High-level radioactive waste management addresses the handling of high-level radioactive materials generated from nuclear power production and nuclear weapons manufacture. Radioactive waste contains both short-lived and long-lived radionuclides, as well as non-radioactive nuclides. In 2002, the United States stored approximately 47,000 tonnes of high-level radioactive waste.
Among the constituents of spent nuclear fuel, neptunium-237 and plutonium-239 are particularly problematic due to their long half-lives of two million years and 24,000 years, respectively. Handling high-level radioactive waste requires sophisticated treatment processes and long-term strategies such as permanent storage, disposal, or conversion into non-toxic forms to isolate it from the biosphere. Radioactive decay follows the half-life rule, which means that the intensity of radiation decreases over time as the rate of decay is inversely proportional to the duration of decay. In other words, the radiation from a long-lived isotope like iodine-129 will be much less intense than that of short-lived isotope like iodine-131.
Governments worldwide are exploring various disposal strategies, usually focusing on a deep geological repository, though progress in implementing these long-term solutions has been slow. This challenge is exacerbated by the timeframes required for safe decay, ranging from 10,000 to millions of years. Thus, physicist Hannes Alfvén identified the need for stable geological formations and human institutions that can endure for extended periods, noting the absence of any civilization or geological formation that has proven stable for such durations. Other scientists contest the requirement for millennia-stable human institutions, stressing that a waste depository can instead be made fail-safe with regards to groundwater intrusion and therefore eliminating the requirement for active maintenance. Indeed, the removal of the management burden from future generations, while ensuring as best as possible they are not exposed to significant radiological hazard, is a key principal behind intergenerational equity.
The management of radioactive waste not only involves technical and scientific considerations but also raises significant ethical concerns regarding the impacts on future generations.Genevieve Fuji Johnson, Deliberative Democracy for the Future: The Case of Nuclear Waste Management in Canada , University of Toronto Press, 2008, p.9 The debate over appropriate management strategies includes arguments for and against the reliance on geochemical simulation models and natural geological barriers to contain radionuclides post-repository closure.Bruno, Jordi, Lara Duro, and Mireia Grivé. 2001. The applicability and limitations of the geochemical models and tools used in simulating radionuclide behavior in natural waters: Lessons learned from the blind predictive modelling exercises performed in conjunction with natural analogue studies. QuantiSci S. L. Parc Tecnològic del Vallès, Spain, for Swedish Nuclear Fuel and Waste Management Co.
Despite some scientists advocating for the feasibility of relinquishing control over radioactive materials to geohydrologic processes, skepticism remains due to the lack of empirical validation of these models over extensive time periods.Shrader-Frechette, Kristin S. 1988. "Values and hydrogeological method: How not to site the world’s largest nuclear dump" In Planning for Changing Energy conditions, John Byrne and Daniel Rich, eds. New Brunswick, NJ: Transaction Books, p. 101 Others insist on the necessity of deep geologic repositories in stable formations.Shrader-Frechette, Kristin S. Burying uncertainty: Risk and the case against geological disposal of nuclear waste Berkeley: University of California Press (1993) p. 2 Shrader-Frechette, Kristin S. Expert judgment in assessing radwaste risks: What Nevadans should know about Yucca Mountain. Carson City: Nevada Agency for Nuclear Projects, Nuclear Waste Project, 1992 Forecasts concerning the health impacts of long-term radioactive waste disposal are critically assessed, with practical studies typically considering only up to 100 years for planning and cost evaluation. Ongoing research continues to inform the long-term behavior of radioactive wastes, influencing management strategies and national policies globally.
Deep geologic disposal
The selection process for permanent repositories for high-level radioactive waste and nuclear spent fuel is underway in several countries. The only purpose-built deep geological repository that is currently licensed for disposal of nuclear material is the Waste Isolation Pilot Plant (WIPP) in the USA, but it does not have a licence for disposal of used fuel or HLW. Plans for disposal of spent fuel are particularly well advanced in Finland, as well as Sweden, France, and the USA, though in the USA there have been political delays. In Canada and the UK, deep disposal has been selected and the site selection processes have commenced. The basic concept involves identifying a large, stable geological formation and using mining technology to excavate a deep tunnel or shaft using tunnel boring machines, between below the surface, where rooms or vaults can be created for the disposal of radioactive waste. The aim is to isolate the waste permanently from the human environment. Concerns about immediate stewardship cessation of such disposal methods have been raised with suggestions that continuous management and monitoring would be preferable.
Given that certain radioactive isotopes have half-lives exceeding one million years, even minimal rates of container leakage and radionuclide migration must be taken into account. It is estimated that several half-lives may pass before some nuclear materials diminish in radioactivity to levels that are not harmful to living organisms. A 1983 review by the National Academy of Sciences endorsed the Swedish nuclear waste program’s estimate that isolation of waste might be necessary for up to one million years.
The land-based subductive waste disposal method proposes disposing of nuclear waste in a subduction zone accessible from land. This method is not restricted by international treaties and is recognized as a feasible and advanced technology for nuclear waste disposal.
At the natural nuclear fission site discovered at the Oklo mine in Gabon, where nuclear fission reactions occurred 1.7 billion years ago, fission products have moved less than three meters. This minimal movement is attributed possibly more to retention within the uraninite crystal structure than to actual insolubility or sorption by moving groundwater. The uraninite crystals at Oklo are better preserved than those in spent fuel rods, likely due to the incomplete nuclear reactions that make the reaction products less vulnerable to groundwater.Krauskopf, Konrad B. 1988. Radioactive waste and geology. New York: Chapman and Hall, 101–102.
The horizontal drillhole disposal method involves drilling over one kilometer vertically and two kilometers horizontally into the earth’s crust to dispose of high-level waste forms such as spent nuclear fuel and specific isotopes like caesium-137 or strontium-90. Following placement and a period of retrievability, the drillholes would be sealed. In 2018 and again in 2019, a US-based private company conducted tests demonstrating the emplacement and retrieval of a test canister in a horizontal drillhole, though no actual high-level waste was used in these tests.
Materials for geological disposal In order to store the high level radioactive waste in long-term geological depositories, specific waste forms need to be used which will allow the radioactivity to decay away while the materials retain their integrity for thousands of years.Clark, S., Ewing, R. Panel 5 Report: Advanced Waste Forms. Basic Research Needs for Advanced Energy Systems 2006, 59–74. The materials being used can be broken down into a few classes: glass waste forms, ceramic waste forms, and nanostructured materials.
The glass forms include borosilicate glasses and phosphate glasses. Borosilicate nuclear waste glasses are used on an industrial scale to immobilize high level radioactive waste in many countries which are producers of nuclear energy or have nuclear weaponry. The glass waste forms have the advantage of being able to accommodate a wide variety of waste-stream compositions, they are easy to scale up to industrial processing, and they are stable against thermal, radiative, and chemical perturbations. These glasses function by binding radioactive elements to nonradioactive glass-forming elements. Phosphate glasses while not being used industrially have much lower dissolution rates than borosilicate glasses, which make them a more favorable option. However, no single phosphate material has the ability to accommodate all of the radioactive products so phosphate storage requires more reprocessing to separate the waste into distinct fractions. Both glasses have to be processed at elevated temperatures making them unusable for some of the more volatile radiotoxic elements. Understanding the corrosion rates of nuclear glasses is of great importance during the planning of a deep geological repository.
Ceramic waste forms offer higher waste loadings than the glass options because ceramics have crystalline structures which can incorporate large amounts of specific radionuclides at specific lattice sites. Also, mineral analogues of the ceramic waste forms provide evidence for long term durability. Due to this fact and the fact that they can be processed at lower temperatures, ceramics are often considered the next generation in high level radioactive waste forms. The high waste loading of ceramic waste forms comes at the cost of lowered flexibility. Often specific ceramic waste forms must be designed for the immobilisation of specific radionuclides, due to the waste nuclide occupying a specific site in the crystal lattice which other radionuclides may not easily incorporate into.
National management plans Finland, the United States and Sweden are the most advanced in developing a deep repository for high-level radioactive waste disposal. Countries vary in their plans on disposing used fuel directly or after reprocessing, with France and Japan having an extensive commitment to reprocessing. The country-specific status of high-level waste management plans are described below.
In many European countries (e.g., Britain, Finland, the Netherlands, Sweden and Switzerland) the risk or dose limit for a member of the public exposed to radiation from a future high-level nuclear waste facility is considerably more stringent than that suggested by the International Commission on Radiation Protection or proposed in the United States. European limits are often more stringent than the standard suggested in 1990 by the International Commission on Radiation Protection by a factor of 20, and more stringent by a factor of ten than the standard proposed by the U.S. Environmental Protection Agency (EPA) for Yucca Mountain nuclear waste repository for the first 10,000 years after closure. Moreover, the U.S. EPA’s proposed standard for greater than 10,000 years is 250 times more permissive than the European limit.
The countries that have made the most progress towards a repository for high-level radioactive waste have typically started with public consultations and made voluntary siting a necessary condition. This consensus seeking approach is believed to have a greater chance of success than top-down modes of decision making, but the process is necessarily slow, and there is "inadequate experience around the world to know if it will succeed in all existing and aspiring nuclear nations".M.V. Ramana. Nuclear Power: Economic, Safety, Health, and Environmental Issues of Near-Term Technologies, Annual Review of Environment and Resources, 2009, 34, p. 145.