REVIEWS
In contrast to global
fallout ts the local
fallout associated with nu-
clear explosions and low level chronic releases from nuclear fuel processing. The local fallout from nuclear explosions and stack effluents
Francis (1973) and Price (1973) reviewed the literature through 1971 on
‘plutonium and other transuranics in soils, plants, and animals. They
found several works on plutonium and americium migration or distribution
in soils, but information on other transuranics was lacking.
Several
Papers described laboratory leaching studies on the movement of radio-
active transuranic waste materials through soils.
In general, these
early papers showed that plutonium and americium can move through soils
and are influenced by such factors as nature and oxidation state of
source material,
soil pH and organic matter content, presence of com-
Plexing agents, and cultural practices,
It was suspected that, under
natural conditions, most of the plutonium moved as colloidal or discrete dénse plutonium oxide particles and not as solubilized species,
the soluble plutonium being tightiy bound by exchange mechanisms in the
soil.
Wilhelmi (1974) reviewed the Literature through 1973 and listed all
the known sources of plutonium and transuranicsS added to the environment.
Plutonium movement through the soil was discussed,
and typical
profiles, where available, were presented for fallout plutonium and
for accidental plutonium releases at Rocky Flats, Colorado.
Fallout
plutonium was reportedly found to depths exceeding 30 cm, although the
proportion of total profile plutonium found below 30 cm was only several percent. Wilhelmi (1974) pointed out that plutonium was strongly
bound to soil material and migrated slowly; however, plutonium was
found to migrate rapidly through cracks and fissures in geologic materials underlying soils.
The review also revealed that there was
little information on the influence of such factors as physical and
chemical nature of soil and soil organic matter.
SOURCES OF TRANSURANICS
from processing are deposited onto the soil surface soon after release
and enter into the soil weathering processes immediately.
A number of nuclear weapons tests were conducted at the Nevada Test
Site
(NTS)
and Tonopah Test Range
no fission yleld.
These
{TTR)
which resulted in little or
tests were chemical high explosive detonations
of, or associated with, components of nuclear devices to determine the
degree of safety or stability of the devices to the impact of an ex-
Plosion. These tests were calied "Safety Shots." The conduct of these
tests resulted in the limited dispersion of the nuclear fuel, mostly
plutonium and some americium as an impurity but in some cases natural
or enriched uranium.
The nuclear material was dispersed in the form
of discrete metallic or oxide particles formed from the burning of the
metal in air.
The high temperatures attained in a nuclear explosion
were not present; thus, the dispersed material had different characteristics from those it would have had if it had been involved in a nuclear
explosion.
There have been a number of accidental releases of transuranic nuclides.
Typical of accidental releases are the occasional low level releases
from waste disposal facilities; accidental destruction of nuclear
weapons as that which occurred over Palomares, Spain; and possible
localized leaks of stored transuranic contaminated materials. Wilhelmi
(1974)
summarized all known accidental releases and noted that there
were very few observations of transuranic nuclide distributions
soils associated with the accidental releases.
in
Expanding efforts to provide energy From nuclear sources will increase
the inventory of transuranics and may increase the potential for an additional burden cf transuranics in the environment. Those transuranic
radionuclides of greatest concern are shown in Table 1 and Table 2, as
compiled by Perkins (1975) and Langham (1971), respectively. Not all
transuranic nuclides are considered hazardous, either because of the
small amounts produced or the short radioactive half-lives.
The source of transuranic nuclides in the environment, for purposes
of discussion, can be categorized into global fallout, local fallout,
safety shots,
and accidental releases.
Wilhelmi
(1974)
summarized the
sources and noted that except for atmospheric nuclear explosions and
the atmospheric burnup of a SNAP-9 power generator, almost all of the
other sources were localized.
Global fallout is produced primarily from nuclear weapons explosicns
in the atmosphere, where substantial quantities of the radioactive
debris are injected into the stratosphere.
This material is slowly
added to the environment over long periods of time and appears somewhat as a continuous source.
42
A projected 100-fold increase in total curies of transuranics in waste
over the next 24 years indicates the urgency for more information.
However,
this does not mean that there will be a 100-fold increase
in
the environmental burden of these transuranics.
DISTRIBUTION OF TRANSURANICS
IN SOILS
There have been a number of studies dealing with the distribution of
plutonium in various environmental situations,
43
and only a
few laboratory