- Plutonium in the environment
Plutonium in the environment is an article which is part of the
actinides in the environmentseries. Almost all plutoniumpresent in the environment is due to human activity because the majority of plutonium isotopes are shortlived on a geological timescale. [http://www.ead.anl.gov/pub/doc/plutonium.pdf] It has been argued that some natural plutonium (the very long lived 244Pu isotope) can be found in nature. [P.K. Kuroda, "Accounts of Chemical Research", 1979, 12(2), 73-78 [http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6315763] ] This isotope has been found in lunar soil, [KURODA, P.K., MYERS, W.A., "Plutonium-244 Dating III Initial Ratios of Plutonium to Uranium in Lunar Samples." J. Radioanalyt Chem. 150, 71.] , meteorites, [MYERS, W.A., and KURODA, P.K., "Plutonium-244 Dating IV. Initial Ratios of Plutonium to Uranium in the Renazzo, Mokoia and Groznaya Meteorite." J. Radioanalyt. Nucl. Chem. 152, 99.] and in the Oklonatural reactor. [KURODA, P.K., "Plutonium-244 in the Early Solar System and the Pre-Fermi Natural Reactor (The Shibata Prize Awardee's Lecture)". Geochem. J. 26, 1.] But in general it is normally considered that the bulk of all plutonium is man made. According to one paper on marine sediments for plutonium in marine sediments, bomb fall out is responsible for the majority of the 239Pu and 240Pu (66% and 59% respectively of that found in the english channel) while nuclear reprocessingis responsible for the majority of the 238Pu and 241Pu present in the sea (bomb tests are only responsible for 6.5 and 16.5% of these isotopes respectively). [O.F.X. Donard, F. Bruneau, M. Moldovan, H. Garraud, V.N. Epov and D. Boust, "Analytica Chimica Acta", 2007, 587, 170-179]
About 3.5 tons of plutonium have been released into the environment by atomic bomb tests. While this might sound like a large amount it has only resulted in a very small dose to the majority of the humans on the earth. Overall the health effects of the
fission productsare far greater than the effects of the actinides released by a nuclear bomb detonation. The plutonium from the Pu fuel of the bomb is converted into a high fired oxidewhich is carried high into the air. It slowly falls to earth as global fallout and is not soluble, hence as a result it is difficult for this plutonium to be incorporated into an animal if taken by mouth. Much of this plutonium will become tightly absorbed onto sediments of lakes, rivers and oceans. However, about 66% of the plutonium from a bomb explosion is formed by the neutron capture of uranium-238; this plutonium is not converted by the bomb into a high fired oxide as it is formed more slowly. As a result this formed plutonium is more soluble and more able to cause harm when it falls to earth. [Radiochemistry and Nuclear Chemistry, G. Choppin, J-O. Liljenzin and J. Rydberg, 3rd Ed, Butterworth-Heinemann, 2002]
Some of the plutonium can be deposited close to the point of detonation. The glassy
trinititeformed by the first atom bomb has been examined to determine what actinides and other radioisotopes it contained. A recent paper [P.P. Parekh, T.M. Semkow, M.A. Torres, D.K. Haines, J.M. Cooper, P.M. Rosenberg and M.E. Kitto, "Journal of Environmental Radioactivity", 2006, 85, 103-120] reports the levels of long lived radioisotopes in the trinitite. The trinitite was formed from feldsparand quartzwhich were melted by the heat. Two samples of trinitite were used, the first (left hand side bars) was taken from between 40 and 65 meters of ground zero while the other sample was taken from further away from the ground zeropoint.
The 152Eu and 154Eu was mainly formed by the neutron activation of the
europiumin the soil, it is clear that the level of radioactivity for these isotopes is highest where the neutron dose to the soilwas larger. Some of the 60Co is generated by activation of the cobaltin the soil, but some was also generated by the activation of the cobalt in the steel(100 foot) tower. This 60Co from the tower would have been scattered over the site reducing the difference in the soil levels.
The 133Ba and 241Am are due to the neutron activation of barium and plutonium inside the bomb. The
bariumwas present in the form of the nitrate in the chemical explosives used while the plutonium was the fissilefuel used.
It is interesting to note that the 137Cs level is higher in the sample which was further away from the ground zero point. This is thought to be because the precursors to the 137Cs (137I and 137Xe) and the caesium to a lesser degree are volatile. The natural radioisotopes in the glass are about the same in both locations.
In this paper a sample of the glass was digested and the plutonium extracted from it, and the mass ratio of the isotopes was calculated from the radiometric measurements. In light green the isotopic signature for the plutonium used for making the bomb is shown, and on the right in dark green the signature of the plutonium in the trinitite glass is shown. It is very clear that 238Pu and 241Pu were generated during the detonation, so it is reasonable to conclude that some 240Pu was formed during the detonation.
As the 239Pu/240Pu ratio only changed slightly during the detonation, it has been commentedY. Saito-Kokubu, F. Esaka, K. Yasuda, M. Magara, Y. Miyamoto, S. Sakurai, S. Usuda, H. Yamazaki, S. Yoshikawa and S. Nagaoka, "Applied Radiation and Isotopes", 2007, 65(4), 465-468] that this isotope ratio for the majority of atom bombs ("In Japan the 239Pu/240Pu ratio in soil is normally in the range 0.17 to 0.19")S. Yoshida, Y. Muramatsu, S. Yamazaki and T. Ban-nai, "Journal of Environmental Radioactivity", 2007, In Press doi:10.1016/j.jenvrad.2007.01.019] is very different than from the bomb dropped upon Nagasaki, so the forest soil and the lake sediment layer containing the local
falloutfrom the second world warbomb is very different from the layers due to global fallout from bomb tests conducted later.
Bomb safety trials
One form of release of plutonium into the environment has been "safety trials" in these experiments
nuclear bombshave been subjected to simulated accidents or have been detonated with an abnormal initiation of the chemical explosives. An abnormal implosion will result in a compression of the pit which is less uniform and smaller than the designed compression in the device. Such an abnormal implosion could result from an accident which triggers one or more of the detonators which trigger the chemical explosive charges.
As a result of these experiments (where no or very little
nuclear fissionoccurs) plutonium metal has been scattered around near the site of the experiment. While some of these tests have been done inside holes in the ground, other such tests were conducted in open air. A paper on the radioisotopes left on an island by the French nuclear bombs tests of the 20th century has been printed by the International Atomic Energy Agencyand a section of this report deals with plutonium contamination resulting from such tests. [http://www-pub.iaea.org/MTCD/publications/PDF/Pub1028_web.pdf]
Other related trials were conducted at
Maralinga, South Australiahere both normal bomb detonations and "safety trials" have been conducted. While the activity from the fission products has decayed away almost totally (as of 2006) the plutonium remains active. A report ("warning it is very big") can be read at [http://www.radioactivewaste.gov.au/pdf_documents/maralinga/martac_report/martac_report.pdf] while a smaller report can be seen at [http://www.mapw.org.au/conferences/mapw2000/papers/parkinson.html] .
Another potential source of plutonium being introduced into the environment is the reentry of artificial satellites containing atomic batteries. There have been several such incidents, the most prominent being the
Apollo 13mission. The Apollo Lunar Surface Experiment Packagecarried on the Lunar Modulere-entered the atmosphere over the South Pacific. Many atomic batteries have been of the Radioisotope thermoelectric generator(RTG) type.
Chain reactions do not occur inside RTGs, so such a
nuclear meltdownis impossible. In fact, some RTGs are designed so that fission does not occur at all; rather, forms of radioactive decaywhich cannot trigger other radioactive decays are used instead. As a result, the fuel in an RTG is consumed much more slowly and much less power is produced.
RTGs are still a potential source of
radioactive contamination: if the container holding the fuel leaks, the radioactive material will contaminate the environment. The main concern is that if an accident were to occur during launch or a subsequent passage of a spacecraft close to Earth, harmful material could be released into the atmosphere. However, this event is extremely unlikely with current RTG cask designs.
In order to minimise the risk of the radioactive material being released, the fuel is typically stored in individual modular units with their own heat shielding. They are surrounded by a layer of
iridiummetal and encased in high-strength graphiteblocks. These two materials are corrosion and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the earth's atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, minimising the risk of vaporization and aerosolization. The ceramic is also highly insoluble.
The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The Apollo 13 accident represents an extreme scenario due to the high re-entry velocities of the craft returning from cislunar space. This accident has served to validate the design of later-generation RTGs as highly safe.
The Plutonium-238 used in RTGs has a
half-lifeof 88 years, as opposed to the plutonium-239 used in nuclear weaponsand reactors, which has a half-lifeof 24,100 years.
Some heart pacemakers which are powered by RTGs using 238Pu have been made.
Nuclear fuel cycle
Plutonium has been released into the environment in aqueous solution from
nuclear reprocessingand uranium enrichmentplants. The chemistry of this plutonium is different from that of the metal oxides formed from nuclear bombdetonations.
One example of a site (military not civil) where plutonium entered the soil is
Rocky Flatswhere in the recent past XANES(a X-rayspectrscopy) has been used to determine the chemical nature of the plutonium in the soil. [http://www-ssrl.slac.stanford.edu/research/highlights_archive/rockyflats.html] . The XANES was used to determine the oxidation stateof the plutonium, while EXAFSwas used to investigate the structure of the plutonium compound present in the soil and concrete. [http://www.wmsym.org/Abstracts/2002/Proceedings/6b/188.pdf]
Because plutonium oxide is very involatile, most of the plutonium in the reactor was not released during the fire. However that which was released can be measured. V.I. Yoschenko "et al." reported that grass and forest fires can make the
caesium, strontiumand plutoniumbecome mobile in the air again. ("Journal of Environmental Radioactivity", 2006, 86, 143-163.) As an experiment fires were set and the levels of the radioactivity in the air downwind of these fires was measured.
One case exists of a German man who attempted to poison his ex-wife with plutonium stolen from WAK (Wiederaufbereitungsanlage
Karlsruhe). WAK was a small scale reprocessing plant where he worked. He did not steal a large amount of plutonium, just some rags used for wiping surfaces and a small amount of liquid waste. This man was sent to prisonfor his crime. [http://www10.antenna.nl/wise/index.html] [http://www10.antenna.nl/wise/555/5321.html] At least two people (besides the criminal) were contaminated by the plutonium. [http://www.germnews.de/archive/dn/2005/02/24.html#16] . Two flats in Rhineland-Palatinatewere contaminated. These were later cleaned at a cost of two million euro.
For photographs of the case and details of other
nuclear crimes see [http://www.jrc.cec.eu.int/more_information/infodays/200210_speech/ray.pdf] which was presented by a worker at the ITU. A general over view of the forensicmatters associated with plutonium exists. [Maria Wallenius, Klaus Lützenkirchen, Klaus Mayer, Ian Ray, Laura Aldave de las Heras, Maria Betti, Omer Cromboom, Marc Hild, Brian Lynch, Adrian Nicholl, "et al.", "Journal of Alloys and Compounds", In press doi:10.1016/j.jallcom.2006.10.161]
The details of how the two flats in
Landauwere cleaned has been recorded [http://ean.cepn.asso.fr/pdf/program7/Session%20C/C2_HOEFE.pdf] . In addition it has been claimed that a house in Reading, Berkshire) has been contaminated with plutonium. [http://www.corporatewatch.org/?lid=2180] [http://www.corporatewatch.org/?lid=2407] [http://www.davidrowan.com/2003/11/daily-telegraph-mysterious-radiation.html]
Plutonium like other actinides readily forms a dioxide plutonyl core (PuO2). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygen moieties (OH-, NO2-, NO3-, and SO4-2) to form charged complexes which can be readily mobile with low affinities to soil.
PuO2 formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO2 which is resistant to complexation. Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium.
Binding to soil
Plutonium is known to bind to soil particles very strongly, see above for a X-ray spectroscopic study of plutonium in soil and
concrete. While caesiumhas very different chemistry to the actinides, it is well known that both caesium and many of the actinides bind strongly to the minerals in soil. Hence it has been possible to use 134Cs labeled soil to study the migration of Pu and Cs is soils. It has been shown that colloidal transport processes control the migration of Cs (and will control the migration of Pu) in the soil at the Waste Isolation Pilot Plantaccording to R.D. Whicker and S.A. Ibrahim, "Journal of Environmental Radioactivity", 2006, 88, 171-188.
Mary Neu (at
Los Alamosin the USA) has done some work which suggests that bacteriacan accumilate plutonium because the irontransport systems used by the bacteria also function as plutonium transport systems. [http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818042.pdf] [http://rds.yahoo.com/_ylt=A0geushu23pFXtIAw8dXNyoA;_ylu=X3oDMTE2MmVkNGMxBGNvbG8DZQRsA1dTMQRwb3MDMgRzZWMDc3IEdnRpZANGODUzXzk0/SIG=13580qe29/EXP=1165765870/**http%3a//pubs.acs.org/subscribe/journals/esthag-w/2001/jun/science/rs_microbes.html] [http://www.lbl.gov/ERSP/generalinfo/pi_meetings/PI_mtg_05/05_PI_Mtg_pdf/Neu_NABIR05_pres.pdf]
Plutonium ingested by or injected into humans is transported in the
transferrinbased iron(III) transport system and then is stored in the liverin the iron store ( ferritin), after an exposure to plutonium it is important to rapidly inject the subject with a chelating agent such as calciumcomplex [http://www.multum.com/Ca-DTPA.htm] of DTPA[http://www.orau.gov/reacts/calcium.htm] [http://www.multum.com/Zn-DTPA.htm] . This antidote is useful for a single one off exposure such as that which would occur if a glove boxworker was to cut their hand with a Pu contaminated object. The calcium complex has faster metal binding kinetics than the zinccomplex but if the calcium complex is used for a long time it tends to remove important minerals from the person. The zinc complex is less able to cause these effects.
Plutonium that is inhaled by humans lodges in the lungs and is slowly translocated to the
lymph nodes. Inhaled plutonium has been shown to lead to lung cancer in experimental animals.
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