The objectives of nuclear criticality safety are to prevent a self-sustained nuclear chain reaction. This Safety Guide provides guidance and recommendations on how to meet the relevant requirements for ensuring subcriticality when dealing with fissile material and for planning the response to criticality accidents. The recommendations address how to ensure subcriticality in systems involving fissile materials during normal operation and during credible abnormal conditions, from initial design through commissioning, operation and decommissioning. This publication also provides recommendations on identification of credible abnormal conditions; performance of criticality safety assessments; verification, benchmarking and validation of calculation methods; safety measures to ensure subcriticality; and management of criticality safety. The guidance and recommendations are applicable to both regulatory bodies and operating organizations.

• 1. INTRODUCTION
  • Background
  • Objective
  • Scope
  • Structure
• 2. THE APPROACH TO ENSURING CRITICALITY SAFETY
  • General considerations for ensuring criticality safety
  • Subcritical limits and safety margins
  • Exemption criteria for fissile material
  • Management system for criticality safety
    • Management responsibility
    • Resource management
    • Process implementation
    • Measurement, assessment, evaluation and improvement
• 3. MEASURES FOR ENSURING CRITICALITY SAFETY
  • General principles for ensuring criticality safety
    • Defence in depth
    • Passive safety
    • Fault tolerance
  • Safety functions and safety measures for criticality safety
    • Control parameters for criticality safety
    • Factors affecting subcriticality
  • Engineered safety measures for criticality safety
    • Passive engineered safety measures for criticality safety
    • Active engineered safety measures for criticality safety
  • Administrative safety measures for criticality safety
    • General considerations for administrative safety measures for criticality safety
    • Operating procedures
    • Responsibilities and authorities for criticality safety
  • Implementation and reliability of criticality safety measures
• 4. CRITICALITY SAFETY ASSESSMENT
  • General considerations for criticality safety assessment
  • Performance of a criticality safety assessment
    • Defining the reference fissile medium
    • Defining the processes and operations involving the fissile material
    • Defining the methodology for conducting the criticality safety assessment
    • Verifying and validating the calculation methods
    • Performing and documenting the criticality safety analyses
• 5. CRITICALITY SAFETY FOR SPECIFIC PRACTICES
  • Criticality safety in uranium conversion and enrichment
  • Criticality safety in fuel fabrication and reconversion
    • Fissile material cross-over
    • Machining, grinding and cutting of fissile material
    • Handling and storage of fresh fuel
  • Criticality safety in spent fuel operations before reprocessing, long term storage or disposal
    • Events during the handling of spent fuel
    • Maintaining spent fuel geometry
    • Loss of soluble or fixed absorbers
    • Changes in storage arrangements within a spent fuel facility
    • Misloading events involving spent fuel
    • Taking account of changes in spent fuel composition as a result of irradiation
    • Burnup credit
  • Criticality safety in fuel reprocessing
    • The wide range of forms of fissile material in fuel reprocessing facilities
    • Mobility of solutions and the potential for their misdirection in fuel reprocessing facilities
    • Maintaining chemistry control in fuel reprocessing facilities
    • Holdup and accumulation of fissile material in fuel reprocessing facilities
    • Moderator control in furnace operations in fuel reprocessing facilities
  • Criticality safety in radioactive waste management
    • Variation and uncertainty in waste forms
    • Degradation of engineered barriers over long timescales
  • Criticality safety in decommissioning
  • Criticality safety in the transport of fissile material and during the on-site movement of fissile material
  • Criticality safety in research and development laboratories
    • The range of fissile and non-fissile materials in research and development laboratories
    • Overlap of criticality controlled areas and interfaces between materials in research and development laboratories
    • Inadvertent consolidation of fissile material in research and development laboratories
    • Specialized education and training of personnel in research and development laboratories
    • Subcritical assemblies
• 6. EMERGENCY PREPAREDNESS AND RESPONSE TO A CRITICALITY ACCIDENT
  • General considerations for emergency preparedness and response to a criticality accident
  • Functional considerations for emergency preparedness and response to a criticality accident
    • Managing the medical response in the event of a criticality accident
    • Dose estimation for a criticality accident
  • Infrastructural considerations for emergency preparedness and response to a criticality accident
  • Causes and stabilization of a criticality accident
    • Re-entry, rescue and stabilization
  • Criticality detection and alarm systems
    • Performance and testing of criticality detection and alarm systems
• REFERENCES
• Annex BIBLIOGRAPHY
• CONTRIBUTORS TO DRAFTING AND REVIEW