Plutonium‐238 oxide (238PuO2) is used in the fabrication of general purpose heat sources (GPHS) or light‐weight radioisotope heater units (LWRHUs). The heat sources supply the thermal energy used in radioisotope thermoelectric generators to power spacecraft for deep space missions and to heat critical components in the cold environs of space. Los Alamos National Laboratory has manufactured heat sources for approximately two decades. The aqueous purification of238PuO2is required, due to rigorous total Pu‐content, actinide and non‐actinide metal impurity, and neutron emission rate specifications. The238PuO2aqueous purification process is a new capability at Los Alamos National Laboratory as previously, aqueous purified238PuO2occurred at other DOE complexes. The Pu‐content and actinide and non‐actinide metal impurity specifications are met well within specification in the Los Alamos process, though reduction in neutron emission rates have been challenging. High neutron emission rates are typically attributed to fluoride content in the oxide. The alpha decay from238Pu results in &agr;,n reactions with light elements such as17O,18O, and19F resulting in high neutron emission rates in the purified238PuO2. Simple16O‐exchange takes care of the high NER due to17O, and18O. A new method to reduce the NER due to19F in the purified238PuO2is presented in this paper. The method involves addition of water to purified238PuO2, followed by heating to remove the water and liberating fluoride as HF. © 2004 American Institute of Physics