DS562 - Safety of Nuclear Power Plants: Design

Status: STEP 4

Revision von SSR-2/1 (Rev. 1)

Beteiligte IAEO-Komitees: NUSSC, RASSC, TRANSSC, WASSC, EPReSC, NSGC

Specific Safety Requirements

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IAEA Safety Standards Series No. SSR-2/1 (Rev. 1), Safety of Nuclear Power Plants: Design (2016) was developed to establish requirements for the design of nuclear power plants (NPPs) to be met to ensure the fundamental safety objectives. The development of the requirements in SSR-2/1 (Rev. 1) was based on the initial version, published in 2012 (SSR-2/1). The requirements in SSR-2/1 were revised to incorporate the lessons learned from the Fukushima Daiichi nuclear power plant accident and available feedback from operational experience. Furthermore, the main objective of the requirements in SSR-2/1 (Rev. 1) was to strengthen the plant design basis to prevent severe accidents and to mitigate the consequences of those accidents if they were to happen.

NPPs with non-water-cooled reactor technologies are not included in SSR-2/1 (Rev. 1) although Member States have been considering deploying these technologies in recent years, to establish or to enlarge their nuclear power programmes. Those NPPs with non-water-cooled reactor technologies differ fundamentally and incorporate innovative design features, as compared to those with water cooled reactors, and their potential deployment applications include both electricity generation and non-electrical applications. Some of the specific features considered are different neutron spectrums, different coolants, and different fuel types. Other important design features considered by advanced reactor technologies are the modularity and modularization, different power outputs and Transportable NPPs, including propulsion (such as nuclear merchant ships).

The revision of SSR-2/1 (Rev.1), hereinafter called SSR-2/1 (Rev.2), is expected to enhance the clarity, applicability, and usability of the safety requirements for a broader range of reactor technologies while offering more practical guidance for regulatory bodies, design organizations, and technical support organizations, especially in Member States deploying NPPs with advanced reactors technologies and designs, or Member States embarking on nuclear power programmes.

The requirements will strive to keep the extant philosophy of technology-neutral, technology-inclusive, and technology-specific requirements to support:

1. Consideration in the design basis of the structures, systems and components in nuclear power plants to prevent accidents and mitigate their consequences, ensuring the highest level of safety reasonably achievable;
2. The implementation of the defence in depth concept in nuclear power plant design, ensuring that the independence between their different levels, and the barriers considered at such levels, is achievable, demonstrable and maintained as far as reasonably practicable;
3. An appropriate balance between prevention and mitigation in the design to ensure the fundamental safety functions, taking into account all safety features, including inherent safety features;
4. Adequate safety margins to account for uncertainties and to avoid cliff-edge effects to ensure reliable performance within different plant states;
5. The concept of practical elimination in the design of nuclear power plants to prevent plant event sequences that could lead to early radioactive releases or large radioactive releases, ensuring they are either physically impossible or they could be considered with high level of confidence to be extremely unlikely to arise.

The revision will expand the current scope in SSR-2/1 (Rev. 1) to consider all power producing nuclear reactors (e.g. electrical generation, process heat, desalination, marine propulsion) used for civil purposes and to integrate updated considerations for water-cooled (including advanced) and non-water-cooled reactor technologies (e.g. High Temperature Gas Cooled Reactors (HTGRs) , Liquid Metal Fast Neutron Reactors (LMFRs) and Molten Salt Reactors (MSRs)). In addition, specifics of NPPs with small modular reactors and micro reactor designs, and corresponding deployment options (e.g. NPP with multi module units (i.e. modularity), remote locations, underground installation, transportable NPPs (i.e. modularization, and propulsion), will be considered.

Nuclear reactors for aviation or outer space applications will be out of scope of the requirements in SSR-2/1 (Rev. 2). Similarly, Accelerator-Driven System (ADS) will be out of scope of the requirements in SSR-2/1 (Rev. 2).