Radiometric specialist measurements are required for a variety of activities at Sellafield such as support to operational plants, building management, waste management and decommissioning. Measurements are performed using mainly standard components in a novel configuration or using standard products for a non standard application. They are required, for example, to characterise radioactive material which may be outside the normal operating envelope of installed monitoring systems, provide radiometric characterization to aid plant operations, characterise the neutron moderating / absorption properties of materal and vessels, identify the source and characteristics of blockages which may occur in plant vessels and pipes etc. Examples of recent projects have included: • Special investigations of residue material from fuel manufacturing operations, using a combination of Total Neutron Counting, Neutron Coincidence Counting and High Resolution Gamma Spectrometry. • Dose rate measurements and surveys in environments up to 100 Sv/hr in various locations at the Sellafield reprocessing plants. Applications include in-cell measurements and underwater measurements in fuel ponds. • Neutron transmission measurements to verify the presence of absorbing material in plant vessels. • HRGS gamma surveys to identify and quantify a wide variety of radionuclides in waste handling and decommissioing operations. This paper provides insight into BNFL Instrument’s Special Investigation work and will provide examples of interesting projects which have been successfully carried out recently at Sellafield and Dounreay.

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