Methodology - s3007cn10045

DOE-STD-3007-93

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

supercritical.

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.

2-14