ML20235E157
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i OCT 12' 1971 Docket No. 50-263
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Northern States Power Company j
ATTN: Mr. Arthur V. Di~enhart Manager of Engineering 414 Nicollet Hall Minneapolis, Minnesota 55401 Gentlemen:'
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l On March 10, 1971, the AEC issued Safety Guide 7,." Control of Combustible l
Gas Concentrations in Containment Following a Loss-of-Coolant Accident,"
which describes a solution to the safety issue concerning the control
- of combustible gas that is acceptable to the regulatory staff. In accor-1 dance with the Commission's regulation in 10 CFR Part 50.109, we are currently reviewing the possible need for backfitting of plants, such as the Monticello Nuclear Generating Unit 1, that received a construction per-mit prior to the date Safety Guide 7 was issued to provide hydrogen control q
a systems other than purging. In order for us to complete our review,.we l
need certain information from you concerning the calculated doses that might result from purging of the Monticello containment'after the design basis loss-of-coolant accident using the assumptions given in Safety.
Guides 3 and 7.
We need the following.information:
1.
Using the assumptions contained in Table 1 of Safety Guide 7, cal-culate the time at which initiation of venting would be required and the rate at which venting must continue to keep both the l
hydrogen and oxygen concentrations below the limits listed in Safety Guide 7.
Include consideration of hydrogen that might be produced by metal corrosion, using realistic estimates of temperature as a function of time and any contribution to hydrogen production from containment coatings.
2.
Using (a) the fission product release fraction assumptions given in Safety Guide 3, (b) the same fission product removal rates and/or radioactive decay rates used in the evaluat. ion of your design basis LOCA, (c) the accident meteorology applicable for your site, and (d) an equivalent containment leak rate composed of the allowed contain-ment leak rate plus the venting rate, calculate the infinite-time incremental thyroid and whole body doses due to venting alone at both the site boundary and low population zone distances.
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Repeat the analysis for the design basis IDCA with the effect of venting omitted.
For use in evaluating the acceptability of containment venting as a hydrogen control measure in the context of 10 CFR 50.109, we plan to establish guideline incremental dose values (as determined from items 2 and 3, above) that should not be exceeded as a result of venting operations. We are presently considering 2.5 rem whole body and 30 ren thyroid at the site 4
boundary as guideline incremental doses, beyond which one should consider additional hydrogen control capability. The implementation of such additional capability to limit incre-
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l mental purge doses to values in the range discussed above, or l
the implementation of means of controlling hydrogen generation without relying on purging should be included as part of your response to the items requested above, and will be considered j
by the Regulatory Staff in accordance with 10 CFR 50.109.
We would appreciate your sending this information with the supporting calculations and your views or plans on such hydrogen system capability as discussed above for our review within the next few months. We are available for any desired discussion of the above matters.,
Sincerely, ericinel sired W potw A. Merris Peter A. Morris, Director Division of Reactor Licensing cc: Gerald Charnoff Shaw, Pittman, Potts, Trowbridge and Madden (Pg. 2 retyped as per Task Force - 10/7/71) omce >
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