Technetium Behaviour in Soils of the Canadian Precambrian Shield

Abstract

Technetium-99, produced by the fission of ²³⁵U and ²³⁹Pu, has a radiological half-life of 2·15 x 10⁵ years and has been dispersed in the environment via weapons testing and releases from establishments using it for medical or industrial purposes. Technetium could also reach the environment via releases from nuclear power plants, nuclear fuel processing facilities or nuclear fuel waste disposal vaults. Environmental impact assessments associated with the licensing of such nuclear facilities usually include analysis of radiation exposure pathways that involve the transport of radionuclides through agricultural soils and their uptake by crop plants. The environmental assessment of the Canadian concept for the permanent disposal of nuclear fuel waste in plutonic rock differs from the assessments required for surface nuclear facilities in that the source of radionuclides in the fuel waste disposal vault is located 500–1000 m deep in a rock mass. Thus, the models for the assessment of this concept must predict radionuclide migration up from the vault, through the geosphere and into the biosphere, and the eventual radiological dose to man [1]. Only radionuclides with very long half-lives could reach the biosphere and, of those, only the most mobile nuclides could escape from the vault and the surrounding rock. Technetium has both of these properties and so is important in the research supporting the Canadian Nuclear Fuel Waste Management Program.