A number of advanced reactor concepts and accident-tolerant fuels (ATFs) are under development or in the initial stages of deployment and testing in the nuclear power industry. Many of these concepts incorporate chemical or material forms that have not traditionally been used in the nuclear industry and may present challenges for nuclear criticality safety validation. Sensitivity/uncertainty methods are ideally suited for assessing the applicability of existing critical experiments to these potentially challenging applications. This paper presents two case studies recently completed at Oak Ridge National Laboratory (ORNL) which investigated the use of the TSUNAMI tools within the SCALE code system to perform such assessments.Many advanced reactor concepts include uranium enrichments above 5 wt% 235U but below the 20 wt% limit of low-enriched uranium (LEU). This material, referred to as high assay LEU (HA-LEU), poses difficulties across the entire infrastructure of nuclear power, including enrichment, transportation, fabrication, and storage. A potentially representative transportation package was selected to perform a criticality safety validation assessment for UF6 containing HA-LEU. Sensitivity data were generated using the TSUNAMI-3D sequence, and an assessment of the applicability of a range of critical experiments was performed using the TSUNAMI-IP tool. The critical experiments were drawn from the set of available sensitivity data files distributed with the International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook. The results indicate that a sufficient number of available experiments may be available to perform validations for these systems.Many different cladding materials and fuel dopants are included in ATFs to mitigate the consequences of a loss of coolant accident. Some of these systems have already been fabricated and introduced as lead test assemblies in commercial reactors, while others are still being developed. Several concepts were considered for pressurized-water reactors (PWRs) and boiling-water reactors (BWRs) in comparison to the current Zircaloy and UO2 fuel system. In most of these cases, the ATF materials did not significantly impact the number of applicable experiments for validation. Some fuel and cladding materials were identified, however, which may reduce the number of available experiments and which will increase the nuclear data–induced uncertainty in neutron multiplication.

Marshall, William (B.J.)↗

DOE OSTI2019

SCALE/Sampler Sensitivity Indices

The Sampler sequence of the SCALE code system for random sampling–based uncertainty analyses has recently been extended by including a sensitivity analysis. In uncertainty analyses with respect to uncertainties in the nuclear data, the determination of two multiple correlation coefficients—R2 and SPC2—allows for the identification of nuclide reactions that are significantly contributing to the investigated output uncertainty. Individual nuclide reactions are ranked by importance, allowing suggestions for additional measurements and evaluations to significantly reduce the observed output uncertainty. A brief description of the theory is provided herein, followed by application of this analysis to a sodium-cooled fast reactor pin cell.

Bostelmann, Rike↗

DOE OSTI2019

Initial Investigations of the Criticality Safety Validation Basis for HA-LEU Transportation

Many proposed advanced nuclear energy systems require so called high-assay low enriched uranium (HALEU), which has a 235U enrichment >5 wt% and <20 wt%, where the current fleet of light water reactors (LWRs) utilize enrichments of 5 wt% or less. With few benchmark experiments in HA-LEU enrichment range, the interplay of the cross sections for multiple nuclei become important, especially for LEU experiments where 1H, 16O, 235U, 238U and others are applied simultaneously in the calculation of the integral keff response. With continuing evidence that nuclear data are tuned to reproduce expected keff values for selected criticality experiments, which likely do not include those with 20 wt% 235U, particular attention must be given to validation.This paper describes the impact of recent nuclear data changes on HA-LEU and provides a preliminary sensitivity/uncertainty-based assessment of the applicability of available of criticality experiments for the validation of licensing calculations for the transportation of small quantities of 20 wt% UF6.

Rearden, Bradley↗

DOE OSTI2019