KYT SURFACE:Complementary Considerations in Assessing Performance of a Landfill-Type Near Surface Repository

Design basis and performance targets for a landfill type near surface repository have been examined as part of the KYT2022 SURFACE project, as well as the differences between a near surface repository and a landfill for hazardous waste landfill. The main difference comes from legislation and from ensuring passive safety for the repository after closure. The effect of site conditions on the engineered barriers was studied from the perspective of low temperatures during winter in Finland. Numerical modelling shows that freezing of some or all of the engineered barriers in the cover layer can take place during a cold winter, especially in a situation when there is lack of sufficient snow coverage that would provide insulation. In normal and hazardous waste landfills, the frost shall not penetrate to the level of the mineral sealing layer. This leads to a recommendation of performing site and design specific numerical modelling on the frost penetration and, based on the results, considering cover top layer thicknesses that are more than the typical minimum 1 m used in normal and hazardous waste landfills. The potential impacts of post closure forestation also supports use of a thicker top layer to avoid puncture of synthetic liners by tree roots.Limiting water inflow into the repository through the cover layer was identified as one of the key factors in ensuring long-term and passive safety for the near surface repository. This can be done by combining water tight synthetic liners with a mineral sealing layer. Limiting water flow to the repository decreases the quantity of formed leachates and can slow the generation of landfill gas.The need for gas management systems depends on the rate at which gas is generated in the waste. In order to minimize gas generation from soft waste pallets containing organic waste, placing this waste into metallic packages was reviewed as an option. This would also enhance the mechanical stability of the repository. Performance of the drainage systems at the foundation structure and collection and handling leachate waters was also assessed as part of this work. Some of the drainage is in any case needed for preventing accumulation of leachate water in the bottom of the repository. However, the effect of the drainage and leachate water collection system for post closure safety requires further considerations. If the cover layer works as expected and the waste is not in direct contact with the water, the generation of leachate water should be minimal.Final recommendations concerning the design of the landfill type near surface repository will be summarised in 2022 including the analysis of results from KYT2022 SURFACE tasks 1 (radionuclide migration) and 3 (steel corrosion and microbial activity) on the repository design recommendations

Waste Management of Small Modular Nuclear Reactors in Finland

Small modular nuclear reactors (SMRs) represent advanced technology in nuclear energy aim-ing to produce low carbon energy at smaller unit size and enhanced passive safety in compar-ison to traditional nuclear power plants (NPPs). The management of spent nuclear fuel (SNF) and low- and intermediate-level waste (LILW) from SMRs is an issue that needs to be resolved as part of any deployment of SMR technology in Finland. Currently, spent nuclear fuel from NPPs in Finland is planned to be disposed in the ONKALO® deep geological repository applying the KBS-3V disposal concept. This concept should be applicable for spent fuel from SMRs using light-water reactor (LWR) technology. However, there are some differences in the waste forms, most obviously the length of the fuel assemblies, but also in the spent fuel characteristics that need to be considered in the further development of the concept for spent fuel from SMRs. Preliminary 2D calculations were made with the continuous-energy Monte Carlo code Serpent to compare the spent fuel characteristics from two example LWR-SMRs to spent nuclear fuel from currently operating NPPs in Finland. In one example case, a NuScale Power ModuleTM was considered as it is one of the most advanced LWR-SMRs in the world. The other example case is an SMR planned in Finland for district heating purposes. The main differences between the SMR and NPP spent fuels are linked to lower burnups in the SMRs. Lower discharge burnups are to be studied further from the point of view of criticality safety at disposal. Other-wise, the lower average discharge burnup of these SMR fuel types, in principle, generally tends to make the handling of spent fuel assemblies less demanding with respect to the decay heat and ionizing radiation emitted from the assembly. However, rigorous calculation of the dose rates would require 3D calculations to determine the axial burnup distribution within a fuel as-sembly, which was outside the scope of this study. Published studies indicate that possibly larger masses (per GWe-year) of SNF and other HLW and larger volumes (per GWe-year) of LLW will be produced in a LW-SMR compared to a large NPP. However, because of the lower decay heat in the SMR SF (due to the lower burnup), less excavated volume and, consequently, less clay-based filling material (deposition tunnel back-fill) may be needed in a repository. Depending on the number of SMR units located at sites in Finland, the amounts of spent fuel and other waste streams can be relatively small so that a centralised waste management facility and repository could be the most feasible option for processing and disposal of all the nuclear waste. Alternatively, the wastes can be disposed of locally (near SMR sites in smaller facilities) or a hybrid model, where, e.g., only SNF is disposed centrally, could be considered. These alternatives will depend strongly on the ownership structure of the SMRs deployed in Finland. Local stakeholder and public opinion will be very important as well. Other issues, such as ge-ological suitability of the SMR sites for disposal, transport and interim storage will need to be assessed. In terms of final disposal of SNF from LWR-SMRs, the only currently available option is the KBS-3V concept, especially considering the state of the licencing process for this concept in Finland. Deep borehole disposal represents an intriguing, particularly in the case of local disposal for relatively small amounts of waste, but not yet fully developed alternative. The suitability of deep borehole disposal in the crystalline rock conditions prevailing in Finland will be studied in the next phase of the project. Spent fuel from non-LWR SMRs, i.e., high-temperature-gas-cooled, fast neutron-spectrum and molten salt-type SMRs, was also discussed briefly. Challenges were identified in the pre-treat-ments needed for SNF from these reactors prior to disposal including lack of suitable facilities in Finland and potential proliferation issues. In some cases, e.g., reactors with graphite mod-erators, the disposal of the LILW waste streams was considered problematic as the current methodologies in use in Finland for disposal of LILW would not be applicable. More extensive studies would be required to specifically identify the waste streams from non-LWR SMRs and how the waste characteristics would need to be taken into account for disposal

Joidenkin sulfidimineraalien mikroaaltokäsittelyn numeerinen mallinnus

Microwave pre-treatment of rock is a promising way to decrease rock strength during rock comminution processes. The microwave radiation transfers heat to the rock which then heats up and expands. This induces stresses within the rock. In this study, numerical modelling is used to assess how different material and irradiation parameters affect the induced stresses. The study is divided into two numerical models: one for a simulated rock sample and one for a digitized rock sample. In both models, a rock sample was irradiated with microwave radiation within a simulated microwave oven. In the first model, the rock sample was modelled so that its material parameters could be easily varied. The rock sample consisted of two materials with different capabilities to absorb heat from microwave radiation. The varied material parameters included the mineral composition, the ratio between the two minerals, grain size and mineral shapes of the rock sample. Additionally, microwave input power was varied and the effect of the wave pattern inside the microwave oven studied In the second model a rock sample from Pyhäsalmi mine was digitized into a 3D model which then replaced the simulated rock sample within the modelled microwave oven. The sample consisted of four minerals: pyrite, chalcopyrite, sphalerite and pyrrhotite. The model was used to study where the induced stresses were situated in the rock sample and the magnitude of the induced stresses. The results showed that increasing the fraction of the mineral with a high capability to absorb microwave radiation increased the temperatures in the sample significantly. However, heterogenous mineral composition was required to concentrate the stresses on mineral boundaries. More heterogenous mineral composition was achieved with larger grains and minerals with different mechanical properties. Highest stresses were observed on mineral boundaries between two minerals with different, but high elastic moduli and coefficient of thermal expansion. Narrower angles within the minerals also resulted in higher stresses.Kiven mikroaaltokäsittely on lupaava keino vähentää kiven lujuutta jauhatusprosessin aikana. Mikroaallot siirtävät lämpöä kiveen, joka lämpenee ja laajenee. Tämän johdosta kiveen indusoituu jännitteitä. Tässä tutkimuksessa tutkitaan eri materiaali- ja säteilyparametrien vaikutusta indusoituihin jännitteisiin numeerisella mallinnuksella. Tämä tutkimus on jaettu kahteen numeeriseen malliin: ensimmäisessä mallinnetaan simuloitua,kivinäytettä ja toisessa digitoitua näytettä. Molemmissa malleissa kivinäytettä säteilytettiin simuloidussa mikroaaltouunissa. Ensimmäisen mallin näyte mallinnettiin siten, että sen materiaaliparametrejä voitiin muuttaa helposti. Näyte koostui kahdesta eri mineraalista, joilla oli eri kyvyt absorboida lämpöä mikroaaltosäteilystä. Muunnettaviin materiaaliparametreihin kuuluivat kiven mineraalirakenne, kahden mineraalin määrän välinen suhde, raekoko ja rakeiden muoto. Lisäksi mikroaaltosäteilyn tehoa muutettiin ja sähkömagneettisen kentän muodon vaikutusta tutkittiin. Toisessa mallissa Pyhäsalmen kaivoksesta oleva kivinäyte digitoitiin 3D-malliksi, joka sijoitettiin mallinnettuun mikroaaltouuniin simuloidun kivinäytteen tilalle. Kivi koostui neljästä mineraalista: pyriitistä, kuparikiisusta, sinkkivälkkeestä sekä magneettikiisusta. Mallilla tutkittiin, mihin jännitteet indusoituvat kivinäytteessä sekä indusoitujen jännitteiden suuruutta. Tuloksista kävi ilmi, että lisättäessä mineraalia, jolla on hyvä kyky absorboida lämpöä mikroaaltosäteilystä, kivinäytteen lämpötilat nousivat huomattavasti. Jotta mineraalien rajoille syntyi jännitteitä, mineraalien tuli olla heterogeenisiä rajan molemmin puolin. Heterogeeninen materiaalirakenne muodostui esimerkiksi suuremmalla raekoolla ja mineraalien eri mekaanisilla ominaisuuksilla. Korkeimmat jännitteet olivat rajoilla, joiden eri puolilla olevien mineraalien elastiset kertoimet sekä lämpölaajenemiskertoimet olivat korkeat, mutta erosivat toisistansa

Twin transition in the built environment – Policy mechanisms, technologies and market views from a cold climate perspective

This paper studies the implementation of twin transition, i.e., the combination of digital technologies and European Green Deal goals, to achieve sustainable solutions supporting the creation of impactful, net-zero carbon and a resilient built environment with a focus on Northern Europe, specifically Finland. The subject was examined from policies, technology and market perspectives. Numerous European regulations and policies are driving the twin transition since many of them include obligatory requirements for the member states. Technologies and technology combinations exist to support the twin transition in the Nordic built environment. It was assessed that energy technologies are the most important and control, monitoring and automation technologies are the second most important technology category for the twin transition. In addition, individual technologies’ maturity and relevance to the twin transition in the built environment in cold climates were evaluated. By analyzing case studies, it was found that the markets are not mature enough to lead the twin transition, but external boosts are needed. However, this can also be seen as an opportunity for service business. The results are focused on Northern Europe, but European legislation also supports the international SDGs