Credit: SRS Photography

Radioactive materials have enormous potential as a source of energy, but some isotopes are available in such small quantities that their use as an energy source is limited.

In the 1950s, scientists at the Savannah River Site in Aiken, South Carolina, developed a method of producing plutonium-238, a manufactured radioactive isotope, in large enough quantities that its energy could be harnessed to fuel the nuclear batteries of spacecraft. This development not only catalyzed the exploration of deep space but also highlighted the US nuclear and space programs’ efforts to collaborate on developing peaceful uses for radioactive materials.

On Nov. 1, 2018, the American Chemical Society designated the production of 238Pu as fuel for radioisotope thermoelectric generators, which convert heat from radioactive materials into electrical energy, as a National Historic Chemical Landmark. The ceremony took place at the Savannah River Site Museum in Aiken in conjunction with a symposium about 238Pu﻿ during the nearby ACS Southeastern Regional Meeting in Augusta, Georgia.

“Production and purification of this plutonium isotope represented the culmination of an extraordinary collaboration among scientists, engineers and thousands of other employees at the Savannah River Site,” said Peter K. Dorhout, then ACS president. “The American Chemical Society is honoring their work because chemistry was central to that effort.”

Sign up for C&EN's must-read weekly newsletter Email Address * Subscribe » Contact us to opt out anytime

Around 1959–60, scientists at the Savannah River Site optimized a method of producing neptunium-238 by irradiating an oxide of 237Np with neutrons. 238Np decays into 238Pu.

In the decades that followed, Savannah River Site expanded its production of 238Pu. In 1961, the isotope fueled the first radioisotope thermoelectric generator used in space, which was launched aboard the Transit 4A Navy navigational satellite.

“These nuclear batteries power and warm spacecraft and the research instruments they carry, enabling exploration of deep space,” reads the citation on the Chemical Landmark plaque. “SRS produced nearly all the plutonium-238 for every U.S. mission that has relied on these batteries.”

Credit: US Department of Energy

NASA missions where the radioisotope thermoelectric generator was used include several Apollo flights, the Viking 1 and 2 Mars landers, Voyager 1 and 2 space probes to the outer planets of our solar system, and the New Horizons mission to Pluto.

In 1988, the Cold War was ending, and so was the production of 238Pu﻿ at Savannah River Site. Stockpiles of the fuel were projected to be depleted by 2018. However, in 2015, the US Department of Energy reestablished the production of 238Pu at Oak Ridge National Laboratory for future NASA missions.

“Many people dedicated their working lives to programs like 238Pu﻿ production at the Savannah River Site. They were never really able to tell their family or friends what they did. I hope this designation allows them to finally say, ‘We did that,’ ” said Michael Budney, manager of the Department of Energy’s Savannah River Operations Office. “Forty years later, their ideas and processes are still being used to help us explore the bounds of space—a true testament to its historical significance.”