ML20207J956

Exemption from Control Room Operability Requirements of 10CFR50.44(c)(3)(iii) for RCS High Point Vents

ML20207J956
Person / Time
Site:	Yankee Rowe
Issue date:	12/29/1986
From:	Novak T Office of Nuclear Reactor Regulation
To:	YANKEE ATOMIC ELECTRIC CO.
Shared Package
ML20207J954	List: ML20207J952 ML20207J956
References
NUDOCS 8701090047
Download: ML20207J956 (6)

Text

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6' 7590-01 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMLaI0N In the Matter of )

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YANKEE ATOMIC POWER COMPANY Docket No.50-029 (Yankee Nuclear Power Station) )

EXEMPTION I. .s Yankee Atomic Power Company (the licensee) is holder of Facility Operating License No. DPR-3 which authorizes operation of the Yankee Nuclear Power Station (Yankee) (the facility) at steady-state reactor power levels not in excess of 600 megawatts thermal (rated power). Yankee consists of a pressurized water reactor (PWR) located at the licensee's site in Franklin County, Massachusetts. The license provides, among other things, that it is subject to all rules, regulations, and Orders of the Nuclear Regulatory Commission (the Commission) now or hereafter in effect.

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II.

Section 50.44(c)(3)(iii) of 10 CFR Part 50 requires a licensee to provide high point vents for the reactor coolant system and the reactor vessel head to provide improved operational capability to maintain adequate core cooling following an accident beyond the design basis of the plant. The vents are to be designed to remove noncondensible gases that might result in loss of function of cooling systems. The high point vents are to be remotely operated from the control room. Also, the vent system shall be designed to ensure a low probability that there would be inadvertent actuation.

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When originally installed, the Yankee high point vents were operable from the control room, except in the event of loss of non-emergency power.

Operator action outside the control room (in the switchgear room) was necessary to provide emergency power to the vent valves. It would have required about 30 minutes for an operator to complete the necessary actions for backfeeding of the buses from the emergency diesel generators. This design was approved by the staff as satisfying the requirements of TMI Action Plan Item II.B.1 Reactor Coolant System Vents, on September 14, 1983.

Subseouently, the licensee has changed the power supplies so the valves could be powered from emergency buses. However, there is a potential for a control room fire to cause inadvertent actuation of the valves. As part of their commitments to satisfy 10 CFR 50.48 and Appendix R to Part 50 (Fire Protection Requirements), the licensee has proposed to remove power from the valves during nomal plant operations and to locate the power supply switches in an accessible area outside the control room (the switchgear room). Once the switches are closed, the vents can be remotely operated and controlled from the control room. The licensee's approach is not in strict compliance with the requirement of 50.44(c)(3)(iii) that the vent valves be remotely operated from the control room. Therefore, by letter dated October 3, 1986, the licensee requested an exemption from the requirement for control room operability of the reactor coolant system high point vents.

In the October 3, 1986 submittal, the licensee provided information relevant to the "special circumstances" finding required by revised 10 CFR 50.12(a) (See 50 FR 50764). The licensee stated that strict interpr,etation  ;

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. 7590-01 of "... operated from the control room" is not necessary to accomplish the underlying purpose of the rule. The rule requires the vents to be remotely operated from the control room for accessibility, operational capability ano ease of control and monitoring of the vent function. Once the operator action to restore- power is complete, the vents can be operated and controlled from the control room. The power supply switches are located in the switchgear room, which would be easily accessible to the control room after an accident requiring operation of the valves. Modifying the system so that the valves could be continuously powered without the concern for inadvertent operation in the event of a fire, would require the expenditure i of engineering and construction resources that would represent an unwarranted I

j burden on licensee resources without a corresponding significant increase in safety. Therefore, the staff concludes that special circumstances exist for the licensee's requested exemption in that application of the regulation in

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these particular circumstances is not necessary to achieve the underlying purposes of 10 CFR 50.44(c)(3)(iii). See 10 CFR 50.12(a)(2)(ii).

The Commission staff has found that the operability provisions for the reactor coolant system vents, as described in the licensee's October 15, 1985 and October 3, 1986 letter, are acceptable because:

1. The power supplies for the valves will be located in the switchgear room, which is directly below the control room. In the event of an accident requiring operation of the vents, this room would be readily accessible. .

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7590-01

2. The operator action required to restore power to the valves is very straightforward (operating four switches). Operators would have ample time following a severe accident to restore power to the vent line valves. This is because use of the vents is not postulated until during the recovery phase of an accident when core cooling by natural circulation has been restored so that the reactor system can be cooled and depressurized. If a bubble of noncondensible gas were present in the reactor vessel head, the gas could be relieved through the vent lines to prevent its accumulating and entering the If the gas entered the steam generators, natural

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steam generators.

circulation would be retarded. Since use of the vents is not postulated until the recovery period after an accident when core cooling has been restored, the staff concludes that ample time will

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be available to restore power to the valves in the vent lines.

3." Once power is restored, the valves can be remotely operated from .

the control room.

4 The four vent valves will be directly powered from emergency buses so no additional operator actions are needed to allow operation uf the valves in the event of loss of offsite power.

5. The proposed design would reduce the likelihood of spurious actuation of the vents in the event of a control room fire. Low probability of spurious actuation is also a requirement of 50.44(c)(3)(iii).

2 7590-01 Based on the above reasons the staff has concluded that, while the reactor coolant system high point vents do not meet the explicit requirements of 10 CFR 50.44(c)(3)(iii) regarding control roca. operability, the presently installed system provides an adequate level of safety and that the requested exemption should be granted.

III.

Accordingly, the Comission has determined that, pursuant to 10 CFR 50.12(a)(1), the exemption requested by the licensee's letter of October 3, 1986, is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security. In addition, the Comission has determined that, pursuant to 10 CFR 50.12(a)(2)(11), special circumstances are present for this exemption in that application of the regulation in the particular circumstances is not necessary to achieve the underlying purposes of the rule. The Comission

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hereby grants to the licensee an exemption from the requirements of 10 CFR 50.44(c)(3)(iii) with respect to control room operability requirements for the reactor coolant system high point vents.

Pursuant to 10 CFR 51.32, the Comission has determined that the issuance of the exemption will have no significant impact on the environment (October 28, 1986, 51 FR 39441).

For further details with respect to this action, see the licensee's  ;

requests dated October 15, 1985 and October 3, 1986, which are available for public inspection at the Commission's Public Document Room, 1717 H Street.

N.W., Washington, D.C. 20555, and at the Greenfield Comunity College,1 College Drive, Greenfield, Massachusetts 01301.

7590-01 This Exemption is effective upon issuance.

FOR THE NUCLEAR REGULATORY COMMISSIQN 3% =, -

Thomas M. Novak, Acting Director Division of PWR Licensing-A Dated at Bethesda, Maryland this 29th day of December,1986.

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