ML19344A918
| ML19344A918 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 07/07/1978 |
| From: | Broehl D PORTLAND GENERAL ELECTRIC CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19344A919 | List: |
| References | |
| REF-GTECI-A-36, REF-GTECI-SF, TASK-A-36, TASK-OR NUDOCS 8008220588 | |
| Download: ML19344A918 (2) | |
Text
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PonTLAND GENEnAL ELucTurc COMPANY las S. W. SALwoN STREET PORTLAND, OREGON 97204 ogeisumt v.ca s=ser sioeur July 7, 1978 Trojan Nuclear Plant Docket 50-344 4
License NPF-1 Director of Nuclear Reactor Regulation ATTN:
Mr. A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors THIS DOCUMENT CONTAINS U. S. Nuclear Regulatory Commission P00R QUAUTY PAGES Washington, D.C. 20555
Dear Mr. Schwencer:
Forwarded are three signed originals and 40 copies of this letter in response to your letter dated March 2,1978 requesting additional infor-mation and stating the NRC Staff position concerning a postulated fuel handling accident inside Containment at the Trojan Nuclear Plant.
Our analysis of this postulated accident was submitted to NRC by letter dated March 7, 1977.
Supplemental analyses were submitted by letter dated October 17, 1977.
In accordance with your March 2,1978 request, attached is a report by Bechtel entitled Spent Fuel Pool Ventilation Exhaust System Study (February 1975). This report describes the results of air-flow pattern tests at the refueling floor of the Susquehanna Steam Electric Station.
The basis for application of these results to Trojan is described in our letter of March 7,1977.
The dose reduction credit that is afforded by mixing of radioactive materials above the pool prior to exhausting from Containment depends upon the location in the Refueling Cavity where the fuel handling accident is postulated to occur.
In our previous submittals, this mixing volume was estimated to be 20,000 f t3
'Ihis volume is applicable for an accident occurring in the vicinity of the reactor vessel (west end of pool); it is conservative for other locations, excluding the edges of the refueling cavity, since a greater mixing volume exists beyond the partial enclosure of the missile barrier at the west end of the pool. Were an accident to occur near the edges of the pool, a smaller mixing volume could conceivably result.
For a fuel handling accident that occurs along the north edge of the Refueling Cavity, the estimated thyroid dose at the exclusion area boundary is 74 rem, using Regulatory Guide 1.25 source terms and assuming the Containment isolates in 23.1 sec. The applicable mixing volume is 500 ft3, with an exhaust flow from this mixing volume of 1250 cfm.
0
PORTLAND OENERAL ELCCTRIC COMPANY Hr. A. Schwencer July 7, 1978 Page two The volume of 500 ft3 consists of a half-cylinder that is 12.6 ft in
- length (i.e., the length 'of a fuel assembly), with a 5-f t radius (estimated capture zone of surface exhausters from attached report).
The axis of
. the half-cylinder is parallel to the pool surface and edges. This hal f-cylinder is assumed to be exhausted by a maximum of two of the surface exhausters which have a minimum spacing of 6 f t, and an exhaust flow of 625 cfm each. Air within this mixing volume is assumed to be mixed as a result of the dominant upward thermal convection flow of f the warm pool surface, combined with a weaker horizontal exhaust flow into the surface exhausters, and eddies occurring between the fuel handling bridge and pool surface.
We continue to believe that the assumptions of Regulatory Guide 1.25 for gap activities and for partition factors are overly conservative by a factor of approximately 55, and should not be applied to operating reactors. This conservatism notwithstanding, the offsite doses from this postulated accident are well within the guidelines of 10 CFR 100.
Sincerely, f,o c:
Dr. Fred D. Miller, Director State of Oregon Department of Energy
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