Event Timeslots (1)

Day 2 – June 21
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The major source of anthropogenic radionuclides in the seabed sediment in the UK can be traced to three main sources as follow: the global and local fallout due to nuclear weapon testing, the nuclear reprocessing plant at Sellafield and the fallout from accident at Chernobyl without omitting secondary main sources such as the nuclear power stations, the fuel production facilities, nuclear research facilities and dumping of low-level radioactive waste.

This project looks at the design and testing of an innovative underwater system with the intent that it will dig unaided into the sediment. A variety of design models have been produced but only two of them have been retained because of their capabilities to detect low-level, low-energy gamma ray radioactivity present under the seabed or ocean floor, autonomously. The materials to be detected are classified as alpha-rich such as americium-241 and related actinides, and beta-rich such as fission product like caesium-137 and higher energy radiation like cobalt-60. However, the complication in the design model arises from the detection of americium-241 and the actinides because they are relatively difficult to detect due to the shielding effect of the sediment. Amercium-241 arises from the beta decay of plutomium-241 and so, by detecting americium-241 under the seabed or ocean floor, plutonium abundance can also be inferred.

The seabed sediment, where the anthropogenic insoluble radioactive particles are located, is made of sand, silt or clays. The radioactive particles, to be detected by the designed and built system, are known as a localised aggregation of radioactive atoms that gives rise to inhomogeneous distribution of radionuclides significantly different from that of matrix background. The key important points in this project is the underwater system discovery and characterisation of radioactive particles. Series of analytical tools are available for identification, isolation and characterisation. Radioactive particles can be characterised by using as a minimum gamma spectrometry which determine the isotope composition of radionuclides. However, non-destructive solid-state characterisation, such as the SEM-EDX, is the best method to adopt for this project because it provides size distribution, surface morphology, elemental composition and distribution. For specific low-level, low energy gamma ray, a non-destructive technique known as LEPS can be used for activities and isotopic ratio of americium-241, plutonium-239 and plutonium-240.

Nevertheless, several digging devices have been reported in the research often inspired by how aquatic animals dig and drill on the seabed or ocean floor such as clams or worms as well as digging for the planting of trees and adapted screw burying themselves. It is inspiring to observe the performance of these designed underwater systems especially when these radiometric systems are fully submerged through their digging process.

This project main objective is to build an autonomous underwater system that can dig itself into the seabed for the purpose of low-level, low-energy radioactivity characterisation. This has required the development of two innovative design models that would allow crossing to a desired underwater location, drilling the seabed or ocean floor and remaining stable while buried with option to reposition to different location.