PROVIDING A PERMANENT AND SAFE SOLUTION FOR THE MANAGEMENT OF RADIOACTIVE WASTE AND SPENT FUEL
Spent fuel is generated in NPP KrškoNEK) and in raziskovalnem reaktorju Triga na Institutu “Jožef Stefan". NEK stores spent fuel in the area of the power plant, and the "Jožef Stefan" Institute has so far returned all spent fuel from the research reactor to the manufacturer in the USA. High-level radioactive waste (HLW) will be generated during the decommissioning of the nuclear power plant.
Directions Resolucije o nacionalnem programu ravnanja z radioaktivnimi odpadki in izrabljenim gorivom za obdobje 2023 – 2032 (ReNPROIG 23 – 32) stipulate that it is first necessary to ensure the safe storage of spent fuel (SF) and highly radioactive waste (HLW) and then their safe disposal. According to the third revision of the NEK Decommissioning Program and the RW and SF disposal Program from the NEK, it is foreseen:
- wet storage of the spent fuel in a pool on the power plant location, followed by
- dry storage of the spent fuel
- packing and preparation for disposal
- and waste disposal in deep geological deposit
Considering the technological progress in the last decade, it would make sense to study other possibilities of processing and recycling spent fuel into reprocessed nuclear fuel. Up-to-date procedures make it possible to significantly reduce the volume, half-life and radiotoxicity of spent fuel and highly radioactive waste. In any case, in the end, highly radioactive waste remains and has to be permanently disposed.
The guidelines contained in the National Programme for Managing Radioactive Waste and Spent Fuel 2016–2025 provide that Slovenia should pay equal regard to two options:
- the monitoring of and participation in initiatives for a shared geological repository in an EU Member State or,
- if a shared repository is not possible, the planning of a geological repository in Slovenia for waste generated by the country’s own nuclear program.
Disposal of high-level waste and spent fuel in Slovenia
Conservative estimates of the amount of spent fuel at the end of operation in 2043 amount to less than 2,500 spent fuel elements. During the decommissioning of the Krško Nuclear Power Plant (NEK) is expected to create another 82 tons of HLW. This HLW is activated materials originating primarily from the Core Instrumentation System, the Nuclear Instrumentation System, and the Control and Rod Position System. Currently, spent fuel elements are stored in the spent fuel pool at the NPP.
SF and HLW are first stored in dry storage at the NPP Krško, the construction of which was completed in 2023 and 592 fuel elements were moved from the pool to dry storage. The duration of the storage is determined taking into account the cooling of the SF and the optimal filling of the disposal containers in two variants of the scenarios: the duration of the storage 60 years after the closure of the NEK until the year 2103 (basic scenario-optimal solution) and the duration of the storage 32 years after the closure of the NEK until the year 2075 (alternative solution ). Road transport of SF from dry storage to the disposal is planned.
In the HLW and SF disposal study that was made in 2019, it is planned that SF and HLW will be permanently disposed of in a geological repository.
The construction of the geological disposal will begin 6 years before the start of regular operation with the construction of auxiliary above-ground facilities, then the construction of the encapsulation plant and the construction of underground structures will begin. The construction of these structures will take 5 years.
In the baseline scenario, disposal of SF and HLW begins in 2093, and in the alternative scenario after a shorter storage period in 2065. In both cases, all the necessary activities related to the siting, construction, operation, decommissioning and closure of the disposal are the same, and the operation lasts for 10 years . The disposal concept in both scenarios is based on the Swedish disposal model SKB KBS-3V and at the location of disposal foresees all the assemblies of components, systems and structures necessary for the repository to operate as an independent nuclear facility.
Due to operational requirements and to ensure the necessary physical protection, the entire disposal area will be divided into four areas: an unfenced area with supporting buildings and systems, an industrial area with fences to ensure industrial physical protection, a technological above-ground area with fences to ensure radiological and nuclear safety (with a plant for encapsulation, service buildings and auxiliary systems) and underground facilities (with access ramp and tunnels, service area and disposal tunnels with disposal wells).
The encapsulation facility will include units for receiving transport containers with spent fuel for encapsulation in copper containers, with an area for manipulation, for shipping and transporting containers to underground disposal facilities, LILW processing and packaging unit, an administrative building, storage and auxiliary facilities and systems.
The fuel cells will first be placed in massive copper containers, which will then be sealed. The main function of containers is to isolate spent fuel elements from the environment. The container has a cylindrical shape and a diameter of approx. 1 meter and 4.7 m high with a 5 cm thick anti-corrosion copper coating. It is reinforced on the inside with a cast iron insert that can accommodate four fuel elements in the case of spent pressurized water reactor fuel. After inserting the spent fuel elements into the container, the lid of the container is sealed with an electron beam welding machine. A container filled with SF weighs about 25 tonnes.
The underground part of the disposal lies at a depth of 500 m below the surface. As an alternative, a depth of 800 m is also considered. It comprises two areas: a central service area and a disposal area. The underground part can be reached in several ways: personnel can reach it through a service shaft, for waste via a spiral ramp or through a vertical access shaft with a clear diameter of 8.0 m. The ramp is 5 km long (alternatively 8 km), 7 m wide and 7 m high. The service shaft has a clear diameter of 5 m. The service shaft will also serve as part
In addition to spent fuel and highly radioactive waste, long-lived institutional low- and intermediate-level radioactive waste, HLW from the decommissioning of the NPP and long-lived waste from the NPP, HLW and other RW from the decommissioning of the dry storage, long-lived RW and HLW from operation and decommissioning of disposal.
Decommissioning of the geological repository begins in 2104 and its closure in 2108 by filling underground tunnels and disposal areas. The disposal tunnels will be sealed with 6 m thick concrete plugs.
In addition to the basic scenario, alternative solutions are also analysed, e.g. 50-year long-term post-closure control, encapsulation at a joint regional encapsulation facility, and disposal at an international disposal, as well as some alternatives to the baseline design.
Disposal of high-level radioactive waste and spent fuel in the regional or multinational disposal
Each European country must take care of its own radioactive waste. Few countries have so far adopted a final solution for their spent fuel and high-level waste. The only safe solution recognized so far is disposal in a geological repository deep below the Earth's surface. This type of solution is the most sustainable as it does not shift environmental burdens to the next generations. The construction of a national repository for spent fuel and high-level radioactive waste is still an unresolved issue for many countries.
Even countries that do not have nuclear power plants use nuclear technologies that produce smaller amounts of long-lived highly radioactive waste. Having your own disposal is a great technical and economic challenge for countries where this type of waste is scarce. The development of one or a smaller number of regional disposals can also be a sensible solution, which brings many technical and economic advantages. By sharing the costs of planning and operating a disposal, countries can save hundreds of millions of euros.
Within the framework of initiatives for a joint geological repository in one of the EU countries, ARAO participates as an active member in the ERDO association, whose mission is to prepare the organizational foundations for the realization of the development of a common European approach to the disposal of HLW and SF.
We also participate in the activities of the European technology platform IGD-TP (Implementing Geological Disposal of Radioactive Waste technological Platform, which enables the acquisition of knowledge and competences for the construction of a geological disposal for HLW and SF. In addition, ARAO participates in the international association for cooperation in the field of nuclear energy (IFNEC – The International Framework For Nuclear Energy Cooperation) and in the working groups of the association World Nuclear Association (WNA).
In 2019, as part of the preparation of the third revision of the Program for Disposal of RW and IG from the NPP, a study on the disposal of RW and IG was prepared, where the possibility of disposing of HLW and SF in an international disposal facility was also discussed. For this purpose, two options were analysed, the concept of a commercial disposal service in a multinational disposal and the concept of a partnership with cost-sharing for disposal in a multinational repository. The concept of a commercial service involves a service provider country developing a geological repository for the purpose of receiving spent fuel from several countries (e.g. pobuda Južne Avstralije iz 2016), while the concept of cooperation includes cooperation between partner countries in a joint project for the development and construction of a disposal facility in one of the partner countries.
The analysis of both concepts shows that such a possibility of postponement is a sensible and, in principle, feasible solution. In the case of a conservative estimate for the concept of partnership cooperation of 5 countries, which would equally share the investment costs of building a joint geological repository, and the operating costs were proportional to the inventory of disposed HLW and SF, the cost of disposal of all HLW and SF from the Krško NPP would amount to approximately half of the costs comparising to independent solution.
Načrti za razvoj skupnih rešitev in tehnologij za ravnanje z radioaktivnimi odpadki v Evropi were also analyzed in the European EURAD project. Many countries are aware of the benefits of sharing good practices, information and cooperation with other countries regarding various aspects of radioactive waste management, e.g. development and exchange of technologies, methodologies, approaches, training and exchange of personnel, etc. In addition, some countries are willing to share information about facilities that may be available for sharing in the future. Experience so far shows that although most of the proposed common solutions for radioactive waste management have been technically feasible and economically attractive, such projects have mostly failed for other non-technical reasons, such as various political and economic reasons.
