High-level radioactive waste management

High-level radioactive waste management addresses the handling of 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. Long set of workshops on Fundamentals of Radioactive waste treatment, vitrification technology and Vitreous Materials for Nuclear Waste Immobilization Thas been jointly organized by The Abdus Salam International Centre for Theoretical Physics (ICTP) and the International Atomic Energy Agency (IAEA) by Michael Ojovan and co-workers.

The management of radioactive waste not only involves technical and scientific considerations but also raises significant ethical concerns regarding the impacts on future generations. 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.

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. Others insist on the necessity of deep geologic repositories in stable formations. 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, with the first expected to be operational after 2017. 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.

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. 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.

The ceramic waste forms offer higher waste loadings than the glass options because ceramics have crystalline structure. 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. Ceramic waste forms offer great potential, but a lot of research remains to be done.

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".

Moreover, most communities do not want to host a nuclear waste repository as they are "concerned about their community becoming a de facto site for waste for thousands of years, the health and environmental consequences of an accident, and lower property values".

Asia

China

In China (People's Republic of China), ten reactors provide about 2% of electricity and five more are under construction. China made a commitment to reprocessing in the 1980s; a pilot plant is under construction at Lanzhou, where a temporary spent fuel storage facility has been constructed. Geological disposal has been studied since 1985, and a permanent deep geological repository was required by law in 2003. Sites in Gansu Province near the Gobi desert in northwestern China are under investigation, with a final site expected to be selected by 2020, and actual disposal by about 2050.

Taiwan

In Taiwan (Republic of China), nuclear waste storage facility was built at the Southern tip of Orchid Island in Taitung County, offshore of Taiwan Island. The facility was built in 1982 and it is owned and operated by Taipower. The facility receives nuclear waste from Taipower's current three nuclear power plants. However, due to the strong resistance from local community in the island, the nuclear waste has to be stored at the power plant facilities themselves.

India

India adopted a closed fuel cycle, which involves reprocessing and recycling of the spent fuel. The reprocessing results in 2-3% of the spent fuel going to waste while the rest is recycled. The waste fuel, called high level liquid waste, is converted to glass through vitrification. Vitrified waste is then stored for a period of 30–40 years for cooling.

Sixteen nuclear reactors produce about 3% of India’s electricity, and seven more are under construction. Spent fuel is processed at facilities in Trombay near Mumbai, at Tarapur on the west coast north of Mumbai, and at Kalpakkam on the southeast coast of India. Plutonium will be used in a fast breeder reactor (under construction) to produce more fuel, and other waste vitrified at Tarapur and Trombay. Interim storage for 30 years is expected, with eventual disposal in a deep geological repository in crystalline rock near Kalpakkam.

Japan

In 2000, a Specified Radioactive Waste Final Disposal Act called for creation of a new organization to manage high level radioactive waste, and later that year the Nuclear Waste Management Organization of Japan (NUMO) was established under the jurisdiction of the Ministry of Economy, Trade and Industry. NUMO is responsible for selecting a permanent deep geological repository site, construction, operation and closure of the facility for waste emplacement by 2040. Site selection began in 2002 and application information was sent to 3,239 municipalities, but by 2006, no local government had volunteered to host the facility. Kōchi Prefecture showed interest in 2007, but its mayor resigned due to local opposition. In December 2013 the government decided to identify suitable candidate areas before approaching municipalities.

The head of the Science Council of Japan’s expert panel has said Japan's seismic conditions makes it difficult to predict ground conditions over the necessary 100,000 years, so it will be impossible to convince the public of the safety of deep geological disposal.

Europe

Belgium

Belgium has seven nuclear reactors that provide about 52% of its electricity. Belgian spent nuclear fuel was initially sent for reprocessing in France. In 1993, reprocessing was suspended following a resolution of the Belgian parliament; spent fuel is since being stored on the sites of the nuclear power plants. The deep disposal of high-level radioactive waste (HLW) has been studied in Belgium for more than 30 years. Boom Clay is studied as a reference host formation for HLW disposal. The Hades underground research laboratory (URL) is located at in the Boom Formation at the Mol site. The Belgian URL is operated by the Euridice Economic Interest Group, a joint organisation between SCK•CEN, the Belgian Nuclear Research Centre which initiated the research on waste disposal in Belgium in the 1970s and 1980s and ONDRAF/NIRAS, the Belgian agency for radioactive waste management. In Belgium, the regulatory body in charge of guidance and licensing approval is the Federal Agency of Nuclear Control, created in 2001.

Finland

In 1983, the government decided to select a site for permanent repository by 2010. With four nuclear reactors providing 29% of its electricity, Finland in 1987 enacted a Nuclear Energy Act making the producers of radioactive waste responsible for its disposal, subject to requirements of its Radiation and Nuclear Safety Authority and an absolute veto given to local governments in which a proposed repository would be located. Producers of nuclear waste organized the company Posiva, with responsibility for site selection, construction and operation of a permanent repository. A 1994 amendment to the Act required final disposal of spent fuel in Finland, prohibiting the import or export of radioactive waste.

Environmental assessment of four sites occurred in 1997–98, Posiva chose the Olkiluoto site near two existing reactors, and the local government approved it in 2000. The Finnish Parliament approved a deep geologic repository there in igneous bedrock at a depth of about in 2001. The repository concept is similar to the Swedish model, with containers to be clad in copper and buried below the water table beginning in 2020. An underground characterization facility, Onkalo spent nuclear fuel repository, was constructed at the site from 2004 to 2017.

France

With 58 nuclear reactors contributing about 75% of its electricity, the highest percentage of any country, France has been reprocessing its spent reactor fuel since the introduction of nuclear power there. Some reprocessed plutonium is used to make fuel, but more is being produced than is being recycled as reactor fuel. France also reprocesses spent fuel for other countries, but the nuclear waste is returned to the country of origin. Radioactive waste from reprocessing French spent fuel is expected to be disposed of in a geological repository, pursuant to legislation enacted in 1991 that established a 15-year period for conducting radioactive waste management research. Under this legislation, partition and transmutation of long-lived elements, immobilization and conditioning processes, and long-term near surface storage are being investigated by the Commissariat à l’Energie Atomique (CEA). Disposal in deep geological formations is being studied by the French agency for radioactive waste management (Agence nationale pour la Gestion des Déchets radioactifs), in underground research labs.

Three sites were identified for possible deep geologic disposal in clay near the border of Meuse and Haute-Marne