ML19319C155
| ML19319C155 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 07/29/1977 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19319C152 | List: |
| References | |
| NUDOCS 8001310514 | |
| Download: ML19319C155 (3) | |
Text
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Q SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR OFAULATION i
FOR THE RADIOLOGICAL CONSE00EfiCES OF A POSTULATED FUEL HANDLING ACCIDENT INSIDE CONTAIf4 MENT FOR THE DAVIS-3E5SE NUCLEAR POWER STATION, UNIT 1 TOLEDO EDISON C0ftPANY AND CLEVELAND ELECTRIC ILLUMINATING COMPANY i
DOCKET NO. 50-346 l
On flarch 10, 1977, we requested that the Toledo Edison Comnany nrovide a detailed analysis of the radiological consequences of a nostulated fuel handling accident inside containment for Davis-Besse Unit 1.
The Toledo Edison Company submitted their analysis for this nostulated accident on fiay 6, 1977. The analyses provided utilized assunntions comparable to those given in Regulatory Guide 1.25, "Assunntions Used for Evaluating the Potential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and Storage Facilit" for " oiling and Pressurized Water Reactors," assuming the worst single failure inside the containment building. We have reviewed Toledo Edison Connany's analysis for this postulated accident and we have indenendently evaluated the consequences of this accident for Davis-3 esse, Unit 1.
Our review, evaluation and conclusions regarding the present plant systems available to mitigate the postulated accident as well as our own conservative assumptions used to derive the accident doses resultina from this nostu-lated accident are delineated below.
The Davis-Besse, Unit No. I containment ventilation design, which will be in operation during refueling operations, consists of a containnent recirculation system with intake ducts located in the containment dome which exhausts air across an air gap into a set of fan coolers having a total capacity of 234,000 cubic feet per ninute, and which are located in the uoper portions of the containment. The fan coolers blow the cooled air to the lower portions of the containment where one-fifth (about 46,000 cubic feet per minute) is exhausted past the containment purge isolation valves to the atmosphere, while the remainder is returned to the fan coolers for recirculation.
Two safety grade radiation monitors are located within the containment and upon receipt of a high radiation signal, will close the containment purge isolation valves. The valve closure time is 10 seconds as noted 8001310k
in the facility technical specifications, Table 3.6.2, Containment Isolation Valves; and technical specification Table 3.3.5, Safetv Features Actuation System Resoonse Time, specifies a systen resoonse time of 15 seconds for isolating the containnent from the environnent.
flon-safety grade radiation monitors are also located in the contain-ment purge duct downstream of the outboard containment isolation valve. Upon receipt of a high radiation signal, these monitors will also automatically cause containment isolation.
In the event of a fuel handling accident inside containment, we believe it likely that any activity released would be mixed in the containment atmosphere, thereby causing the radiation monitors inside containment to isolate the containment. Because the contaminated air is likely to be significantly diluted and containment isolation will be rela-tively promot, we believe the dose consequences are likely to be low.
It is possible, however, that any initial release of activity might he directed downward away from the radiation monitors. We have, therefore, conservatively assumed in our analysis that the entire activity release
{
is directed initially into the lower portions of the containment and that one-fifth of the activity is released to the environment before i
isolation of the containment can occur. The portion of the activity recirculated to the containment would cause the in-containment monitors to detect the release and isolate the containment.
In addition, in this event, the release would cause the radiation monitors located in the purge duct to also isolate the containment. He conclude that a l
release of one-fifth of the activity to the atcosphere is a conservative estimate of the activity released as a result of a fuel handling accident inside containment due to the recirculation induced by the fan coolers and the time for valve closure and isolation, as discussed ahove. Our assumptions and dose consequences are listed in Table 1 of this renort.
As can be seen from this table, the doses are well within the guideline j
values of 10 CFR Part 100.
Our independent assessment of a postulated fuel handling accident inside containment has conservatively assumed the operation of existing plant systems for Davis-Besse, Unit 1.
!le conclude that these systems will effectively mitigate the consequences of such an event, that the l
doses are well within the guideline values of 10 CFR Part 100, and are, therefore, acceptable.
l
TABLE I ASSUMPTIONS FOR AND CONSEQUENCES OF A POSTULATED FUEL HANDLING ACCIDENT INSIDE OF CONTAINHENT FOR THE DAVIS-BES5F NUCLEAR POWER STATION, UNIT 1 Power Level 2772 Mega-watts thermal Peaking Factor 1.65 Operating Time 3 years Number of Rods Failed 208 Number of Rods in Core 38,816 Fraction of Inventory in Gap:
Noble Gases 10 Percent Iodines 10 Percent Effective Iodine Decontamination Factor in Pool 100 Shutdown Time-72 hours Safety Features Actuation System Response Time for Isolation Valve Closure 15 seconds Containment Purge Flow 46,666 cubic feet per minute Containment Air Cooler Fan Flow (2) 234,000 cubic feet per minute Ratio of Purge Flow / Air Cooler Flow
.20 X/Q Relative Concentration Values 0-2 hours @ 732 meters 2.2 x 10-4 seconds per cubic meter 0-? hours 9 3200 meters 8.2 x 10-6 seconds cer cubic meter Dose, rem Thyroid Whole Pody Exclusion Area Boundary 10 less than 1 Low Population Zone less than 1 less than 1