Preparation and characterization of oxalate-based 237NpO2 powder

238Pu, a radioisotope heat source, is produced by irradiating reactor targets containing 237NpO2. The neptunium oxide is obtained by precipitating and calcining 237Np(IV) oxalate. The effects of oxalate precipitation conditions (temperature, reagent concentrations, valence of neptunium ion and the rate and sequence of reagent addition) on particle morphology and size distribution of 237NpO2 powder were established to provide process controls for making reactor targets. NpO2 powders were produced with a median particle size between 10 and 20 μm and with different morphologies; i.e., rosettes and square plates of varying degrees of agglomeration