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

Day, George (2018). The immobilisation of Caesium and Strontium from nuclear waste captured by IONSIV. University of Birmingham. Ph.D.

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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.