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DTRA’s advancements in nuclear and radiological detection
A new, more complex nuclear age has begun. Echoing the tensions of the Cold War amid rapidly evolving nuclear and radiological threats, preparedness in the modern age is a contest of scientific innovation. The Research and Development Directorate (RD) at the Defense Threat Reduction Agency (DTRA) is charged with winning this contest.
Peter Schwanke, Eleodor Nichita
Nuclear Science and Engineering | Volume 200 | Number 4 | April 2026 | Pages 1012-1046
Regular Research Article | doi.org/10.1080/00295639.2025.2497024
Articles are hosted by Taylor and Francis Online.
Space-time Analysis with Implicit Neutron Transport (SAINT) is a newly developed general computational framework for high-fidelity, multigroup space-time kinetics analyses. It is based on using an implicit time discretization scheme to reduce the time-dependent neutron transport equation to a series of time-independent, fixed-source transport problems that can be solved directly by any static neutron transport solver without the need for code modifications. SAINT can thus be used with any angle and spatial discretization approach. Results presented here use the method of collision probabilities as implemented by the transport code DRAGON. To demonstrate its functionality and to verify its results, SAINT is applied to the two-dimensional cases of Phase I, the kinetics phase, of the Organisation for Economic Co-operation and Development, Nuclear Energy Agency C5G7-TD benchmark. The test cases consist of control rod insertions and moderator voiding in four fuel assemblies of a miniature light water reactor with each assembly consisting of a 17 ×17 arrangement of fuel pins. The transient total core fission rates for the various test cases are found to be within ±2% of the values available from the Michigan Parallel Characteristics Transport code (MPACT). During maximum rod insertion and moderator voiding, the distribution in the fission rates of the individual fuel pins (normalized to steady state) are found to vary by as much as 18% from their steady-state values for the rod insertion cases and by 28% for the moderator-voiding cases.