ML20207G421
| ML20207G421 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/30/1986 |
| From: | Standerfer F GENERAL PUBLIC UTILITIES CORP. |
| To: | Travers W Office of Nuclear Reactor Regulation |
| References | |
| 0149P, 149P, 4410-86-L-0220, 4410-86-L-220, NUDOCS 8701070294 | |
| Download: ML20207G421 (3) | |
Text
e GPU Nuclear Corporation Ng gf Post Office Box 480 Route 441 South Middletown, Pennsylvania 17057-0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Nurnber:
(717) 948-8461 4410-86-L-0220 Document ID 0149P December 30, 1986 TMI-2 Cleanup Project Directorate Attn: Dr. W. D. Travers Director US Nuclear Regulatory Commission c/o Three Mile Island Nuclear Station Middletown, PA 17057
Dear Dr. Travers:
Three Mile Island Nuclear Station, Unit 2 (TMI-2)
Operating License No. DPR-73 Docket No. 50-320 Canister Dewatering The purpose of this letter is to provide additional information in support of GPU Nuclear's request for NRC approval of an alternative dewatering acceptance criterion for defueling canisters. GPU Nuclear letter 4410-86-L-0193 dated November 10, 1986 requested NRC approval for a fuel canister dewatering acceptance criterion based on the quantity of exposed catalyst in the canister. The dewatering acceptance criterion in this letter was expressed in terms of the weight of water removed as a function of canister payload.
Satisfying that expression would achieve at least a factor of safety of three on the required quantity of catalyst. The letter also requested NRC concurrence that a catalyst factor of safety of 1.5 is acceptable.
GPU Nuclear has determined that a fuel canister dewatered to 25% void volume would expose, as a minimum, 25 grams of catalyst for the canister in any orientation. This minimum quantity of exposed catalyst considers the maximum allowable tolerance in the placement of the catalyst beds in the lower head; i.e., previously addressed in the November 10, 1986 letter. As noted in the referenced letter, 65 grams of exposed catalyst achieves a catalyst factor of safety of 4.2 for 1760 pounds (800 kg) of fuel debris. Since the factor is proportional to the quantity of catalyst, 25 grams of exposed catalyst would achieve a catalyst factor of safety of 1.6, i.e., = 4.2 x (25/65), for 1760 pounds of fuel debris. Thus, dewatering a fuel canister to obtain 25% void 8701070294 861230 PDR ADOCK 05000320 P
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0 GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation 7
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Dr. Travers December 30, 1986 4410-86-L-0220 volume would achieve a minimum catalyst factor of safety greater than 1.5 for j
any canister payload less than or equal to 1760 pounds since the factor of safety is inversely proportional to the quantity of fuel debris. Therefore, GPU Nuclear proposes that a 25% void volume is an acceptable dewatering criterion for fuel canisters.
The November 10, 1986 letter also proposed that the maximum internal pressure be determined for each canister not dewatered to at least 50% void volume in order to assure that the maximum canister internal pressure in the Safety Analysis Report for the NuPac 125B Shipping Cask (Cask SAR) is not exceeded.
This determination would be based on projecting the hydrogen appearance rate (obtained from the dewatered canister gas sample) for one year, the actual void volume of the devfatered fuel canister, and the remaining assumptions given in the Cask SAR. This determination would be maoe to show that the internal pressure calculated in the Cask SAR would be bounding. In lieu of determining the maximum internal pressure for each fuel canister dewatered to less than a 50% void volume, GPU Nuclear has determined the maximum pressure in a shippable canister based on a one year buildup of gases generated from the radiolysis of water entrained in the canister. This pressure is less than the pressure calculated in the Cask SAR.
The cask certificate of compliance (C of C) requires that the quantity of hydrogen be limited to 5 percent by volume of the canister gas (void) volume, or 5 percent by volume of the quantity of oxygen in those portions of the canister which could have hydrogen greater than 5%, for twice the expected shipping time. The shipping time is the summation of the canister storage time at TMI-2 (TO), cask loading time (6 days), cask transit time (10 days),
and cask unloading time (11 days) or To + 27 days. To meet this C of C requirement, GPU Nuclear determines the allowable canister storage time at TMI-2 (To) based on the limiting gas appearance rate (either hydrogen or oxygen) using the following expression:
0.05V = 2 x (To + 27) x R Where: V = Canister Void Volume, liters To = Allowable Storage Time, days R = Limiting Gas Appearance Rate, liters / day j
The worst case shippable canister would have no allowable storage time (To =
not credible since based on the chemical formula for water, H 0, the oxygen 2
I appearance rate could not be greater than one-half of the hydrogen appearance rate). Thus, the total gas appearance rate would be R = (2)(0.05)(V)/((2)(27))
or (0.00185)(V) liters / day. For a one-year buildup, the total quantity of radiolytic gas in the canister is (0.00185)(v)(365) or less than (0.68)(V) liters. The quantity of argon (or other cover gas) in the canister is (2)(V) liters since 2 atm. of cover gas is injected into the canister.
1 Dr. Travers December 30, 1986 4410-86-L-0220 Conservatively, considering that the radiolytic gas appearance rate and the injection of the cover gas are at a temperature of 320F, the canister internal ~
pressure at 2000F (the temperature assumed in the Cask SAR) from the radiolytic gases and the cover gas is
[O.68V+2V)lx b k
2000F + 4600 V
320F + 4600 Y
Y or 3.6 atm. Including water vapor at 2000F, the total internal pressure in the worst case shippable canister is 3.6 + 0.78 or approximately 4.4 atm. At an atmospheric pressure of 14.7 psi, the internal pressure is 50 psig, i.e.
(4.4-1)(14.7). This pressure is for the worst case shippable canister following a one year buildup of radiolytic gas and is independent of canister void. volume and canister type. Therefore, further pressure determinations of dewatered canisters are not necessary since the pressure in a shippable canister following a one year buildup of gas could not exceed the pressures calculated in the Cask SAR.
In conclusion, GPU Nuclear proposes that a 25% void volume is an acceptable dewatering criterion for fuel canisters and that this reduction from the previous dewatering acceptance criterion of 50% does not impact the bounding evaluations given in the Cask SAR. Additionally, GPU Nuclear is evaluating the void volume required to achieve a catalyst safety factor of 1.5.for filter and knockout canisters. This' evaluation, when corppleted, will be submitted for your review and approval.
Sincerely,h kua N
F. R. Standerfer Vice President / Director, TMI-2 FRS/RDW/eml