acids or molten salts. The best solvents are 1216M HNO3 with
0.100.1M HF, 56M HI, and 9M HBr (Cleveland, 1964; Holley et
al., 1958). New processes are being developed to correct this
deficiency using a superacid, HF/SbF5 (Olaha et al., 1985) and
CEPOD, a fluoride-free electrochemical dissolver that uses the silver
anion as a redox catalyst (Bray et al., 1987).
18.104.22.168 Plutonium Hydride
Plutonium hydride has recently become a compound of interest for
separating plutonium scrap from other materials that do not readily
unite with hydrogen.2 The reaction between plutonium and hydrogen
apparently proceeds by the initial formation of PuH2. As more
hydrogen is added, the dihydride becomes PuH2+x. The hexagonal
PuH3 begins to form when the H/Pu ratio becomes about 2.75; when
the H/Pu ratio reaches 2.9 to 3.0, only the hexagonal form remains.
A wide spread is reported in the measured induction period for the
first reaction (Haschke, 1991). Because the hydriding reaction is
fully reversible, plutonium metal can be recovered by pumping off
the hydrogen in a suitable vacuum furnace. This metal typically
contains significant amounts of plutonium oxide but is suitable for
feed to either molten salt extraction or electrorefining processes. The
hydride can also be converted to the oxide. The advantage of the
hydride recovery process is its ability to recover a large fraction of
the scrap in metallic form. This method, therefore, has a major
economic advantage over chemical recycling and subsequent
reduction to metal. It is being used as a production aid for metallic
22.214.171.124 Plutonium Sulfates
Plutonium sulfate tetrahydrate, Pu(SO4) 2· 4H2O, has not been of any
process importance but has been of interest as a primary standard for
plutonium. It is a good example of a stable compound that could be
suitable as an interim storage form. Samples stored at relative
humidities of up to 75% showed no evidence of alpha radiolysis of
the water of crystallization after 28 months. The compound is
hygroscopic in air of 95% relative humidity, and stable up to 650°C,
at which point it quickly decomposes to PuO2 (Cleveland, 1970). The
potassium salt, K4Pu(SO4) 4- 1H2O, was under study as a possible
primary standard for 238Pu. Crystals stored in an air-tight steel
container, which also functioned as a heat sink, proved to be stable.
The solubility product of this compound was determined to be 10-18.
2 The properties of plutonium hydrides may be found in Volume 3 of the Handbook of Physics and Chemistry of the Actinides (Ward,
1985). Kinetics of the plutonium hydrogen reaction are reviewed by Haschke (1991).