ML20081C646

Responds to 830906 Request to Reevaluate Position on NUREG-0737,Item II.E.4.2(7).Monitor Capable of Promptly & Reliably Providing Isolation Signal Would Not Be Sufficiently Sensitive to Detect Release Rates

ML20081C646
Person / Time
Site:	Pilgrim
Issue date:	10/25/1983
From:	Harrington W BOSTON EDISON CO.
To:	Vassallo D Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.E.4.2, TASK-TM NUDOCS 8310310306
Download: ML20081C646 (2)

Text

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• BOSTON Eoss0N COMPANY B00 BOVLaTON STREET BOSTON, M AssAcHUBETTs 02199 WILUAM D. HARRINGTO N einson visa ensaassur

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October 25, 1983 BECo 83-264 Mr. Domenic B. Vassallo, Chief Operating Reactors Branch #2 Division of Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 License No. DPR-35 Docket No. 50-293 Containment Isolation on High Radiation (NUREG-0737, Item II.E.L.2.(7))

Dear Sir:

This responds to a request transmitted in your letter of September 6,1983 that Boston Edison re-evaluate its position on Item II.E.4.2.(7) and apprise you of the results of the re-evaluation.

We have closely examined the feasibility of installing a monitor designed to automatically isolate the Primary Containment in the event of primary coolant leakage during purging operations. We have concluded that a monitor capable of promptly and reliably providing an isolation signal would not be sufficiently sensitive to detect release rates that result in offsite concentrations at the low limits of those specified in 10CFR20 for unrestricted areas.

As you are aware,10CFR20 restricts annual offsite doses to 500 mrem /yr to the whole body and 1500 mrem /yr to the thyroid (of a child or infant). Although such a monitor might detect release rates that result in offsite dose rates equivalent to 500 mrem /yr whole body, it would not be capable of detecting release rates of halogens that result in offsite dose rates equivalent to 1500 mre.n/yr to the thyroid.

The maximum offsite dose rates which would result from a leakage of 25 gpm of spiked primary coolant into the drywell during purging operations, assuming 10%

iodine partitioning and 50% plateout, are calculated to be only about 0.06 mrem /

hr to the whole body and about 2.0 mrem /hr to the thyroid.

The corresponding maximum gamma dose rate on the surface of a 20" purge line, assumed to be 20 ft. in length, carrying the drywell atmosphere radionuclide concentrations specified above, would be approximately 2.0 mrem /hr.

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e SQ3 TON Eos ON COMPANY Mr. Domenic B. Vassallo, Chief Page 2 In fact, a leakage rate greater than 125 gpm of primary coolant into the drywell could be experienced before such a monitor would indicate a reliably measurable increase above ambient background radiation levels.

It is our position that a sufficiently reliable and appropriate monitor which could provide rapid isolation could not reliably and consistently detect release rates of radioactive material at the comparitively low offsite dose rate levels of 10CFR20. This is primarily due to background fluctuations in normal background radiation levels. Installation of such a device could only occur with the under-standing that these sensitivity limits would not always be met.

We believe that drywell sump level, drywell humidity and temperature indication, and the existing drywell airborne radiation monitor are adequate to detect quan-tities of leakage which could result in significant offsite doses.

-Our calculations and technical staff are available to you should you wish to discuss this item further.

Very truly yours, PMK/ mat l