtain data of interest to the NRC Headquarters regulatory staff.

In this regard, efforts are also needed to assure that failures in nuclear power plant safety-related heating, ventilating and air conditioning (HVAC) systems are included in the Nuclear Plant Reliabil-ity Data System (NPROS) since the Subcommittee understands that they will not be included in the proposed revisions of the NRC LER system.

The reasons that INPO did not agree to provide to the NRC Staff data on HVAC systems developed by consultants to nuclear power plant utilities also need to be clarified.

Specific Comments

1.

The formal response by the NRC Staff to our recommendations for a generic diffusion study to assist in determining the optimum location of alternate air intakes for control room systems was negative, on the basis that close-in structures and terrain features would invali-date their diffusion models.

Yet, at the Subcommittee meeting, they acknowledged that, in fact, a downwash analysis would be applicable to this kind of assessment.

We agree that such an analysis is generically applicable because of similarities among control room air systems in standardized nuclear power pl ants.

We therefore recommend that the NRC Staff reevaluate this subject on the basis of the discussions during the Subcommittee meeting.

2.

Conditions for human comfort within a control room are based on a

maximum acceptable temperature of 120°F.

When humidity from human perspiration is added to a room under these conditions, possibly combined with a low air exchange rate, the situation could readily become intolerable.

Also to be considered is the possibility that the charcoal preheaters in the air recirculating system may contribute an added heat load.

The Subcommittee believes that these factors should be given careful consideration and that the criterion for temperature limits in a control room should be revised, if necessary.

3.

The Subcommittee believes that the NRC Staff needs to develop a protocol for testing control room HVAC systems.

Criteria for acceptance should be based on conditions that permit continuing equipment functionability and human comfort during prolonged emergency situations.

Al 1 ports, including dampers, ducts, etc., should be tested simultaneously as a complete system under both positive and negative pressures.

Particular attention should be given to assure that sections of such systems that are under negative pressure will not bring in contaminants, which later can gain access to the control room.

Possible damage to vital equipment due to pressure surges and disruption of HVAC systems should also be evaluated.

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4.

The Subcommittee believes that the quality assurance aspects of HEPA filter manufacturing, installation and testing need to be given more attention by the NRC Staff.

Included in Regulatory Guide 1.52 are references to ANSI N-509 and N-510 which, in turn, reference the ap-plicable military specifications.

The Subcommittee was told, however, by a representative of one of the filter manufacturers, that some nuclear power plant operators are purchasing HEPA filters that do not meet these specifications.

This information should be transmitted to the appropriate NRC Offices (e.g., IE) for further investigation, and corrective action should be taken, if needed. The question of whether Quality Product Listing (QPL) certification is an essential part of the

~ilitary specifications was not clear.

The NRC should contact appropri-ate groups such as the Edgewood Arsenal and the ASME Committee on Nu-clear Air and Gas Treatment for clarification of this matter.

Relevant information and decisions, as appropriate, should be included in the revision of Regulatory Guide 1.52.

5.

The NRC Staff indicated that fire dampers are intended to prevent the spread of a fire but are not designed or certified to hold back the accompanying smoke or potentially toxic gases.

If this is true, the Subcommittee believes that data need to be obtained on allowable leak rates for such dampers and whether the design leak rate is achieved in practice.

If leak rates are as high as was indicated by the NRC Staff, are there situations and/or systems in which auxiliary dampers should be installed to provide supporting seals?

Simply to state that fire dampers "have been proven in industrial operations" is not adequate.

Recent reviews of LERs indicate that damper failures frequently occur in nuclear installations~

6.

The reasons given by the Staff for rejecting our earlier recommendation that consideration be given to increasing the depth of charcoal beds in nuclear adsorption systems are not convincing.

Two factors appear relevant to this matter.

First, deeper beds are just as effective for high acute exposures as they are for chronic low exposures (up to the capacity of the charcoal to retain the contaminants).

As a result, deeper beds are better ab 1 e than thinner beds to handle high acute contaminant concentrations. Second, the U.S. philosophy that the control room be sealed rather than be designed to cope with high air intake concentrations will be fully effective only for those plants having auxiliary compressed air tanks for pressurizing the room; others must take in outside air to maintain pressurization.

7.

The Subcommittee noted

~ range of additional potential problems that appear to need evaluation in terms of control room habitability.

These include:

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a.

The impact of the loss of all AC power, of auxiliary services to the chiller systems, of service air, and of component cooling water;

b.

Careful evaluation of all potential sources of heat input in assessing possible temperature increases in degraded operating modes;

c.

The potential need for monitoring oxygen concentrations and steam intrusion;

d.

Whether the current detection limits for contaminants in the intake air to control rooms are sufficient to protect personnel.

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