Source: Albany Daily Times | | June , 2016

Plutonium-238 is the fuel of NASA’s choice for deep-space exploration. But for nearly 30 years, nobody in the United States was making it. The plutonium isotope is efficient for spacecraft power systems both because of its relatively low radiation for handlers, its ability to produce plenty of heat to keep instruments warm, and can power spacecraft for several decades.

NASA only has access to 35 kilograms, about 77 pounds, of Pu-238 to power space exploration missions

NASA was running out to fuel its Mars rovers. The success of project to create Plutonium-238 is considered as a major milestone by chemists and space technology experts. ORNL team has produced 50 grams of plutonium-238 and it will be helpful in future deep space missions.

As it decays, Plutonium-238 produces heat and can be used as power source for various space program instruments. The newly created Plutonium-238 will undergo analysis for testing its chemical purity. The production process will be scaled up after a team of researchers validates its efficiency.

On Tuesday, that all changed. The Department of Energy announced that 50 grams of the stuff had been made by researchers at the Oak Ridge National Laboratory in Oak Ridge, Tenn.

Fifty grams isn’t much, but this is the first time the substance has been made in the country since the Savannah River Plant in South Carolina stopped making it in the late 1980s.

ORNL said in a statement that they now have a complete infrastructure that can provide steady and growing supply of Plutonium-238 for future space missions. The lab expects to produce 300 to 400 grams of Pu-238 per year and eventually ramp up annual production to about 1.5 kilograms.

Production begins at Idaho National Laboratory, which stores the existing inventory of neptunium-237 feedstock and ships it as needed to ORNL. Engineers mix the neptunium oxide with aluminum and press the mixture into high-density pellets. They use the High Flux Isotope Reactor, a DOE Office of Science User Facility at ORNL, to irradiate the pellets, creating neptunium-238, which quickly decays and becomes plutonium-238.

The success of Wham and a team of engineers and technicians at ORNL comes two years after NASA began funding the DOE Office of Nuclear Energy through a roughly $15 million per year effort to revive the department’s capability to make plutonium-238.

Production begins at Idaho National Laboratory, which stores the existing inventory of neptunium-237 feedstock and ships it as needed to ORNL. Engineers mix the neptunium oxide with aluminum and press the mixture into high-density pellets. They use the High Flux Isotope Reactor, a DOE Office of Science User Facility at ORNL, to irradiate the pellets, creating neptunium-238, which quickly decays and becomes plutonium-238.

The irradiated pellets are then dissolved and ORNL staff use a chemical process to separate the plutonium from remaining neptunium. The plutonium product is converted to an oxide and shipped to Los Alamos National Laboratory, where the material will be stored until needed for a mission. Remaining neptunium is recycled into new targets to produce more plutonium-238.

Plutonium-238, not to be confused with its weapons-grade variant, Pu-239, powers spacecraft by producing heat through radioactive decay. The method has powered previous missions such as the Viking missions on Mars, the Voyager spacecraft and, more recently, the Curiosity Mars Rover and New Horizons spacecraft.

“This significant achievement by our teammates at DOE signals a new renaissance in the exploration of our solar system,” John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington, said in a DOE news release.

“Radioisotope power systems are a key tool to power the next generation of planetary orbiters, landers and rovers in our quest to unravel the mysteries of the universe,” he said.

Right now, NASA only has access to 35 kilograms, about 77 pounds, of Pu-238 to power space exploration missions. That’s just enough to last into the middle 2020s, powering just two or three proposed missions.

So regaining the capability to make Pu-238 has been much needed.

“As we seek to expand our knowledge of the universe, the Department of Energy will help ensure that our spacecraft have the power supply necessary to go farther than ever before,” Franklin Orr, Under Secretary for Science and Energy at DOE, said in the government news release. “We’re proud to work with NASA in this endeavor, and we look forward to our continued partnership.”

Two years ago, NASA began funding efforts to make Pu-238 again in ernest. The agency has put about $15 million each year toward the DOE’s Office of Nuclear Energy’s efforts.

The new capabilities aren’t yet ready for full production. Researchers still have to verify that they can produce Pu-238 on a larger scale without losing its purity or other characteristics. They may have to make some adjustments to the process.

“Once we automate and scale up the process, the nation will have a long-range capability to produce radioisotope power systems such as those used by NASA for deep space exploration,” Bob Wham, who leads the project for the ORNL’s Nuclear Security and Isotope Technology Division, said in an ORNL press release.

But, he said, “With this initial production of plutonium-238 oxide, we have demonstrated that our process works and we are ready to move on to the next phase of the mission.”

When plutonium-238 starts to decaying, it gives off heat, which can be harnessed to power spacecraft instruments

The irradiated pellets are then dissolved and ORNL staff use a chemical process to separate the plutonium from remaining neptunium. The plutonium product is converted to an oxide and shipped to Los Alamos National Laboratory, where the material will be stored until needed for a mission. Remaining neptunium is recycled into new targets to produce more plutonium-238.

There are currently only 35 kilograms, or about 77 pounds, of plutonium-238 set aside for NASA missions, and only about half of this supply meets power specifications. This is only sufficient to power two to three proposed NASA missions through the middle of the 2020s. Fortunately, the additional material that will be produced at ORNL can be blended with the existing portion that doesn’t meet specifications to extend the usable inventory.

With continued NASA funding, DOE’s Oak Ridge and Idaho national laboratories can ensure that NASA’s needs are met, initially by producing 300 to 400 grams of the material per year and then, through automation and scale-up processes, by producing an average of 1.5 kilograms per year.

“With this initial production of plutonium-238 oxide, we have demonstrated that our process works and we are ready to move on to the next phase of the mission,” Wham said.

The next NASA mission planning to use a radioisotope thermoelectric generator is the Mars 2020 rover, due to be launched in July 2020. The mission seeks signs of life on Mars and will test technology for human exploration and gather samples of rocks and soil that could be returned to Earth