To help power American's deep space probes, the Oak Ridge National Laboratory (ORNL) has automated key steps in the process to make plutonium-238 (PU-238) nuclear fuel for radiothermal generators (RTG). By turning over the production of neptunium oxide-aluminum pellets to machines, the agency says fuel production will increase to 1.5 kg (3.3 lb) per year by 2025.
NASA's ambitions to send more unmanned probes to the outer solar system, nuclear-powered rovers to Mars, and setting up manned outposts of the Moon face a major bottleneck as the agency's stockpile of PU-238 dwindles to below 35 kg (77 lb). To bolster stocks, ORNL has been funded to produce more of the fuel needed for missions where solar panels aren't a practical solution.
PU-238 is an unstable plutonium isotope that produces 0.5 watts of thermal power as it naturally decays into uranium-234, and RTGs use this heat to generate electricity to power spacecraft systems. It's a system that's worked well since the 1960s, but producing the PU-238 is a bit laborious.
To create the plutonium isotope, ORNL takes neptunium-237 (NP-237), converts it to neptunium oxide, mixes it with aluminum, and presses it into dense pellets. These are then passed through the laboratory's High Flux Isotope Reactor where the radiation turns the NP-237 into NP-238, which decays into PU-238. The plutonium is then chemically processed to purify it and converted into fuel pellets.
Previously, production was limited to only 80 pellets per week, but ORNL says that automated parts of the production line has boosted this to 275 per week.
"Automating part of the Pu-238 production process is helping push annual production from 50 grams to 400 grams, moving closer to NASA's goal of 1.5 kilograms per year by 2025," says ORNL's Bob Wham. "The automation replaces a function our team did by hand and is expected to increase the output of pressed pellets from 80 to 275 per week."
The video below outlines the new automated process.
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