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Safe management of radioactive waste is challenging to waste producers and waste management organisations. Deployment of thermal treatment technologies can provide significant improvements: volume reduction, waste passivation, organics destruction, safety demonstration facilitation, etc. The EC-funded THERAMIN project enables an EU-wide strategic review and assessment of the value of thermal treatment technologies applicable to Low and Intermediate Level waste streams (ion exchange media, soft operational waste, sludges, organic waste, and liquids). THERAMIN compiles an EU-wide database of wastes, which could be treated by thermal technologies and documents available thermal technologies. Applicability and benefits of technologies to the identified waste streams will be evaluated through full-scale demonstration tests by project partners. Safety case implications will also be assessed through the study of the disposability of thermally treated waste products. This paper will communicate the strategic aims of the ongoing project and highlight some key findings and results achieved to date.

VTT has developed a gasification-based technology for processing low- and intermediate-level waste (LILW) rich in organic matter. VTT’s process is based on well-controlled thermal fluidised-bed gasification followed by efficient gas cleaning, gas conditioning/oxidation, wet scrubbing of the oxidised gas (flue gas), and finally, filtering through a high efficiency particulate air (HEPA) filter, which acts as a backup cleaning system. In the case of an organic ion exchange resin (IXR) the primary product from thermal gasification is fine filter dust. In addition, the process produces some bottom ash, which consists mainly of the bed material. The wet scrubber liquid may also contain some activity. Demonstration trials were carried out using unspent organic IXR containing a small amount of added stable Cs in order to simulate Cs content in spent IXR. Gasification tests confirmed the capability of the process to remove organic matter from the IXR and clean the resulting off-gas as required. Simulated waste IXR was reduced to approximately 1 wt-% of its original mass before immobilisation. Filter dust and bottom ash have to be immobilised before final disposal. VTT has previously developed an advanced immobilisation technology based on geopolymerisation and this has been applied to samples from the THERAMIN test trials. VTT’s technology has been designed as a compact process, which can be operated at the nuclear power plant site. Until now, all development and verification test trials have used simulated waste materials. The next step is the demonstration of the process using real radioactive waste.

A combination of gasification of low and intermediate level radioactive waste (LILW) and conditioning of the resulting product within a geopolymer matrix is a potential alternative for vitrification technologies as an immobilisation method. Geopolymer matrices have demonstrated good retention capability for radionuclides in many studies and the technology has been implemented at an industrial scale in Slovakia and Czech Republic. However, the practical waste loading has been limited by the mechanical properties of the encapsulated matrix. Even a small amount of ion exchange resin (IXR) decreases the strength of the matrix and cohesion of the matrix is lost when the fraction of resin exceeds 15-20%. In this study, the potential to combine gasification as thermal treatment and various inorganic binders as encapsulation matrices was evaluated. After gasification, the mechanical properties were not similarly sensitive to the encapsulation of IXR. Gasification enabled substantially higher loading of IXR into the sample. Also, gasification of the IXR decreased matrix apparent Caesium diffusion. Very low apparent diffusion coefficients of Cs were calculated when gasified resin was encapsulated in metakaolin matrix. Theoretically, the amount of Cs within the same volume of encapsulated material could be increased by 800 times following gasification and encapsulation within an alkali-activated metakaolin (MK) binder.