The computational bias of criticality safety computer codes must be established through the validation of the codes to critical experiments. A large collection of suitable experiments has been vetted by the International Criticality Safety Benchmark Evaluation Project (ICSBEP) and made available in the International Handbook of Evaluated Criticality Safety Benchmark Experiments (ICSBEP Handbook). More than 600 cases from this handbook have been prepared and reviewed within the Verified, Archived Library of Inputs and Data (VALID), which is maintained by the Reactor and Nuclear Systems Division at Oak Ridge National Laboratory. The performance of the KENO V.a and KENO-VI Monte Carlo codes within the SCALE 6.2.4 code system is assessed using the VALID models of benchmark experiments. A range of nuclear cross section libraries based on Evaluated Nuclear Data File (ENDF)/B-VII.1 in both multigroup (MG) and continuous energy (CE) formats is considered.The critical experiments available to validate the KENO V.a code cover 15 broad categories of systems. These systems use a range of fissile materials, including a range of uranium enrichments, various plutonium isotopic vectors, and some mixed uranium/plutonium oxides. The physical forms of the fissile material also vary and are represented as metal, solutions, or arrays of rods or plates in a water moderator. The neutron energy spectra of the systems also vary and cover fast, intermediate, mixed, and thermal spectra. Over 550 of the total cases use the KENO V.a code for the four nuclear data libraries considered in this report.The validation of the KENO-VI code considers 57 cases drawn from three broad categories of systems. The fissile materials in the added systems vary and include high and intermediate enrichment uranium and mixed uranium/plutonium. The physical form of the fissile material is either metal or oxide rod arrays in water. Both fast and thermal neutron energy spectra are represented in the systems considered.The results indicate generally good performance of both the KENO V.a and KENO-VI codes across the range of systems analyzed except for intermediate and mixed spectrum solution systems fueled with 233 U. The bias of calculated keff from expected values is less than 1% Δk in all other cases, and it is less than 0.5% Δk for most systems. The CE library generally manifests smaller magnitude biases than the MG data. The systems that are only considered in KENO-VI show slightly larger biases than the same experiment categories modeled in KENO V.a. This is likely due primarily to modeling systems having more geometric complexity, making them more difficult to describe accurately.Two additional conclusions can be drawn from the results of this validation effort: (1) that some evaluations in the ICSBEP Handbook should be updated to provide more rigorous expected keff values and uncertainties, and (2) that potential cross section errors can be identified by detailed review of the results of this validation. Biases are generally lower in SCALE 6.2.4 than in SCA...

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