(plutonium oxalate) are insoluble in water. The chlorides, nitrates, perchlorates, and
sulfates are soluble in water. Plutonium (IV) ions complex readily with organic and
inorganic compounds. Of particular importance for radiological safety considerations
are the solubility, particle size, and surface area of plutonium compounds. These
properties play an important part in the transportability of plutonium in the
environment and in the body. All plutonium compounds, except the oxides, are
assumed in ICRP 30, Part 1 (ICRP, 1979) to behave as class W compounds in the
ICRP lung model. Plutonium oxides are assumed to be class Y. The solubility of
plutonium compounds is an important parameter in avoiding "unintentional"
homogeneous reactors. Knowledge of this property for both aqueous and organic
solvents plays a key role in criticality safety and deserves a high priority.
Unfortunately, little data on particle-size are available, and those that have been
generated focus on the reactivity of the materials in the separation and conversion
processes. Much of the data are reported as crystallite size, which relates to surface
area and solubility but not necessarily to the way the particles would be dispersed in
the air. Surface area plays a role in the ability of materials to adsorb gases and vapors
that can affect the long-term storage behavior of plutonium compounds. Pressure
buildup in storage containers, either from out gassing due to self-heating or radiolytic
effects, will depend on the stability of the compound and the amounts of chemisorbed
or physisorbed water or other substances.
The following sections discuss the essential compounds of plutonium: plutonium
nitrate and associated compounds, plutonium dioxide, plutonium hydride, plutonium
sulfate, plutonium chlorides, and plutonium fuel mixtures.
22.214.171.124 Plutonium Nitrate, Oxalate, Peroxide, and Fluorides
Plutonium (IV) nitrate is the most used of all plutonium compounds.
Essentially all chemical processing of plutonium has been conducted in
nitrate solutions. These solutions of appropriate acidities range from
concentrations of 10g to 250g of Pu/L for efficient precipitation processes.
Intermediate compounds are also used in the processing of plutonium
prepared from the nitrate: plutonium (III) fluoride, plutonium (II or IV)
oxalate, and plutonium peroxide. Plutonium (IV) fluoride can be prepared
from any of the preceding solids by hydrofluorination. Plutonium fluoride
has been the compound of choice for reduction to the metal with calcium,
principally because it is nonhygroscopic. The solubilities in various media,
bulk densities, and particle sizes of these compounds are given in Table 2.6.