ML20004B640

Advises That No Mods Will Be Made to TMI Action Plan Item II.E.4.2 Re Containment Isolation Dependability.Signals Used for Containment Isolation Are Redundant & Diverse & Adequate to Ensure Safe Operation

ML20004B640
Person / Time
Site:	Haddam Neck, Millstone  File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	05/20/1981
From:	Counsil W CONNECTICUT YANKEE ATOMIC POWER CO., NORTHEAST NUCLEAR ENERGY CO.
To:	Eisenhut D Office of Nuclear Reactor Regulation
References
TASK-2.E.4.2, TASK-TM A01379, A1379, TAC-42588, TAC-44864, NUDOCS 8105290215
Download: ML20004B640 (3)

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May 20, 1981 Docket Nos. 50-213 50-245 50-336 AOl379 Mr. Darrell G. Eisenhut, Director Division of Licensing Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C.

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References:

(1)

D. G. Eisenhut letter to All Operating Plants and Applicants for Operating Licensees and IIolders of Construction Permits, dated October 31, 1980, forwardir, NUREG-0737.

(2)

W. G. Counril letter to D. G. Eisenhut, dated December 13 1980.

(3)

W. G. Counsil letter to D. L. Ziemann, dated April 27, 1979.

Gentlemen:

lladdam Neck Plant Millstone Nuclear Power Station, Unit Nos. 1 and 2 TMI Action Plan Item II.E.4.2; Containment Isolation Dependability l

l Position (7) of Item II.E.4.2 of Reference (1) states that containment purge and vent isolation valves mus' close on a high radiation signal.

Connecticut Yankee Atomic Power Company (CYAPCO), on behalf of the IIaddam Neck Plant, and Northeast Nuclear Evergy Company (NNECO), on behalf of Millstone Unit Nos. 1 and 2, are docketing this supplement to l

Reference (2) prior to the required implemer.tation date given in Reference (1) in order to respond to the Staff's concern.

The fladdam Neck Plant uses a purge and vent system to reduce airborne activity prior to commencement of refueling or other shutdown operation.

Normal Operating Procedure NOP 2-13-5 requires that the 42-inch purge l

valves and the 8-inch purge bypass valves be closed before containment integrity can be established. These valves are not opened during any operational modes, as the IIaddam Neck plant Technical Specifications require that containment integrity be maintained during operational modes. There is a 3/4-inch line which may be used to vent the containment l

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,i 'N during operation to prevent pressure increases inside containment from exceeding the Limiting Condition for Operation. Since the Haddam Neck Plant is a four-loop plant which is licensed for three-loop operation, there have been times when work has been performed on the isolated loop inside containment during operation. The use of the breathing air system increases the internal containment pressure, and the 3/4-inch vent line may be used to relieve this pressure. The flow rate for this line is about 10 SCFM.

This line automatically isolates on receipt of a High Containment Pressure signal. This vent line has been used on less than five occassions in over 12 years of operation.

Since both the 42-inch and 8-inch purge valves are closed during operation and since the 3/4-inch vent line is rarely used, the requirement to close these valves on receipt of a high radiation signal is unnecessary.

As such, no modification is planned.

At Millstone Unit No.1, the drywell and torus may be vented or purged through either of two lines. The 18-inch lines are used almost exclusively for inerting and de-inerting the containment. Technical Specification 3.7. A.6 requires that the containment atmosphere oxygen concentration be reduced to less than 5% by weight within the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period subsequent to placing the reactor in the run mode. De-inerting may commence 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to a shutdown.

Therefore, since the 18-inch valves are only allowed to be open for these short durations and remain closed when containment integrity is required, there would be no appreciable increase in safety by requiring that these valves automatically close on a high radiation signal. These valves automatically isolate on high drywell pressure or low reactor water level. The offsite dose consequences which would result from failure to isolate the purge exhaust valve, if open at the time of the accident,.were submitted in Reference (3).

The two-inch lines are opened periodically.to maintain the 1.0 psid pressure differential between the drywell and the torus and to control drywell oxygen concentration. Procedures require that exhaust from these lines be directed to the Standby Gas Trcatment System. Effluent i

to the stack is continuously monitored so that if exhaust from the two-inch lines were inadvertantly directed to the stack, it would automatically be directed to the Standby Gas Treatnent System if high radiation were detected. Since vent exhaust is directed to Ctandby Gas Treatment System, these lines do not provide an opcn path from the containment to l

the atmosphere. As clarified in telephone conversations between NRC l

Staff and representatives of General Electric and the BWR Owners Group, i

the high radiation signal should close any line that provides an open path from the containment to the environment. Therefore, this requirement does not apply to the two-inch vent valves.

NNECO has concluded that the signals used for containment isolation are redundant and diverse and are adequate to ensure the safe operation of Millstone Unit No. 1.

As such, no modifications to the containment isolation signals are planned.

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Millstone Uni No. 2 has two systems for purging and venting of the containment. The 42-inch butterfly valves on the large purge lines are locked closed during operational modes, as required by Amendment 61 to DPR-65.

The 6-inch vent valves automatically isolate on higi: containment pressure or low pressurizer pressure. NNECO has determined that these diverse signals are adequate to ensure that the vent valves will isolate when required, and as such, no modifications are planned.

In the event of a loss of coolant accident, the high containment pressure and low pressurizer pressure signals would precede a high radiation signal and

' isolate the containment. Thus, the addition of a high radiation signal is neither desirable nor necessary to ensure safe operation of Millstone Unit No. 2.

For these reasons, no modifications to the containment isolation logic at the Haddam Neck Plant or at Millstone Unit Nos. 1 and 2 are planned.

We trust this information adequately addresses the Staff's concern.

Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY NORTHEAST NUCLEAR ENERGY COMPANY

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rW I 71 rl4 W. G. Counsil

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Senior Vice President

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