ML20212N840

SER Supporting Util Response to Item 1.C of NRC Re No Specific Time Limit Necessary on Containment Purging & Venting During Reactor Operation

ML20212N840
Person / Time
Site:	Pilgrim
Issue date:	08/22/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20212N829	List: ML20212N826 ML20212N840
References
NUDOCS 8608290202
Download: ML20212N840 (3)

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e jourg4; UNITED STATES

. !. n NUCLEAR REGULATORY COMMISSION

$ .E WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGt!LATION RELATING TO THE TIME LIMIT ON CONTAINMENT VENTING AND PilRGING BOSTON EpISON COMPANY PILGRIM NtlCLEAR POWER STATION p0CKET NO. 50-293

1.0 INTRODUCTION

In a letter to the licensee dated November 29, 1978, the staff identified two areas of concern associated with operation of the containment vent and purge valves while the plant is at power. The concerns relate to the following possible events: 1) a LOCA occurring while the isolation signals for opening the purge / vent valves are overridden, and 2) a LOCA occurrina durina purge / vent valve operations. Both of these events could produce unacceptable radioactive releases. The letter requested the licensee to propose a technical specifica-tion either to prohibit venting and purging during onwer operation or to limit the venting and purging operations to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year with adequate justifi-cation. As an alternative, the licensee could provide justification for unlimited usage of the vent and purge lines. In response to the letter, the licensee provided information concerninc the operation of their vent and purge valves. On the basis of that informaticn, the staff issued safety evaluations (SE) on April 11 and September 24, 198/. These SEs indicated that the licensee's approach was acceptable, pending receipt of adequate justification for not requiring a vent and purge time limitation.

By letters dated April 1, 1985 and October 23, 1985, the licensee submitted additional information supporting its proposal not to have any operational limitation on use of the vent and porce valves during power operation. This evaluation deals with the acceptability of that proposal. ,

2.0 EVAltlATION The April 1,1985 letter provided the results of a licensee LOCA dose analysis for the 20-inch vent and purge valves. The analysis assumed the following l

( conditions:

• A large pipe break inside the containment instantaneously releases the entire primary coolant mass to the drywell.

• No core damage or fuel perforation for the first 17 seconds. '

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• The entire prirary coolant inventory of noble pases and iodine, including spiking, is released to the drywell and becomes airborne.

No credit is given for plateout.

• The standby gas treatment system (SGTS) is inoperable due to a postulated failure of its associated ductwork.

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• The release of the drywell atmosphere activity is via the reactor building vent, yielding an unfiltered ground level release to the environment prior to drywell isolation.

• The release is, at a rate of .323 Mlbs/hr, directly to the environment.

The results of the analysis indicate that the 2-hour site boundary dose to the thyroid would be 40.6 rem, with a whole body aamma dose of 1.34 rem and a beta and gamma skin dose of 5.80 rem. The licensee's analysis is in conformance with the dose assessment guidelines of Position B.5.a of NRC Branch Technical Position CSB 6-4, " Containment Purgina During Normal Plant Operations." The offsite doses are less than those identified in 10 CFR Part 100. Furthermore, the licensee has replaced the 70-inch valves ir the vent and ourge lines with 8-inch valves which are fully qualified to close under the LOCA conditions.

The use of S-inch valves is in conformance with Position B.I.c of the Branch Technical Position CSB 6-4.

The forces associated with the LOCA conditions will not fail the ductwork to the SGTS. Hence, the SGTS can be assumed to be available. The availability of the SGTS will reduce further the offsite doses such that the need for limiting i the operational time for the vent and purge valves does not exist. Our review indicates the licensee's assessment of such ar. accident is reasonable and satisfies Position B.S.a of Branch Technical Position CSB 6 a.

While the number of hours per year of operation of the vent and purge valves has not been specifically limited, there are other constraints which will effectively minimize the coeration of these valves. For example, 10 CFR 50.44(c)(3)(i) requires all BWRs to have inerted containments. Pilgrim Technical Specification 3.7.A.1.1 requires that a pressure differential be maintained between the torus and the drywell. In addition, Technical Specifi-cation 3.7.A.5.a states that the primary contai_nment atmosphere shall be reduced to less than 4% o'jgen by volume with nitrogen gas durina reactor power operation with the reactor coolant pressure above 100 psig, except as specified in 3.7.A.S.b. Technical Specification 3.7.A.S.b provides a limit of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after placing the reactor in the run mode to reduce the oxygen content to less than 4% and also allows the de-inerting to commence 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to shutdown. On the basis of these restraining items, there is reasonable assurance that the number of hours when the vent and purge valves will be used during power operation will be minimized. Therefore, the staff concludes the likelihood of a design basis LOCA resulting in an accident producing a release as severe as discussed in Regulatory Guide 1.3, while venting and purging, is sufficiently low that it need not be considered for this evaluation. Hence, the licensee's request to eliminate any operational time limit on these valves is acceptable. l l

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3.0 CONCLUSION

We conclude that there is no need to impose a 90-hour limitation on the operation of the vent and purge valves at Pilgrim for the followino reasons:

1) The offsite deses predicted for a LOCA while purging are within the reouire-ments of 10 CFR Part 100; 2) Installation of the 8-inch valves in the 20-inch purge lines assures the availability of the SGTS to further reduce the offsite consequences; and 3) the present te-hnical specifications limiting the oxygen in the primary containment provide assurance that the number of hours of vent and purge operations will be minimized.

Principal Reviewer: .1. Ridgely Dated: August 22, 1986 t

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