PLUTONIUM
163
6. POTENTIAL FOR HUMAN EXPOSURE
6.2.2
Water
Fallout from atmospheric weapons testing, accidents involving nuclear weapons, planned as well as
accidental reactor effluent releases, and disposal of radioactive wastes are all means by which plutonium
can be introduced into water systems (Harley 1980; NEA/OECD 1981). In a typical 1,000 megawatt
electric (MWe) light water reactor in a nuclear power plant, about 200 kg of plutonium [equivalent to
1.3x10
4
Ci (4.8x10
14
Bq), one curie of
239
Pu=16 g] are generated per year of operation (DOE 1980g;
NEA/OECD 1981). Contaminated cooling water containing plutonium from nuclear production facilities
may have been discharged into oceans or rivers. If release occurs from waste containers, buried
radioactive wastes may migrate or seep into groundwater (NEA/OECD 1981). As an example of plant
emissions, the Mound Plant in Miamisburg, Ohio, discharged a total of about 0.5 Ci (2x10
10
Bq)
238
Pu
into a river near the site from the beginning of its operation through 1976 (NEA/OECD 1981). The
Savannah River Site, South Carolina, which produced plutonium and tritium as well as other nuclear
materials from 1954 to 1988, released 2.3x10
10
Bq (0.62 Ci) of plutonium to site streams and ponds
during the period of 1954–1989 (Carlton et al. 1996). From 1954 to 1988, the plutonium and uranium
extraction (PUREX) process was used in the F-area of the Savannah River Site to recover
239
Pu, as well as
other radionuclides, from irradiated
238
U. During this time, the total reported release of
239
Pu to the
seepage basin at the F-area was 2.09x10
11
Bq (5.65 Ci) (Dai et al. 2002).
Liquid effluent containing various radionuclides is discharged from some of the facilities at the Hanford
Site. During 2004, 5.5x10
-6
Ci (2.0x10
5
Bq) of
239,240
Pu were released to the Columbia River from the
100 areas at the Hanford Site (DOE 2005c).
In January, 1968, while attempting to make an emergency landing, a U.S. military aircraft with four
nuclear weapons on board crashed in Thule, Greenland. The impact resulted in detonation of the high
explosives in all four nuclear weapons aboard. The oxidized plutonium was dispersed by both the
explosion and the fire involving the fuel in the jet (Harley 1980). Amounts of plutonium released to the
air in this accident have been estimated at 24 Ci (8.9x10
11
Bq) of insoluble plutonium (NEA/OECD
1981). The maximum concentration of plutonium in ocean sediments was found 1 km from the point of
impact. The sediment-bound plutonium was found to migrate both downward in the sediment column
and horizontally from the point of impact. The concentrations decreased with distance from the point of
impact.
PLUTONIUM
164
6. POTENTIAL FOR HUMAN EXPOSURE
Sediments can act as both a repository for and a source of waterborne plutonium. Atmospheric fallout
reaching surface water can settle in the sediments. The plutonium in the ocean sediments at Bikini Atoll,
for example, was found to be resuspended and released to the bottom waters (DOE 1980b). In a
freshwater waste pond at the Hanford reactor, plutonium was found to be bound to the sediments and was
not available for uptake by plants or animals in the pond (DOE 1980f). The difference between the
observations in the two ecosystems may be due to the dynamic nature of the ocean water near Bikini Atoll
versus the relatively static nature of a waste water pond.
On May 4, 2000, a prescribed burn grew out of control in Cerro Grande, New Mexico near the Los
Alamos National Laboratory (LANL), which burned about 7,400 acres of forest on the LANL site (DOE
2004). The burned landscapes resulted in increased storm runoff and transport of various contaminants,
which included plutonium and other radionuclides by runoff and erosion in the canyons traversing LANL.
Compared with amounts measured in the 5 years before the fire, the yearly average amount of
radioactivity carried by storm runoff flows beyond LANL downstream boundary in the two to three years
following the fire increased about 55 times for
239,240
Pu. The increases were due mostly to erosion of
LANL contaminated sediments. Annually, the estimated postfire transport of
239,240
Pu downstream ranged
from 2 millicuries (mCi) in the first year after the fire to 28 mCi in year 1 and a total of about 64 mCi of
239,240
Pu was transported downstream in storm runoff through the 4-year period from 2000 through 2003
(DOE 2004).
Plutonium has been identified in 6 groundwater and 7 surface water samples collected from 1,689 NPL
hazardous waste sites, where it was detected in some environmental media (HazDat 2007).
6.2.3
Soil
Plutonium has been detected in extremely small amounts as a naturally occurring constituent of some
minerals and ores. Uranium and thorium ores in Canadian pitchblende, Belgium Congo pitchblende,
Colorado pitchblende, Brazilian monazite, and North Carolina monazite have been found to contain
244
Pu
at a weight ratio of up to 9.1x10
-12
kg plutonium/kg ore (Leonard 1980).
Soils may become contaminated from fallout associated with nuclear weapons tests, such as those
conducted at the Trinity Site in southern New Mexico, the Pacific Proving Ground at the Enewetak Atoll,
and the Nevada Test Site or with accidental, nonnuclear detonation of nuclear weapons, such as occurred
at Palomares, Spain. Research facilities, such as the Los Alamos National Laboratory, Los Alamos, New
Dostları ilə paylaş: |