Conceptual Analysis of the Thermo-Hydraulic Characteristics of Fission Electric Cell Reactors

The United States Department of Energy, Nuclear Energy Research Initiative (NERI) Direct Energy Conversion (DEC) project has as its goal the development of a direct energy conversion process suitable for commercial development. Direct energy conversion is defined as any fission process that returns usable energy without using an intermediate thermal process. This project includes the study of the fission electric cell (FEC). Inherent to the FEC is a cathode insulated from the rest of the cell by a vacuum. This arrangement has the potential to trap energy on the cathode, increasing temperatures and potentially causing structural problems and gas emissions. This paper describes the project efforts to address this and similar thermal issues. This paper describes the development of a Thermal Model that integrates thermodynamic and heat transfer considerations into an overall Design Model. The Thermal Model begins with the basic energy balance. It then applies heat transfer methods to these models to develop a general relationship between temperature and system operating parameters. Finally, the model uses published correlations to relate the general parameters to specific geometric configurations. The Thermal Model demonstrates that the low energy densities typical of fission electric cells result in assemblies whose available heat transfer mechanisms efficiently transport any waste heat the systems generate. This results in a design at this conceptual level with significant opportunities to optimize system operations and economics using operating temperature. The model also demonstrates that for the same reasons, heat buildup has a weak correlation with system operating voltage.