A Model to Determine the Radiological Implications of Non-fixed Radioactive Contamination on the Surfaces of Packages and Conveyances

The surfaces of packages and conveyances used to transport radioactive materials can sometimes become contaminated with radioactive material. This usually occurs as a result of the transfer of radioactive material from areas in which these packages and conveyances are handled. This contamination may subsequently be transferred to transport equipment, workers and to areas accessible to the public. This can represent a significant radiation safety issue that requires careful management. The current regulatory limits for non-fixed contamination on packages and conveyances have been in use for over 40 years, and are based on a simple exposure model. However, the bases on which these limits were derived have been subject to changes, as a result of successive revisions of international recommendations. In recognition of this need for a review and analysis of the current contamination limits an IAEA Co-ordinated Research Project (CRP) on the “Radiological Aspects of Package and Conveyance Non-Fixed Contamination” was initiated to review the scientific basis for the current regulatory limits for surface contamination. The CRP was also to develop guidance material for evaluating the radiological significance of surface contamination to workers and the public in light of state-of-the-art research, technical developments and current transport practices. The specific objectives of the work undertaken within this multi-national CRP were, in accordance with the terms of reference: • To ensure that appropriate models exist for all package types including consideration of the aspects pertinent for assessing and revising a surface contamination model for transport, • To collect - where possible - contamination, operational and dosimetric data to ensure modelling consistency, • To use models for assessing the limitations and optimisation of radiation doses incurred in transport operations, and • To consider preventive methods for package and conveyance contamination. The CRP was to include a review of the dose pathways for non-fixed surface contamination on packages and conveyances under routine conditions of transport and to quantify the resulting internal and external radiation dose to transport workers and the public (per unit of surface contamination on packages). This assessment was to take into account the different categories of radioactive material packages used in contemporary practices and related transport operations. Six countries and one international organization agreed to undertake research to support the project. These were: France, Germany, Japan, Sweden, United Kingdom, United States of America, and the World Nuclear Transport Institute (WNTI).