Manufacture, Properties, and Hazards

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

2.0

MANUFACTURE, PROPERTIES, AND HAZARDS

This chapter briefly describes the manufacture of plutonium and presents the nuclear, physical,

chemical, and radiobiological properties of plutonium (and/or sources for these data) that form the

basis for radiological and toxic control limits. The data and discussion are intended to provide a

basis for understanding the changes in hazards as a function of such parameters as isotopic

composition, age since chemical processing, physical form, and chemical form. Data are presented

to facilitate the calculation of radiation effects, which occur from a variety of plutonium sources.

Plutonium is the first man-made element produced on an industrial scale. The special nuclear

properties of 239Pu and 238Pu have led scientists to focus their efforts on these two isotopes. The

fission cross-section of 239Pu makes it a useful energy source for atomic weapons and nuclear power

reactors. The 87.7-year half-life of 238Pu makes it an excellent heat source for space applications.

Unfortunately, the same nuclear properties of plutonium that make it attractive to science also make

this element hazardous to human beings. All 15 plutonium isotopes are radioactive, with half-lives

ranging from 26 minutes for 235Pu to 7.6 x 107 years for 244Pu.

2.1

MANUFACTURE OF PLUTONIUM

Because of its high specific alpha activity and high decay heat, 238Pu has been used as an isotopic

heat source for devices that generate thermoelectric power, such as the Space Nuclear Auxiliary

Power (SNAP) systems used in lunar and deep space missions. Small amounts of 238Pu with low

236

Pu content were used as a power source for medical prosthetic devices such as cardiac

pacemakers and a prototype artificial heart, but lithium batteries have replaced these plutonium

power sources. 238Pu containing a few parts per million of 236Pu is produced by irradiating 237Np

with slow neutrons. It can also be produced by irradiating 241Am to form 242Cm, which quickly

decays to 238Pu.

In the past, most plutonium in DOE facilities was produced for nuclear weapons and was composed

of greater than 90 wt% 239Pu and about 6 to 8 wt% 240Pu. This material has been referred to as

"weapons grade" or "low exposure" plutonium. It is produced on a large scale by irradiating 238U in

moderated production reactors (see Figure 2.1). Plutonium has also been produced as a byproduct

in the operation of research reactors, and commercial nuclear power plants. It is recovered and

purified by solvent extraction and ion exchange processes. The resulting highly concentrated

Pu(NO3)4 product solution is converted to a nonhygroscopic PUF4 intermediate by one of the

several processes before being reduced to metal with calcium. Plutonium is also produced from the

waste streams of the conversion processes and scrap recovery operations, which include material

from research and development efforts. Other processes for reduction to metal include direct

reduction of the oxide and electrolytic reduction. Typical isotopic compositions of three common

grades of plutonium are given in Table 2.1.

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