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Discussion of Contigencies
Guidelines For Preparing Criticality Safety Evaluations at Department of Energy Non-Reactor Nuclear Facilities
Evaluation and Results cont'd - s3007cn10052

As stated previously, each subassembly consisted of four fuel plates. Each subassembly
has an insulating air gap of 0.030 inches (0.0762 cm) between the outer fuel plates and the outer
cladding. The dimensions of a subassembly are given as 3.665 inches x 0.426 inches x 25.25
inches (9.309 cm x 1.082 cm x 64.140 cm). A full BORAX V Superheater fuel assembly consists
of five subassemblies and has dimensions given as 3.633 inches x 3.875 inches x 25.462 inches
(9.228 cm x 9.843 cm x 64.674 cm). The superheater fuel assembly was modeled as previously
described and shown in Figures 4, 5, & 7.
Currently 34 BORAX V Superheater Fuel Elements are in inventory at the ICPP. This
inventory consists of a combination of central and peripheral fuel elements, each at a U235
enrichment of approximately 93%. The maximum U235 loading per assembly is listed as 679
grams for a peripheral assembly and 429 grams per central assembly. Several series of
calculations were performed to determine reactivity effects. The calculational models considered
in this evaluation consisted only of the highly loaded peripheral assemblies.
Evaluated in the first series of cases were various arrays surrounded only by water. This
was done to determine the minimum number of assemblies needed to achieve a critical system. A
pictorial representation of reactivity as a function of array size is given in Figure 8. Each block
represents one BORAX V Superheater fuel assembly. As shown in Figure 8, a 3 x 3 x 1 array of
fuel assemblies exceeded the keff+ 2s > 0.95 safety limit criteria and a 3 x 4 x 1 array is shown to
be critical with keff+ 2s > 1.0.
Considered in the next series of calculations were arrays that were reflected not only by
water but also by concrete. Due to the physical dimensions of the fuel assemblies and the width
of the concrete channel walls, it was only possible to store fuels in arrays that were either one or
two assembly units wide. In this series of calculations, in which the concrete12 channel walls and
basin floors were modeled, various arrangements of fuel assemblies were evaluated. These
arrangements are shown in Figure 9. As shown in Figure 9, a 2 x infinite x 1 array of fuel
elements placed in a water filled concrete storage channel gives a keff+ 2s = 1.0386. Current
technical specifications (TS/S 4.6A1) limit each storage bucket to four BORAX V Superheater

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