ML19254C975
| ML19254C975 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/27/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML111090060 | List:
|
| References | |
| FOIA-80-515, FOIA-80-555 NUDOCS 7910180851 | |
| Download: ML19254C975 (5) | |
Text
4d *tCygk UNITED STATES S 7, s n ( (
NUCLEAR REGULATORY COMMISSION
& /. I WASHINGTON D. C. 20555
.NEI[f t
s, SAFETY E'/ALUATION BY THE OFFICE C" NUCLEAR REACTOR REGULATICM REGARDING THE FUEL HANCLING ACLIDENT INSIDE CCNTAINPENT THREE MILE ISLAND NUCLEAR STAT!CN, UNIT 1 PETROPOLITAN EDISCH CGMPANY DOCKET NO. 50-289 I ntroduction By letter dated January 17, 1977, the staf# requested."etropolitan Edison Cenpany (the licensee) to evaluate the previously unevaluated ;otential consequences of a postulated Fuel Handling Accident Inside Containment (FHAIC) at Three Mile Island, Unit 1 (TMI-1). The licensee subnitted the evaluation of the FMAIC in a letter dated April 20, 1977.
The licensee stated that the potential consecuences of the postulated accident are 25.4 ren thyroid and 0.65 ren whole body at the Exclusion Area Soundary (EAB). The licensee concluded that these doses are appropriately within the guidelines of 10 CFR Part 100.
In the evaluation, the licensee assuned the operation of the Reactor Building Purge Exhaust Systen (RBPES). The staff requested the licensee, by letter dated February 5,1979, to (1) propose technical specifications requiring use and surveillance on the R8 PES or (2) either confirn that a mininum delay tire between shutdown and refueling of 400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br /> is less than the tine needed to begin noving fuel or propose a technical s;ecification incorporating this limit. The licensee responded in a letter dated May 9,1979, stating that the design of the RSPES does not permit bypassing of the filters in the RSPES during containment purging and that the operability of the systen is required before refueling in TMI-l Technical Specification 3.8.9.
By letters dated January 30, 1975, and supplemented by letters dated Decen-ber 11, 1975 and February 13, 1976, the licensee pro:osed technical speci-fications on the operation and surveillance of the RBPES filters. These proposed specifications included surveillance on the PPPES charcoal filters requiring a 90', nethyl iodine charcoal removal efficiency test periodically.
Eva'uation We have concleted our review of the licersee's April 20, 1977 and May 8, 1979 subnitial s, which address the potential consecuerces of an accident involving scent fuel handling inside contairnent. We nave perfer ed an independent analy-sis of the FMAIC. Our assumptions and the resulting :otentia! consequences
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2-at the EAB are given in Table 1.
The conclusions of this evaluation are con-tingent upon the licensee's inplementing the proposed surveillance technical specifications on RBPES charcoal filters' methyl iodine removal efficiency that was submitted in letters dated January 30, 1975; December 11, 1975; and February 13, 1976. The proposed technical specifications require that the charcoal filters have a 90*, methyl iodine removal efficiency when peri-edically tested. These croposed technical specifications, when implemented on the RBPES filters, will provide adequate assurance that these filters will have at least the removal efficiencies assuned in our evaluation of the FFAIC given in Table 1.
The RBPES is not equipped with heaters to compensate for high relative humidity in the air flow and there should be high hunidity in the containment during refueling operations. 'his will act to decrease the charcoal fodine removal efficiency. Therefore, based on the proposed techni-cal specification on the RSPES charcoal filters and the possible high humidity in the air ficw, we have assigned a credit of 70*, for total radiciodine re-noval efficiency for the RBPES charcoal filters. For our evaluation to be valid, the proposed technical specifications must be implenented to assure the potential consequences of a FHAIC are appropriately within the guide-lines of 10 CFR Part 100.
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 prcbability of this event relative to other events which are evaluated against 10 CFR Part 100 excesure guidelines. Whole body doses were also examined, but they are nat controlling due to decay of the short-lived radio-isotopes prior to fuel handling. The po ~ential consequences of this postulated accident at the Law Population Zone Boundary are less than those given for the EAB in Table 1.
In our review, we did not require that the RBPES be safety grade and did not consider the Single Failure Criteria, IEEE Standards, seismic design and equip-nent cuality group classification. The RBPES is not safety grade. We conclude that this is acceptable because the potential consecuences of the postulated FHAIC are within the exposure guidelines of 10 CFR Part 100 with no credit g i v e't for operation of the RBPES.
In addition, the surveillance recuirements we require for the RSPES filters disucssed above are less than the requirements on safety grade ventilation filter systems because to have the potential consequences of this accident appropriately within the excosure guidelines of 10 CFR Part 100, nore stringent surveillance requirements on the non-safety grade RBPES filters are not needed. Therefore, we assuned only an overall iodine filter efficiercy of 70"> in this evaluation.
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. 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 FHAIC. This study has indicated that up to all of the fuel pins in two spent fuel assenblies, the one dropped and the one hit, may be damaged because of the enbrittlement of fuel cladding material frca radiation ir the core. The radiation embrittlenent would occur within the fuel's first few months of operation.
The probability of the postulated fuel handling accident inside containment is smal l. Not only have there been several hundred reactor-years of plant operating experience with only a few accidents 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 assJap-tion that a spent fuel assembly falls about 14 feet directly onto one other assembly in the core; an impact which results in the greatest energy available for crushing the fuel pins in both assemblies. This type of impact is unlikely because the fall-ing assembly would be subjected to drag forces in the water which should cause the assembly to skew out of a vertical fall 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 assenblies is suffi-ciently small that refueling inside contairnent is not a safety concern which re-quires immediate renedial action. However, because there is a chance that more than one spent fuel assembly nay be damaged during refueling, we are reviewing the study and the procability and consequences of dropping a spent fuel assemoly in the core and damaging more fucl pins than the equivalent of one assemoly. The objective of this review is to detemine if any additional restrictions on fuel handling operations or plant operating crocedures are needed. Any conclusions of this review which are applicable to this plant will be implemented.
We have, hcwever, conservatively calculated the potential radiological conse-cuences of a fuel assembly drop onto the reactor core with the rupture of all the fuel pins in two fuel assemblies.
If, for both assemblies, we use the assumptions given in Regulatory Guide 1.25 and do not give credit for the non-safety grade RSPES, 1.
J. N. Singh, " Fuel Assembly Handling Accident Analysis," EG3G Idaho Technical Report RE-A-78-227, October 1978.
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. the potential consequences are greater than the guidelines of 10 CFR Part 100.
ever, the source tern defined in Regulatory Guide 1.25 is conservative because (1)
How-these two assenblies are unlikely to both have the high power peaking factor and clad gap activity used in Regulatory Guide 1.25 and (2) the pool decontanination factor for inorganic iodine may well be greater than that used in Regulatory Guide 1.25.
Taking into account nere realistic values for power peaking factor activity and pool decontanination, we conclude that potential consequences, of thisclad gap postulated accident should not be greater than the exposure guidelines of 10 CFR Part 100 and, because of this, no additional restrictions on fuel handling opera-tions and plant operating procedures are needed while our review is under way.
The results of this analysis warranted an investigation of a similar accident in the spent fuel pool. For this, a drop of 2-1/2 feet was postulated and the analysis perfomed in the sane nanner as previously described.
Results indi-cate that in this scenario damage to the nissile or target is minimal.
fuel pins in either fuel assembly were calculated to be ruptured.
No Environnental Considerations The environmental inpacts of an accident involving the handling of spent fuel inside containnent have been addressed in Section 6.1 of the Final Environ-nental S'atenent (FES) dated Decenber 1972 for the operation of TM-I.
Conclusion As discussed c5cve, the staff has evaluated the licensee's analysis of the postulated FHAIC.
After perforning an independent analysis of the radiological consequences of a FHAIC to any individual located at the nearest exclusion boundary, the staff concludes that the doses for one assenbly failure are ap-propriately within the guideline values of 10 CFR Part 100 and for failure of two assemblies within the guideline values of 10 CFR Part 100 and are, therefore, acceptable. For our conclusion to be valid the licensee must inclenent the proposed technical specifications concern,ing the operation and surveillance of the RSPES filters.
The staf' has also concluded, based on the considerations discussed above, (1) because this action does not involve a significant increase in that:
the prchability or consequences of accidents previously considered and dres involve a significant decrease in a safety nargin, it dces not involve not a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed nanner, and (3) such activities will be conducted in cenpliance with the Cornissdon's regulations and the issuance of this anendment will not be ininical to the cennon defense and security or to the health and safety of the public.
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TABLE 1 ASSUMPTIONS FOR AND POTENTIAL CONSE0VENCES OF THE POSTULATED FUEL HANDLING ACCIDENTS AT THE EXCLUSION AREA BOUNDARY FOR THREE MILE ISLAND NUCLEAR STATION, UNIT 1 Assumptions:
Guidance in Regulatory Guide 1.25 Power Level 2620 Mwt Fuel Exposure Time 3 years Power Peaking Factor 1.7 Equivalent Number of Assem-blies damaged 1
Nunber of Assenblies in core 177 Charcoal Filters' Icdine Removal Efficiency Organic and Inorganic Combined 705 Decay time before moving fuel 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 0 - 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> X/0 Value, Exclusion
-4 3
Area Boundary (ground level release) 8.3 x 10 sec/m Doses, Ren Thryoid Whole Body Exclusion Area Soundary (EAB)
Consequences froo Fuel Handling Accidents Inside Containrent 67 0.83 2 ))b 0