Regulatory guidance in ENSI Guideline G03 (ENSI 2023) states that a period of up to one million years shall be considered by the safety case, and that the temporal development of the radiological hazard potential of the emplaced waste and the predictability of the long-term geological evolution must be taken into account9. In NTB 08‑05 (Nagra 2008), by considering the decrease in radiotoxicity that occurs over time, the time period for assessment (referred to in the context of site comparison as the time period under consideration) was defined as extending up to 100,000 years for an L/ILW repository and up to one million years for an HLW repository. These time frames are also adopted for SGT-E3 when considering separate HLW and L/ILW repositories (see NAB 24‑05 (Nagra 2024a) for details). The shorter period considered for the L/ILW repository, based on considerations of radiotoxicity, is also consistent with guidance from ENSI in ENSI 33/649 (ENSI 2018)10.

For a geological repository for both HLW and L/ILW, a one-million-year time period for assessment is considered, although the time frame specific to the assessment of certain processes or phenomena (e.g., heat production from HLW) can be significantly shorter. In case of the calculations of radionuclide release, retention and transport carried out for the analysis of radiological consequences, ENSI Guideline G03 lists the additional requirement that the dose calculations shall be performed up to the time of the maximum radiological impact of the deep geological repository11. To meet this requirement, dose calculations are carried out up to the maximum radiological impact time, extending to 107 years for HLW and 106 years for L/ILW releases. Analyses for volatile radionuclides, which focus on 14C with a 5,700-year half-life, are carried out for a 105-year period. After this time period, 14C will have decayed to activities that are insignificant.

Beyond the time period for assessment, ENSI Guideline G03 requires determination of the range of potential impacts by considering uncertainties and scenarios involving geological processes. Notably, glacial and non-glacial (fluviatile) erosion, impacting the repository barrier system, is addressed in the dedicated report NAB 24‑08 Rev. 1 (Nagra 2024q), taking into account time frames well beyond the time period for assessment.

Für den Sicherheitsnachweis ist ein Nachweiszeitraum von bis zu einer Million Jahre festzulegen. Die zeitliche Entwicklung des radiologischen Gefährdungspotenzials der eingelagerten Abfälle und die Prognostizierbarkeit der geologischen Langzeitentwicklung sind zu berücksichtigen. ↩

Falls gezeigt werden kann, dass durch das geologische Tiefenlager aufgrund des radiologischen Gefährdungspotenzials der Abfälle bereits nach weniger als einer Million Jahre nur noch vernachlässigbar kleine radiologische Auswirkungen für Mensch und Umwelt zu erwarten sind, kann der Nachweis für einen kürzeren Betrachtungszeitraum geführt werden. ↩

In der Sicherheitsanalyse sind Dosisberechnungen bis zum Zeitpunkt der maximalen radiologischen Auswirkungen des geologischen Tiefenlagers durchzuführen, mindestens jedoch bis zum Ende des Nachweiszeitraums. ↩