The use of sodium iodide detectors to locate buried radioactive particles in the seabed off Dounreay nuclear facility, Scotland

摘要

As part of a wider programme dealing with the monitoring of radioactive particles in the marine environment around Dounreay, UKAEA and our contractor Fathoms Ltd tested the viability of using remotely-operated sodium iodide detectors, as a potential alternative to the more risky method of diver-operated hand-held monitors. In 2003, a small frame-mounted detector was deployed successfully underwater and showed that buried particles could be detected out to 70 cm offset distance. In order to survey large areas underwater, however, a more sophisticated system was required. A remotely-operated vehicle (ROV) equipped with a much larger detector was designed, built and commissioned within nine months of conception. The system was tested in static mode in a laboratory environment and in dynamic mode offshore to verify the detection capabilities prior to undertaking area surveys underwater. The ROV design and particle detection methodology are described and the results of initial seabed surveys are presented. An area of 30,000 m~2 of seabed has been surveyed and over 120 contacts were obtained and mapped. These preliminary measurements are consistent with diver-recovered finds in a north-easterly direction from the Dounreay effluent discharge point. They also show the absence of particles in other areas. Further ROV surveys are required to delineate the extent of seabed contamination.