ML19211C204
| ML19211C204 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/31/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19211C200 | List: |
| References | |
| NUDOCS 8001110060 | |
| Download: ML19211C204 (5) | |
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o UNITED STATES E \\. s. c ;,j NUCLEAR REGULATORY COMMISSION g ^- ",^. !
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SAFETY EVALUATION S' THE OFFICE OF NUCLEAP REACTOR REGULATION REGARD!.':G THE UEL MANDLING ACC. DENT INSIDE CONTAIN! ENT THREE M!LE ISLAND MUCLEAR STAT!0N, UNIT 1
.tE RCDCLITAN EDISON COMPANY DOCKET NO. 50-289 M;roduct1on By lettar dated January ,1977, we requested Metropolitan Edison Company (the licensee) to evaluate the previously unevaluated cotential consecuences of a oestulated Fuel Hancling Accident Inside Containment (FHA!C) at Three "il e :sland, Unit 1 'TMI-1).
The licensee subnitted the evaluation of the N:C in a letter dated April 20, 1977 (GQL 0484). The licensee stated that the potential consequences of the postulated accident are 25.4 rem thyroid and 0.65 rem whole body at the Exclusion Area Bour.dary (EAB). The licensee concluded that these doses are appropriate 1v witn1n the guidelines of 10 CFR Part 100.
In the evaluation, the licensee assured the operation of the Reactor Builcing Purge Exhaust Systen (RSPES). The staff requested the licensee, by lette*
dated February 5,1979, to (1) procose tecnnical soecifications requiring use anc surveillance on the RSPES or (2) either confirn that a mininun delay -ine between shutdown and re#ueling of 400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br /> is less than the time needed to begin noving 'uel o propose a technical specification incorporating this limit. The licensee responded in a letter dated May 8,1979 (GQL 0460),
stating that the design of the RBPES does not permit bypassing of the filters in the RBPES during containment purging and that the operability of the system is required before refueling in TMI-1 Technical Specification 3.8.9.
By letters dated January 30, 1975 (GQL 0706), and supplemented by letters dated December 11, 1975 (GQL 1799), and February 13,1976 (GQL 0190), the licensee proposed technical specifications on the operation and surveillance of the RBPES filters. These proposed specifications included surveillance on the RBPES charcoal filters requiring a 90'; methyl iodine charcoal reroval efficiency test periodically.
1738 248 Evaluation We reviewed the licensee's April 20, 1977, and May 8, 1979 submittals, wnich address the pctential consequences of an accident involving spent fuel handling inside containment. We have performed an independent anal /-
sis of the FHAIC. Our assumptions and the resulting potential consequer.:es p"o "D "A]
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. at the Exclusion Area Boundary (EAB) are given in Table 1.
Our evaluation assumes that the licensee implements his proposed technical specifications on the surveillance program of RBPES charcoal filters based on methyl iodine removal efficiency. The licensee submitted the proposed technical specifi-cations by letters dated Janaury 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 periodically tested. These proposed technical specifications will provide adequate assurance that the RBPES filters will at least have the removal efficiencies assumed in our evaluation of the FHAIC 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 humidity in charcoal iodine removal efficiency. Therefore, based on the proposed technical specification on the RBPES charcoal filters and the possible high humidity in the air flow, we have assigned a credit of 70% for total radiciodine removal efficiency for the RBPES charcoal filters.
For our evaluation to be valid, the proposed technical specifi-cations must be implemented to assure the potential consequences of a FHAIC are appropriately within the guidelines of 10 CFR Part 100.
Since we have assumed the operation and surveillance technical specifications on the RBPES filter as being in place, until this is implemented, any future fuel handling inside the reactor building is considered an unreviewed safety question under 10 CFR 50.59a. Furthermore, RBPES filter system is being reviewed for possible upgrading under the restart program. Therefore, the conclusions in this evaluation are considered as interim pending further staff rev'2w regarding any upgrading under the restart program.
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 even s which are evaluated against 10 CFR Part 100 exposure guidelines. Whole body doses were also examined, but they are not controlling due to decay of the short-lived radio-isotopes crior to fuel handling. The potential consequences of this postulated accident at the Low 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 t~ Single Failure Criteria, IEEE Standards, seismic design and equip-nent quality group classification. The RBPES is not safety grade. We conclude that this is acceptable because the potential consequences of the postulated FHAIC are within the exposure guidelines of 10 CFR Part 100 with no credit given for operation of the RBPES.
In addition, the surveillance requirements we recuire for the RSPES filters discussed above are less than the recuirements on safety grade ventilation filter systems because to have the potential consecuences of this accident approcriately within the exposure guidelines of 10 CFR Part 100, more stringent surveillance recuirenents on the non-safety grade RSPES filters are not needec. Therefore, we assumed only an overall iodine filter efficiercy of 705 in this evaluation.
1738 249 oggo B
A recent study-1/has indicated that dropoing a spent fuel assembly into the core during refueling operations may potentially cause damage to nore 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 assemblies, the one dropped and the one hit, may be damaged because of the embrittlement of fuel cladding naterial from radiation in the core. The radiation enbrittlement would occur within the fuel's first few nonths c# operation.
The pectatility of the costulatec fuel handling accident inside containnent is sna11. Not only have there been several hundred -eactor-years o# plant operating experience with only a few accidents involving spent fuel being cropped into the core, but none of these accidents has resulted in neasurable releases of activity.
The potential damage to 5;ent fuel estinated by the study was based on the assump-tion that a spent fuel assen:ly 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 inpact is unlikely because the fall-ing assembly would be subjected to drag forces in the water which :hould cause the assembly to skew out of a vertical fall path.
Based on the above, we have concluted that the likelihood of a s;ent fuel assembly falling into the core and danaging all the fuel Dins in two asserblies is suffi-ciently snall that refueling inside containment is not a safety concern which re-auires innediate remedial action. However, because there is a chance that more than one scent fuel assembly may be damaged during refueling, we are reviewing the study anc the proba0ility and consequences of dropping a scent fuel assembly in the core and danaging more fuel pins than the equivalent of one assembly. The objective of this review is to detertaine 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 inplemented.
We conservatively calculated the potential radiological consequences of a fuel assembly drop onto the reactor core with the rupture of all the fuel pins in two fuel assemblies.
If the assumptions given in Regulatory Guide 1.25 are used for both assemblies and no credit taken for the non-safety grade RSPES, l.
J. N. Singh, " Fuel Assen ly Handling Accident Analysis," EMG Idaho Technical Re cet RE-A-78-227, October 1973.
1738 250
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. the potential consequences are greater than the guidelines of 10 CFR Part 100 these two assenblies are unlikely to both have the high po How-clad gap activity used in Regulatory Guide 1.25 and (2 1.25.
Taking into account more realistic values for power peaking factor postulated accident should not be greater than the exposu Part 100 and, because of this, tions and plant operating procedures are needed while our review is u The results of this analysis warranted an investigation of a similar accident in the spent fuel pool.
analysis per'orned in the sane nanner as creviously described.For this, a d Results indi-cate that in this scenario danage to the nissile or target fuel pins in either fuel assembly were calculated te be ruptured.
is minimal. No Environmental Considerations The environnental impacts of an accident involving the handling of spent fuel inside containment have been addressed in Section 6.1 of the Final Env mental Statenent (FES) dated Decenber 1972 for the operation of TM-I.
Conclusion As d % cussed above, the staff has evaluated the licensee's analysis of the postulated FHAIC.
consequences of a FRAIC to any individual located at the nearest boundary, the staff concludes that tne doses for one assenbly failure are ap-procriately within the guideline values of 10 CFR Part 100 and for failure of two assemblies within the guideline values of 10 CFR Fart 100 and are, therefore, acceptable. For our conclusion to be valid the licensee must implenent the proposed technical specifications concern,ing the cperation and surveillance of the RSPES filters.
The staff has also concluded, based on the considerations discussed above, (1) because this action does not involve a significant increase in that:
the probability or consequences of accidents previously considered and does involve a significant decrease in a sa#ety nargin, it does not involve not a significant ha::ards consiceration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the prooosed manner, and (3) such activities will be conducted in cenpliance with the Connission's regulations and the issuance of this a:nendrent will not be inirical to the cc. :n defense and security or to the health and safety of the outlic.
1738 251 P0 OR,0 RED [
4 TABLE 1 ASSUf9TIONS FOR AN? 00TENTIAL CONSECUENCES OF THE' POSTULATED FUEL HANDLING ACC:0ENTS AT THE EXCLUSION APEA BOUNDARY FOR THREE MILE ISLAND NUCLEAR STATION, UNIT 1 Assunctions:
Fiuicance in Degul atory Psuice 1.25 Power Level 2620 Pwt Fuel Exposure 'ine 3 years Power Peaking Factor 1.7 Equivalent Number of Assen-blies damaged 1
':urber of Asserolies in core 177 Charcoal Filters' Iodine Penoval Efficiency Organic and :norganic Combined 7 C *,
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/O Value, Exclusion
-4 3
Area Boundary (ground level release) 8.3 x 10 sec/m Doses. Ren Thrycid Whole Gcev Exclusion Area Soundary (EAB)
Consecuences fron Fuel Handling Accidents Insice Containrent 67 0.33 1738 252 D TY A
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