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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.
Kaltrina Shehu, Daniel Bonete Wiese, Christian Reiter
Nuclear Science and Engineering | Volume 200 | Number 1 | March 2026 | Pages S366-S377
Research Article | doi.org/10.1080/00295639.2025.2455348
Articles are hosted by Taylor and Francis Online.
The Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) reactor is utilized for active engagement in international efforts toward the goal of decreasing usage of highly enriched uranium in civil cycles. This goal can be achieved by changing the current fuel system with a high-density low-enriched uranium fuel. This work is part of a broad parameter study that aims to assess different potential conversion scenarios for FRM II, Germany’s most powerful neutron source. Several geometrical parameters of the core are the subject of the parameter study. Therefore, investigation of the core in terms of neutronics and thermal hydraulics is crucial. The components of the coupling between neutronics and thermal hydraulics are Serpent 2 and Ansys CFX, respectively. Because of the rotational symmetry of the FRM II core, the current thermal-hydraulic calculations are performed on one single plate. Despite the robust and efficient nature of this approach, in this work, the neutronics and computational fluid dynamics (CFD) calculations are taken a step further by taking into account the influence of the hot and cold source installations on the thermal-hydraulic behavior. Furthermore, a proof of concept of the CFD capabilities sequentially coupled to neutronics to model the full core is beneficial for future calculations. Two different cases representing a symmetric heating profile and an asymmetric profile are shown and discussed. The total power deposited in the core remains constant in both cases, while the maximum fuel temperature, cladding temperature, and water temperature calculated for the asymmetric heating case increase by 1.7%, 1.5%, and 1.5%, respectively. Therefore, power asymmetry has minor effects.