ML19225A253
| ML19225A253 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/18/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19225A252 | List: |
| References | |
| NUDOCS 7907180693 | |
| Download: ML19225A253 (4) | |
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NUCLEAR REGULATOE COMMISSION WASHINGTON, D. C. 20555
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Enclosure SAFETY EVALUAT'ON BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGA'R K TiiE FUEL HANDLING ACCIDUfT INSIDE CONTAINMENT
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CALVERT CLIFFS NUCLEAR POWER PLANT UNITS 1 AND 2 BALTIMORE GAS AND ELECTRIC COMPANY DOCKET NOS. 50-3i 7, -318 Introduction By letter dated January 17, 1977, the staff requested the Baltimore Gas and Electric Company (the licensee) to evaluate the prev ously unevaluated potential consequences of a postulat^d Fuel Inndling Accident Inside Con-tainment (FHAIC) at Calvert Cliffs 1/t. The licensee submitted, in a letter dated March 21, 1977, an evaluation of the FHAIC.
The licensee stated that the potential consequence of this postulate accident is 4.4 Rem thyroid at the Exclusion Area E 4 ry ( E AB).
The The licensee concluded that this dose is well wi thin ti.e guidelines of 10 CFR Part 100.
Evaluation We have completed our review of the licensee's March 21, 1977, submi ttal which addresses the potential consequences of an accident involving spent fuel handling inside containnent.
We have perfonned an independent analy-sis of the FHAIC. Our assumptions and the resulting potential consequences at the EAB are given in Table 1.
The calculated potential consequences of the postulated fuel handling accident inside containment are appropriately within the guidelines of 10 CFR Part 100 and are, therefore, acceptable.
Appropriately within the guidelines of 10 CFR Part 100 has been defined as less than 100 Rem to the thyroid. This is based on the probability of this event relative to other events which are evaluated against 10 CFR Part 100 exposure guidelines. Whole body doses were aho examined, but they are not controlling due to decay of the short-lived radioisotopes prior to fuel hand-ling. The potential consequences of this postulated accident at the Low Popu-lation Zone Boundary are less than those given for the EAB In Tab.le 1.
A recent study-1/has indicated that dropping a spent fuel assembly into the core during refueling operations may potentially cause damage to more fuel pins than has been assumed for evaluating the Fuel Handling Accident Inside Containment. This study has indica-ted that up to all of the fuel pins in two spent fuel assemblies, the one dropped and the one hit, may be damaged because of the em-brittlement of fuel cladding material from radiation in the core.
1 J. N. Singh, " Fuel Assembly Handling Accident Analysis," EG&G Idaho Technical Report RE-A-78-227, Octcber 1978.
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. The robability of the postulated fuel handling accident inside containment is small. Not only have there been several hundred reactor-years of plant operating experience with only a few acci-dents involving spent fuel being dropped into the core, but none of these accidents has resulted in measurable releases of activity.
The potential damage to spent fuel estimated by the study was based on the assumption that a spent fuel assembly falls about 14 feet directly onto one other assembly in the core; an impact w; ich re-sults in the greatest energy available for crushing the fuel pins in both assemblies. This type of impact is unlikely because the falling assembly would be subjected to drag forces in the water which should cause the assembly to skew out of a vertical f all path.
Based on the above, we have concluded that the likelihood of a spent fuel assembly falling into the core and danaging all the fuel pins in two assemblies is sufficientiy small that refueling inside containment is not a safety concern which requires immediate remedial action.
We have, however, conservatively calculated the potential radiolo5 cal i
consequences of a fuel assembly drop onto the reactor core with the rupture of all the fuel pins in two fuel assemblies.
We have also assumed for this postulated accident that the source term for both spent fuel assemblies is that given in Regulatory Guica 1.25.
This is co.1servative because (1) these two assemblies should not have the power peakina f actor and clad gap activity recommended in Regulatory Guide 1.25 and (2) the pool decontamination factor for inorganic iodine should be greater than that recommended in Regulatory Guide 1.25.
The calculated potential radiological consequences at the ex-clusion area tm 7dary for the complete rupture of fuel pins in two assemblies are twice the values given in Table 1.
These conserva-tively calculated potential consequences, due to the 1mver probability of two assembly failures, have been judged against and found less than the guidelines of 10 CFR Part 100. Consequently, we have concluded that the potential consequences of this postulated accident are acceptable.
Environmental Considerations The envirorimental impacts of an accident involving the handling of spent fuel inside containment have been addressed in Section VI.A of the Final Environnental Statement (FES) dated April,1973, for the operation of Calvert Clif f s 1/2.
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. Conclusion The staf f has evaluated the licensee's analys' the postulated FHAIC. After performing an independent analy.
f the radiological consequences of a FHAIC to any individual loct' at the nearest ex-clusion area boundary, the staff concludes that use doses for one assembly failure are appropriately within the guideline values of 10 CFR Part 100 and f or f ailura of two assemblies within the guide-line values of 10 CFR Part 100 and are, therefore, acceptable.
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Table.
ASSUMPTIONS FOR AND POTENTIAL CONSEQUENCES OF THE POSTULATED FUEL HANDLING ACCIDENTS AT THE EXCLUSION AREA BOUNDARY FOR CALVERT CIIFFS NUCLEAR POWER PLANT UNITS 1 AND 2 Assumptions:
Guidance in Regulatory Guide 1.25 Power Level 2700 Mwt Fuel Exposure Time 3 years Power Peaking Factor 1.65 Equivalent Number of Assem-blies damaged 1
Number of Assemblies in core 217 Cha ioal Filters available None Decay time before moving fuel 72 nours 0-2 hours X/O Value, Ex-clusior. Area Boundary
_4 3
(ground level release) 1.1 x 10 sec/m Doses, Rem TD 3 6 Whole Body Exclusion Area Boundary (EAB)
Consequences from Accidents Inside Containment 24 0.1 3
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