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# The immobilisation of Caesium and Strontium from nuclear waste captured by IONSIV

Day, George (2018)
Ph.D. thesis, University of Birmingham.

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## Abstract

A previous study revealed Cs$$_2$$TiNb$$_6$$O$$_1$$$$_8$$ to be the major Cs-containing phase after hot isostatic pressing Cs-loaded IONSIV (a commercial exchanger) which demonstrated excellent wasteform properties. Both experimental and theoretical studies have been carried out in order to assess if Cs$$_2$$TiNb$$_6$$O$$_1$$$$_8$$ is able to retain $$^1$$$$^3$$$$^7$$Ba$$^2$$$$^+$$, the transmutation product of $$^1$$$$^3$$$$^7$$Cs$$^+$$. A series of samples with different charge compensation mechanisms have been synthesised including Cs$$_2$$$$_-$$$$_x$$Ba$$_x$$Ti$$^($$$$^4$$$$^+$$$$^)$$$$_1$$$$_+$$$$_x$$Nb$$^($$$$^5$$$$^+$$$$^)$$$$_6$$$$_-$$$$_x$$O$$_1$$$$_8$$, Cs$$_2$$$$_-$$$$_x$$Ba$$_x$$Ti$$^($$$$^3$$$$^+$$$$^)$$$$_x$$Ti$$^($$$$^4$$$$^+$$$$^)$$$$_1$$$$_-$$$$_x$$Nb$$_6$$O$$_1$$$$_8$$ and Cs$$_2$$$$_-$$$$_x$$Ba$$_x$$TiNb$$^($$$$^4$$$$^+$$$$^)$$$$_x$$Nb$$^($$$$^5$$$$^+$$$$^)$$$$_6$$$$_-$$$$_x$$O$$_1$$$$_8$$. Analysis suggested that Ba incorporation was not successful because of the identification of Ba impurities in the X-ray diffraction patterns. A series of atomistic simulations have also been performed to support the experimental work, using the General Utility Lattice Program code which suggested that Ba incorporation is not energetically favourable.

Sr-loaded IOSNIV has also been thermally converted via calcination (in air) and hot isostatic pressing. The removal and immobilisation of Sr is an important process on account of $$^9$$$$^0$$Sr being one of the more problematic radionuclides produced from the fission process. Both thermal conversion methods produced crystalline phase assembles which were analysed by X-ray diffraction, X-ray fluorescence and microscopy studies. The HIPed materials performed well in aqueous durability tests, suggesting these wasteforms will be suitable for final disposal in a geological disposal facility.

Type of Work: Ph.D. thesis. Hriljac, Joseph A. Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Chemistry TA Engineering (General). Civil engineering (General)TP Chemical technology University of Birmingham 8206
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