In addition to the calculation of the annual individual effective dose, the performance and safety of the repository system can further be illustrated using additional, complementary safety and performance indicators.

The indicators described in the following sections are based on the concept of radiotoxicity (RT) as a measure of the relative potential hazard of radioactive material. RT is defined as the effective dose received in the case of hypothetical direct ingestion of radionuclides in dissolved form into the body. RT, in units of sieverts (or millisieverts, where appropriated), is calculated from the activity Ai(t) [Bq] of a nuclide i at a time t and the ingestion dose conversion factor Fi [Sv/Bq] of the nuclide i

RT(t) = ∑i Ai(t) × Fi

 

RT fluxes and concentrations can be calculated in an analogous way to RT itself, by replacing the activity Ai(t) in the equation above by activity flux or activity concentration, respectively.

The consideration of these complementary indicators can provide additional arguments for safety that avoid, to some extent, the difficulties faced in evaluating and interpreting doses and risks that may occur in the far future (OECD/NEA 2004, 2012b). A comprehensive review of complementary indicators used in post-closure safety cases, including the reference values for safety indicators, is reported in (OECD/NEA 2012a).

In the following sections RT, RT fluxes and RT concentrations are used to illustrate:

  1. the declining radiological hazard from the waste packages for SF, RP-HLW and L/ILW over time,

  2. the evolving distribution and decay of RT in the repository barrier system, and

  3. how the RT fluxes and concentrations associated with the repository system compare with other RT fluxes and concentrations in natural systems and from human activities, in order to place those associated with the repository system in perspective.