Plutonium Hydride - doe-std-1128-98

DOE-STD-1128-98

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).

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) 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 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.

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).

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