Comprehensive international principles and guidelines for dealing with radioactive substances and for deep geological disposal establish a robust framework for the Swiss waste management programme and are presented in detail in NAB 24-18 Rev. 1 (Nagra 2024s). In the following, the most relevant aspects are summarised.

The International Commission on Radiological Protection (ICRP) has contributed significantly to the framework with its system of radiation protection, updated in ICRP Publication 103 (ICRP 2007b). This system is built on the principle of dose limitation. Furthermore, ICRP Publication 81 (ICRP 1998) emphasises that future generations should receive at least the same level of protection from radioactive waste as the current generation. This principle involves applying current quantitative dose and risk criteria to estimated future doses or risks for appropriately defined critical groups. 

At a high level, safety principles and provisions are laid down in the International Atomic Energy Agency (IAEA) Joint Convention on the Safety of Spent Fuel and on the Safety of Radioactive Waste Management (IAEA 1997), to which Switzerland is a signatory. Safety standards and safety guides establish more detailed guidelines and requirements: IAEA Safety Standard SF-1 (IAEA 2006) underlines the fundamental safety objective to protect humans and the environment from harmful effects of ionising radiation. This standard articulates ten associated safety principles that provide the foundation for requirements and measures for the protection of humans and the environment against radiation risks and for the safety of facilities and activities generating those risks. More specific safety guides are concerned with the safe development of deep geological repositories, referred to here as geological disposal facilities (SSG-14; IAEA 2011b) and with the safety case and safety assessments (SSG-23; IAEA 2012). Furthermore, specific safety requirements are given in SSR‑5 (IAEA 2011a).

Internationally recognised principles that underlie the disposal concepts and designs for deep geological disposal include passive safety and a stepwise and iterative development of the repository for the optimisation of protection. While many detrimental phenomena and uncertainties can be avoided, reduced, or their effects mitigated by optimisation, some uncertainty will inevitably remain. It is by following the principle of robustness that geological disposal systems are sited and designed in such a way that post-closure safety can be demonstrated irrespective of the remaining uncertainty. The Nuclear Energy Agency (NEA) of the Organisation for Economic Cooperation and Development (OECD) has stated that “robust systems are characterised by a lack of complex, poorly understood or difficult to characterise features and phenomena, demonstrated quality control, and an absence of, or relative insensitivity to, detrimental phenomena arising either internally within the repository and host rock, or externally in the form of geological and climatic phenomena that introduce processes with the potential to compromise safety” (OECD/NEA 2013).

Regarding the design of a disposal facility, IAEA SSR-5 (IAEA 2011a) states that “the disposal facility and its engineered barriers shall be designed to contain the waste with its associated hazard, to be physically and chemically compatible with the host geological formation and/or surface environment, and to provide safety features after closure that complement those features afforded by the host environment”. Safety is provided by means of multiple safety functions, which provide defence-in-depth, according to IAEA SSR-5 (IAEA 2011a):

  • “the host environment shall be selected, the engineered barriers of the disposal facility shall be designed and the facility shall be operated to ensure that safety is provided by means of multiple safety functions”,

  • “a safety function may be provided by means of a physical or chemical property or process that contributes to containment and isolation, such as: impermeability to water; limited corrosion, dissolution, leach rate and solubility; retention of radionuclides; and retardation of radionuclide migration” and

  • “adequate defence-in-depth has to be ensured by demonstrating that there are multiple safety functions, that the fulfilment of individual safety functions is robust and that the performance of the various physical components of the disposal system and the safety functions they fulfil can be relied upon, as assumed in the safety case and supporting safety assessment”.

Thus, the safety case is built on multiple types of evidence and lines of argument for the performance of individual barriers, including their contributions to the safety functions, and for the performance and robustness of the disposal system as a whole.