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Spring/Summer 2009 Vol. 9 Number 1

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Plutonium, Part 2

The Return of a Long-Defunct Isotope Program

©Donald Gruener/iStockphoto

On May 25, the U.S. Department of Energy announced it would start making plutonium-238, a radioactive isotope created as a byproduct of the nuclear weapons industry that has not been produced in the U.S. since the end of the Cold War. Hours before DOE’s announcement, the National Research Council released a new report stating that if the U.S. did not start producing plutonium-238 again, the nation’s space programs could be in jeopardy.

These isotopes are needed in space to generate electrical power. As radioactive elements like plutonium decay, they give off heat, which can be converted to electricity. Radioactive power systems are particularly important on space missions where solar energy may be too weak to generate useful power, such as deep-space missions. Maintaining electrical power is primarily dependent upon having sufficient radioactive isotopes for the mission.

The best isotope for use in radioactive power systems is plutonium-238 (Pu238), which historically came from U.S. government facilities supporting the nuclear weapons industry. But once the Cold War ended, DOE shut down these facilities. Since then, the U.S. space program has been running on leftovers. Ironically, Russia, a chief rival in the Cold War race to stockpile nuclear weapons, has been one of the United States’ principal suppliers of Pu238. The stocks of both the U.S. and Russia are now nearly depleted, however, and no other nations are actively producing Pu238. DOE will soon accept its final shipment of Russian Pu238.

A worldwide shortage of Pu238 could be devastating for space research. NASA is already making mission decisions based upon declining availability of Pu238. The Mars Science Lab and an outer-planet mission tentatively scheduled for 2020 will likely use the last of the existing stores.

The National Research Council estimated that Pu238 production could be restarted at nuclear reactors in Idaho and Tennessee, and recommended that DOE produce 5 kilograms annually. DOE’s 2010 budget request included $30 million for Pu238 production. While these funds may be enough to restart the program, they are likely not adequate to achieve the goal of 5 kilograms per year, leaving the long-term future of Pu238 in space uncertain.  — Rebecca Alvania

 Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration. Radioisotope Power Systems Committee, Space Studies Board and Aeronautics and Space Engineering Board, Division on Engineering and Physical Sciences (2009, 68 pp.; ISBN 0-309-13857-4; available from the National Academies Press, tel. 1-800-624-6242; $21.00 plus $4.50 shipping for single copies.

The committee was co-chaired by William Hoover, U.S Air Force (retired), and Ralph McNutt, senior space physicist, Johns Hopkins University, Baltimore. The study was funded by NASA.

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Copyright 2009 by the National Academy of Sciences