ML20008E564

Provides Justification for Min Containment Pressure Used to Initiate Containment Isolation for Facility,Per NRC 801231 Request Re NUREG-0737.Present Containment Isolation Setpoint Is Adequate & No Reduction in Setpoint Is Warranted

ML20008E564
Person / Time
Site:	Millstone
Issue date:	02/27/1981
From:	Counsil W, Fee W NORTHEAST NUCLEAR ENERGY CO.
To:	Clark R Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.E.4.2, TASK-TM A01328, A1328, TAC-42588, TAC-44864, NUDOCS 8103090211
Download: ML20008E564 (2)

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-x Docket No. 50-336 gg hfp A01328 Director of Nuclear Reactor Regulation Attn:

Mr. Robert A. Clark, Chief o

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Operating Reactors Branch #3 M

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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 License and Holders of Construction Permits.

dated October 31, 1980, forwarding NUREG-0737 (2)

W. G. Counsil letter to D. G. Eisenhut, dated December 31, 1980.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Containment Isolation Pressure Setnoint Reference (1) required Northeast Nuclear Energy Company (NNECO) to provide and justify the minimum containment pressure used to initiate containment isolation for Millstone Unit No. 2.

In Reference (2), the Staff was in-formed that NNECO had reviewed the feasibility of reducing the containment isolation pressure setpoint to the minimum value compatible with normal operating conditions from the present setpoint of 4 5 psig, and that a brief review had identified the potential for a minor setpoint reduction.

NNECO also noted in Reference (2) that the implications of a setpoint change had not yet been fully addressed and that the Staff would be advised of NNECO's conclusions by thrch 1,1981.

Since a containment isolation signal (CIAS) is also used to initiate safety injection (SIAS), it is imperative that a reactor scram be in pro-gress prior to initiation of containment isolation and safety injection.

Thus, the setpoint for the High Containment Pressure Reactor Trip must be lower than the setpoint for containment isolation. Technical Specification 3 3.2.1 requires that the containment be isolated when containment pressure is 4 5 psig.

Technical Specification 2.2.1 requires that the reactor trip h

when containment pressure is f.75 psig. The High Containment Pressure Reactor Trip setpoint (3 51 9 psig) precedes the containment isolation pressure setpoint (3.81 9 psig) by 0 3 psi.

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-g-The Limiting Condition for Operation (LCO) for Technical Specification 3.6.1.4 requires that internal containment pressure not exceed 2.1 psig during normal operation. The minimum value for the High Containment Pressure Reactor Trip of 2.6 psig provides a 0.5 psi margin above the LCO of 2.1 psig. NNECO bas concluded that this margin is necessary to minimize the possibility of inadverte.t containment isolation and safety injection. Previous accident analyses have demonstrated the adequacy of the current pressure setpoint in that analyses show that these setpoints ensure that the peak containment pressure will not be exceeded.

NNECO has concluded that it is necessary to maintain the 0.3 psi margin between the High Containment Pressure Reactor Trip and the Containment Isolation setpoints, and, therefore, a reduction in the Containment Isolation

_setpoint would require that the Reactor Trip setpoing also be reduced. NNECO has determined that the 0.5 psi margin between the LCO for containment pressure and the reactor trip setpoint is necessary for continued safe operation.

Therefore, NNECO concludes that the present containment isolation setpoint is adequate and no reduction in the setpoint is warranted.

We trust you will find this information responsive to your request.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY M[

W. G.6tounsil Senior Vice President

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e W. f. Fee Executive Vice President i

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