Radionuclide Biogeochemistry in Cementitious Wasteforms

Abstract

Intermediate level waste (ILW) in the UK is encapsulated in cementitious material for storage prior to disposal within a geological disposal facility (GDF). Cement acts as one of the components of the multibarrier system retarding radionuclides due to its high alkalinity, in-turn preventing release of contaminants to the biosphere. Metals and organic matter present in ILW can provide energy for anaerobic microbial respiration which also has the potential to increase retention of radionuclides by reducing their mobility. The effects of microbial activity have been highlighted as a key remaining uncertainty that must be addressed before implementation of the first GDF within the UK and other “nuclear” nations. Much work has been done on well-mixed homogenous systems but in order to make the disposal of radioactive waste much less conservative, more work needs to be focused on investigating heterogeneous systems. These systems are more representative of ILW matrices as microniches may promote the survival of microbial communities, in turn affecting the biogeochemical evolution of a wasteform. Determining heterogeneity at the submicron level is necessary in order to understand the microscale heterogeneity in a wasteform and therefore to extrapolate to the macroscale. Visualising heterogeneity can be achieved using spatially resolved fluorescence imaging techniques and XRF elemental mapping. This in conjunction with geochemical and DNA analysis, in experiments with clear heterogeneous interfaces (e.g. between cement and cellulosic material in ILW wasteforms) and promoted heterogeneity within sediment systems, (with respect to microbial colonisation and terminal electron acceptor distribution) can provide insight to the possible formation of microniches at extremes of pH (>12). Responses to unique local changes at the microscopic level, can be used to assess the influence of heterogeneity on biochemical processes occurring under cementitious waste repository conditions, in correspondence to radionuclide fate. Another challenge here is the imaging the bio-mineral interface without disturbance to the heterogeneity of the system. Therefore the other aspect of this project will be to develop sensitive selective fluorescent probes to image regions of interest to be used in fluorescence imaging techniques.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Samuel Shaw (Supervisor), Jonathan Lloyd (Supervisor) & Louise Natrajan (Supervisor)