UN Development of uranium nitride composite for space reactors application

(U1-x,Zrx)N

FROM UN TO (U1-X,ZrX)N COMPOSITE: A POSSIBLE FUEL FOR SPACE REACTORS KTH Fuel Lab Introduction option due to the combination of its fuel, and also the increasing in high fissile nuclide density, high thermal conductivity resulting in low thermal conductive, and a high thermal gradient over the fuel, which Nuclear reactors has being melting point. could minimize the fission gas considered for space application for release and swelling. All these factors support human life, in Moon and Mars However under irradiation, nitrides make this compound of great interest exploration, and for propulsion fuel tend to swelling significantly, for application in space reactors. purposes. Nuclear powered leading to pellet-clad mechanical spacecraft will enable missions well interaction, which has given cause to (U1-x,Zrx)N manufacture consists of beyond the capabilities of current the majority of the fuel pin failure in development of three stages; chemical, radioisotope thermoelectric the past. It was observed that the manufacturing UN and ZrN (both in generator and solar technologies. nitride fuel swelling is sensitive to the high purity, i.e. O and C <500 ppm), fuel temperature rather than to the and then the processing of (U,Zr)N Characteristics including operating achieved burnup, which is quite composite itself. Obtaining a product temperature, coolant, neutron flux, significant for space reactor of high purity and ensure the neutron spectrum, fuel type, and applications. achievement of homogeneous solid lifetime must all be considered in the solution are mandatory for this space reactor design. However, while KTH Fuel Lab activities composite shows the expected all of these factors are important, the performance under irradiation, but reactor operating temperature is the this is still one major challenge. primary criteria. Since the reactor size KTH Fuel Lab has been development nitrides fuel fabrication technology for must be kept to a minimum, high Investigation on processing by application in GEN-IV reactors and operating temperatures (>1,000 K) mechanical alloying and sintering for accelerator-driven sub-critical are desirable to enable high thermal plasma sparking (SPS) has been systems (ADS), for nuclear waste conversion efficiencies and high conducted to establish parameters to transmutation. specific energies. This high produce a material that meets nuclear temperature is even higher than the Having established good experience fuel space reactor specifications. specified for the next generation in UN fabrication by the hydriding- Additionally, thermo physical test reactors (GEN-IV). Moreover, space nitriding process, KTH Fuel Lab has such as thermal diffusivity and fission reactors may be required to specific heat are programmed to operate in this temperature for 15–20 started a research stream of manufacturing and characterization of allow evaluation of different years without the benefit of compositions of this composite as maintenance. (U1-x,ZrX)N compound nitride. It has been suggested that if in solution with fuel, as well as to drive a phase transformation study to investigate These entire requirements turn the ZrN, the performance of nitride fuel the occurrence of a miscibility gap for focus to the UN nuclear fuel. Uranium could be improved. As the solution is some compositions. nitride is an attractive material fuel more stable at high temperature this leads to reduced dissociation of the 2

Preliminary results of this project were presented at the workshop of Democritus (Demonstrators for Conversion Reactor, Radiator and Electric Propulsion Systems for Thrusters) conducted in Jan. 26-27 2016. DEMOCRITOS is an European consortium with the objective of investigate the necessary demonstration activities in order to mature technologies for nuclear electric propulsion (NEP) in space. KTH Fuel Lab is following this initiative to adequate the research project in progress with the fuel requirement update.