ML20112G345
| ML20112G345 | |
| Person / Time | |
|---|---|
| Site: | Bellefonte  |
| Issue date: | 12/26/1984 |
| From: | Shell R TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| IEB-84-03, IEB-84-3, NUDOCS 8501160309 | |
| Download: ML20112G345 (6) | |
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 374ot 1630 Chestnut Street Tower II w
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85 JAN 8 AS: do December 26, 1984 4
U.S. Nuclear Regulatory Commission i
Region II Attn:
Mr. James P. O'Reilly, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Mr. O'Reilly:
BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 - IE BULLETIN 84-03 REFUELING CAVITY WATER SEAL This letter is in response to IE Bulletin 84-03 issued August 24, 1984. In accordance with item 2 of the subject Bulletin, enclosed is an evaluation of the potential for and consequences of a refueling cavity water seal failure for the Bellefonte Nuclear Plant. NRC-0IE Inspector D. M. Verrelli was notified on December 4, 1984 concerning the subject report, a new submittal date of December 28, 1984 was established.
-If you have any questions, please get in touch with me at FTS 858-2688.
To the best of my knowledge, I declare the statements contained herein are complete and true.
Very truly yours, TENNESSEE VALLEY AUTHORITY R. H. Shell Nuclear Engineer
-Enclosure oc: Mr. Richard C. DeYoung, Director (Enclosure)
- Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Records Center (Enclosure)
Institute of Nuc'. ear Power Operations 1100 Circle 75 Iarkway, Suite 1500 Atlanta, Georgia 30339 h9 h
DR 0
PDR I
An Equal Opportunity Employer ggg
ENCLOSURE BELLEFONTE NUCLEAR PLANT UNITS 1 AND 2 RESPONSE TO IE BULLETIN 84-03 REFUELING CAVITY WATER SEAL The reactor vessel (RV) refueling water seal design at Bellefonte Nuclear Plant (BLN) is a flat-plate-on-0-ring design (see figure 1) that is considerably different from the Haddam Neck design. The present seal aesign at BLN has never experienced gross failure in its application at operating plants, but has leaked at rates between 2 and 40 gal / min at Arkansas Nuclear One-1 (ANO-1) and the Oconee plants.
Based on operating experience, the potential for gross seal failure on the BLN cesign is very small; expected leak rates are clearly within makeup capabilities a-o v,nid -pose no safety threat. Since the chance of thic type of seal (noninflated) failing is so small, wu have no means at this time rce precicting gross seal failure. Therefore, we will assume a gross failure would produce leak rates similar to those experienced at Haddam Neck (10,000 gal / min).
If this failure occurred at BLN, the leakage water would have flow access to all areas within primary containment below the RV flange at elevation 639.0 (see figure 2, the layout of the containment and spent fuel storage (auxiliary) building). If the fuel transfer tubes were open and not isolated during this incident and the spent fuel (SF) pool gates were removec, the whole SF pool and refueling canal would drain to elevation 639.0, a flood volume of 74,600 ft3 (558,000 gal) of water. Previous calculations show more than twice this volume draining into the reactor cavity will result in a primary containment flood level of elevation 635.3.
If the refueling canal and SF pool levels crain to elevation 639.0, 2.9 feet of water will remain over the 14.1-foot high SF storage racks. Similarly, any fuel in the fuel transfer upender basket will remain covered by 2.5 feet of water (the top of the vertical basket is at elevation 636'-6").
The SF cooling system would be temporarily lost, as the deeper of its pool suction lines is at elevation 652.5'.
However, decay heat can be adequately removed by pool boiling on a temporary basis. The design basis heat load (1058 fuel assemblies) of 37.7E6 Btu /hr would result in pool boiling in about 3 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> upon loss of pool cooling. The 82 gal / min boil-off rate will not disable the SF pool area heating, ventilating, and air-conditioning (HVAC) system (though charcoal adsorber efficiencies would be recuced) and can be easily made up from the BWST. Although raciation releases due t6 pool boiling are greater than normal, calculated offsite doses are still below 10 CFR 100 limits.
With the loss of more than half the SF pool water inventory, worst case expectations woulc be that pool boiling begins about one hour after the refueling canal seal failure.
Recovery from this event requires isolation of the fuel transfer tubes and refilling of the SF pool from the BWST or the chemical addition and boron recovery system (CABRS) (via makeup and purification system (MUPS) batch controllers). Even without specific emergency procedures, this recovery action should be achievable before SF pool boiling. Even though recovery from SF pool boiling may not be possible with only the SFCS (due to NPSH, limitations on the SFC pumps, etc.) when the boiling pool is full, recovery would be easier from boiling in the drainea-
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'down pool. This is because refilling the pool from the BWST (or CABRS) would provide cooling sufficient to subcool the pool so that the SFCS can be restarted and maintain the pool subcooled.
Should pool boiling occur before recovery, no cladding damage is expected (though any existing pinhole leaks would expand and release additional fission products to the water); the large heat load from the more recently discharged SF. assemblies is distributed over large clad surface areas, hence a low heat flux is maintained. Should a full emergency core offload exist in the SF pool at this time, there may be difficulty recovering from pool boiling via the SFCS only. However, in this condition, use of the decay heat
. remcyal (DHR) system for pool cooling is allowable (little or no fuel in the core) and will be fully adequate to reduce pool temperatures to acceptable levels. From the SF pool storage consideration, then, a gross-refueling cavity scalifailur, la easily manage 7Ple with acceptable s~afet onsequ-
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For any fuel that remains in the core following a gross refueling cavity seal failure, the DHR system remains adequate to cool this fuel by normal operation.
Were a SF assembly to be in transit on the refueling crane when the refueling cavity seal fails, the Hadaam Neck experience suggests that action to immerse that fuel assembly would have to be achieved within about 56 minutes at a 10,000 gal / min leak rate.
In spite of the hoist speed limits within the core, a SF assembly can be easily reinserted back into the core within the available time. The fuel handling bridges have a maximum 40 ft/ min travel speea, their trolleys a maximum of 20 ft/ min, and their hoists a maximum of 20 ft/ min. These briage components are interlocked against simultaneous movement and the hoist is interlocked to-travel at its low speed of 5 ft/ min within the core and fuel storage racks. Depending on the SF assembly's transient location during the cavity seal failure, a decision can be made to transport it either to the deep end of the refueling canal or the RV.
The RV would be a more desirable deposit location because of DHR system availability. The distance between the RV center and the center of the refueling canal deep end is 41 feet. Thus, if an SF assembly were suspended over the refueling canal deep ena, it.could be moved over the core in well under. two minutes,: lowered into the RV upper ' plenum region in about one minute, and then repositioned into the core with relative leisure. Any SF in storage baskets in the refueling canal deep end would have the same coverage as fuel in the SF pool and would not require immediate attention.
Although any fuel in the refueling canal deep end would remain covered folloking the cavity seal failure, efforts to cool it would eventually be required. As a worst case, assume one SF assembly in each fuel basket in the
.upenaers, one in the failed fuel detector can, and one lowered and suspended by a' refueling bridge. Thus, a ' maximum of four SF assemblies could be in the refueling canal deep end, assuming the worst-case heat load from these assemblies the time before the refueling canal deep end boils is 22.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />.
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Clearly then, there is adequate time to isolate the spent fuel storage pool, refill it, then reprime the SF cooling pumps so that makeup can be provided to the refueling canal from the BWST. This makeup will remove heat as it overflows fecm the refueling canal deep end to the RV cavity. Before this time, these fuel assemblies will be cooled by natural circulation and the sensient heat capacity of the ambient water.
Conclusion Although extremely improbable with the present BLN design, gross failure of the refueling canal RV cavity seal can be tolerated; no serious safety hazards would result regardless of short-term operator actior s.
This conclusion applies for SF in the SF fuel storage pool, in the refueling canal deep end, in the RV, and 3F in trarisit,
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Apart from th2 case of SF in transiu, no emergency operator actions would be immediately required. As discussed, SF in transit must be deposited either in the RV or deep end of the refueling canal. Even though actions to mitigate a refueling cavity seal failure would appear to be common sense, consideration will be given to them when we finalize the written refueling procedures at a later date.
Consequences of smaller seal leaks are bounded by those of the gross refueling cavity seal failure, hence the above conclusions apply for smaller leaks also.
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