Development program to recycle and purify plutonium-238 oxide fuel from scrap

Nuclear Materials Technology (NMT) Division of Los Alamos National Laboratory (LANL) has initiated a development program to recover & purify plutonium-238 oxide from impure sources. A glove box line has been designed and a process flowsheet developed to perform this task on a large scale. Our initial effort has focused on purification of (PuO2)-Pu-238 fuel that fails to meet General Purpose Heat Source (GPHS) specifications because of impurities. The most notable non-actinide impurity was silicon, but aluminum, chromium, iron and nickel were also near or in excess of limits specified by GPHS fuel powder specifications. U-234 was by far the largest actinide impurity observed in the feed material because it is the daughter product of Pu-238 by alpha decay. An aqueous method based on nitric acid was selected for purification of the (PuO2)-Pu-238 fuel. All aqueous processing used high purity reagents, and was performed in PTFE apparatus to minimize introduction of new contaminants. Impure (PuO2)-Pu-238 was finely milled, then dissolved in refluxing HNO3/HF and the solution filtered. The dissolved Pu-238 was adjusted to the trivalent state by an excess of reducing reagents to compensate for radiolytic effects, precipitated as plutonium(III) oxalate, and recovered by filtration. The plutonium(III) oxalate was subsequently calcined to convert the plutonium to the oxide. Decontamination factors for silicon, phosphorus and uranium were excellent. Decontamination factors for aluminum, chromium, iron and nickel were very good. The purity of the (PuO2)-Pu-238 recovered from this operation was significantly better than specifications. Efforts continue to develop the capability for efficient, safe, cost-effective, and environmentally acceptable methods to recover and purify (PuO2)-Pu-238 fuel in a glove box environment. Plutonium-238 materials targeted for recovery includes impure oxide and scrap items that are lean in Pu-238 values.