Year
2016
Abstract
Plutonium-238 produces heat as it decays and can be used to power systems that require high power density and independence from external power sources. A new plutonium-238 oxide sample represents the first end-to-end demonstration of a plutonium-238 oxide preparation capability in the United States since production of the material ceased in the late 1980s. Chemical purity and plutonium-238 content has been determined by chemical analysis at Los Alamos National Laboratory (LANL), and demonstrates that the plutonium-238 oxide meets specifications for use in thermoelectric generators. Chemical and isotopic analysis will be used to verify production efficiency models and determine whether adjustments need to be made before scaling up the process at Oak Ridge National Laboratory (ORNL). Production at ORNL begins with a mixture of neptunium oxide and aluminum, pressed into high-density pellets. Irradiating the pellets in the High Flux Isotope Reactor (HFIR) creates neptunium-238, which quickly decays and becomes plutonium-238. Irradiated pellets are dissolved and the plutonium is separated from the remaining neptunium. The plutonium oxide is shipped to LANL. Analysis capabilities at Los Alamos have recently been expanded and improved to provide rapid turnaround and increased accuracy in chemical characterization of the plutonium oxide. Spectroscopic plutonium assay determines the total plutonium content. Plutonium isotopic distributions are determined by inductively coupled plasma mass spectrometry, which also provides concentrations of americium-241 and neptunium-237. Radiochemical analyses are completed by separating uranium and thorium isotopes from the solution using UTEV A® and TEV A® columns, respectively. Uranium and americium concentrations are determined by alpha counting, and thorium by UV-Vis spectrophotometry. Trace metals are determined using DC arc spectrometry. Once fully characterized, the newly generated material that is produced at ORNL can be blended with existing plutonium-238 oxide to restore it to a power level that is high enough for efficient use in thermoelectric generators. Initially, 300 to 400 grams of the material will be produced per year in 2019 through 2023. Automation and scale-up processes will allow ORNL to produce an average of 1.5 kilograms per year in 2024 and thereafter, and will provide the nation with a long-term capability to produce radioisotope power.