Evolution of radiometric instrumentation systems on operating reprocessing and waste handling facilities

A wide variety of special purpose radiometric instrumentation systems are now in use in the Sellafield Magnox fuel reprocessing facility and in the associated plants and waste handling operations. These systems, which were developed by the Physical Science and Engineering Development Group have accumulated many years of successful operation. However as processes have been improved and regulatory requirements have become increasingly stringent, it has become necessary to re-assess the monitoring approach employed in a number of these devices. As examples of this process of evolution, which is being carried out in parallel with the development of other special instrumentation for the new plants now under construction at Sellafield, the paper outlines the way in which two of the existing devices are currently being replaced by more sophisticated and versatile systems. For the monitoring of crated waste, a flexible neutron coincidence monitor will incorporate high resolution gamma spectrometry to provide a more reliable overall assessment of plutonium and to assess the presence and distribution of U-235 contamination. Swarf arising from the decanning of Magnox fuel will be monitored by high resolution gamma spectrometry and the data analysis extended in order to provide a quantitative assessment of some 40 specified radioisotopes