Plutonium in the environment

Since the mid-20th century,plutonium in the environmenthas been primarily produced by human activity. The first plants to produceplutoniumfor use incold waratomic bombswere theHanford nuclear site,in Washington, andMayaknuclear plant, inChelyabinsk Oblast,Russia. Over a period of four decades,"both released more than 200 million curies of radioactive isotopes into the surrounding environment – twice the amount expelled in theChernobyl disasterin each instance. "

The majority ofplutoniumisotopesare short-lived on ageological timescale,though it has been argued that traces of the long-lived²⁴⁴Puisotope still exist in nature.This isotope has been found inlunar soil,meteorites,and in theOklonatural reactor.However, one study on plutonium inmarinesedimentsindicates that the atomic bomb fallout accounts for 66% of the²³⁹Puand 59%²⁴⁰Puin theEnglish Channel.In contrast,nuclear reprocessingcontributes the majority of the²³⁸Puand²⁴¹Puin the Earth's oceans, whereas nuclear weapons testing is responsible for only 6.5% and 16.5% of these isotopes, respectively.

Sources of plutonium

Plutonium production

TheHanford siterepresents two-thirds of the nation's high-level radioactive waste by volume. Nuclear reactors line the riverbank at the Hanford Site along theColumbia Riverin January 1960.

Richland, Washingtonwas the first city established to support plutonium production at the nearbyHanford nuclear site,to power the American nuclear weapons arsenals.Ozersk, Russiasupported plutonium production to power the Soviet nuclear arsenals at theMayaknuclear plant. These were the first two cities in the world to produce plutonium for use incold waratomic bombs.

In the 2013 book,Plutopia: Nuclear Families, Atomic Cities, and the Great Soviet and American Plutonium Disasters,Kate Brownexplores the health of affected citizens in both the United States and Russia, and the "slow-motion disasters" that still threaten the environments where the plants are located.According to Brown, the plants at Hanford and Mayak released over 200 millioncuriesof radioactive isotopes into the surrounding environment over four decades, which is twice the amount expelled in theChernobyl disasterin each instance.

Most of theradioactive contaminationover the years from Hanford and Mayak were part of normal operations. Unforeseen accidents did occur, but plant management kept this secret, and the pollution continued unabated. Even today, as pollution threats to health and the environment persist, the government conceals information about the associated risks from the public.

Bomb detonations

Levels of radioactivity in the trinitite glass from two different samples as measured bygamma spectroscopyon lumps of the glass. The americium content is the current content while all other isotopes have been back-calculated to shortly after the moment of detonation.

Isotopic signatures of the plutonium before and after the detonation.

About 3.5 tons of plutonium have been released into the environment by atomic bomb tests. While this might sound significant, it has only resulted in a very small dose to the majority of the humans on earth. Overall the health effects offission productsare far greater than the effects of theactinidesreleased by a nuclear bomb detonation. The plutonium from the fuel of the bomb is converted into a high-firedoxidethat is carried high into the air. It slowly falls to earth as globalfalloutand is notsoluble,and as a result it is difficult for this plutonium to be incorporated into an organism if ingested. Much of this plutonium is absorbed into 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. This formed plutonium is more soluble and more harmful as fallout.

Some plutonium can be deposited close to the point of detonation. The glassytrinititeformed by theTrinity bombhas been examined to determine what actinides and otherradioisotopesit contained. A 2006 paperreports the levels of long lived radioisotopes in the trinitite.¹⁵²Eu and¹⁵⁴Eu was mainly formed by the neutron activation of theeuropiumin the soil, and the level of radioactivity for these isotopes is highest where the neutron dose to thesoilwas larger. Some of the⁶⁰Co was generated by activation of thecobaltin the soil, but some was also generated by the activation of the cobalt in thesteel(100 foot) tower on which the bomb stood. This⁶⁰Co from the tower would have been scattered over the site reducing the difference in the soil levels.¹³³Ba and²⁴¹Amwere created by the neutron activation of barium and plutonium inside the bomb. Thebariumwas present in the form of thenitratein the chemical explosives used while the plutonium was thefissilefuel used.

As the²³⁹Pu/²⁴⁰Pu ratio only changed slightly during the Trinity detonation, it has been commentedthat this isotope ratio for the majority of atomic bombs (in Japan the²³⁹Pu/²⁴⁰Pu ratio in soil is normally in the range 0.17 to 0.19) is very different than from the bomb dropped uponNagasaki.

Bomb safety trials

The two basic fission weapon designs.

Plutonium has also been released into the environment insafety trials.In these experiments,nuclear bombshave been subjected to simulated accidents or detonated with an abnormal initiation of their chemical explosives. An abnormal implosion will result in a compression of theplutonium pit,which is less uniform and smaller than the designed compression in the device. In these experiments where no or very littlenuclear fissionoccurs, plutonium metal has been scattered around the test sites. While some of these tests have been done underground, other such tests were conducted in open air. A paper on theradioisotopesleft on an island by theFrenchnuclear bombs tests of the 20th century has been printed by theInternational Atomic Energy Agencyand a section of this report deals with plutonium contamination resulting from such tests.

Other related trials were conducted atMaralinga, South Australiawhere 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.

Space

Diagram of an RTG used on theCassini probe

Plutonium can also be introduced into the environment via the reentry of artificial satellites containingatomic batteries.There have been several such incidents, the most prominent being theApollo 13mission. TheApollo Lunar Surface Experiments Packagecarried on theLunar Modulere-entered the atmosphere over the South Pacific. Many atomic batteries have been of theradioisotope thermoelectric generator(RTG) type. The Plutonium-238 used in RTGs has ahalf-lifeof 88 years, as opposed to the plutonium-239 used innuclear weaponsandreactors,which has ahalf-lifeof 24,100 years.In April 1964 aSNAP-9Afailed to achieve orbit and disintegrated, dispersing roughly 1 kilogram (2.2 lb) ofplutonium-238over all continents. Most plutonium fell in the southern hemisphere. An estimated 6300GBqor 2100 man-Sv of radiation was releasedand led to NASA's development of solar photovoltaic energy technology.

Image of (mostly) thermally isolated, RTG pellet glowing red hot because ofincandescence.

Chain reactions do not occur inside RTGs, so anuclear meltdownis impossible. In fact, some RTGs are designed so that fission does not occur at all; rather, forms ofradioactive 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 ofradioactive 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 ofiridiummetal and encased in high-strengthgraphiteblocks. 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 highlyinsoluble.

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.

Nuclear fuel cycle

Plutonium has been released into the environment in aqueous solution fromnuclear reprocessinganduranium enrichmentplants. The chemistry of this plutonium is different from that of the metal oxides formed fromnuclear bombdetonations.

One example of a site where plutonium entered the soil isRocky Flatswhere in the recent pastXANES(X-rayspectroscopy) has been used to determine the chemical nature of the plutonium in thesoil.The XANES was used to determine theoxidation stateof the plutonium, whileEXAFSwas used to investigate the structure of the plutonium compound present in the soil andconcrete.

The XANES experiments done on plutonium insoil,concreteand standards of the differentoxidation states.

Chernobyl

See also:Chernobyl disaster

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 thecaesium,strontiumandplutoniumbecome mobile in the air again.

Fukushima

See also:Fukushima Daiichi nuclear disasterandFukushima Daiichi Nuclear Power Plant

The ongoing crisis at this site includes Spent Fuel Pools on the upper floors, exposed to the elements with complex MOX and plutonium products. The Japanese Government Taskforce has asked for submissions to the International Research Institute for Nuclear Decommissioningin regards to the ongoing Contaminated Water Issues.

Nuclear crime

There have been 18 incidencesof theft or loss ofhighly enriched uranium(HEU) andplutoniumconfirmed by the IAEA.

One case exists of aGermanman who attempted to poison his ex-wife with plutonium stolen from WAK (WiederaufbereitungsanlageKarlsruhe), a small scale reprocessing plant where he worked. He did not steal a large amount of plutonium, just rags used for wiping surfaces and a small amount of liquid waste. The man was sent toprisonfor his crime.At least two other people were contaminated by the plutonium.Two flats inRhineland-Palatinatewere also contaminated.These were later cleaned at a cost of two millioneuro.

Environmental chemistry

Overview

Plutonium, like other actinides, readily forms a dioxideplutonylcore (PuO₂). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygenmoieties(OH⁻,NO₂⁻,NO₃⁻,and SO₄²⁻) to form charged complexes which can be readily mobile with low affinities to soil.

• PuO₂(CO₃)₁²⁻
• PuO₂(CO₃)₂⁴⁻
• PuO₂(CO₃)₃⁶⁻

PuO₂formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO₂which 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 an X-ray spectroscopic study of plutonium in soil andconcrete). Whilecaesiumhas very different chemistry to the actinides, it is well known that both caesium and many of the actinides bind strongly to themineralsin soil. Hence it has been possible to use¹³⁴Cs labeled soil to study the migration of Pu and Cs in soils. It has been shown thatcolloidaltransport processes control the migration of Cs (and will control the migration of Pu) in the soil at theWaste Isolation Pilot Plantaccording to R.D. Whicker and S.A. Ibrahim.J.D. Chaplin et al. recently reported advances in theDiffusive gradients in thin filmstechnique, which have provided a method to measure labile bioavailablePlutoniumin soils, as well as in freshwater and seawater.

Microbiological chemistry

Mary Neu (atLos Alamosin the USA) has done some work which suggests thatbacteriacan accumulate plutonium because theirontransport systems used by the bacteria also function as plutonium transport systems.

Biology

Plutonium ingested by or injected into humans is transported in thetransferrinbasediron(III) transport system and then is stored in theliverin the iron store (ferritin), after an exposure to plutonium it is important to rapidly inject the subject with achelatingagent such ascalciumcomplexofDTPA.This antidote is useful for a single exposure such as that which would occur if aglove boxworker were to cut his or her hand with a plutonium-contaminated object. The calcium complex has faster metal binding kinetics than thezinccomplex 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 thelymph nodes.Inhaled plutonium has been shown to lead to lung cancer in experimental animals.

See also

• Actinides in the environment