Xenon-135m in Nuclear Thermal Propulsion

摘要

There has been recent interest at NASA for developing Nuclear Thermal Propulsion (NTP) to support a human Mars mission in the 2030's time frame. NTP offers superior performance over chemical propulsion systems and can greatly reduce the overall mass (and therefore cost) and travel time of a Human Mars mission. This work investigates the effect of the metastable state of ~(135)Xe (~(135m)Xe) on the operation of thermal NTP systems. Current models indicate that ~(135m)Xe has an appreciably larger absorption cross-section than the ground state of ~(135)Xe but ~(135m)Xe only has a 15.3 minute half-life. NTP systems work in a unique high power density, medium time length regime where the effect of ~(135m)Xe has a notable effect on the reactivity of the NTP reactor. In LEU graphite composite SULEU NTP systems it was found that the maximum decrease in reactivity during operation was 62.8 % greater when ~(135m)Xe was included in the burn up model. In LEU tungsten cermet SCCTE NTP systems, it was found that the maximum decrease in reactivity during operation was 93.1% greater when ~(135m)Xe was included in the burn up model. This work was accomplished with infinite lattice calculations in Serpent 2 and the TENDL 2014 nuclear library cross-sections for ~(135m)Xe. Understanding the effects of ~(135m)Xe and generating validated cross sections for ~(135m)Xe will be important in developing NTP control systems.