ISO DIS 21391

Description / Abstract: Nuclear criticality safety is achieved by methods of control in accordance with ISO 1709. The application of some of these methods of control (such as geometry, interaction…) to ensure the nuclear criticality safety of a unit may lead to a requirement to limit geometrical dimensions. These geometrical dimensions are called nuclear criticality safety dimensions.

This International Standard provides guidance and recommendations related to the verification of the compliance between the geometrical dimensions of the unit specified in design (design dimensions) or as-built dimensions with the nuclear criticality safety dimensions specified in the nuclear criticality safety assessment. The stages presented in this International Standard are summarized in the flow diagram in annex A.

This International Standard is applicable to nuclear facilities and to transport of fissile material. This International Standard is applicable to applications for which nuclear criticality safety is achieved by limiting geometrical dimensions. The exception for this is for nuclear power reactor cores and dimensions defining the geometry of fuel assemblies, fuel rods and fuel pellets.

This International Standard does not specify requirements related to the control of material compositions.

The Quality Assurance associated with the fabrication and layout of the unit and to the control of correct unit fabrication based on specifications (e.g. drawings) is a prerequisite of this International Standard and ensures the consistency between the unit geometry and its general purpose and its intended functioning. Nuclear criticality safety requirements are defined and controlled under the Quality Assurance system.

NOTE An example of this standard application is presented in annex B. Normative reference