Plutonium dispersion

A second source of plutonium, dispersed more locally, is liquid effluent from fuel reprocessing facilities. One such is the fuel reprocessing plant at Windscale, Cumbria in the United Kingdom where liquid waste is released to the Irish Sea(6). Chemical analysis of this effluent shows that about one percent or less of the plutonium is in an oxidized form before it contacts the marine water(7). Approximately 95 percent of the plutonium rapidly adsorbs to particulate matter after discharge and deposits on the seabed while 5 percent is removed from the area as a soluble component ). Because this source provided concentrations that were readily detected, pioneering field research into plutonium oxidation states in the marine environment was conducted at this location. 

Environmental chemists funded by the Department of Energy have studied these sources to learn as much as they can about the chemistry of plutonium dispersed in freshwater and marine ecosystems. Much of the early work determined the concentrations in various water bodies and the distribution between water and sediment. Table I shows results of various freshwater and marine surveys(10). 

Americans used TNT, RDX and HMX for nuclear weapons in the initial years but their use posed additional hazard of aerosolized-plutonium dispersal. The scattering of this long-lived isotope poses a great danger to human life as well as... 

Weapons-grade plutonium, dispersed at military accidents such as Thule in 1968 or as non-fissioned weapon particles after detonation of a Pu-bomb can be characterized by high Pu content relative to the other Pu-isotopes, while accidentally dispersed Pu from the previously widely used nuclear-powered satellites are characterized by high Pu content." The ratio of americium-241 to plutonium isotopes (as " Am is formed by the decay of Pu) is proportional to the initial " Pu concentration, thus it can also be used as an indicator to assess the origin of contamination. However, in most cases, as several sources may contribute to the transuranics content in environmental samples, mixing models applying several isotope ratios are required to assess the origin of possible contamination sources. 

Atmospheric testing of nuclear weapons has been the main source of plutonium dispersed in the environment. Accidents and routine releases from weapons production facilities are the primary sources of localized contamination. Consumer and medical devices containing plutonium are sealed and are not likely to be environmental sources of plutonium (WHO 1983). Plutonium released to the atmosphere reaches the earth s surface through wet and dry deposition to the soil and surface water. Once in these media, plutonium can sorb to soil and sediment particles or bioaccumulate in terrestrial and aquatic food chains. 

When the above described reactor is operated with the plutonium dispersed as plutonium sulphate in solution in a light water (H2O) moderator, a typical reactor of this type is as follows ... 

Alpha monitoring Evacuation to prevent inhalation dose resulting from resuspenstion of ground contamination resulting from an accident involving Plutonium dispersal (e.g., nuclear weapon accident). Alpha scintillation or proportional coimters 5 to 10 cm... 

A practically unlimited source of plutonium was present, so that its concentration in solution (dissolved or otherwise dispersed) could, at least in theory, increase continuously with time until a steady-state situation was reached. 

The glass phase furnished an active surface for the possible deposition of dispersed plutonium species. 

Nuclear Weapons Testing Range, Maralinga, South Australia, site of 12 hydronuclear experiments at Taranaki in 1960, 1961, and 1963 (Vixen B Trials) in which 22.2 kg of plutonium was dispersed, having been ejected 2,500feet vertically into the atmosphere. Cooper etal. 1994... 

The spent firel issue is central to long-term fuel cycle policy, not simply because large volumes are threatening to clog the arteries of the nuclear power industry but because spent fuel is the repository of most of the worid s plutonium, some 1000 tons at present, and is already dispersed among the 30-odd countries in which nuclear power plants are located. The indefinite accumulation of these dispersed inventories has proliferation implications that are at least comparable in their gravity to the surplus weapons plutonium inventories in Russia... 

Redox initiation, in aqueous dispersion polymerization, 11 197—198 Redox neutral atmosphere, 14 84 Redox potentials, of plutonium in acid,... 

Nuclear fuel and associated waste products also include plutonium and enriched uranium (<20% U-235) and associated waste or fission products that emit intense radiation and can pose significant threats if dispersed with conventional explosives (i.e., by a dirty bomb). Industrial sources include a range of devices used in geological investigation and radiography, and may also pose significant hazards if dispersed by a dirty bomb. Examples of radioactive materials that could be used in a dirty bomb include ... 

The British had proceeded less expeditiously. The Chiefs of Staff advised in October 1945 that the best defence against atomic bombs was likely to be the deterrent effect that the possession of the means of retaliation would have on a potential aggressor, and in January 1946 they said that a stock in the order of hundreds rather than scores would be necessary to deter a country with widely dispersed industries and population (like the Soviet Union). In December 1945, ministers in the Gen 75 committee approved the construction of the first reactor capable of producing plutonium, and in August 1946 the CAS sent the first requisition for an atomic bomb to the Ministry of Supply. The McMahon Act was amended in October 1950 to allow rather more cooperation between American and British scientists but the first British test did not take place until 3 October 1952, in the hold of a ship off Australia. The first test of a British atomic bomb dropped by an aircraft did not occur until 11 October 1956. 

Figure 3 illustrates the distributions found for Pu and Am when a mixed sample of these tracers was infiltrated into a large (30 cm x 30 cm) block of Bandolier tuff (6). The nuclide activities were determined simultaneously by coring sections of the tuff and represent the activity distributions in the rock. It is obvious that although the activities are both normalized at 100% at the surface the increased dispersion of the plutonium concentration during elution leads to an increase of almost an order of magnitude in its activity relative to Am at the 5-6 cm depth. It is highly unlikely that abnormal flow paths or movement of colloidal clay particles would discriminate between americium and plutonium therefore this experimental result tends to discount these possible types of mechanisms. However, a pure Pu polymer could carry the Pu more rapidly downstream. 

Migration of Plutonium in Rock Incorrect Dispersion Formula," H. Krugmann, Science, 200, 88 (1978). 

Plutonium is so toxic that processing and fabrication are always done in sealed cells or glove boxes, but accidental dispersions of aerosol occur from time to time. Following combustion of Pu metal chips in a production area at Rocky Flats, Colorado, in 1964, airborne contamination was widespread. Alpha tracks from individual particles caught on membrane filters were detected on nuclear film, and the Pu content, and hence the particle size, was deduced (Fig. 5.2, curve E). The activity median diameter was 0.3 /urn (Mann Kirchner, 1967). The same method, used during normal operations in a production area at Los Alamos, gave activity median diameters in the range 0.15 to 0.65 /urn (Moss et al., 1961). However, when a spill occurred, followed by clean-up operations, the Pu particles were found to be associated with inert dust particles of mass median diameter 7 /urn. 

Plutonium has been dispersed globally by weapon tests and by the burn-up of the S.N.A.P. satellite in the upper atmosphere. There have also been local operational and accidental dispersions (Harley, 1980). Some of the major events are discussed below. 

In some tests carried out at the Nevada Test Site in 1956-8, fission was incomplete and some plutonium was dispersed. Also some weapons were exploded chemically without nuclear fission in safety tests. Analysis of soil from an area extending about 500 km north-eastwards from the N.T.S. into the neighbouring state of Utah showed excess Pu over the amounts expected from global fallout (Hardy, 1976). The Pu from these low-level, low-yield tests was distinguished from global fallout by two criteria ... 

Most radioactive particles and vapours, once deposited, are held rather firmly on surfaces, but resuspension does occur. A radioactive particle may be blown off the surface, or, more probably, the fragment of soil or vegetation to which it is attached may become airborne. This occurs most readily where soils and vegetation are dry and friable. Most nuclear bomb tests and experimental dispersions of fissile material have taken place in arid regions, but there is also the possibility of resuspension from agricultural and urban land, as an aftermath of accidental dispersion. This is particularly relevant to plutonium and other actinide elements, which are very toxic, and are absorbed slowly from the lung, but are poorly absorbed from the digestive tract. Inhalation of resuspended activity may be the most important route of human uptake for actinide elements, whereas entry into food chains is critical for fission products such as strontium and caesium. 

Resuspension of dust from the floor is an important source of indoor pollution. Jones Pond (1966) studied resuspension of plutonium from the floor of a laboratory which had been deliberately contaminated. Droplets were dispersed over the floor and allowed to dry out. Pu was present in the droplets either as a suspension of particles, mass median diameter 15 /mi, or as nitrate in solution. The activity per unit area was measured with a floor probe. After 16 h had elapsed, airborne Pu was measured while operators performed various tasks in the laboratory. 

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