U.S. restarts Plutonium 238 production for space probes

A glowing red hot pellet of plutonium-238 dioxide to be used in a radioisotope thermoelectric generator for space missions.

The Department of Energy has produced its first batch of non-weapons grade plutonium, used to power space probes, since a nuclear reactor shutdown 25 years ago, NASA officials said on Monday.

The U.S. space agency turned to buying radioactive plutonium-238 from Russia after safety issues prompted the Department of Energy to close its Savannah River Site in South Carolina in the late 1980s.

The Russian supply line ended in 2010, leaving NASA with a small and aged supply of plutonium for space probes flying missions that are ill-suited for solar power.

Plutonium naturally radiates heat, which can be converted into electricity by a device called a radioisotope thermo-electric generator.

NASA has been flying nuclear-powered probes since the 1970s. Ongoing missions using such probes include the Mars rover Curiosity, the Saturn-orbiting Cassini spacecraft, Pluto-bound New Horizons and the twin Voyager probes, which are leaving the solar system.

"The new plutonium is very important to us," Jim Green, the head of NASA's planetary science division, said during a briefing at a Lunar and Planetary Science Conference in Houston.

In partnership with NASA, the Department of Energy irradiated the radioactive metal neptunium-237 with neutrons at the Oak Ridge National Laboratory in Tennessee for about a month and successfully produced a small amount plutonium.

"This is just a test," Green said, adding that a report from the Energy Department on production plans and costs should be finished before the end of the year.

NASA is looking for the department to produce about 3.3 to 4.4 pounds (1.5 to 2 kg) of plutonium-238 per year.

Newly made plutonium has the added benefit of reviving older plutonium that has decayed past the point of being viable for deep space probes.

"The new material when we add with our old plutonium, which is more than 20 years old in some cases, really allows us to get the appropriate energy density out," Green said.

NASA also has been working on a more energy efficient generator, called the Advanced Stirling Radioisotope Generator, which can produce four times more electrical power per kilogram of plutonium-238.

Green said two such flight-ready generators are on schedule for completion in 2016. Neither has yet been assigned for a specific mission.