A fledgling effort by the Department of Energy to revive domestic production of plutonium-238 (Pu-238) in order to fuel deep space missions by NASA shows promise but still faces challenges, according to a Government Accountability Office report released Oct. 4.
The Energy Department has demonstrated “a proof of concept” by producing 100 grams of Pu-238 since the inception of a joint NASA/DOE project in 2011. But DOE has work to do before it can meet the NASA target of 1.5 kilograms of Pu-238 annually by 2026.
Pu-238 would be used in the radioisotope power systems, or RPS, which one source likened to a “space battery.” This power source is considered more reliable for deep space missions than solar panels. NASA plans to use an RPS in Mars 2020, a “flagship” mission expected to cost more than $2 billion.
Past flagship missions that have used RPS include the Galileo, Cassini, and Curiosity missions, according to the GAO report. An RPS has a working life of a decade or more and has no moving parts. Its electrical output is low, however, about enough to power a light bulb.
But planned NASA missions could exhaust domestic supplies of Pu-238 within a decade. Large-scale U.S. production of the isotope ended in 1988 — and DOE has not bought Pu-238 from Russia since 2009.
As a result, NASA has provided DOE an average of $50 million per year since 2014 to support the RPS fuel project. NASA has indicated it needs more information from DOE before it can fully calculate the cost of the supply program.
The Energy Department has not mastered the chemical processing needed to remove the Pu-238 from irradiated material to meet the production goal.
In addition, DOE will need to employ both the Advanced Test Reactor (ATR) at the Idaho National Laboratory and the High Flux Isotope Reactor at the Oak Ridge National Laboratory in Tennessee. Both units will irradiate neptunium targets for conversion to Pu-238. But only certain positions, or locations within the reactors where targets are bundled for irradiation, are suitable for Pu-238 production, according to the GAO.
A GAO official said the Pu-238 production would create some additional waste streams for the affected facilities, but it would be a manageable amount. “DOE did not present it as a show-stopper issue given the relatively low level of Pu-238,” the GAO source said.
The report also notes that certain technology improvements now being developed could reduce the amount of Pu-238 needed to power NASA missions.
The Energy Department agreed with the issues identified by GAO and will work with NASA to complete its plans for Pu-238 production in September 2019.
