BACKGROUND

1.1. This Safety Guide was prepared under the IAEA programme for safety standards for nuclear power plants. It is a revision of the Safety Guide on Design of the Reactor Containment Systems in Nuclear Power Plants (Safety Series No. 50-SG-D12) issued in 1985 and supplements the Safety Require­ments publication on Safety of Nuclear Power Plants: Design [1]. The present Safety Guide was prepared on the basis of a systematic review of the relevant publications, including the Safety of Nuclear Power Plants: Design [1], the Safety Fundamentals publication on The Safety of Nuclear Installations [2], Safety Guides [3-5], INSAG Reports [6, 7], a Technical Report [8] and other publications covering the safety of nuclear power plants.

1.2. The confinement of radioactive material in a nuclear plant, including the control of discharges and the minimization of releases, is a fundamental safety function to be ensured in normal operational modes, for anticipated operational occurrences, in design basis accidents and, to the extent practi­cable, in selected beyond design basis accidents (see Ref. [1], para. 4.6). In accordance with the concept of defence in depth, this fundamental safety function is achieved by means of several barriers and levels of defence [6]. In most designs, the third and fourth levels of defence are achieved mainly by means of a strong structure enveloping the nuclear reactor. This structure is called the ‘containment structure’ or simply the ‘containment’. This definition also applies to double wall containments.

1.3. The containment structure also protects the reactor against external events and provides radiation shielding in operational states and accident conditions. The containment structure and its associated systems with the functions of isolation, energy management, and control of radionuclides and combustible gases are referred to as the containment systems.