Fission product 701333 224615184 2008-07-09T17:46:22Z JWB 273993 /* Iodine */ '''Fission products''' are the atomic fragments left after a large nucleus [[Nuclear fission|fissions]]. Typically, a large nucleus like Uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat (kinetic energy of the nuclei), gamma rays and neutrinos. The two smaller nuclei are the "fission products". == Formation and decay == The sum of the [[atomic weight]] of the two atoms produced by the fission of one [[atom]] is always less than the [[atomic weight]] of the original atom. This is because some of the mass is lost as free [[neutron]]s and large amounts of [[energy]]. Since the nuclei that can readily undergo fission are particularly [[neutron]]-rich (e.g. 61% of the [[nucleon]]s in uranium-235 are neutrons), the initial fission products are almost always more neutron-rich than stable nuclei of the same mass as the fission product (e.g. stable [[ruthenium]]-100 is 56% neutrons, stable [[xenon]]-134 is 60%). The initial fission products therefore may be unstable and typically undergo [[beta decay]] towards stable nuclei, converting a neutron to a [[proton]] with each beta emission. (Fission products do not emit [[alpha particles]].) A few neutron-rich and short-lived initial fission products first decay by emitting a neutron. This is the source of [[delayed neutron]]s which play an important role in control of a [[nuclear reactor]]. The first beta decays are rapid, and may release high energy beta particles or [[gamma radiation]]. However, as the fission products approach stable nuclear conditions, the last one or two decays may have a long [[halflife]] and release less energy. Exceptions are: *[[Sr-90]] (high energy beta, halflife 30 years) *[[Cs-137]] (high energy gamma, halflife 30 years) *[[Sn-126]] (even higher energy gamma, but long halflife of 230,000 years means a slow rate of radiation release, and the [[fission product yield|yield]] of this nuclide per fission is very low) == Yield == {{Main|Fission product yield}} [[Image:fission yield.png|thumb|450px|Fission product yields by element at different cooling times after the fuel has been used. Percentages are of total fission products (out of 100%) rather than per fission (out of 200% because two fragments for each fission)]] [[Image:ThermalFissionYield.svg |thumb|450px|Fission product yields by mass for thermal neutron fission of U-235, Pu-239, a combination of the two typical of current nuclear power reactors, and U-233 used in the thorium cycle]] Each fission of a parent atom produces a different set of fission product atoms. However, while an individual fission is not predictable, the fission products are statistically predictable. The amount of any particular isotope produced per fission is called its [[fission product yield|yield,]] typically expressed as % per parent fission; therefore, yields total to 200% not 100%. While fission products include every element from [[zinc]] through the [[lanthanides]], the majority of the fission products occurs in two peaks. One peak occurs at about (expressed by atomic number) [[strontium]] to [[ruthenium]] while the other peak is at about [[tellurium]] to [[neodymium]]. The exact yield is somewhat dependent on the parent atom, and also on the energy of the initiating neutron.[http://www.science.uwaterloo.ca/~cchieh/cact/nuctek/fissionyield.html] In general the higher the energy of the state that undergoes nuclear fission, the more likely that the two fission products have similar mass. Hence as the neutron energy increases and/or the energy of the [[fissile]] atom increases, the valley between the two peaks becomes more shallow. For instance, the curve of yield against mass for [[Pu-239]] has a more shallow valley than that observed for [[U-235]] when the neutrons are [[thermal neutron]]s. The curves for the fission of the later [[actinides]] tend to make even more shallow valleys. In extreme cases such as <sup>259</sup>Fm, only one peak is seen. The adjacent figure shows a typical fission product distribution from the fission of uranium. Note that in the calculations used to make this graph, the activation of fission products was ignored and the fission was assumed to occur in a single moment rather than a length of time. In this bar chart results are shown for different cooling times (time after fission). Because of the stability of nuclei with even numbers of protons and/or neutrons, the curve of yield against element is not a smooth curve but tends to alternate. (But note that the curve against mass number is smooth [http://www.science.uwaterloo.ca/~cchieh/cact/nuctek/fissionyield.html].) ==Characteristics== {{Medium-lived fission products}} {{Long-lived fission products}} The adjacent tables provides information on the half-life, yield and decay energies for some more important fission products. A more detailed description of individual products is provided in [[Fission products (by element)]] and in [[Long-lived fission products]], and in articles on specific radionuclides. The following chart provides information on the electronegativity of the fission products. {| WIDTH="80%" align="CENTER" |- align="CENTER" | | [[Alkali metal|'''1''']] | [[Alkaline earth|'''2''']] | [[Group 3 element|'''3''']] | [[Group 4 element|'''4''']] | [[Group 5 element|'''5''']] | [[Group 6 element|'''6''']] | [[Group 7 element|'''7''']] | [[Group 8 element|'''8''']] | [[Group 9 element|'''9''']] | [[Group 10 element|'''10''']] | [[Coinage metal|'''11''']] | [[Group 12 element|'''12''']] | [[Boron group|'''13''']] | [[Carbon group|'''14''']] | [[Pnictogen|'''15''']] | [[Chalcogen|'''16''']] | [[Halogen|'''17''']] | [[Noble gas|'''18''']] |- align="CENTER" | [[Period 4 element|'''4''']] | colspan="12"|[[Ionization energy]] increases → [[Electronegativity]] increases → | bgcolor="#ffa900" | [[Gallium|Ga]]<br/>1.81 | bgcolor="#ff9900" | [[Germanium|Ge]]<br/>2.01 | bgcolor="#ff8c00" | [[Arsenic|As]]<br/>2.18 | bgcolor="#ff6f00" | [[Selenium|Se]]<br/>2.55 | bgcolor="#ff4f00" | [[Bromine|Br]]<br/>2.96 | bgcolor="#ff4c00" | [[Krypton|Kr]]<br/>3.00 |- align="CENTER" | [[Period 5 element|'''5''']] | bgcolor="#fff600" | [[Rubidium|Rb]]<br/>0.82 | bgcolor="#ffec00" | [[Strontium|Sr]]<br/>0.95 | bgcolor="#ffd700" | [[Yttrium|Y]]<br/>1.22 | bgcolor="#ffce00" | [[Zirconium|Zr]]<br/>1.33 | bgcolor="#ffb900" | [[Niobium|Nb]]<br/>1.6 | bgcolor="#ff8d00" | [[Molybdenum|Mo]]<br/>2.16 | bgcolor="#ffa200" | [[Technetium|Tc]]<br/>1.9 | bgcolor="#ff8a00" | [[Ruthenium|Ru]]<br/>2.2 | bgcolor="#ff8400" | [[Rhodium|Rh]]<br/>2.28 | bgcolor="#ff8a00" | [[Palladium|Pd]]<br/>2.20 | bgcolor="#ff9f00" | [[Silver|Ag]]<br/>1.93 | bgcolor="#ffb200" | [[Cadmium|Cd]]<br/>1.69 | bgcolor="#ffab00" | [[Indium|In]]<br/>1.78 | bgcolor="#ff9d00" | [[Tin|Sn]]<br/>1.96 | bgcolor="#ff9600" | [[Antimony|Sb]]<br/>2.05 | bgcolor="#ff9200" | [[Tellurium|Te]]<br/>2.1 | bgcolor="#ff6700" | [[Iodine|I]]<br/>2.66 | bgcolor="#ff6b00" | [[Xenon|Xe]]<br/>2.67 |- align="CENTER" | [[Period 6 element|'''6''']] | bgcolor="#fff800" | [[Caesium|Cs]]<br/>0.79 | bgcolor="#fff000" | [[Barium|Ba]]<br/>0.89 | bgcolor="#ffe000" | [[Lanthanum|La]]<br/>1.1 | bgcolor="#ffde00" | [[Cerium|Ce]]<br/>1.12 | bgcolor="#ffde00" | [[Praseodymium|Pr]]<br/>1.13 | bgcolor="#ffdd00" | [[Neodymium|Nd]]<br/>1.14 | bgcolor="#ffde00" | [[Promethium|Pm]]<br/>1.13 | bgcolor="#ffda00" | [[Samarium|Sm]]<br/>1.17 | bgcolor="#ffd800" | [[Europium|Eu]]<br/>1.2 | bgcolor="#ffd800" | [[Gadolinium|Gd]]<br/>1.2 | bgcolor="#ffe000" | [[Terbium|Tb]]<br/>1.1 | bgcolor="#ffd700" | [[Dysprosium|Dy]]<br/>1.22 | colspan="6" align="left"| [[Lanthanides]] act like Group 3 |- align=CENTER |colspan="3"| | bgcolor="#ffe000" | [[Actinium|Ac]]<br/>1.1 | bgcolor="#ffd000" | [[Thorium|Th]]<br/>1.3 | bgcolor="#ffc100" | [[Protactinium|Pa]]<br/>1.5 | bgcolor="#ffca00" | [[Uranium|U]]<br/>1.38 | bgcolor="#ffcc00" | [[Neptunium|Np]]<br/>1.36 | bgcolor="#ffd200" | [[Plutonium|Pu]]<br/>1.28 | bgcolor="#ffde00" | [[Americium|Am]]<br/>1.13 | bgcolor="#ffd200" | [[Curium|Cm]]<br/>1.28 | bgcolor="#ffd000" | [[Berkelium|Bk]]<br/>1.3 | bgcolor="#ffd000" | [[Californium|Cf]]<br/>1.3 |colspan="6" align="left"|[[Group number of lanthanides and actinides|Not]] all [[Actinides]] act like Group 3 |} == Fission product production == Small amounts of fission products are naturally formed as the result of either [[spontaneous fission]] of natural uranium, which occurs at a low rate, or as a result of neutrons from radioactive decay or reactions with cosmic ray particles. The microscopic tracks left by these fission products in some natural minerals can be used to provide a method of dating old materials. About 1.5 billion years ago, in a uranium ore body in Africa, a [[natural nuclear fission reactor]] operated for a few hundred thousand years and produced approximately 5 tonnes of fission products. These fission products were important in providing proof that the natural reactor had occurred. More details are provided in the [[natural nuclear fission reactor|linked article]]. Fission products are produced in [[nuclear weapons]], with the amount depending on the type of weapon. The largest source of fission products is from nuclear reactors. In current nuclear power reactors, a small percentage of the uranium in the fuel is converted into fission products as an unavoidable by-product of energy generation. Most of these fission products remain in the fuel unless there is fuel failure, or an accident, or the fuel is reprocessed. == Applications == === Supply of radioactive isotopes === Some fission products (such as [[Cs-137]]) are used in medical and industrial radioactive sources. === Nuclear reactor control === Some fission products decay with the release of a neutron. Since there may be a short delay in time between the original fission event (which release its own "prompt" neutrons immediately) and the release of these neutrons, the latter are termed "delayed neutrons". These delayed neutrons are important to nuclear reactor control. === Nuclear reactor poisons === Some of the fission products have a high neutron absorption capacity, such as [[Xenon|xenon-135]] and [[Samarium|samarium-149]]. Since a nuclear reactor depends on a balance in the neutron production and absorption rates, these fission product remove neutrons from the reactor and will tend to shut the reactor down or "poison" the reactor. Nuclear fuels and reactors are designed to address this phenomena through such features as burnable poisons and control rods. More details are provided in the article on [[Nuclear poison|nuclear reactor poisons]]. == Fission Product Decay with time == [[Image:Totalexternaldoseratecher.png|thumb|left|300px|The external gamma dose for a person in the open near the Chernobyl site.]] [[Image:Airdosechernobyl2.png|thumb|right|300px|The portion of the total radiation dose (in air) contributed by each isotope versus time after the [[Chernobyl disaster]], at the site thereof. Note that this image was drawn using data from the OECD report, [http://atom.kaeri.re.kr] and the second edition of 'The radiochemical manual'.]] {{Main|Long-lived fission product}}{{Main|Fission products (by element)}} For fission of Uranium-235 the most common radioactive fission products include isotopes of [[iodine]], [[caesium]], [[strontium]], [[xenon]] and [[barium]]. It is important to understand that the size of the threat becomes smaller with the passage of time, locations where radiation fields which posed immediate mortal threats (such as much of the Chernobyl power plant on day one of the accident and the ground zero sites of Japanese atomic bombings [6 hours after detonation]) are now safe as the radioactivity has decayed away. Please for instance see the graph below of the gamma dose rate due to Chernobyl fallout as a function of time after the accident. Many of the fission products decay through very shortlived isotopes to form stable isotopes, but also a considerable number of the radioisotopes have [[half-life|half lives]] longer than a day. The radioactivity in the fission product mixture is mostly short lived isotopes such as [[Iodine-131|I-131]] and <sup>140</sup>Ba, after about four months <sup>141</sup>Ce, <sup>95</sup>Zr/<sup>95</sup>Nb and <sup>89</sup>Sr take the largest share, while after about two or three years the largest share is taken by <sup>144</sup>Ce/144</sup>Pr, <sup>106</sup>Ru/<sup>106</sup>Rh and <sup>147</sup>Pm. Later <sup>90</sup>Sr and <sup>137</sup>Cs are the main radioisotopes, being succeeded by <sup>99</sup>Tc. Note that in the case a release of radioactivity from a power reactor or used fuel that only some elements are released, as a result the isotopic signature of the radioactivity is very different from an open air nuclear detonation where all the fission products are dispersed. == Fission products in power reactors == In a nuclear power reactor, the main types of radioactivity are fission products, actinides and activation products. Fission products are the largest amount of radioactivity for the first several hundred years, while actinides are dominant roughly 10<sup>3</sup> to 10<sup>5</sup> years after fuel use. Fission occurs in the nuclear fuel, and the fission products are primarily retained within the fuel close to where they are produced. These fission products are important to the operation of the reactor because (as noted above) some fission products contribute delayed neutrons that are useful for reactor control while others are neutron poisons that tend to inhibit the nuclear reaction. The buildup of the fission product poisons is a key factor in determining the maximum duration a given fuel element can be kept within the reactor. The decay of short-lived fission products also provide a source of heat within the fuel that continues even after the reactor has been shutdown and the fission reactions stopped. It is this decay heat that sets the requirements for cooling of a reactor after shutdown. More details on these topics are provided in the articles on [[nuclear power plants]] and [[used nuclear fuel]]. If the fuel cladding around the fuel develops holes, then fission products can leak into the primary [[coolant]]. Depending on the fission product chemistry, it may settle within the reactor core or travel through the coolant system. Coolant systems include chemistry control systems that among other purposes, will tend to remove such fission products. In a well-designed power reactor running under normal conditions, the radioactivity of the coolant is very low. == Fission products in nuclear weapons == Nuclear weapons use fission as either the partial or the main energy source. Depending on the weapon design and where it is exploded, the relative importance of the fission product radioactivity will vary compared to the activation product radioactivity in the total fallout radioactivity. The immediate fission products from nuclear weapon fission are essentially the same as those from any other fission source, depending slightly on the particular nuclide that is fissioning. However, the very short time scale for the reaction makes a difference in the particular mix of isotopes produced from an atomic bomb. For example, the <sup>134</sup>Cs/<sup>137</sup>Cs ratio provides an easy method of distinguishing between fallout from a bomb and the fission products from a power reactor. Almost no [[Cs-134]] is formed by nuclear fission (because [[xenon]]-134 is stable). The <sup>134</sup>Cs is formed by the [[neutron activation]] of the stable <sup>133</sup>Cs which is formed by the decay of isotopes in the [[isobar]] (A = 133). so in a momentary criticality by the time that the [[neutron]] flux becomes zero too little time will have passed for any <sup>133</sup>Cs to be present. While in a power reactor plenty of time exists for the decay of the isotopes in the [[isobar]] to form <sup>133</sup>Cs, the <sup>133</sup>Cs thus formed can then be activated to form <sup>134</sup>Cs only if the time between the start and the end of the criticality is long. According to Jiri Hala's textbook the radioactivity in the fission product mixture (due to an [[atom bomb]]) is mostly caused by short-lived isotopes such as [[Iodine-131|I-131]] and [[Barium|Ba]]-140. After about four months [[Cerium|Ce]]-141, [[Zirconium|Zr]]-95/[[Niobium|Nb]]-95, and [[Strontium|Sr]]-89 represent the largest share of radioactive material. After two to three years, [[Cerium|Ce]]-144/[[Praseodymium|Pr]]-144, [[Ruthenium|Ru]]-106/[[Rhodium|Rh]]-106, and [[Promethium-147]] are the bulk of the radioactivity. After a few years, the radiation is dominated by [[Strontium-90]] and [[Caesium-137]], whereas in the period between 10,000 and a million years it is [[Technetium]]-99 that dominates. == Countermeasures against the worst fission products found in accident fallout == The purpose of radiological emergency preparedness is to protect people from the effects of radiation exposure after an accident at a [[nuclear power plant]]. Evacuation is the most effective protective measure in the event of a radiological emergency because it protects the whole body (including the thyroid gland and other organs) from all radionuclides and all exposure pathways. However, in situations where evacuation is impossible, calling for in-place sheltering, there are measures which lend some degree of protection against harmful radioisotopes The mixture of [[radioactive]] fission products found in the [[nuclear fallout|fallout]] from a [[nuclear bomb]] are very different in nature to those found in spent power [[reactor]] fuel. This is because the reactor fuel will have had more time for the short lived isotopes to decay, and because for many accident types that the volatile elements are liberated while the involitiles are retained at the accident site. As a result the contribution of many shortlived (eg <sup>97</sup>Zr) and/or involtiles to the off site gamma dose is less for accident fallout than it is for local fallout from a bomb detonation. === Iodine === At least three [[isotopes of iodine]] are important. [[Iodine-129|<sup>129</sup>I]], [[Iodine-131|<sup>131</sup>I]] (Radioiodine) and <sup>132</sup>I. An overview of [[iodine]] exposure in the [[USA]] (resulting from bomb tests) can be seen at [http://rex.nci.nih.gov/massmedia/Fallout/contents.html]. Open air nuclear testing and the [[Chernobyl disaster]] both released iodine-131. [[Image:US fallout exposure.png|right|250px|thumb|Per capita thyroid doses in the continental United States of [[iodine-131]] resulting from all exposure routes from all atmospheric nuclear tests conducted at the [[Nevada Test Site]]. See also [[Downwinders]].]] The shortlived isotopes of iodine are particularly harmful because the [[thyroid]] collects and concentrates iodide -- radioactive as well as non-radioactive -- for use in the production of [[metabolic]] [[hormones]]. Absorption of radioiodine can lead to acute, chronic, and delayed effects. Acute effects from high doses include [[thyroiditis]], while chronic and delayed effects include [[hypothyroidism]], thyroid nodules, and [[thyroid cancer]]. It has been shown that the active iodine released from Chernobyl and Mayak<ref>G. Mushkacheva, E. Rabinovich, V. Privalov, S. Povolotskaya, V. Shorokhova, S. Sokolova, V. Turdakova, E. Ryzhova, P. Hall, A. B. Schneider, D. L. Preston, and E. Ron, "Thyroid Abnormalities Associated with Protracted Childhood Exposure to 131I from Atmospheric Emissions from the Mayak Weapons Facility in Russia", ''Radiation Research'', 2006, '''166'''(5), 715-722</ref> has resulted in an increase in the incidence of thyroid cancer in the former [[Soviet Union]]. One measure which may protect against this risk is taking large doses of [[potassium iodide]] before exposure to radioiodine -- the non-radioactive iodide 'saturates' the thyroid, causing less of the radioiodine to be stored in the body. Because this countermeasure simply takes advantage of the [[pharmacokinetics]] regarding iodide uptake, it affords no protection against other causes of [[radiation poisoning]]. Administering potassium iodide reduces the effects of radio iodine by 99%, and is a prudent, inexpensive supplement to sheltering. The [[Food and Drug Administration]] (FDA) has approved potassium iodide as an over-the-counter [[medication]]. As with any medication, individuals should check with their doctor or pharmacist before using it. A low-cost alternative to commercially available iodine pills is a [[saturated solution]] of potassium iodide. It usually possible to obtain several thousand doses for prices near US$ 0.01/dose. Long term storage of KI is normally in the form of reagent grade crystals, which are convenient and available commercially. The purity is superior to "pharmacologic grade". Its concentration depends only on temperature, which is easy to determine, and the required dose is easily administered by measuring the required volume of the liquid. At room temperature, the U.S. standard adult radiological protective dose of 130mg is four drops of a saturated solution. A baby's dose is 65mg, or two drops. It should be noted that these doses are sufficient to cause [[nausea]] and sometimes [[emesis]] in most individuals. It's normally administered in a ball of bread, because it tastes incredibly bad. Use is contraindicated in individual known to be allergic to iodine; for such persons [[sodium perchlorate]] is one alternative (see chap 13, Kearney). #Cresson Kearny, Nuclear War Survival Skills, available on line at [http://www.oism.org/ Oregon Institute of Science and Medicine], created with the permission of the author. The information on KI is near the end of chapter 13. This manual has proven technical info on expedient fallout shelters, and assorted shelter system needs that can be created from common household items. OISM also offers free downloads of other civil defense and shelter information as well. === Caesium === The [[Chernobyl]] accident released a large amount of caesium isotopes, these were dispersed over a wide area. For instance they can be found in the soil of [[France]] at low levels while in some areas of the former [[Soviet Union]] the concentration in soil is sometimes much higher. For a review of the methods used to decontaminate an urban environment please see the [[scope]] report [http://www.icsu-scope.org/downloadpubs/scope50/chapter06.html Behaviour and Decontamination of Artificial Radionuclides in the Urban Environment]. Also see chapter four of the [[Nuclear Energy Agency|NEA]] reports [http://citeseer.ist.psu.edu/cache/papers/cs/28102/http:zSzzSzwww.nea.frzSzhtmlzSzrpzSzchernobylzSzchernobyl-1995.pdf/chernobyl-ten-years-on.pdf Chernobyl ten years on] and [http://www.nea.fr/html/rp/reports/2003/nea3508-chernobyl.pdf Chernobyl twenty years on] for details of how farming methods can be changed to reduce the impact of accident fallout. ==== Prussian blue ==== In [[livestock]] farming an important countermeasure against <sup>137</sup>Cs is to feed to animals a little [[prussian blue]]. This [[iron]] [[potassium]] [[cyanide]] compound acts as a [[ion-exchanger]]. The cyanide is so tightly bonded to the iron that it is safe for a human to eat several grams of prussian blue per day. The prussian blue reduces the [[biological half life]] (different from the [[half-life|nuclear half life]]) of the caesium. The physical or nuclear half life of <sup>137</sup>Cs is about 30 years. This is a constant which can not be changed but the biological half life is not a constant. It will change according to the nature and habits of the organism it is expressed for. [[Caesium]] in humans normally has a biological half life of between one and four months. An added advantage of the prussian blue is that the caesium which is stripped from the animal in the droppings is in a form which is not available to plants. Hence it prevents the caesium from being recycled. The form of prussian blue required for the treatment of humans or animals is a special grade. Attempts to use the [[pigment]] grade used in [[paint]]s have not been successful. For further details of the use of prussian blue please see the [[IAEA]] report on the [[Goiânia accident]].[http://www-pub.iaea.org/MTCD/publications/PDF/Pub815_web.pdf] ==== Ploughing or the removal of the top layer ==== <sup>137</sup>Cs is an isotope which is of long term concern as it remains in the top layers of soil. Plants with shallow root systems tend to absorb it for many years. Hence [[grass]] and [[mushroom]]s can carry a considerable amount of <sup>137</sup>Cs which can be transferred to humans through the [[food chain]]. One of the best countermeasures in dairy farming against <sup>137</sup>Cs is to mix up the soil by deeply [[ploughing]] the soil. This has the effect of putting the <sup>137</sup>Cs out of reach of the shallow [[root]]s of the grass, hence the level of radioactivity in the grass will be lowered. Also after a nuclear war or serious accident the removal of top few cm of [[soil]] and its burial in a shallow trench will reduce the long term gamma dose to humans due to <sup>137</sup>Cs as the gamma [[photon]]s will be attenuated by their passage through the [[soil]]. The deeper and more remote the trench is, the better the degree of protection which will be afforded to the human population. ==== Release from the Chernobyl fire ==== More details about the caesium release from the [[Chernobyl accident]] can be found at [http://www.icsu-scope.org/downloadpubs/scope50/chapter02.html#t2.7] . A definitive report on Chernobyl is at [http://www.nea.fr/html/rp/chernobyl/allchernobyl.html] - table 1 in chapter two lists the radioisotopes released in the fire. The percentage of the inventory which was released was controlled largely by how volatile the fission product is. Hence a greater proportion of the [[xenon]] and [[iodine]] than the [[cerium]] and [[plutonium]] were released. === Strontium === Also by the addition of [[Agricultural lime|lime]] to soils which are poor in [[calcium]] the uptake of [[strontium]] by plants can be reduced, likewise in areas where the soil is low in [[potassium]], the addition of a potassium [[fertiliser]] can discourage the uptake of caesium into plants. However such treatments with either [[Agricultural lime|lime]] or [[potash]] should not be undertaken lightly as they can alter the soil chemistry greatly so resulting in a change in the plant [[ecology]] of the land. == Fission products within the back end of the nuclear fuel cycle == ===Caesium=== It is known that the isotope responsible for the majority of the [[external]] gamma exposure in [[nuclear reprocessing|fuel reprocessing]] plants (and the Chernobyl site in 2005) is [[Cs-137]]. <sup>137</sup>Cs does appear to be an indicator of nuclear fission, as it is only formed by nuclear fission of an actinide. <sup>137</sup>Cs is often removed from waste waters in the nuclear industry by means of solid [[ion exchange]]rs. A range of [[zeolite]]s can be used for this task. In nuclear reactors both <sup>137</sup>Cs and <sup>90</sup>Sr are found in locations remote from the [[fuel]], this is because these isotopes are formed by the beta decay of noble gases (xenon-137 {halflife of 3.8 minutes}and krypton-90 {halflife 32 seconds}) which enable these isotopes to be deposited in locations remote from the fuel (eg on control rods and in the space inside a [[fuel pin]] between the fuel and the cladding) ===Iodine=== <sup>133</sup>I decays by [[beta particle]] decay (with a [[half life]] of 20.8 hours) to <sup>133</sup>Xe which in turn decays by [[beta decay]] (with a half life of 5.2 days) to <sup>133</sup>Cs. The isotopes which decay to <sup>133</sup>I are very short lived. [[iodine-129|<sup>129</sup>I]] is very long lived and this is one of the major radioactive elements which enter the sea from reprocessing plants. ===Fission products which form anions=== Some fission products are very long lived, examples of these include [[iodine]]-129 and [[technetium]]-99. Both of these are very mobile in solid/water as they form [[anionic]] species (Iodide and <sup>99</sup>TcO<sub>4</sub>-). ===Absorption of fission products on metal surfaces=== ====Tc==== It is interesting to note that in common with [[chromate]] and [[molybdate]] that <sup>99</sup>TcO<sub>4</sub>- ion can react with steel surfaces to form a [[corrosion]] resistant layer. In this way these metaloxo anions act as [[anode|anodic]] [[corrosion inhibitor]]s. The formation of <sup>99</sup>TcO<sub>2</sub> on steel surfaces is one effect which will retard the release of <sup>99</sup>Tc from nuclear waste drums and nuclear equipment which has become lost prior to decontamination (eg [[submarine]] reactors which have been lost at sea). This <sup>99</sup>TcO<sub>2</sub> layer renders the steel surface passive, it inhibits the [[anodic]] [[corrosion]] reaction. ====I==== In a similar way the release of iodine-131 in a serious power reactor accident could be retarded by absorption on metal surfaces within the nuclear plant. A [[PhD]] [[thesis]][http://www.nc.chalmers.se/AVHANDL/DRAVH/HGLAN.HTM] was written on this subject at The [[Nuclear chemistry]] department[http://www.nc.chalmers.se/PUBLIC.HTM] at [[Chalmers University of Technology]] in [[Sweden]]. * H. Glänneskog. Interactions of [[Iodine|I]]<sub>2</sub> and [[Methyl iodide|CH]]<sub>3</sub>I with reactive metals under BWR severe-accident conditions, ''Nucl. Engineering and Design'', 2004, '''227''', pages 323-329. * H. Glänneskog. Iodine chemistry under severe accident conditions in a nuclear power reactor, Ph.D. Thesis, Chalmers University of Technology, October, 2005. A lot of other work on the iodine chemistry which would occur during a bad accident has been done.[http://www.sbf.admin.ch/htm/services/publikationen/international/frp/eu-abstracts/html/fp/fp5/5eu99.0423.html][http://www.nea.fr/html/nsd/docs/2000/csni-r2000-12.pdf][http://www.ing.unipi.it/~dimnp/CD/supporto/pdf/paci03.pdf] ==References== {{Reflist}} '''Radioactivity, Ionizing Radiation and Nuclear Energy''', by J. Hala and J.D. Navratil [http://www.em.doe.gov/stakepages/wmdi_llwapxc.aspx DOE: Key Radionuclides and Generation Processes] [[Category:Nuclear technology]] [[Category:Nuclear chemistry]] [[Category:Nuclear physics]] [[Category:Inorganic chemistry]] [[Category:Radiobiology]] [[Category:Fission products| ]] [[de:Spaltprodukt]] [[fr:Produit de fission]] [[he:ביקוע גרעיני#תוצרי הביקוע]]