Technical Report NTB 82-11

Establishing Storage Criteria for a Swiss Low-Level Waste Repository

A methodology based upon safety criteria has been developed for the allocation of future Swiss radioactive waste arisings to one of the three repository types envisaged for the national waste disposal concept. The methodology has been applied to low-level wastes from decommissioning activities, intended primarily for storage in the so-called Type A repository. For this initial application 4 scenarios were considered. Three of these are related to the catastrophic failure of the repository and one to anticipated normal water intrusion.

Maximum average concentrations for 59 radionuclides of interest have been derived for the four scenarios and resulting maximum permissible concentrations for radionuclides, in the waste capable of being stored in a Type A repository have been obtained. The results show 39 radionuclides to be relevant for further investigations and an appropriately grouped specific activity inventory of these 38 radionuclides in decommissioning wastes was established. Using this inventory a first attempt was made to partition the wastes and determine the potential storage capabilities for a Type A repository.

In the work a simple repository model which does not take full account of combined effects of the engineered safety barriers was used. A storage capability of much less than half of the originally envisaged capacity has been arrived at. This result can be accounted for by the differences between present modelling assumptions and parameters and those used previously, by the fact that the partitioning of the wastes was not detailed, and by the conservative assumptions made concerning concentrations of radionuclides in the waste. It is clear that more detailed information on waste arisings and on the behaviour of the technical safety barriers in the repository system can lead to increases in the storage capacity predicted for a Type A repository.