ML20098D896
| ML20098D896 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 09/17/1984 |
| From: | Larson C NORTHERN STATES POWER CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| IEB-84-03, IEB-84-3, NUDOCS 8409280022 | |
| Download: ML20098D896 (4) | |
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Nodhern States Power Company 414 Nicollet Mall Minneapohs, Minnesota 55401 Tetephone (612) 330-5500 September 17, 1984 Mr J G Keppler Regional Administrator, Region III Office of Inspection and Enforcement US Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137 Prairie Island Nuclear Generating Plant Docket No. 50-282, License No. DPR-42 Docket No. 50-306, License No. DPR-60 In response to IE Bulletin 84-03, the following is offered.
Potential for and the consequences of a refueling cavity water seal failure have been evaluated. The evaluation included consideration of:
gross seal failure; maximum leakage rate due to failure of active components such as inflated seals; makeup capacity; time to cladding damage without operator action; potential effect on stored fuel and fuel in transfer; and emergency operating procedures.
The gap between the reactor vessel flange and the refueling cavity floor is 2 inches. The gap is bridged by a single inflatable seal.
See Figure attached. Testing has shown that the seal is leaktight whether inflated or deflated. Failure of an active component will not cause significant leakage f rom the cavity.
Since the Prairie Island seal is a passive component, we could not postulate a credible failure that would result in fuel clad damage.
In order to address the items in the Bulletin, however, an event which we consider extremely unlikely was postulated.
The seal is covered with holddown plates before flooding the cavity.
We postulated one holddown plate was removed and the seal under the plate torn away, opening the 2-inch gap between the adjacent helddown plates.
Conservative calculations give an initial leakage rate of about 4200 gal / min.
Makeup can be supplied from the CVCS blender to the spent fuel pool, the CVCS holdup tanks to the spent fuel pool, or the RHR pumps from containment sump B to the reactor coolant system.
Flow rates and capacities of these methods are:
SEP 2 4 B84 8409280022 840917 PDR ADOCK 05000282 G
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J G Keppl;r September 17, 1984 Page 2 Northem States Power Company FLOWRATE CAPACITY CVCS blender from RMU Tank 80 gpm/ pump 40,000 gal / tank
.(4 pumps) 320 gpm 160,000 gal CVCS holdup tanks 500 gpm 18,000 - 65,000 gal RHR from Sump B (1 pump) 2,000 gpm unlimited (2 pumps) 4,000 gpm recire Makeup could result in a decrease in boron concentration. Conse rvative calculations show that fuel in all locations remains suberitical.
Assuming the maximum leakage rate and no operator action, fuel in the reactor vessel, refueling cavity fuel transfer area and spent fuel pools will remain underwater and no fuel damage will result.
Fuel being handled by the manipu-lator crane in containment or the spent fuel handling crane in the spent fuel pool area could become uncovered without operator action.
The estimated mini-mum time to fuel clad damage is 50 minutes after initiation of the leak.
The operator has at least 30 minutes to begin lowering the fuel assembly into an area where it will remain covered before high radiation levels caused by reduced shielding would require his departure from the area.
The procedure governing reactor refueling operations addresses a decrease in refueling cavity water level. Alarm response procedures for containment sump C high level or spent fuel pool low level lead the operator to the refueling procedure above. The immediate actions of the procedure are to lower any fuel in the manipulator crane or on the spent fuel handling crane to a level below the cavity _ seal.
In the worst case, active fuel would be covered with 7 inches of water. This would result in 133R/hr at the surface of the water and 64mR/hr at the refueling floor level above the assembly. Although there is a signifi-cant increase in radiation level, repair of the seal could be done.
In conclusion, the evaluation showed there is no active failure which could cause significant leakage from the refueling cavity. The leakage that was postulated here is extremely unlikely and small enough that operator action can easily place the fuel assembly where it will remain covered.
Unit 2 is currently shutdown for refueling.
It is intended that fuel handling begin on Friday, September 21.
c -P cq m C E Larson Vice President Nuclear Generation ec: G Charnoff J Hard NRC Document Control Desk Attachment L
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UNITED SiATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket No. 50-282 Docket No. 50-306 RESPONSE TO I.E. BULLETIN 84-03 Northern States Power Company, a, Minnesota corporation, hereby submits the response to I.E.Bulletin 84-03 for the Prairie Island Nuclear Generating Plant.
This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY By:
C. E. Latson)
Vice President Nuclear Generation I M day of d > J d-1984, before me a notary public On.this-in and for said County, personally appeared C. E. Larson, Vice President Nuclear Generation, and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof and that to the best of his knowledge, information and belief, the statements made in it are true and that it is not interposed for delay.
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