Heat generated by radioactive decay in plutonium, its alloys, or its
compounds can be calculated from data provided in Table 2.4, together with
the isotopic composition and plutonium fraction. The power output of
reactor-produced 239Pu metal is usually in the range of 2 to 10 W/kg.
According to Van Tuyl,3 the equilibrium surface temperature of a metal can
that contains 1.2 kg of plutonium at the higher specific power would be
150°C. This calculation is complex because it depends on the thermal
conductivities and configuration of all the materials in the shipping container.
Thermal diffusivity measurements reported by Kruger and Robbins (1975)
were combined with existing heat capacity values to derive a curve for the
thermal conductivity of the Pu-1wt% Ga alloy from room temperature to
600°C. Gram quantities of 238Pu can melt from self-heating under poor heat-
transfer conditions. The major effects to be expected from self-heating are
phase transformation, dimensional changes, chemical reactions (depending
on the gaseous environment or other materials in contact with the
plutonium), and desorption of previously sorbed gases or vapors.
In gases, liquids, and covalently bonded solids, the chemical effects of alpha
particles and the associated recoil nucleus can cause ionization, excitation,
and dissociation of molecules. From the energy requirement for ion pair
formation, only about half the energy causes ionization; the other half goes
into molecular excitation. Radiation effects are commonly measured by a
quantity called the G-value, i.e, the number of molecules destroyed for each
100 eV of energy absorbed. For free radical production, this quantity is
expressed as the GR-value. For organic liquids, GR-values typically range
from 0.85 for carbon disulfide to 70 for carbon tetrachloride (Prevost-Bérnas
et al., 1952).
Although there is a considerable body of data on the radiolysis of aqueous
solutions, organic liquids, and solids irradiated by gamma rays, X-rays, and
fast electrons, little has been published on the radiolysis of plutonium
compounds, solvents containing plutonium, or radiation-induced damage in
materials that come in contact with plutonium. Nevertheless, radiation-
induced damage can affect all aspects of plutonium handling.
3 Van Tuyl, H. H. 1981. "Packaging of Plutonium for Storage or Shipment." Unpublished report by the Pacific Northwest Laboratory
task force chairperson to the U.S. Department of Energy.