Experiences of Waste Assay and Management Issues Encountered in Decommissioning Old Radioactive Facilities

Abstract

The history of nuclear programmes has now given rise to a legacy of radioactive contaminated facilities in the UK and elsewhere. In the UK these facilities were associated with the initial R&D programmes, both civil and military, and subsequent reprocessing programmes to reclaim ²³⁵U and plutonium produced in fission reactors. The principle radioactive species produced in these systems are fission products, characterised by Cs-137 (Ba-137m), activation products, characterised by Co-60, and actinides, which are in general more difficult to assay as many of these do not have a characteristic gamma signature.

In addition, the UK was also the base for the Joint European Torus (JET), a pioneering fusion research facility. Several particle accelerator facilities were also designed and built, such as Van de Graaf machines and various cyclotron/synchrotron particle research systems. The radioactive waste types from these are activated materials from fast and slow neutron capture and more exotic radionuclides produced from particle-nucleus interactions.

Of the various waste characterisation methods, gamma techniques are the simplest to use because they enable a significant volume of waste material to be interrogated, whereas alpha and beta measurements are generally of limited range and are best used in laboratory measurements. Furthermore, the detection limits for neutron measurement techniques are usually so poor that they are greater than most relevant waste sentencing criteria. Nuvia has developed a range of in-situ and ex-situ gamma based systems for monitoring wastes and these will be described in detail in the paper. These include dose rate measurements in high gamma fields (g.t. 100μSv/h), gross gamma systems for mapping and bulk waste sentencing, and gamma spectrometry systems for in-situ contamination and package (200 litre drum, 1-2 tonne bag) monitoring. These systems include the Nuvia GROUNDHOG GPS-based contaminated land mapping system, a concrete core profiling system, 2D and 3D room mapping, conveyor monitoring, excavator bucket monitoring and purpose designed gamma spectrometry systems for bulk waste monitoring.

Examples of completed projects will be described; these will cover the range of radioactive wastes produced and the appropriate measurement systems used.