Testing of safety and performance indicators (SPIN)

The long-term safety of a geological repository can be assessed by means of numerical radionuclide release calculations. Magnitudes which are suitable to provide such an assessment by comparison with reference values are often called safety indicators. The most common safety indicator is the effective dose rate. Because of the relatively high uncertainty of dose rate calculations it seems desirable to have additional indicators to improve the reliability of performance assessments. As long as the functioning of the barrier system is to be shown other types of indicators can be used which refer to parts of the barrier system and are called performance indicators. The SPIN project identified and tested seven safety and 14 performance indicators. The indicators were tested by re-calculating four existing European performance assessment studies. The results have been compared and assessed in view of the general applicability of the specific indicators. Regulatory values as well as widely reported concentrations and fluxes were used as reference values. It was concluded that two additional safety indicators seem appropriate to supplement the effective dose rate, and several performance indicators can be used to show different aspects of the functioning of the individual compartments of the multi-barrier system.