ML20099J529
| ML20099J529 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek, Callaway, 05000000 |
| Issue date: | 11/26/1984 |
| From: | Petrick N STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM |
| To: | James Keppler, Martin R NRC OFFICE OF ADMINISTRATION (ADM), NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III), NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| IEB-84-03, IEB-84-3, SLNRC-84-127, NUDOCS 8411290105 | |
| Download: ML20099J529 (6) | |
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3 SNUPPS standsemess heiser unit Powe, ment syneem s choke cherry nees Nicholas A. Petrick neekvises, wand aesso Executive Director 001) assecto November 26, 1984 SLNRC 84-127 FILE: 0278.10 SUBJ:
IE Bulletin 84-03: Refueling Cavity Water Seal Mr. James G. Keppler Regional Administrator, Region III U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 Mr. Robert D. Martin Regional Administrator, Region IV l
U. S. Nuclear Regulatory Commission Suite 1000, Parkway Central Plaza Arlington, Texas, 76012 l
U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Docket Nos. STN 50-482 and STN 50-483 Gentlemen:
1 i
The subject Bulletin described an incident in which a refueling cavity water seal failed and requested an evaluation of the potential for and consequences of a refueling cavity water seal f ailure at the SNUPPS 1
l plants - Callaway Plant Unit No. I and Wolf Creek Generating Station Unit No. 1.
The attached report provides a summary of the requested evaluation.
Based on the report, it is concluded that the SNUPPS refueling cavity water seal design makes a gross seal failure an extremely unlikely event.
In addi-tion, SNUPPS plant design features provide for adequate spent fuel cooling and for safe plant recovery from a postulated gross failure of the seal.
Very truly yours, ht%c Nicholas A. Petrid MHF/nldl3b3&4 Attachment j
cc: See Page 2.
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t SLNRC 84-127 Page 2.
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D. F. Schnell UE G. L. Koester KGE J. M ' Evans KCPL H. Bundy USNRC/WC J. Neisler/B. Little USNRC/ CAL W. L. Forney USNRC/RIII D. R. Hunter USliRC/RIV
,8 Attachment to SLNRC 84-127 SNUPPS Response to IE Bulletin 84-03, " Refueling Cavity Water Seal" I.
Introduction The SNUPPS Standard Plant FSAR contains several sections which are appli-cable to the evaluation of the potential for and consequences of a refuel-ing cavity water seal f ailure. These are:
Section 9.1.2 SNUPPS Spent Fuel Storage Facility (SFSF) design, boration requirements.
Section 9.1.3 Fuel Pool Cooling and Cleanup System design, sources of normal and emergency makeup water.
Section 9.1.4 Fuel Handling System and Operations.
l Section 1.2 Fuel Building Plan Drawings.
I II. Potential for Refueling Cavity Water Seal Failure A review of the SNUPPS and Haddam Neck refueling cavity seal designs reveals several differences which make the type of failure experienced at Haddan Neck extremely unlikely at the SNUPPS plants.
Details of the SNUPPS seal design are shown in Figure 1.
The major difference is the manner in which the SNUPPS seal fits into the annular opening between the reactor vessel flange and the refueling cavity.
At the outer radius of the SNUPPS seal, near each radial stiffener, are two keepers (for a total of 48 keepers) which provide a 1/8" alignment between the seal l
assembly and the refueling cavity.
This feature preven'.s misalignment of the seal such as occurred at the Haddam Neck Plant.
The SNUPPS seal rubber material is significantly harder than the Haddam Neck seal material.
l This and the guide stud support arrangement for the SNUPPS seal provide increased resistance to the seal distortion or buckling.
If the pneunatic l
(primary) seal were to lose air pressure, leakage could occur through the seal; however, the wedge part of the SNUPPS seal provide substantial passive sealing capability.
A leak through the seal of more than one gpm for one hour will be detected, and an alarm is provided in the control room.
Also, if the leakage fills the incore instrument tunnel, this condition is alarmed in the control room.
III.. Consequences of a Gross Refueling Cavity Water Seal Failure Although the SNUPPS seal design makes a gross seal failure an unlikely event, to comply with I.E.Bulletin 84-03, a gross f ailure of the SNVPPS reactor cavity water seal was evaluated.
During fuel transfer, a gross seal failure of the SNUPPS reactor cavity water seal would, due to design of the structure, result in only a partial drainage of the refueling pool, fuel transfer canal and spent fuel pool.
Level alarms will alarm
Page 2.
locally and in the control room with a 3" drop in water level in the spent fuel pool.
Also, operators in the area of the spent fuel pool, fuel transfer canal and refueling pool would be able to visually observe a level drop in these areas.
Assuming a drainage rate similar to that reported at Haddam Neck, (200,000 gallons within 20 minutes) a drop of approximately 9 feet would occur in the refueling pool and spent fuel pool af ter 20 minutes.
A drop of 9 feet of water level represents approximately S0,000 gallons of spent fuel pool water volume.
If there is fuel in the Transfer tube, the operator will clear the tube and close the valve.
The plant operators should be able to clear the tube within 5 minutes and close the fuel transfer tube isolation valve in less than 15 minutes, thereby, limiting the amount of water lost out of the spent fuel pool to approximately 90,000 gallons.
These times are based on a review of the Westinghouse Fuel Transfer System Technical Manual, and are considered conservative.
A 9 foot drop in water level in the spent fuel pool will leave approximately 15 feet of water above the fuel assemblies.
This depth provides sufficient shielding such that the dose rate from direct radiation shine fr om stored spent fuel will not exceed allowable dose rates for the area.
Even if the transfer tube valve were not closed the fuel stored in the $3ent fuel pool will not become uncovered since the elevation of the top of the fuel assemblies are below the refueling cavity water seal elevation.
Also, the design of the spent fuel pool will not allow draining to a lesel below the top of the spent fuel racks.
Forced fuel pool cooling will not be available once the fuel pool level drops below a certain elevaticn since the fuel pool cooling pumps are tripped by level switches. The f uel pool cooling pumps will be available once refilling of the spent fuel 3001 is completed. As noted in the SNVPPS FSAR, boration of makeup water to the SFSF is not required; therefore, emergency makeup from the Essential Service Water system or fire protection system can be used in an emergency.
The ref ueling pool in containment cannot be isolated from a leaking cavity seal, therefore, all water above the seal / reactor vessel flange level will drain out into the containment.
Fuel in transit from the vessel to the transfer cart would not be exposed within 20 minutes since the top of the assembly in the full up pos* tion in the refueling machine is more than 9 feet below the normal water level.
Operator action will assure that fuel in transit is placed in a safe position in either the reactor vessel or the upending machine.
Fuel assemblies in the upending machine or the rod control cluster change assembly will be under water whenever the refueling pool water level is at or above the reactor vessel I
flange / seal elevation.
Makeup to the refueling pool, as required to replace water loss through evaporation, can be provided from the RWST via the Residual Heat Removal (RHR) system through the reactor vessel.
A procedure for mitigation of reactor cavity seal leakage has been imple-mented at Wolf Creek plant.
This procedure assures that fuel assemblies are moved to appropriate safe locations and other mitigating actions are taken in the event of a leaking cavity water seal.
A similar procedure will be implemented at Callaway Plant prior to beginning the first refuel-ing outage.
3*
I Page 3.
IV. Conclusion Based on the above evaluation, the likelihood of a refueling cavity seal f ailure, similar to that experienced at Haddan Neck, is extremely remote based on SNVPPS plant design features.
The evaluation shows that, even for the assumption of gross seal failure, SNVPPS design features provide adequate. cooling for.the spent fuel assemblies both inside containment and in the Fuel Builoing and seal repairs could be effected and plant conditions returned to normal through the use of recovery procedures.
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