Overview - EN ISO 7753:2025 (ISO 7753:2023)
EN ISO 7753:2025 provides requirements and guidance for the use of Criticality Accident Alarm Systems (CAAS) during operations at nuclear facilities. It applies to operations with fissile materials outside nuclear reactors but within the boundaries of nuclear establishments and is intended for cases where a need for CAAS has already been established (see informative Annex C). The standard focuses on the operational use of CAAS - detection, alarm, positioning, testing, resilience and management of unavailability - while CAAS design details are covered by IEC 60860. It is concerned primarily with gamma and neutron radiation rate‑sensing systems, though integrating and single‑type detector systems are addressed as equivalent options.
Key topics and technical requirements
- Scope of application: Operations handling or storing fissile material outside reactors within nuclear sites.
- Primary function: Prompt detection of criticality accidents and activation of alarms to enable rapid evacuation and reduce personnel dose.
- Detection types: Gamma and neutron rate‑sensing systems; integrating systems and single‑type detectors can be used where appropriate.
- Detection criterion & MAC: Guidance on defining detection criteria and the Minimum Accident of Concern (MAC) is provided (informative Annex A).
- Positioning and coverage: Criteria and principles for detector placement and definition of detection zones (Annex B).
- System resilience: Management of unavailability, detector failures, false alarms, obsolescence and spare parts.
- Alarm & connections: Requirements for alarm signalling, interconnections and supervising arrangements.
- Testing and familiarization: Procedures for periodic testing, acceptance and personnel familiarization to support effective emergency response.
- Exclusions: Administrative process details (see ISO 14943) and nuclear accident dosimetry/personnel exposure evaluations are outside the scope.
Practical applications and users
This standard is intended for:
- Nuclear facility operators and safety managers responsible for on‑site operations with fissile material.
- Radiation protection and criticality safety specialists who implement CAAS operational procedures.
- Emergency planners and trainers who develop evacuation and response actions linked to CAAS alarms.
- Regulators and auditors assessing compliance with operational criticality alarm practices.
Typical applications include chemical separations, fuel fabrication, storage and handling facilities where a CAAS has been deemed necessary to protect personnel.
Related standards
- IEC 60860 - CAAS design and equipment requirements
- ISO 11320 - Emergency preparedness and response for criticality events
- ISO 14943 - Management system and administrative steps for criticality safety
- ISO 1709, ISO 16117, ISO 21391 - Related criticality safety and radiation protection guidance
EN ISO 7753:2025 helps bridge operational practice and technical CAAS design, supporting timely detection and evacuation during criticality accidents while integrating with existing nuclear safety and emergency preparedness standards.