ML20217N284
| ML20217N284 | |
| Person / Time | |
|---|---|
| Site: | 07106553 |
| Issue date: | 07/15/1999 |
| From: | UNITED STATES ENRICHMENT CORP. (USEC) |
| To: | |
| Shared Package | |
| ML20217N272 | List: |
| References | |
| KY-665-03, KY-665-R01, NUDOCS 9910280167 | |
| Download: ML20217N284 (10) | |
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USEC A Global Energy Company I
l Paducah Gaseous Diffusion Plant l
KY-665 July 15,1999
[ISS Pages Total]
1 Safety Analysis Report On The "Paducah Tiger" Protective Overpack for 10-Ton Cylinders Of
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- Docket No. 71-6553
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6.0 CRITICALITY EVALUATION
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This chapter identifies and describes the nuclear criticality safety evaluation of the Padu hipping package. The evaluation demonstrates compliance with the performance requireme
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specified in 10 CFR 71.55.
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Paducah Tiger SAR 1
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6.1 Discussion and Results For criticality control, the Paducah Tiger relies upon the following features:
specification of maximum H/U ratio, or equivalently, minimum UF purity, impact absorption by the protective overpack, which prevents damage to the 48X e
cylinder sufficient to cause water in-leakage or reduction of package volume under nonnal and accident conditions, and thermal protection of the 48X cylinder by the overpack, which prevents damage to th 48X cylinder that could cause the contents to leak out or water to leak in.
k Purity control is provided in accordance with ASTM C787 [1] and ASTM C996 [2] which requires a minimum 99.5% UF6 purity. The maximum hydrogen to uranium atomic ratio (H of 0.088 which is allowed in accordance with 49 CFR 173.417, Table 6, corresponds to 0.5%
impurity, with all the impurity being hydrogen fluoride (HF). The drop, puncture, nid fire testing described in Chapter 2 demonstrates that the containment provided by the 48X cylinder not breached. Consequently, water will not lerk in, nor will the contents leak out, under accident conditions.
The testing also demonstrates that the overall dimensions of the overpack will remain essentially the same, so that the spacing assumed in modeling an array of packages i valid for both normal and accident conditions.
A criticality evaluation for 10-ton cylinders is provided in ORNUTM-11947.[3]
This cvaluation is directly applicable to the 48X cylinder and Paducah Tiger overpack. The report evaluates K, using the SCALE 4 computer code system for an infinite array of packages with optimum interspersed moderation, and identifies the worst case to be K, = 0.768 0.002. The worst case calculation is summarized in Table 6.1-1. An infinite array of damaged or undamaged i
packages remaining suberitical corresponds to a transport index for criticality control of zero.
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Paducah Tiger SA\\R pocket No. 71-6553
. Revision 1 Table 6.1-1 Summary of Criticality Evaluation Model conditions Normal and ace d:at using same model' Number ofpackages in contact Infmite kg
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- 0.002 Optimum interspersed moderation Water, specific gravity = 0.005 Close reflection by water Not applicable to infinite array l
Package size, including overpack 96.84 cm radius,389.26 cm height Internal size of 48X cylinder 60.96 cm radius,264.16 cm height Overpack material Water, same as interspersed Package contents UF.,4.5% enriched,99.5% pure,5.1 g/cm',21,069 pounds Temperature 20 C Contents geometry Solid UF. cylinder with central cylindrical void Intemal moderation No water; 0.5 % impurity entirely HF; H/U = 0.088 (1)
The Paducah Tiger overpack was conservatively modeled as a cylindrical and not a rectangular overpack.
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6.2 Packace UF; Loadine 9.M.. -
The Paducah Tiger overpack is used to msport UF. The loading consists of:
Cylinder Type:
Model 48X Maximum Weight of UF.:
21,030 pounds Maximum U-235 Enrichment:
4.5 wt %
Minimum UF Purity:
99.5 wt %
6 Transport Index for Criticality Control:
0.0 Because the contents are loaded as a liquid which solidifies upon cooling before shipment, the geometric configuration of the contents can vary somewhat. The form of the contents is the same for both uormal and accident conditions, except for variations in density relative to temperature. Several possible geometric configurations of the solid UF, and the variations of density with respect to temperature were evaluated in the ORNL criticality calculation.
The 48X cylinder is hydrostatically tested a 2d does not suffer any damage after accident testing is performed which would invalidate the hydrostatic test results. Hydrostatic testing has verified that water will not leak into the 48X cylinder after accident testing. The only moderation internal to the 48X cylinder is provided by the impurities, which may include HF, and which are limited as noted above. For the purpose of the criticality calculation, the maximum H/U ratio,0.088, is assumed.
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[Paducah Tiger SAR _ _ _ _ - - _ _ - - - - -
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- Revision 1 6.3 Model Snecification The model is described in Section 4.1 of ORNL/fM-11947. The model is based upon the Paducah Tiger overpack and most of the calculations, including the worst case, used the outer dimensions of the overpack to maintain the spacing between packages, but replaced the actual overpack materials by water at the density of the interspersed moderator.
This materials substitution is conservative, and makes the model applicable to the Paducah Tiger despite any material differences between the overpacks. The external dimensions of the Paducah Tiger are approximately 72 inches high by 76 inches wide by 153 inches long. The dimensions used in the model are slightly smaller (72.25 inches in diameter and 153.25 inches in length), resulting in closer, and therefore conservative, spacing between packages in the model array.
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MA's Docket No. 71-6553
. Revision 1 6.4 Criticality Calculation The calculations described in the ORNL/TM-11947 report are performed using the CSAS25
' sequence from the SCALE 4 computer code system with the 27 energy group ENDF/B IV cross-section library. The calculations assume an intemal geometric configu ation of the contents to j
approximate a triangular pitch lattice arrangement, a temperature of 20 *C, and a varying water density to determine the optiminn interspersed moderation. The k, values are found to be insensitive to temperature effects, fuel location in the cylinder, and cylinder spacing. The results of the study are summarized in Table 7 of the ORNL/TM-11947 report, and the worst case is summarized in Table 6.1 1.
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6.5 Critical Benchmark Experiments i
j The validation of the computer code and cross-sections was made against a series of 51 critic experiment benchmarks as described in Sections 2.2 and 4.2.5 of the ORNL/mi-11947 re I
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Peducah Tiger SAR
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6.6 References
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1.
ASTM Standard C787, Standard Specification for Uranium Hexapuoride for Enrichment.
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ASTM Standard C996, Standard Specificationfor Uranium Hexafluoride Enriched to Less Than 5% 235y,
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' ORNLITM-11947, Criticality Safey Review of 2-U2,10, and-14-Ton UF Cylinders, 6
B. L. Broadhead, Martin Marietta Energy Systems, Oak Ridge National Laboratory, October,1991.
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4 ENCLOSUkE 2 ORNUTM-11947 - Criticality Safety Review of 2 M,10, and 14-Ton UF. Cylinders
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