Validation of KENO V.a for highly-enriched uranium systems with hydrogen and/or carbon moderation

This report describes the validation of KENO V.a using the 27-group ENDF/B-IV cross section library for systems containing highly-enriched uranium, carbon, and hydrogen and for systems containing highly-enriched uranium and carbon with high carbon to uranium (C/U) atomic ratios. The validation is in accordance with ANSI/ANS-8.1-1983(R1988) and has been performed for two separate computational platforms: an IBM 3090 mainframe and an HP 9000 Model 730 workstation, both using the Nuclear Criticality Safety Software (NCSS) code package. Critical experiments performed at the Oak Ridge Critical Experiments Facility, in support of the Rover reactor program, and at the Pajarito site of Los Alamos National Laboratory were identified as having the constituents desired for this valiation as well as sufficient experimental detail to allow accurate construction of KENO V.a calculational models. Calculated values of k_eff for the Rover critical experiments, which contain uranium, hydrogen, and carbon, are between 1.0012 +/- 0.0026 and 1.0245 +/- 0.0023. Calculation of the Los Alamos experiments, which contain uranium and carbon at high C/U ratios, yields k_effvalues between 0.9746 +/- 0.0028 and 0.9983 +/- 0.0027. Safety criteria can be established for both types of systems using these data.