Bart Leahy
October 15th, 2017
Plutonium-238 fuel (in the form of a ceramic) glows with the heat of its natural decay inside a protective cylindrical shell of graphite, during the assembly of the heat sources for the electrical power system on NASA’s Curiosity Mars rover at the Department of Energy’s Idaho National Laboratory. Photo & Caption Credit: Department of Energy / NASA
Some of NASA’s most accomplished deep-space missions—including Voyager, Cassini, and Mars Science Laboratory—have relied on radioactive plutonium-238 for onboard power and heat. However, a recent Government Accountability Office (GAO) report states that despite efforts to restart domestic plutonium production, NASA is in danger of not having enough of the radioactive material for future missions by the mid-2020s.
A Plutonium-238 oxide pellet glowing from its own heat. Photo Credit: Department of Energy
The long road to shortage
Much of NASA’s problem with plutonium has been a result of the United States’ up-and-down relations with Russia. With a lessening of tensions, the U.S. stopped making and processing plutonium-238 (Pu-238) in 1988 and began importing it from the Russians.
The U.S. facility used to make the highly radioactive material produced Pu-238 as a byproduct of producing nuclear weapons. With the end of the Cold War, that facility was shut down. In 2009, as part of the Strategic Arms Reduction Treaty (START), Russia stopped sending fissile materials to the U.S.
Another GAO report notes: “[…], DOE currently maintains about 35 kilograms (kg) [77 pounds] of Pu-238 isotope designated for NASA missions, about half of which meets power specifications for spaceflight. However, given NASA’s current plans for solar system exploration, this supply could be exhausted within the next decade.”
A 2011 Planetary Science Decadal Survey (for the years 2013–2022) expressed its concern about NASA’s long-term shortage of plutonium, stating: “The committee is alarmed at the limited availability of plutonium-238 for planetary exploration. Without a restart of domestic production of plutonium-238, it will be impossible for the United States, or any other country, to conduct certain important types of planetary missions after this decade.”
To address the plutonium problem, in 2011 NASA provided funding to the Department of Energy (DOE) to restart domestic production of the substance. The program is called the Pu-238 Supply Project. So far, the Project has produced ∼3.5 ounces (100 grams) of Pu-238. DOE identified an interim goal of producing 10 to 17.5 ounces (300 to 500 grams) of new Pu-238 per year by 2019. The goal is to produce 1.5 kilograms of new Pu-238 per year—considered full production—by 2023, at the earliest.
Problems with plutonium production
GAO is questioning the Supply Project’s ability to meet its goal of producing 1.5 kilograms of new Pu-238 per year by 2026. For one thing, the oversight agency’s interviews with DOE officials revealed that the agency hasn’t perfected the chemical processing required to extract new Pu-238 from irradiated targets to meet production goals.
The Mars Science Laboratory’s radioisotope power system was assembled by putting nuclear heat sources within graphite impact shells into high-strength carbon-carbon modules at Idaho National Laboratory. Photo & Caption Credit: Department of Energy
Another problem relates to reactor availability. At present, three DOE national laboratories—Idaho National Laboratory, Oak Ridge National Laboratory, and Los Alamos National Laboratory—are involved in what GAO calls radioisotope power system (RPS) production.
NASA’s plutonium will be produced at two of these reactors, but only one of them is currently qualified to make Pu-238. GAO reported that initial samples of the new Pu-238 did not meet spaceflight specifications because of impurities. However, according to DOE, the samples can be blended and used with existing Pu-238.
GAO also expressed concern about DOE’s lack of an implementation plan “that identifies milestones and interim steps that can be used to demonstrate progress in meeting production goals” as well as addressing the two concerns mentioned above. Such a plan would enable the agency to show progress in implementing its approach and make adjustments when necessary.
Lastly, GAO is not entirely happy with DOE’s production approach, which aims for a constant production rate to ensure steady employment of the energy workforce. The downside of this approach, according to GAO, is that this constant-production method doesn’t improve DOE’s ability to assess the potential long-term effects of chemical processing and reactor availability, or its communication of these effects to NASA.
The bottom line, according to GAO, is that “[w]ithout the ability to assess the long-term effects of known challenges and communicate those effects to NASA, DOE may be jeopardizing NASA’s ability to use RPS as a power source for future missions.”
If left unaddressed, the challenges identified in the GAO report could leave NASA without enough plutonium for its space missions by 2025.
GAO’s recommendations
GAO made three recommendations to DOE to address NASA’s plutonium problem. First, DOE needs to develop a plan with milestones and interim steps for their Pu-238 and RPS production approach. Second, the agency needs to assess and communicate to NASA the long-term effects of the known production challenges. Finally, GAO stated that DOE should develop a more comprehensive system for tracking systemic risks beyond those currently identified in their report. While DOE concurred with GAO’s recommendations, it remains to be seen whether the plutonium problem will be solved by 2025.
Bart Leahy
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.
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