Experiments of water-moderated plutonium metal arrays: part I — description

Experiments of water-moderated plutonium metal arrays: part II — analysis

“…Since it is not known which dimension was more accurate, the horizontal spacing is taken to be an average of the reported value and the converted English value, as recommended by the experimenter. 3 This method leads to a systematic uncertainty of ±0.04 mm for the 90 mm spacing, ±0.29 mm for the 100 mm spacing and ±0.06 mm for the 120 mm spacing. No average value or systematic uncertainty was needed for the 76 mm spacing since these cans were close-packed.…”

“…A typical composition of methyl methacrylate is as follows: 8.03 weight percent hydrogen, 59.72 weight percent carbon, 32.14 weight percent oxygen, and 0.11 weight percent other. This composition was used in this analysis with a density of 1.18 g/cm 3 . The bottom of the tank was modeled as a pure aluminum square slab with a thickness of 1.91 cm and length of 91 cm.…”

“…For Case 17, this difference was 0.0026 ± 0.0008. (a) Composition is standard material from the MCNP manual with the density increased to 3.07 g/cm 3 , due to the additional Fe. Since the walls have little effect on keff, it is assumed that variations in the concrete composition are negligible.…”

“…Calculations show that neglecting the impurities has a statistically insignificant effect on the value of k eff . Therefore, after subtracting the impurities, the plutonium density of the plutonium was calculated to be 19.54 g/cm 3 for the 2x2x2 arrays, 19.52 g/cm 3 for the 2x2x3 arrays, 19.53 g/cm 3 for the 2x2x4 and 2x2x5 arrays, and 19.54 g/cm 3 for the 3x3x3 arrays (Set 2). Also since the isotopic concentration of the plutonium was measured in 1965, the 241 Pu content was adjusted to account for the buildup of 241 Am from the time of measurement to a time during which these experiments were performed (from July 1965 to January 1975 for Set 1 and from July 1965 to May 1982 for Set2).…”

“…As part of the International Criticality Safety Benchmark Evaluation Project (ICSBEP), these experiments were evaluated for use by nuclear criticality specialists in validating computer codes and cross sections. 2,3 This paper will form benchmark descriptions of the experiments, including geometry and material data. In addition, k eff values using the benchmark models will be found for two computer codes and three cross section libraries, namely MCNP 4 with continuous energy ENDF/B-V 5 and ENDF/B-VI 6 cross section data and KENO-V.a 7 with 27-group ENDF/B-IV cross sections.…”