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.
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 236Pu 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 231Am 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.