A significant proportion of the radioactive material which arises on decommissioning of nuclear facilities contains only small amounts and low concentrations of radionuclides, either as surface contamination, or as activation products within the body of the material. The objective of this study is to investigate the implications for waste management systems of various levels and forms of exemption criteria and the corresponding implications for routing low-level waste materials arising from decommissioning. Following a review of the existing information on the volumes and radionuclide contents of the most significant low-level materials which arise during decommissioning, and the current legislative background relevant to the disposal, recycling or reuse of such materials, the study will investigate the full range of radiological implications of adopting alternative clearance levels now under consideration. A number of related factors, such as volumes of materials which would require disposal as "radioactive" waste, the timing and the degree of dismantling, and the requirements for waste packaging are also addressed.
A literature search revealed little of use on the characterization of very low level waste (VLLW) arising from nuclear facility decommissioning. It has been calculated that one installation would produce about 1000 tonnes of steel and 1000 tonnes of concrete contaminated or activated during plant operation. Significant proportions of the total activity were found to be restricted to relatively small fractions of the total volume. The numerical value of radioactivity chosen for the exemption limit would greatly affect the volume of material to be considered radioactive. On the basis of an activity limit in the range 0.1 to 10 Becquerels per gramme, in excess of 95% of the concrete might be suitable for exemption and reuse, and about half the steel might be suitable (possibly after decontamination) for use in processes such as car manufacture.
Owing to the greater opportunity for exposure, doses to members of the public would be greater for disposal options involving reuse or recycling. Estimates of radiological impact have been made, but in view of the different conditions of exposure it has not been possible to recommend single values for either the exemption level or the relevant volume for averaging activity over in disposal. In addition, it might be necessary to revise the current individual dose criterion of 10 microsievers per year on the basis of increased estimates of risk per dose, particularly for radionuclides ingested with food or by inhalation. Higher exemption limits would be appropriate for substances such as tritium or iron-55.
- Characterisation of the waste arisings, the options for the management of the arisings, and the exemption principles and criteria within which the options have to be applied;
- Ranging of parameters which characterise the system identified in B.1., particularly those associated with the formulation of exemption;
- Evaluation of the radiological impacts following adoption of the relevant sets of parameter values characterising the system;
- Evaluation of the implication for routing of wastes following adoption of alternative formulations and levels for exemption by means of a comprehensive assessment and sensitivity analysis.