In situ mechanical analysis of sludge in hazardous environments

Fried, Tomas and Cheneler, David and Monk, Stephen and Taylor, James and Dodds, Jonathan (2021) In situ mechanical analysis of sludge in hazardous environments. PhD thesis, Lancaster University.

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Abstract

The Sellafield site is the focal point of nuclear decommissioning in the UK as it is made up of several hundred nuclear facilities built for a wide range of capabilities. These facilities are tightly packed in a very small area and are in various stages of their lifecycle. One of the biggest challenges is the presence of legacy storage tanks and silos that contain sludge of uncertain properties. The process of clean out and decommissioning of these vessels is informed by analysing the chemical, radiological and most importantly physical properties of the sludge. Shear behaviour is a key parameter describing the movability of legacy waste that needs to be understood in order to decommission these facilities. Several complicating factors, such as access, congested internal structure of vessels and radioactive and hazardous nature of the substances complicate sampling and prohibit the use of sophisticated and sensitive characterisation devices. This thesis discusses the development of a novel, low cost, radiation tolerant and compact device designed for the remotely operated analysis of the shear behaviour of highly radioactive sludge in situ using rapid prototyping and commercial off the shelf components. Two different prototype designs have been developed, utilising different approaches to rheological assessment of rheological properties of suspensions using rotational viscometry. Radiation testing was performed on the electronic components used in these prototypes to determine their suitability for hazardous environments. Further radiation testing was performed on commercial off the shelf microcontrollers to determine their performance during irradiation and assess their suitability for use in nuclear decommissioning environments. The results show that the viscometer designs proposed in this thesis are suitable for further development and deployment in hazardous environments. The first design can be calibrated against any benchtop viscometer or rheometer and can provide data usable for further decision making. The second design is suitable for quality control or monitoring use in hazardous environments and has potential for use in yield stress measurements. Radiation testing has shown high resilience of commercial of the shelf potentiometers and microcontrollers. The method used to test microcontrollers has not been previously used in literature and provides a novel insight into radiation effects on the function of microcontrollers during irradiation.