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4 | APPLIED | WINTER 2019 | SAVANNAH RIVER NATIONAL LABORATORY


        SRS designated National Historic
        Chemistry Landmark for production

        of Pu-238 for space exploration

        In a ceremony at the SRS Heritage Museum in Aiken, S.C., on Nov. 1, 2018,
        the American Chemical Society (ACS) recognized SRS as an ACS National
        Historic Chemistry Landmark (NHCL) for “Pu-238 Production for Space
        Exploration.” ACS President, Professor Peter Dorhout, made the dedication,
        which was accepted by Michael D. Budney, Manager, DOE Savannah River
        Operations Office, on behalf of SRS.
        The mission of the NHCL program is to enhance public appreciation for the
        contributions of the chemical sciences to modern life in the United States
        and to encourage a sense of pride in their practitioners for chemistry’s rich
        history. The program recognizes seminal achievements in the chemical
        sciences, records their histories, and provides information and resources
        about NHCL achievements.

        SRNL applied research enabled

        production of Pu-238 to power

        United States space activities

        In 1959, the Atomic Energy Commission (AEC), a precursor of the DOE,
        commissioned SRS to convert neptunium-237 (Np-237) into plutonium-238
        (Pu-238) as fuel for radioisotope thermoelectric generators (RTGs), which
        convert heat emitted by radioactive materials into electrical energy, to power
        spacecraft.
        Pu-238 is nearly ideal for fueling RTGs on spacecraft. It has a half-life of 87.7
        years, making it a long-lasting source of energy. It exhibits high heat density
        and emits primarily alpha particles. The alpha particles are easily shielded,
        which makes Pu-238 safer to handle than other radioactive materials. High
        heat density and low shielding requirements both make for a lighter device. In
        addition, Pu-238 is non-fissile, so it cannot be used in nuclear power plants or
        nuclear weapons.
        The greatest limitation of Pu-238 is the difficulty of making it in sufficient
        quantities. Researchers at SRNL optimized known methods of irradiating an
        oxide of Np-237 with neutrons to produce Np-238, which decays into Pu-238.
        Between 1959 and 1988, when SRS ceased production of Pu-238 as the Cold
        War came to a close, SRS produced the vast majority of Pu-238 used in RTGs
        that powered US space activities--a total of approximately 660 pounds. Only
        about 22 pounds were obtained from sources other than SRS.
        Initially, the Pu-238 produced at SRS was shipped to other AEC facilities and
        packaged into the fuel used in RTGs. In 1978, SRS opened its own RTG fuel
        fabrication facility, the Plutonium Fuel Form (PuFF) facility within Building 235-F.
        The Pu-238 fuel powered the first RTG used in space, launched aboard the
        Navy TRANSIT 4A Navigational Satellite in 1961. Since then, the fuel has been
        used in nearly every NASA mission that required an RTG, including several   Pu-238 has been used as heat source
        Apollo flights (1969-1982), Voyager 1 and 2 space probes to the outer   material for radioisotope thermoelectric
        planets of our solar system (launched in 1977), and the New Horizons mission   generators, the “nuclear batteries” that have
        to Pluto (launched in 2006).                                   powered early satellites, NASA’s Apollo lunar
                                                                       craft and deep space probes such as Pioneer,
                                                                       Voyager, Galileo, Ulysses, Cassini (illustrated
                                                                       above) and New Horizons.
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