Assessment of the integration of a switched nuclear isomer material with a kinematic Stirling engine

• Published in: Applied thermal engineering 2024-01, Vol.236, p.121708, Article 121708
• Main Authors: Dyreby, John, Shumaker, Justin, E. Schaefer, Kristin, Corey, John, J. Carroll, James, J. Chiara, Christopher, Nellis, Gregory
• Format: Article
• Language: English
• Subjects: Nuclear; Power generation; Second-order model; Stirling engine
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2023.121708

•Switched nuclear isomer material provide energy density that is orders of magnitude larger than combustion fuels.•The integration of kinematic Stirling Engine power converters with switched nuclear isomer material is both feasible and attractive from a power density standpoint for applications in the 6 kW to 60 kW power range.•The Stirling Engine provides particular advantages relative to dealing with the inherently time varying heat output from the from the switched nuclear isomer material. Presently, power systems are limited by the source and energy density of the chemical fuels that are currently in use. In response to this challenge, nuclear energy sources are being developed. Metastable nuclear states, or isomers, have an intrinsic energy density that is many orders of magnitude larger than chemical fuels. Through isomer depletion (or switching), these materials can be transformed from a long-lived half-life energy-storage state to a shorter-lived half-life energy-releasing state. The abundance of energy released by switched nuclear isomer (SNI) materials introduces unique engineering challenges for the power conversion system. Once an SNI material has been switched, its heat output decays with time. In contrast to hydrocarbon-based fuels, which can be throttled, generating constant power from an SNI system requires sufficient material based on duration of use and system efficiency. Despite these challenges, SNI materials could be used to replace chemical fuels for relatively high-power applications providing months of power from a compact energy source. The purpose of this work is to explore the coupling of an SNI heat source to a kinematic Stirling engine in order to assess the potential of such a system. First, the characteristics of a reference SNI material are discussed in the context of the conversion efficiency and power density of the power conversion system that it is coupled to. Second, the integration of an SNI with a kinematic Stirling engine is explored at two power levels, 6 kWe and 60 kWe, in order to explore the feasibility and efficiency of such a power system. In order to carry out this study, a second-order Stirling engine model (the Stirling Engine Trade-space Tool, or SETT) has been developed. The potential of the SETT tool to predict performance trends has been shown through comparison of the predicted to the measured performance for two baseline, well-documented Stirling engines: the GPU-3 (nominally 6 kW) and Mod II (nominall