CHAPTER 2: Introduction to Nuclear Safety

Introduction to Nuclear Safety

This chapter introduces on the one hand the basic principles of nuclear safety, such as fundamental safety principles, Defence-in-Depth and safety functions.

On the other hand, it provides a general introduction of IAEA Safety Standards, with a focus on safety standards for the design of NPPs. Given that the majority of NPP currently in operation were designed when previous standards were applicable, this chapter also provides an overview of the evolution of IAEA Safety Standards for design safety, up to the most up-to-date IAEA Safety Standards Series No. SSR-2/1 (Rev. 1), Safety of Nuclear Power Plants: Design, published in 2016.

SSR-2/1 (Rev. 1), developed and applicable to new NPPs, has marked an evolution in the safety requirements applicable to the design of nuclear power plants, aimed at achieving a higher level of safety: major novelties of SSR-2/1 (Rev. 1) with respect to previous standards are briefly illustrated:

• The extension of the plant states to be considered in the plant design – with consideration of multiple failures potentially leading to severe accidents — aim at “enhancing the plant’s capabilities to withstand, without unacceptable radiological consequences, accidents that are either more severe than design basis accidents or that involve additional failures”;
• SSR-2/1 (Rev. 1) also requires “that the possibility of plant states arising that could lead to an early radioactive release or a large radioactive release be ‘practically eliminated”. SSR-2/1 (Rev. 1) states that conditions “may be considered to have been ‘practically eliminated’ if it would be physically impossible for the conditions to arise or if these conditions could be considered with a high degree of confidence to be extremely unlikely to arise”;
• SSR-2/1 (Rev. 1) strengthens requirements related to the implementation of defence in depth and its independence, in particular for severe accidents, and stresses the need for margins to avoid cliff edge effects;
• Strengthened requirements for the design against external hazards;
• Implementation of supplementary features to allow the use of non-permanent equipment for accident management;
• Strengthened requirements for heat transfer to the ultimate heat sink.
The last part of the chapter introduces the applicability of the SAMG-D Toolkit to both currently operating and new reactors.