create a critical configuration with the peripheral BORAX V Superheater fuel assemblies was
made. At the time of the attempt only sixteen peripheral assemblies existed. The sixteen
peripheral assemblies were configured in a 4 x 4 array as shown in Figure 5. As shown by the
results given in that report this array was slightly subcritical. Estimation by the inverse count rate
curves showed that seventeen assemblies would be critical and eighteen assemblies would be
The resulting multiplication factor for the 4 x 4 array was calculated to be
keff ± 1s = 1.0032 ± 0.0034. This array was modeled using KENO V.a along with 27 group
ENDF/B-IV cross section library. As discussed previously, this array was shown by experiment
to be slightly subcritical, but was shown in the KENO V.a model to be critical thus indicating no
code bias compensation is needed for this case.
The second part of the validation for this report involved the modeling of two critical
experiments involving arrays of SPERT-D fuel elements. The SPERT-D fuel is a uranium-
aluminum plate type fuel. Each fuel element contained about 300 g of U235 in twenty two
aluminum-clad flat plates. Each fuel plate consisted of a uranium-aluminum alloy core (93.17
weight % U - Al), containing 23.8 w/o uranium, completely clad with 0.02 inches (0.0508 cm)
thick type 6061 aluminum. Each fuel plate slid into a set of grooved side plates contained inside a
3 inch (7.62 cm) square, type 6060-T6 aluminum tubing, 27.625 inches (70.1675 cm) long. An
example of the SPERT-D fuel is given in Figure 6. A more detailed description of this fuel can be
found in Reference 8.
The critical arrays assembled consisted of a combination of full and partial fuel assemblies.
Each of the critical arrays were moderated and reflected with demineralized water. Two arrays
were modeled for the purposes of validation. The first of the arrays modeled was listed as the 4 x
3.16 x 1 array with the 0.25 inches (0.635 cm) water gap. (The 3.16 indicates that only four of
the possible twenty two fuel plates were present in four of the fuel assemblies present in the
array.) The effective multiplication factor was calculated to be keff ± 1s = 1.0016 ± 0.0033.