Plutonium Hydride - STD-1128-98master0041

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

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).

2.3.3.3 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 scrap recovery.

2.3.3.4 Plutonium Sulfates

Plutonium sulfate tetrahydrate, Pu(SO4)24H2O, 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 650C, 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.

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).

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