ISO 27467:2009

Overview

ISO 27467 (ISO/FDIS 27467) provides guidance for the analysis of a postulated criticality accident in facilities that handle or process fissile material. The standard defines the scope and essential study areas for criticality accident analysis - including scenario definition, neutronics, dosimetry, detection and alarm siting, airborne release assessment, and emergency preparedness. Note: ISO 27467 does not apply to nuclear power plants and does not prescribe detailed administrative or regulatory criteria, which remain the responsibility of public authorities.

Key topics and technical requirements

The standard recommends a structured analysis that addresses the following technical topics:

• Accident scenario definition

  • Identify credible postulated scenarios (e.g., double batching, procedural violations, reduced effectiveness of neutron absorbers).
  • Specify fissile material, process type (aqueous, high-temperature, mixtures), geometry and chronology of events.

• Neutronics and accident physics

  • Estimate total reactivity insertion, insertion kinetics, first power spike and total number of fissions.
  • Use calculation codes or simplified/experimental models; validate models and recognize uncertainties.

• Criticality accident dosimetry

  • Calculate neutron and gamma fields, individual and collective doses.
  • Use results to define evacuation zones, alarm thresholds, and medical response needs.

• Detection and alarm systems

  • Determine optimal detector locations based on first-spike characteristics and dose distributions.
  • Ensure compliance with ISO 7753 (performance and testing for criticality detection and alarm systems).

• Airborne releases and environmental impact

  • Estimate radionuclide release rates (gases, aerosols, suspendable particulates) driven by accident kinetics.
  • Assess public and environmental radiological consequences.

• Emergency preparedness and response

  • Define required emergency actions, dosimetry-based triage, system shutdown or stabilization, public protection and liaison with authorities.

The standard includes an informative flow diagram (Annex A) that links scenario definition, neutronics, dosimetry, detection and emergency planning.

Practical applications and users

ISO 27467 is intended for professionals involved in nuclear criticality safety and emergency planning:

• Criticality safety specialists and neutronics engineers
• Facility operators and safety managers in fuel processing, research and storage facilities (non-power plants)
• Health physicists and emergency responders
• Designers of criticality alarm and detection systems
• Regulators and auditors assessing preparedness for credible criticality contingencies

Use ISO 27467 to structure postulated criticality accident studies, optimize detector siting, quantify radiological impact, and support emergency response planning.

Related standards

• ISO 7753 - Nuclear energy: performance and testing requirements for criticality detection and alarm systems (normative reference for alarm siting and performance).

Keywords: ISO 27467, nuclear criticality safety, criticality accident analysis, neutronics, criticality alarms, dosimetry, emergency preparedness, airborne releases.