ISO 21391-2019 PDF

Full title and description

ISO 21391:2019 — Nuclear criticality safety — Geometrical dimensions for subcriticality control — Equipment and layout. This International Standard provides requirements, guidance and recommendations for determining and controlling geometrical limits (subcriticality dimensions) of equipment and layout used to ensure subcritical configurations in facilities handling fissile materials.

Abstract

This document addresses the determination of limits on subcriticality dimensions and their compliance with design dimensions or actual measured dimensions. It is applicable to nuclear facilities containing fissile materials (excluding nuclear power reactor cores) and can also be applied to the transport of fissile materials outside nuclear establishment boundaries. The standard does not cover control of material composition or geometry of fuel assemblies, fuel rods or pellets; it emphasizes the role of quality assurance in fabrication and layout.

General information

• Status: Published (confirmed current after systematic review).
• Publication date: 12 August 2019.
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 27.120.30 (Fissile materials and nuclear fuel technology).
• Edition / version: Edition 1 (2019).
• Number of pages: 14.

Scope

ISO 21391:2019 applies to the control of subcriticality by defining and verifying geometrical dimension limits for equipment and layout in facilities that handle fissile materials, except for nuclear power reactor cores. It may also be applied to the transport of fissile materials outside nuclear establishment boundaries. The standard excludes subcriticality controls specifically based on fuel assembly, fuel rod or fuel pellet geometries and does not set requirements on material composition control; it assumes an established quality-assurance program for fabrication and layout.

Key topics and requirements

• Definition and determination of subcriticality dimension limits for equipment and layouts (design dimensions versus actual dimensions).
• Methods for demonstrating compliance of equipment and installation with specified geometrical limits.
• Exclusions: fuel-assembly/rod/pellet geometry controls and composition control are outside the document's remit.
• Emphasis on quality assurance in fabrication and layout to ensure consistency between actual geometry and design intent.
• Guidance flow (staged approach and worked example annexes) to support application in practice.

Typical use and users

Primary users are nuclear criticality safety engineers, facility designers and engineers, safety assessors, QA personnel, regulatory reviewers and designers of packaging and transport arrangements for fissile materials. Typical uses include setting and verifying design and installation tolerances, preparing criticality-safety documentation and applying geometric controls as part of a broader criticality-safety program (in conjunction with principles from ISO 1709 and related criticality standards).

Related standards

Standards commonly used together with ISO 21391 include ISO 1709 (Principles of criticality safety in storing, handling and processing of fissile materials), ISO 22946 (Criticality safety for solid waste), ISO 11320 (Emergency preparedness and response for criticality accidents) and ISO 23133 (Criticality-safety training for operations). These documents form part of the ISO/TC 85/SC 5 portfolio addressing nuclear criticality safety.

Keywords

nuclear criticality safety; subcriticality dimensions; geometrical limits; fissile materials; equipment layout; quality assurance; ISO/TC 85; criticality control; transport of fissile material.

FAQ

Q: What is this standard?

A: ISO 21391:2019 is an ISO International Standard that provides guidance, requirements and recommendations for determining and controlling geometrical dimensions used to ensure subcritical conditions in equipment and facility layouts that handle fissile materials.

Q: What does it cover?

A: It covers determination of limits on subcriticality dimensions, methods to demonstrate compliance with design or actual dimensions, and recommended QA considerations. It excludes fuel assembly/rod/pellet geometry controls and material-composition requirements.

Q: Who typically uses it?

A: Criticality safety engineers, facility designers, QA staff, safety assessors, regulators and transport/package designers involved with fissile materials. It is used in design reviews, safety cases and installation verification.

Q: Is it current or superseded?

A: ISO 21391:2019 is published and, following a systematic review, was confirmed current (ISO indicates it was last reviewed/confirmed in 2024); it remains the current edition.

Q: Is it part of a series?

A: It is part of the body of ISO documents produced by ISO/TC 85/SC 5 on nuclear criticality safety and is intended to be used alongside foundational and complementary standards such as ISO 1709, ISO 22946 and ISO 11320.

Q: What are the key keywords?

A: Subcriticality, geometrical dimensions, fissile materials, equipment layout, criticality control, quality assurance, transport of fissile material.