Self-Heating - doe-std-1128-98

DOE-STD-1128-98

2.5.1

Self-Heating

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

150C. 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

600C. 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.

2.5.2

Radiolysis

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-Brnas

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 Unpublished report by the Pacific Northwest Laboratory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.

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