The ongoing update of the safety case for co-disposal of HLW and TRU waste in Japan will include a more extensive assessment of operational safety than has been carried out in the past. The pre-closure safety case aims to assure both radiological and non-radiological protection of the public and workers.

Radiological protection requires radiation shielding and radionuclide containment within the disposal facilities in the event of operational perturbations. Radiation control and facility design are based on guidelines applied for other nuclear facilities. Within radiation-controlled zones, most operations will be remote-handled or will involve appropriate shielding, avoiding any significant dose to workers.

Operational perturbations, such as physical or thermal impacts on the waste-form, are analyzed using an event tree method and possible cost-effective counter-measures identified that would reduce their likelihood or mitigate their impact. Potential vulnerabilities of operational processes have been considered: most of these would pose little risk to the public, but the complexity of recovery operations and risks to workers could be significant. For example, the mechanical robustness of metal overpacks effectively assures no release of radionuclides as a result of credible incidents.