Long-term radionuclide retention in the near field: collaborative R&D studies within EURAD focusing on container optimisation, mobility, mechanisms and monitoring

Within EURAD, targeted collaborative research activities are performed to further deepen understanding regarding the long-term behaviour of key components in the repository near-field, assess specific radionuclide retention processes as well as developing methods for monitoring safety relevant parameters of repository systems. The ambition of the four EURAD Workpackages (WPs) – CONCORD, FUTURE, CORI, MODATS – presented here, is to investigate topics to meet implementation needs and contribute to Safety Cases in Europe at the highest level of scientific excellence. Work is fully integrated into the EURAD concept, emphasizing interactions between different WPs, involvement of End Users, assuring the link to national programmes and contributing to overarching features like Knowledge Management, Training and Education, or European Integration. Comprehensive initial State-of-the-Art reports were prepared by the WPs or currently under development and are available at the EURAD website. The technical/scientific work performed in the four WPs - CONCORD, FUTURE, CORI, MODATS – is discussed in this contribution

On physics of a hypothetical core disruptive accident in Multipurpose hYbrid Research Reactor for High-tech Applications – MYRRHA

The sensitivity of the reactivity of a fast reactor core to changes in its geometry and/or fuel relocation calls for particular attention with regard to criticality events. A category of these events, the so-called Core Disruptive Accidents (CDAs), are intensively studied in the safety assessment of Sodium-cooled Fast Reactors (SFRs), and more recently also in the case of other systems. Differences between SFRs and Heavy Liquid Metal Fast Reactors (HLMFRs) are significant and therefore warrant an understanding of phenomena and the development of models specific to HLMFRs. This paper provides a qualitative overview of the physics relevant to the investigation of a CDA in HLMFR, with a particular application to the Multipurpose hYbrid Research Reactor for High-tech Applications – MYRRHA. At first, a core compaction mechanism viable for an HLMFR has been postulated. In what follows, simulation by an already existing severe accidents code, as well as modelling based on fundamental physics and engineering, have been performed. It is demonstrated that, for a linear insertion of reactivity due to hypothetical core compaction, the reversal of reactivity evolution happens due to the Doppler effect and the thermal expansion of core materials. Subsequent expansion by fuel melting terminates the prompt-critical event and makes the system delayed-supercritical. Successive fuel and/or coolant boiling is responsible for the hydrodynamic disassembly of the core and it therefore effectively terminates the transient

Relationship between composition, rheological and swelling properties of alkali-silica gels produced in cemented waste packages

ACTIInternational audienc

Présentation dans un séminaire au Massachussetts Institute of Technology

AI, ICTSInternational audienc

Study of alkali-silica reaction occurring in cemented waste packages based on simplified model and concrete medium approaches

International audienceNuclear power production generates radioactive waste, the management of which is an important industrial and environmental issue. Low - or intermediate - level radioactive aqueous waste can be concentrated by evaporation, stabilized and solidified with Portland cement before being sent to dis-posal. Interactions can however occur between the waste and the cement phases or aggregates, and decrease the stability of the final waste forms.The formation of a gel-like product, which results from an alkali-aggregate reaction, has been recently observed at the surface of cemented drums of evaporator concentrates. Its properties differ however from those usually reported for alkali-silica gels in many aspects: (i) very low calcium concentration, (ii) significant presence of Zn$^{2+}$, Cl$^-$, B(OH)$_4$$^-$ and SO$_4$$^{2⁻}$ ions, (iii) high formation rate, (iv) rather limited damage of the cementitious matrix considering the amount of gel produced.This work investigates the progress of alkali-silica reaction in the cemented drums, by studying the deterioration rate of the aggregates in model systems and in simulated concrete specimens.A synthetic alkaline solution, which mimics the pore solution including the waste, was used to de-grade the siliceous aggregates under controlled conditions. The extent of degradation caused by alkali-silica reaction was determined by weighing the residual flint aggregates and quantified by ther-mogravimetric analysis (TGA), specific surface area measurements, and gas pycnometry.A concrete specimen, formulated to be representative of the concrete embedding the radioactive waste, was cast and submitted to a thermal cycle, before being cured at 20°C and 90% relative humidity. Samples were taken from the concrete specimen and were observed at the micrometric scale using a scanning electron microscope coupled with energy dispersive X-ray analysis (SEM-EDX). The aggregates contained in the concrete were then mechanically and chemically retrieved, before being characterized by TGA.The model medium allows highlighting the advanced dissolution of the flint constitutive of the aggregates, leaving intact the most crystalline fraction of the grains. These results comply with the observations led on aggregates extracted from concrete samples, using SEM-EDX. Using this model medium,high degradation extent of the aggregates can be achieved. Indeed, the degradation progress of aggregates in concrete medium after 18 months could be reached in only a few hours using the model mediu

Study of alkali-silica reaction occurring in cemented waste packages based on simplified model and concrete medium approaches

International audienceNuclear power production generates radioactive waste, the management of which is an important industrial and environmental issue. Low - or intermediate - level radioactive aqueous waste can be concentrated by evaporation, stabilized and solidified with Portland cement before being sent to dis-posal. Interactions can however occur between the waste and the cement phases or aggregates, and decrease the stability of the final waste forms.The formation of a gel-like product, which results from an alkali-aggregate reaction, has been recently observed at the surface of cemented drums of evaporator concentrates. Its properties differ however from those usually reported for alkali-silica gels in many aspects: (i) very low calcium concentration, (ii) significant presence of Zn$^{2+}$, Cl$^-$, B(OH)$_4$$^-$ and SO$_4$$^{2⁻}$ ions, (iii) high formation rate, (iv) rather limited damage of the cementitious matrix considering the amount of gel produced.This work investigates the progress of alkali-silica reaction in the cemented drums, by studying the deterioration rate of the aggregates in model systems and in simulated concrete specimens.A synthetic alkaline solution, which mimics the pore solution including the waste, was used to de-grade the siliceous aggregates under controlled conditions. The extent of degradation caused by alkali-silica reaction was determined by weighing the residual flint aggregates and quantified by ther-mogravimetric analysis (TGA), specific surface area measurements, and gas pycnometry.A concrete specimen, formulated to be representative of the concrete embedding the radioactive waste, was cast and submitted to a thermal cycle, before being cured at 20°C and 90% relative humidity. Samples were taken from the concrete specimen and were observed at the micrometric scale using a scanning electron microscope coupled with energy dispersive X-ray analysis (SEM-EDX). The aggregates contained in the concrete were then mechanically and chemically retrieved, before being characterized by TGA.The model medium allows highlighting the advanced dissolution of the flint constitutive of the aggregates, leaving intact the most crystalline fraction of the grains. These results comply with the observations led on aggregates extracted from concrete samples, using SEM-EDX. Using this model medium,high degradation extent of the aggregates can be achieved. Indeed, the degradation progress of aggregates in concrete medium after 18 months could be reached in only a few hours using the model mediu

Quantification of the extent of alkali-silica reaction occurring in cemented waste packages based on simplified model systems

International audienceNuclear power production generates radioactive waste, the management of which is an important industrial and environmental issue. Low - or intermediate - level radioactive aqueous waste can be concentrated by evaporation, stabilized and solidified with Portland cement before being sent to disposal. Interactions can however occur between the waste and the cement phases or aggregates, and decrease the stability of the final waste forms.The formation of a gel-like product, which results from an alkali-aggregate reaction, has been recently observed at the surface of cemented drums of evaporator concentrates. Its properties differ however from those usually reported for alkali-silica gels: (i) very low calcium concentration, (ii) significant presence of Zn2⁺, Cl⁻, B(OH)4⁻ and SO42⁻ ions, (iii) high formation rate, (iv) rather limited damage of the cementitious matrix considering the amount of gel produced. This work investigates the progress of alkali-silica reaction in the cemented drums at early age, by studying the deterioration rate of the aggregates in model systems.A synthetic alkaline solution, which mimics the pore solution including the waste, was used to degrade the siliceous aggregates under controlled conditions. Determination of the extent of degradation caused by alkali-silica reaction was achieved by weighing the residual flint aggregates and by quantifying their deterioration state by 29Si NMR, BET and gas pycnometry

Quantification of the extent of alkali-silica reaction occurring in cemented waste packages based on simplified model systems

International audienceNuclear power production generates radioactive waste, the management of which is an important industrial and environmental issue. Low - or intermediate - level radioactive aqueous waste can be concentrated by evaporation, stabilized and solidified with Portland cement before being sent to disposal. Interactions can however occur between the waste and the cement phases or aggregates, and decrease the stability of the final waste forms.The formation of a gel-like product, which results from an alkali-aggregate reaction, has been recently observed at the surface of cemented drums of evaporator concentrates. Its properties differ however from those usually reported for alkali-silica gels: (i) very low calcium concentration, (ii) significant presence of Zn2⁺, Cl⁻, B(OH)4⁻ and SO42⁻ ions, (iii) high formation rate, (iv) rather limited damage of the cementitious matrix considering the amount of gel produced. This work investigates the progress of alkali-silica reaction in the cemented drums at early age, by studying the deterioration rate of the aggregates in model systems.A synthetic alkaline solution, which mimics the pore solution including the waste, was used to degrade the siliceous aggregates under controlled conditions. Determination of the extent of degradation caused by alkali-silica reaction was achieved by weighing the residual flint aggregates and by quantifying their deterioration state by 29Si NMR, BET and gas pycnometry

Spent nuclear fuel management, characterisation, and dissolution behaviour: progress and achievement from SFC and DisCo

SFC is a work package in Eurad that investigates issues related to the properties of the spent nuclear fuel in the back-end of the nuclear fuel cycle. Decay heat, nuclide inventory, and fuel integrity (mechanical and otherwise), and not least the related uncertainties, are among the primary focal points of SFC. These have very significant importance for the safety and operational aspect of the back-end. One consequence is the operation economy of the back-end, where deeper understanding and quantification allow for significant optimization, meaning that significant parts of the costs can be reduced. In this paper, SFC is described, and examples of results are presented at about half-time of the work package, which will finish in 2024. The DisCo project started in 2017 and finished in November 2021 and was funded under the Horizon 2020 Euratom program. It investigated if the properties of modern fuel types, namely doped fuel, and MOX, cause any significant difference in the dissolution behavior of the fuel matrix compared with standard fuels. Spent nuclear fuel experiments were complemented with studies on model materials as well as the development of models describing the solid state, the dissolution process, and reactive transport in the near field. This research has improved the understanding of processes occurring at the interface between spent nuclear fuel and aqueous solution, such as redox reactions. Overall, the results show that from a long-term fuel matrix dissolution point of view, there is no significant difference between MOX fuel, Cr+Al-doped fuel, and standard fuels