However, such discharges are regulated and controlled, and the maximum radiation dose anyone receives from them is a small fraction of natural background radiation. Nuclear power stations and reprocessing plants release small quantities of radioactive gases e. However, krypton and xenon are chemically inert, all three gases have short half-lives, and the radioactivity in the emissions is diminished by delaying their release. The net effect is too small to warrant consideration in any life-cycle analysis.
A little tritium is also produced but regulators do not consider its release to be significant. The long timescales over which some ILW and HLW — including used fuel when considered a waste — remains radioactive has led to universal acceptance of the concept of deep geological disposal.
Many other long-term waste management options have been investigated, but deep disposal in a mined repository is now the preferred option in most countries. To date there has been no practical need for final HLW repositories. As outlined above, used fuel may either by reprocessed or disposed of directly. Interim storage of used fuel is mostly in ponds associated with individual reactors, or in a common pool at multi-reactor sites, or occasionally at a central site.
At present there is about , tonnes of used fuel in storage. Over two-thirds of this is in storage ponds, with an increasing proportion in dry storage. Storage ponds at reactors, and those at centralized facilities such as CLAB in Sweden, are metres deep to allow for several metres of water over the used fuel assembled in racks typically about 4 metres long and standing on end.
The multiple racks are made of metal with neutron absorbers incorporated. The circulating water both shields and cools the fuel. These pools are robust constructions made of thick reinforced concrete with steel liners. Ponds at reactors are often designed to hold all the used fuel produced over the planned operating lifetime of the reactor. Some fuel that has cooled in ponds for at least five years is stored in dry casks or vaults with air circulation inside concrete shielding.
One common system is for sealed steel casks or multi-purpose canisters MPCs each holding up to about 40 fuel assemblies with inert gas. For storage, each is enclosed in a ventilated storage module made of concrete and steel. These are commonly standing on the surface, about 6m high, and cooled by air convection, or they may be below grade, with just the tops showing. The modules are robust and provide full shielding.
Each cask has up to 45 kW heat load. If used reactor fuel is reprocessed, the resulting liquid HLW must be solidified. The HLW also generates a considerable amount of heat and requires cooling. It is vitrified into borosilicate Pyrex glass, sealed into heavy stainless steel cylinders about 1. This material has no conceivable future use and is universally classified as waste. France has two commercial plants to vitrify HLW left over from reprocessing fuel, and there are also plants active in the UK and Belgium.
The capacity of these Western European plants is canisters t a year, and some have been operating for three decades. The Australian Synroc synthetic rock system is a more sophisticated way to immobilize such waste, and this process may eventually come into commercial use for civil waste see information page on Synroc.
If used reactor fuel is not reprocessed, it will still contain all the highly radioactive isotopes. Spent fuel that is not reprocessed is treated as HLW for direct disposal. It too generates a lot of heat and requires cooling. However, since it largely consists of uranium with a little plutonium , it represents a potentially valuable resource, and there is an increasing reluctance to dispose of it irretrievably.
For final disposal, to ensure that no significant environmental releases occur over tens of thousands of years, 'multiple barrier' geological disposal is planned.
This technique will immobilize the radioactive elements in HLW and long-lived ILW, and isolate them from the biosphere. The multiple barriers are:. Each disc on the floor covers a silo holding ten canisters. Due to the long-term nature of these management plans, sustainable options must have one or more pre-defined milestones where a decision could be taken on which option to proceed with. A current question is whether waste should be emplaced so that it is readily retrievable from repositories.
There are sound reasons for keeping such options open — in particular, it is possible that future generations might consider the buried waste to be a valuable resource. On the other hand, permanent closure might increase long-term security of the facility. After being buried for about 1, years most of the radioactivity will have decayed. The amount of radioactivity then remaining would be similar to that of the naturally-occurring uranium ore from which it originated, though it would be more concentrated.
In mined repositories, which represent the main concept being pursued, retrievability can be straightforward, but any deep borehole disposal is permanent.
France's waste law says that HLW disposal must be 'reversible', which was clarified in a amendment to mean guaranteeing long-term flexibility in disposal policy, while 'retrievable' referred to short-term practicality. The measures or plans that various countries have in place to store, reprocess, and dispose of used fuel and waste are described in an appendix to this paper covering National Policies and Funding.
Storage and disposal options are described more fully in the information paper on Storage and Disposal of Radioactive Waste. Nature has already proven that geological isolation is possible through several natural examples or 'analogues'. The most significant case occurred almost 2 billion years ago at Oklo, in what is now Gabon in West Africa, where several spontaneous nuclear reactors operated within a rich vein of uranium ore.
These natural nuclear reactors continued for about , years before dying away. They produced all the radionuclides found in HLW, including over 5 tonnes of fission products and 1. The study of such natural phenomena is important for any assessment of geologic repositories, and is the subject of several international research projects.
Nuclear power is the only large-scale energy-producing technology that takes full responsibility for all its waste and fully costs this into the product. Financial provisions are made for managing all kinds of civilian radioactive waste. Most nuclear utilities are required by governments to put aside a levy e. The actual arrangements for paying for waste management and decommissioning vary. The key objective is, however, always the same: to ensure that sufficient funds are available when they are needed.
There are three main approaches:. The volume of high-level radioactive waste HLW produced by the civil nuclear industry is small.
The IAEA estimates that , tonnes of heavy metal tHM in the form of used fuel have been discharged since the first nuclear power plants commenced operation. Of this, the agency estimates that , tHM have been reprocessed. In arriving at its estimate, the IAEA has made assumptions with respect to packaging and repository design for countries without confirmed disposal solutions based on the plans proposed by countries more advanced in the process.
Given its lower inherent radioactivity, the majority of waste produced by nuclear power production and classified as LLW or VLLW has already been placed in disposal. Nuclear waste inventory IAEA estimates, 1. Note: all volumetric figures are provided as estimates based on operating and proposed final disposal solutions for different types of waste.
All hazardous waste requires careful management and disposal, not just radioactive waste. The amount of waste produced by the nuclear power industry is small relative to both other forms of electricity generation and general industrial activity.
For example, in the UK — the world's oldest nuclear industry — the total amount of radioactive waste produced to date, and forecast to , is about 4. After all waste has been packaged, it is estimated that the final volume would occupy a space similar to that of a large, modern soccer stadium.
This compares with an annual generation of million tonnes of conventional waste, of which 4. Each radioactive material has a decay rate. The time that it takes for half of the radioactive atoms to decay is called a half-life. For example, the previously mentioned technetiumm has a half-life of six hours which means that, starting with percent, after six hours, we will have 50 percent left.
After six more hours, we have After ten half-lives, only 0. There are three types of half-life. One is the physical half-life.
If you have a container of radioactive material sitting on a counter, the radioactivity decays according to its physical half-life. The second type is a biological half-life. If the radioactive material is in a human, for instance, it gets moved around inside our body just like nonradioactive materials. Sometimes our body will get rid of the material quickly, leading to a short biological half-life. Sometimes the material might go to a spot in our body and stay there, leading to a long biological half-life.
The third type of half-life is when you combine the first two. And how well will they resist corrosion after being interned for eons in a repository environment? After 1, years or so, Goel says, the steel canister surrounding the glass will likely corrode, and groundwater may seep in and interact directly with the glass, degrading it.
So scientists would like to better understand how and if glass might leach any radioactive materials locked inside. Whether groundwater degrades the glass enough to cause it to release its radioactive cargo depends on several processes, experiments have shown.
For alkali-borosilicate glasses, a well-studied family, the degradation steps would include ion exchange between ionic species in the water and alkali ions in the glass; hydrolysis of silica, boria, and other chemical groups that compose the glass network; and dissolution and release of glass components into solution or onto the surface of the reacting glass. Goel and colleagues in the US and the Czech Republic tackled the complex relationship between these and other processes and ways to model them in a recently published study J.
Solids: X , DOI: The authors recommend that to better understand the long-term fate of vitrified materials, researchers in this field should focus on experiments that help determine the rate-limiting mechanisms of glass change over time—especially during long periods of very slow change—and help explain how composition affects the rate at which glass changes.
Related: Radioactive Waste Safety. Some models for predicting how vitrified waste will corrode over millennia in a geological repository assume that the stainless-steel canister eventually disintegrates, leaving groundwater, if present, to react with the glass. A new study, however, shows that water-based solutions can trigger unexpected corrosion chemistry that occurs only at the wet steel-glass interface Nat.
The idea for the study came from Xiaolei Guo and coworkers, who reasoned that if water seeps through cracks in the steel canister, penetrating the microscopic gap between the glass and steel, it could set off reactions in the confined space that would not occur in a more open setting.
The temperature was chosen to accelerate the normally slow corrosion process and to mimic conditions caused by ongoing radioactivity. After a month, they found accelerated pitting and corrosion of the glass and steel compared with control samples in which glass and steel were not held in intimate contact.
Analyses showed that reactions between metal ions and the water acidified the solution. The acidity corroded the steel and glass, releasing additional ions, thereby accelerating the corrosion process.
The study uncovered a previously unknown corrosion mechanism involving dissimilar materials in close contact; some researchers say this process could decrease the durability of glassy nuclear waste. Vienna cautions against drawing that conclusion. According to Vienna, the results suggest that less than 1 in 10, of the waste packages proposed for storage at Yucca Mountain would fail in , years.
Tens of thousands of metric tons of radioactive spent nuclear fuel sit in steel-and-concrete storage casks cutaway at nuclear power plants across the US map as they await permanent disposal. Source: US Energy Information Administration, the most recent year for which data are available. But what about nuclear waste not slated for vitrification? In the US, about 80, metric tons of used, or spent, nuclear fuel sits in casks on-site at power plants around the country.
Hundreds of these tubes, known as fuel rods, are bundled together to form fuel-rod assemblies. And hundreds of assemblies work together in a commercial nuclear reactor to produce intense heat and steam —from splitting uranium nuclei—to drive turbines that generate electricity. After spending roughly 5 years in a reactor constantly being bombarded with radiation, nuclear fuel stops working efficiently. Reactor operators remove the spent fuel and replace it with fresh fuel.
Several countries separate those components to make new fuel, and along the way, they generate high-level waste by-products that are vitrified. The US does not reprocess its fuel. Instead, reactor engineers submerge the assemblies in on-site pools for a few years until the fuel cools and the radioactivity starts to fall. Then they transfer the fuel-rod assemblies to stainless-steel canisters, which are welded shut and packed inside reinforced concrete silos.
And there the spent fuel sits for now , accumulating in so-called dry casks above ground at or near power plants, because the US has no permanent repository for this waste. And the fuel keeps accumulating. And roughly every 2 years, each plant replaces about one-third of its fuel with fresh fuel. Experts consider dry-cask storage safe in the short term. But because the spent-fuel containers sit in limbo, many of them will remain where they are for decades longer than originally intended.
That leaves Eric J. He explains that during manufacturing, stress develops at weld seams as they cool and contract. If corrosion sets in at those spots, then some materials can start to crack and fail. The iron-chrome-nickel-based stainless steel used in dry casks is a material prone to fail when corrosion kicks in. What might cause the corrosion on these concrete-covered casks?
Many nuclear power plants in the US were built along coastlines for convenient access to cooling water. Proximity to the coast means exposure to sea-salt aerosol. Because of the cask design, which blocks radiation but allows air flow—for cooling—between the steel cylinders and concrete silos, aerosols can reach the cylinder surfaces. Salt particles, which are hygroscopic and deliquescent, can settle on canister welds and other stress joints, take up atmospheric water, dissolve, and form chloride-rich corrosive brines.
Those conditions could lead to small cracks that breach a cylinder and release harmful material and radiation.
Schindelholz, together with researchers at Ohio State and Sandia National Laboratories, is developing a model that can be used to predict when, how, and where dry-cask cylinders might crack. These researchers are hoping their efforts will protect the temporarily stored waste until a more permanent solution can be agreed upon in the US. The tens of thousands of metric tons of radioactive waste that accumulated from commercial power plants and years of national defense operations continue to age at sites around the globe.
As the hazardous material and the containers it sits in await permanent disposal, the stockpile keeps growing. Contact the reporter. Submit a Letter to the Editor for publication.
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All we need is few more details to create your reading experience. Not you? Sign in with a different account. Need Help? Membership Categories. Regular or Affiliate Member. Graduate Student Member. Undergraduate Student Member. Benefits Enjoy these benefits no matter which membership you pick. Thank you! Pollution As nuclear waste piles up, scientists seek the best long-term storage solutions Researchers study and model corrosion in the materials proposed for locking away the hazardous waste by Mitch Jacoby March 30, A version of this story appeared in Volume 98, Issue In brief More than a quarter million metric tons of highly radioactive waste sits in storage near nuclear power plants and weapons production facilities worldwide, with over 90, metric tons in the US alone.
Scientists are studying glass samples to understand long-term corrosion of vitrified nuclear waste. These micrographs show the results of accelerated aging tests on two types of aluminosilicate glasses. Ions have leached from the glasses and crystallized on their surfaces: the largest of these false-color crystals yellow on left, pale blue on right are sodium aluminum silicate hydrates of various composition and structure.
And we are—more or less—handing it to our children. Gerald S. Frankel, materials scientist, Ohio State University. Credit: US Department of Energy. These underground tanks in Hanford, Washington, were built in the s to store liquid radioactive waste from plutonium production. Today, the contents have been transferred to newer tanks in preparation for vitrification.
Widespread storage Tens of thousands of metric tons of radioactive spent nuclear fuel sit in steel-and-concrete storage casks cutaway at nuclear power plants across the US map as they await permanent disposal. Credit: Pacific Northwest National Laboratory. Meline pours a sample of molten glass to study corrosion in vitrified nuclear waste. Related: Tank Troubles. Vitrification of nuclear waste seems to be well established by now, but actually it still faces complex problems.
You might also like Nuclear Power. Proposed nuclear waste storage materials may have a corrosion problem. Radioactive Waste Safety. Tank Troubles. Share X. To send an e-mail to multiple recipients, separate e-mail addresses with a comma, semicolon, or both.
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