Unlike LWRs, in principle these fuel cycles could recycle their plutonium and minor actinides and leave only fission products and activation products as waste.
The highly radioactive medium-lived fission products Cs and Sr diminish by a factor of 10 each century; while the long-lived fission products have relatively low radioactivity, often compared favorably to that of the original uranium ore. Although the most common terminology is fuel cycle, some argue that the term fuel chain is more accurate, because the spent fuel is never fully recycled.
Spent fuel includes fission products , which generally must be treated as waste , as well as uranium, plutonium, and other transuranic elements. Where plutonium is recycled, it is normally reused once in light water reactors, although fast reactors could lead to more complete recycling of plutonium.
Not a cycle per se , fuel is used once and then sent to storage without further processing save additional packaging to provide for better isolation from the biosphere. Here, the fission products , minor actinides , activation products , and reprocessed uranium are separated from the reactor-grade plutonium , which can then be fabricated into MOX fuel.
Because the proportion of the non- fissile even - mass isotopes of plutonium rises with each pass through the cycle, there are currently no plans to reuse plutonium from used MOX fuel for a third pass in a thermal reactor. If fast reactors become available, they may be able to burn these, or almost any other actinide isotopes. Similarly as plutonium is not separated on its own in the pyroprocessing cycle, rather all actinides are " electro-won " or "refined" from the spent fuel, the plutonium is never separated on its own, instead it comes over into the new fuel mixed with gamma and alpha emitting actinides, species that "self-protect" it in numerous possible thief scenarios.
It has been proposed that in addition to the use of plutonium, the minor actinides could be used in a critical power reactor. Tests are already being conducted in which americium is being used as a fuel. A number of reactor designs, like the Integral Fast Reactor , have been designed for this rather different fuel cycle.
In principle, it should be possible to derive energy from the fission of any actinide nucleus. With a careful reactor design, all the actinides in the fuel can be consumed, leaving only lighter elements with short half-lives. Whereas this has been done in prototype plants, no such reactor has ever been operated on a large scale. It so happens that the neutron cross-section of many actinides decreases with increasing neutron energy, but the ratio of fission to simple activation neutron capture changes in favour of fission as the neutron energy increases.
Thus with a sufficiently high neutron energy, it should be possible to destroy even curium without the generation of the transcurium metals. This could be very desirable as it would make it significantly easier to reprocess and handle the actinide fuel. Here a beam of either protons United States and European designs    or electrons Japanese design  is directed into a target.
In the case of protons, very fast neutrons will spall off the target, while in the case of the electrons, very high energy photons will be generated.
These high-energy neutrons and photons will then be able to cause the fission of the heavy actinides. As an alternative, the curium, with a half-life of 18 years, could be left to decay into plutonium before being used in fuel in a fast reactor.
- Nonparametric Curve Estimation: Methods, Theory and Applications.
- Classics in Post-Colonial Worlds (Classical Presences).
- chapter and author info.
If actinides are transmuted in a Subcritical reactor , it is likely that the fuel will have to be able to tolerate more thermal cycles than conventional fuel. An accelerator-driven sub-critical reactor is unlikely to be able to maintain a constant operation period for equally long times as a critical reactor, and each time the accelerator stops then the fuel will cool down. On the other hand, if actinides are destroyed using a fast reactor, such as an Integral Fast Reactor , then the fuel will most likely not be exposed to many more thermal cycles than in a normal power station.
Depending on the matrix the process can generate more transuranics from the matrix.
This could either be viewed as good generate more fuel or can be viewed as bad generation of more radiotoxic transuranic elements. A series of different matrices exists which can control this production of heavy actinides. Fissile nuclei, like Uranium, Plutonium and Uranium respond well to delayed neutrons and are thus important to keep a critical reactor stable, and this limits the amount of minor actinides that can be destroyed in a critical reactor. As a consequence, it is important that the chosen matrix allows the reactor to keep the ratio of fissile to non-fissile nuclei high, as this enables it to destroy the long-lived actinides safely.
In contrast, the power output of a sub-critical reactor is limited by the intensity of the driving particle accelerator, and thus it need not contain any uranium or plutonium at all.
Nuclear fission product - Wikipedia
In such a system, it may be preferable to have an inert matrix that doesn't produce additional long-lived isotopes. The actinides will be mixed with a metal which will not form more actinides, for instance an alloy of actinides in a solid such as zirconia could be used. Thorium will on neutron bombardment form uranium U is fissile, and has a larger fission cross section than both U and U, and thus it is far less likely to produce higher actinides through neutron capture.
If the actinides are incorporated into a uranium-metal or uranium-oxide matrix, then the neutron capture of U is likely to generate new plutonium An advantage of mixing the actinides with uranium and plutonium is that the large fission cross sections of U and Pu for the less energetic delayed-neutrons could make the reaction stable enough to be carried out in a critical fast reactor , which is likely to be both cheaper and simpler than an accelerator driven system. It is also possible to create a matrix made from a mix of the above-mentioned materials.
This is most commonly done in fast reactors where one may wish to keep the breeding ratio of new fuel high enough to keep powering the reactor, but still low enough that the generated actinides can be safely destroyed without transporting them to another site. One way to do this is to use fuel where actinides and uranium is mixed with inert zirconium, producing fuel elements with the desired properties. In the thorium fuel cycle thorium absorbs a neutron in either a fast or thermal reactor. The thorium beta decays to protactinium and then to uranium , which in turn is used as fuel. Hence, like uranium , thorium is a fertile material.
After starting the reactor with existing U or some other fissile material such as U or Pu , a breeding cycle similar to but more efficient  than that with U and plutonium can be created. The Th absorbs a neutron to become Th which quickly decays to protactinium Protactinium in turn decays with a half-life of 27 days to U In some molten salt reactor designs, the Pa is extracted and protected from neutrons which could transform it to Pa and then to U , until it has decayed to U This is done in order to improve the breeding ratio which is low compared to fast reactors.
Thorium is at least times more abundant in nature than all of uranium isotopes combined; thorium is fairly evenly spread around Earth with a lot of countries  having huge supplies of it; preparation of thorium fuel does not require difficult  and expensive enrichment processes; the thorium fuel cycle creates mainly Uranium contaminated with Uranium which makes it harder to use in a normal, pre-assembled nuclear weapon which is stable over long periods of time unfortunately drawbacks are much lower for immediate use weapons or where final assembly occurs just prior to usage time ; elimination of at least the transuranic portion of the nuclear waste problem is possible in MSR and other breeder reactor designs.
One of the earliest efforts to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the s. An experimental reactor was built based on molten salt reactor technology to study the feasibility of such an approach, using thorium fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used Th as the fertile material and U as the fissile fuel.
Due to a lack of funding, the MSR program was discontinued in Currently the only isotopes used as nuclear fuel are uranium U , uranium U and plutonium , although the proposed thorium fuel cycle has advantages. Some modern reactors, with minor modifications, can use thorium. Thorium is approximately three times more abundant in the Earth's crust than uranium and times more abundant than uranium There has been little exploration for thorium resources, and thus the proved resource is small. Thorium is more plentiful than uranium in some countries, notably India. Heavy water reactors and graphite-moderated reactors can use natural uranium , but the vast majority of the world's reactors require enriched uranium , in which the ratio of U to U is increased.
Nuclear fission product
The term nuclear fuel is not normally used in respect to fusion power , which fuses isotopes of hydrogen into helium to release energy. From Wikipedia, the free encyclopedia. Process of manufacturing and consuming nuclear fuel. Main article: Uranium mining. Main article: Enriched uranium. Main article: Nuclear fuel. Main article: Post irradiation examination. Main article: Spent nuclear fuel shipping cask. Main article: Nuclear reprocessing. See also: Spent nuclear fuel. Actinides and fission products by half-life v t e.
Main articles: Radioactive waste and Spent nuclear fuel. Main article: Thorium fuel cycle. Retrieved PPL Corporation. Archived from the original PDF on Rondinella VV et al. Preston, J. Dutton and B. Harvey, Nature , , , — Nuclear Engineering and Design. While actually a sub-actinide, it immediately precedes actinium 89 and follows a three-element gap of instability after polonium 84 where no nuclides have half-lives of at least four years the longest-lived nuclide in the gap is radon with a half life of less than four days.
Radium's longest lived isotope, at 1, years, thus merits the element's inclusion here. Nuclear Physics. Bibcode : NucPh.. Ojovan, W. IAEA Bulletin. Archived from the original on Nuclear Engineering at Argonne. Further study may reveal a better choice, but as of this writing graphite is the most economical and experimentally practical choice.
There are various ways to control the environment within the furnace e. For the experiments discussed here the environment within the furnace was not manipulated and yet the key characteristics of the glass samples produced were appropriate for their purpose. It should be noted that the environment existing near ground zero during a nuclear detonation is not well understood.
Irradiating samples in the Pneumatic Tube system at HFIR introduces some error in the radioactive properties of the surrogates. This error arises due to the distinct difference between nuclear weapon and reactor neutron energy spectra. The fission product spectrum will thus be characteristic of a reactor produced by a thermal neutron spectrum rather than a weapon produced by a fast neutron spectrum. In addition, the ratio of fission to activation products will be inaccurate when both are produced by irradiation in situ. Studies are ongoing to better understand and possibly counteract this effect.
The method outlined here will produce a nuclear melt glass surrogate which is accurate in terms of color, texture, porosity, microstructure, mineral morphology, compositional heterogeneity, and degree of amorphousness. There are essentially three key steps to successfully replicate the results presented here: 1 carefully prepare the STF powder according to specifications, 2 safely and quickly heat the powder to a high temperature well above the melting point of the matrix , and 3 cool rapidly quench to avoid recrystallization.
Jump to ...
It is important to note, however, that identical procedures will not produce identical samples and this is perfectly acceptable as the same is true for real nuclear melt glass trinitite samples exhibit a high degree of variability as well. The most critical steps in the protocol are steps 1. Following these steps will lead to the production of a non-radioactive sample with the desired properties. A radioactive sample may be produced by following essentially the same steps with additional caution due to the hazard associated with radioactive materials.
This may be because the snippet appears in a figure legend, contains special characters or spans different sections of the article. J Vis Exp. Published online Jan 4. PMID: Joshua J. Molgaard , 1 John D. Auxier, II , 2 , 3 Andrew V. Giminaro , 2 , 3 Colton J. Oldham , 2 Jonathan Gill , 2 and Howard L. John D. Auxier, II. Andrew V. Colton J. Howard L. Correspondence to: Joshua J. Molgaard at ude. Abstract Realistic surrogate nuclear debris is needed within the nuclear forensics community to test and validate post-detonation analysis techniques.
Keywords: Engineering, Issue , nuclear weapons, nuclear debris, melt glass, trinitite, vitrify, amorphous, crystalline. Open in a separate window. Click here to view. Introduction Concerns over the potential malicious use of nuclear weapons by terrorists or rogue nations have highlighted the importance of nuclear forensics analysis for the purpose of attribution. Protocol Caution: The process outlined here includes the use of radioactive material e. Preparation of the STF Note: Equipment needed includes a microbalance, metal spatulas, a ceramic mortar and pestle, a chemical fume hood, latex gloves, a lab coat, and eye protection.
Use a microbalance and small spatula to precisely measure the mass fractions of each compound as listed in Table 1. For best results prepare g of the non-radioactive precursor matrix at one time. Add Thoroughly mix the powder mixture, including the UNH, using a mortar and pestle. Complete final mixing shortly before the melting step. Carefully measure 1. Carefully place the crucible in the heated HTF using a long pair of steel crucible tongs and melt the mixture for 30 min.
Remove the sample again using the tongs and pour the molten sample into the mortar filled with sand. Production of a radioactive sample Repeat steps 2. Sample Activation Note: The equations that follow were derived assuming the use of weapons grade enriched uranium metal. Activation of a Melt Glass Sample with Uranium Fue Calculate the mass fraction of uranium metal required for the sample using the equation below 13 where m U represents the uranium mass fraction and Y represents the weapon yield :. Optional: Calculate the mass fraction of tamper e.
Calculate the target number of fissions in the sample using the following equation 13 where M s represents the mass of the sample in grams and N f represents the number of fissions produced in the sample during irradiation:. Calculate the required irradiation time using the equation below 13 where m represents the U mass fraction enrichment level and t irr is the irradiation time in seconds:.
Irradiate the sample for t irr seconds at a thermal neutron flux of 4. This has been accomplished for one 0. This sample has been thoroughly analyzed by Cook et al. Follow applicable safety protocols for handling the radioactive sample post-irradiation. Activation of a Melt Glass Sample with Plutonium Fuel Planning Factors Calculate the mass fraction of plutonium metal required for the sample using the equation below 13 where m Pu represents the plutonium mass fraction and Y represents the weapon yield:. Determine the irradiation time required to obtain the desired number of fissions in the melt glass sample.
This time will depend on the composition and grade of the plutonium as well as the neutron energy spectrum. Representative Results The non-radioactive samples produced in this study have been compared to trinitite and Figures show that the physical properties and morphology are indeed similar.
Discussion Note regarding steps 1. Acknowledgments Portions of this study have been previously published in the Journal of Radioanalytical and Nuclear Chemistry. These delayed neutrons are important to nuclear reactor control. Some of the fission products, such as xenon and samarium , have a high neutron absorption cross section. Since a nuclear reactor depends on a balance in the neutron production and absorption rates, those fission products that remove neutrons from the reaction will tend to shut the reactor down or "poison" the reactor. Nuclear fuels and reactors are designed to address this phenomenon through such features as burnable poisons and control rods.
Build-up of xenon during shutdown or low-power operation may poison the reactor enough to impede restart or to interfere with normal control of the reaction during restart or restoration of full power, possibly causing or contributing to an accident scenario. 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. Almost no Cs is formed by nuclear fission because xenon is stable.
- Got a tip?.
- Reactor website!
- Tables of Functions with Formulae and Curves!
So in a momentary criticality by the time that the neutron flux becomes zero too little time will have passed for any Cs to be present. While in a power reactor plenty of time exists for the decay of the isotopes in the isobar to form Cs, the Cs thus formed can then be activated to form 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 in an atom bomb is mostly caused by short-lived isotopes such as I and Ba After a few years, the radiation is dominated by strontium and caesium , whereas in the period between 10, and a million years it is technetium that dominates.
Some fission products such as Cs are used in medical and industrial radioactive sources. In this way these metaloxo anions act as anodic corrosion inhibitors - it renders the steel surface passive. The formation of 99 TcO 2 on steel surfaces is one effect which will retard the release of 99 Tc from nuclear waste drums and nuclear equipment which has become lost prior to decontamination e. In a similar way the release of radio-iodine in a serious power reactor accident could be retarded by adsorption on metal surfaces within the nuclear plant.
For fission of uranium , the predominant radioactive fission products include isotopes of iodine , caesium , strontium , xenon and barium. The threat becomes smaller with the passage of time. Locations where radiation fields once posed immediate mortal threats, such as much of the Chernobyl Nuclear Power Plant on day one of the accident and the ground zero sites of U. Many of the fission products decay through very short-lived isotopes to form stable isotopes , but a considerable number of the radioisotopes have half-lives longer than a day.
Later 90 Sr and Cs are the main radioisotopes, being succeeded by 99 Tc. In the case of a release of radioactivity from a power reactor or used fuel, 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. The purpose of radiological emergency preparedness is to protect people from the effects of radiation exposure after a nuclear accident or bomb. Evacuation is the most effective protective measure.
However, if evacuation is impossible or even uncertain, then local fallout shelters and other measures provide the best protection. At least three isotopes of iodine are important. Open air nuclear testing and the Chernobyl disaster both released iodine The short-lived isotopes of iodine are particularly harmful because the thyroid collects and concentrates iodide — radioactive as well as stable.
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  has resulted in an increase in the incidence of thyroid cancer in the former Soviet Union. One measure which protects against the risk from radio-iodine is taking a dose of potassium iodide KI before exposure to radioiodine.
The non-radioactive iodide 'saturates' the thyroid, causing less of the radioiodine to be stored in the body. A low-cost alternative to commercially available iodine pills is a saturated solution of potassium iodide. Long-term storage of KI is normally in the form of reagent grade crystals.
The administration of known goitrogen substances can also be used as a prophylaxis in reducing the bio-uptake of iodine, whether it be the nutritional non-radioactive iodine or radioactive iodine, radioiodine - most commonly iodine , as the body cannot discern between different iodine isotopes. Perchlorate ions, a common water contaminant in the USA due to the aerospace industry , has been shown to reduce iodine uptake and thus is classified as a goitrogen.
Perchlorate ions are a competitive inhibitor of the process by which iodide is actively deposited into thyroid follicular cells. Studies involving healthy adult volunteers determined that at levels above 0. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland. Prophylaxis with perchlorate-containing water at concentrations of 17 ppm , which corresponds to 0. In another related study where subjects drank just 1 litre of perchlorate-containing water per day at a concentration of 10 ppm, i.
However, when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately 0. Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine. To completely block the uptake of iodine by the purposeful addition of perchlorate ions to a populace's water supply, aiming at dosages of 0. Perchlorate ion concentrations in a region's water supply would need to be much higher, at least 7. The continual distribution of perchlorate tablets or the addition of perchlorate to the water supply would need to continue for no less than 80—90 days, beginning immediately after the initial release of radioiodine was detected.
After 80—90 days passed, released radioactive iodine would have decayed to less than 0. In the event of a radioiodine release, the ingestion of prophylaxis potassium iodide, if available, or even iodate, would rightly take precedence over perchlorate administration, and would be the first line of defense in protecting the population from a radioiodine release. However, in the event of a radioiodine release too massive and widespread to be controlled by the limited stock of iodide and iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply, or distribution of perchlorate tablets would serve as a cheap, efficacious, second line of defense against carcinogenic radioiodine bioaccumulation.
The ingestion of goitrogen drugs is, much like potassium iodide also not without its dangers, such as hypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate, or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions where radioiodine has sufficiently contaminated the environment.
The Chernobyl accident released a large amount of caesium isotopes which were dispersed over a wide area. Plants with shallow root systems tend to absorb it for many years. Hence grass and mushrooms can carry a considerable amount of Cs, which can be transferred to humans through the food chain. One of the best countermeasures in dairy farming against Cs is to mix up the soil by deeply ploughing the soil.
This has the effect of putting the Cs out of reach of the shallow roots of the grass, hence the level of radioactivity in the grass will be lowered. Also the removal of top few centimeters of soil and its burial in a shallow trench will reduce the dose to humans and animals as the gamma photons from Cs will be attenuated by their passage through the soil.
The deeper and more remote the trench is, the better the degree of protection. Fertilizers containing potassium can be used to dilute cesium and limit its uptake by plants. In livestock farming, another countermeasure against Cs is to feed to animals prussian blue. This compound acts as an ion-exchanger. The cyanide is so tightly bonded to the iron that it is safe for a human to consume several grams of prussian blue per day. The prussian blue reduces the biological half-life different from the nuclear half-life of the caesium. The physical or nuclear half-life of Cs is about 30 years.
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.