WASTE PACKAGES IN REPOSITORIES: FEATURES, EVENTS, PROCESSES
Climate changes, ice ages, human intrusions, changing of host rock properties, crack-formation, water ingress and others may have effects on the integrity of the waste package.
The design of the repository has to fulfil fundamental SAFETY CRITERIA:
- REDUNDANCY which is provided by a MULTIPLE BARRIER system
- DIVERSITY by a COMBINATION of natural and technical barriers
- The FAIL SAFE criterion for passive systems like barriers must be fulfilled by ROBUSTNESS
- To mitigate the consequences of damages from COMMON MODE FAILURE two measures can be foreseen:
- a limitation of activity inventory per each waste package and
- spatially separated disposal
Safety requirements include
- continuous optimization of the waste disposal concept from planning to final closure of the repository (in the extreme case of total reversibility: take-out the canisters)
- retrieve ability of waste packages during operation time of repository as well as
- control and safety system for the time post closure: identification of a waste package
- recovery by miners for long years after final closure (German Safety Requirements: 500 years)
Nevertheless, for a given site, many “what if’s” and uncertainties exist, considering a timeframe of 1 Mio years.
In the case of water access corrosion takes place with loss of integrity, chemical reactions with canister surface, hydrogen generation, crack formation …