US develops nuclear batteries for Earth, Oceans and Mars designed to run for decades
From the ocean floor to the surface of Mars, some places simply cannot be reached by a power line or a delivery truck carrying replacement batteries. Oak Ridge National Laboratory is working to make sure those locations never have to go without electricity. The lab is building nuclear batteries designed to keep running for years or even decades without any human intervention.
Brad Johnson leads ORNL's Nuclear Battery Initiative , drawing on a multidisciplinary team and the lab's research tools to develop the technology for both national priorities and global challenges. Johnson said nuclear batteries offer a proven, safe way to deliver long-duration power, and his team is working to improve their performance and safety further.
Picking the right isotope
Nuclear batteries generate electricity from the natural radioactive decay of an isotope rather than a chemical reaction. That makes them well suited to remote locations that need stable power for years without maintenance. Not every radioisotope works for this purpose, though several do.
Johnson said the ideal isotope has a half-life between 10 and 100 years. Shorter half-lives waste too much material before it ever gets used, while longer half-lives require excessive amounts of isotope to generate meaningful power. Ideal candidates also emit alpha and beta particles rather than gamma rays or neutrons, since those shorter-range particles convert more easily into usable electricity.
Plutonium-238 fits that profile well. ORNL produces the isotope for the Department of Energy under a NASA contract, and NASA uses it inside radioisotope thermoelectric generators that power deep space missions. The Perseverance rover's generator uses about 10.6 lb of Pu-238 and carries an expected 14-year lifetime, well beyond the rover's original three-year mission on Mars.
A decades-old research legacy
ORNL's nuclear battery research dates back to the 1960s. An entire building was constructed in the 1970s specifically to process fission products for battery projects. Researcher Hsin Wang is currently studying a retired terrestrial radioisotope thermoelectric generator to learn how these systems degrade over time. The unit was originally built in 1985 using fuel pellets and canisters produced at ORNL.
Johnson called the retired unit a rare opportunity to gather end-of-life performance data from equipment built to last decades. Future missions bring new engineering challenges too. NASA's push for a sustained lunar presence, for instance, runs into a two-week lunar night that makes solar power impractical and requires other methods to keep equipment warm.
Four hurdles still standing
Johnson's team has identified nine candidate isotopes and narrowed that list to three top options. Their picks are based on both the isotopes' properties and how feasible they would be to produce at scale. That production challenge is one of four major obstacles standing between current technology and a new generation of nuclear batteries.
Second, energy conversion needs improvement. Current thermoelectric technology converts only 5 to 8 percent of decay heat into electricity. Pushing that to 10 to 15 percent would cut fuel costs roughly in half. Third, better insulation and thermal management would prevent wasted energy from escaping the system. Fourth, power control and management systems still need refinement.
Johnson said advanced manufacturing techniques, including 3D printing and specialized powder materials, could help address all four challenges at once. He described the effort as an "all-ORNL opportunity." The program draws on expertise from across the lab's various directorates to meet the nation's long-term power needs.
