Handling of timescales in safety assessments of geological disposal: an IRSN-GRS standpoint on the possible role of regulatory guidance

Due to the physical process of radioactive decay, the question of time is an inherent factor of any activity associated with nuclear materials. Hence time has naturally played a role in the definition of radioactive waste management strategies. This has eventually led to differences with other types of hazardous waste and notably to an earlier consideration of potential impacts in the long-term. Time has therefore been early accounted for in the basic objectives of radioactive waste management. These objectives explicitly require the protection of human beings and of the environment now and in the future. In other words this implies the need to adequately manage the waste for 'as long as it contains dangerous amounts of toxic substance', or, in the case of radioactive waste, 'until sufficient decay has occurred'. (authors)