UC Berkeley

The specific power (We/kg) requirements for high powered space missions greater than 1MWe present a significant design challenge to the nuclear engineering community. Energy conversion, and the temperature at which it occurs, is central to this problem and remains a limiting factor to realizing high specific power systems. This thesis investigates a static, in-core thermionic energy conversion (TEC) cycle that uses kinetic energy from fission fragments and their resulting high energy beta decay to produce both heat for thermionic emission and ionization of an interelectrode low temperature plasma. This novel plasma ionization scheme allows for dramatically increased device efficiency and loosened design constraints; both are needed for TEC to be competitive with the dynamic Brayton cycle – currently the only technology slated for high powered space missions. We develop an electrical power model, called the Heavy Ion Thermionic Energy Conversion (HITEC) model in order to investigate electrical power characteristics of both single cell and nuclear reactor scale devices in order to assess this reactor’s performance metrics and its applicability to high powered space missions. HITEC was benchmarked against the only existing experimental data set from a de-classified joint research effort [14], and its power characteristics are in good agreement with this experimental data. The reactor scaling portion of HITEC was used to calculate the electrical performance of a 2.5MWth nuclear reactor. Four separate cases were tested on a single core design: we found that in three of the four cases, the HITEC reactor exceeded NASA’s specific power limits for the 1-10 MWe power output range (> 60We/kg). When auxiliary power was implemented for additional plasma ionization, the maximum specific power attained was 348 We/kg. This makes HITEC, an attractive static alternative to the dynamic Brayton cycle for power producing nuclear reactors applied to high power mission sets.