This Safety Guide provides recommendations on how to meet the requirements established in IAEA Safety Standards Series No. SSR-2/1 (Rev. 1) in relation to the reactor coolant system and associated systems for nuclear power plants. It is a revision of IAEA Safety Standards Series No. NS-G-1.9, which it supersedes. The publication takes into account developments, experience and practices in the design of nuclear power plants throughout their lifetime. It references and considers other IAEA safety standards that are relevant and related to the design of the reactor coolant system and associated systems for nuclear power plants. Recommendations to achieve the required reliability of the capabilities designed to transfer residual heat to the ultimate heat sink in the different plant states are also included. As those systems are dependent on specific reactor technologies, more appropriate recommendations have been developed respectively for pressurized light water reactors, boiling water reactors and pressurized heavy water reactors.

• 1. INTRODUCTION
  • Background
  • Objective
  • Scope
  • Structure
• 2. Extent of the reactor coolant system and associated systems
  • Reactor coolant system
  • Systems for heat removal in shutdown conditions
  • Systems for coolant inventory control in operational states
  • Systems for control of core reactivity in operational states
  • Systems for core cooling and residual heat removal in accident conditions
  • Systems for control of core reactivity in accident conditions
  • Ultimate heat sink and residual heat transfer systems in all plant states
• 3. DESIGN BASIS OF THE REACTOR COOLANT SYSTEM AND ASSOCIATED SYSTEMS
  • General
  • Safety functions
  • Postulated initiating events
  • Internal hazards
  • External hazards
  • Accident conditions
    • Design basis accidents
    • Design extension conditions without significant fuel degradation
  • Design limits and acceptance criteria
  • Reliability
    • Systems designed to cope with design basis accidents
    • Safety features for design extension conditions without significant fuel degradation
  • Defence in depth
  • Safety classification
  • Environmental qualification of items important to safety
  • Loads and load combinations
  • Materials
    • Materials in contact with radioactive fluids
    • Materials exposed to high neutron flux
  • Manufacturing and installation
  • Calibration, testing, maintenance, repair, replacement, inspection and monitoring
    • Pre-service and in-service inspection of the reactor coolant system
    • Inspection of steam generators
  • Overpressure protection
  • Layout
  • Radiation protection
  • Combustible gas accumulation in normal operation
  • Venting and draining
  • Interfaces between the reactor coolant system and associated systems
  • Containment isolation
  • Instrumentation
  • Multiple units at a site
  • Codes and standards
  • Use of probabilistic analyses in design
• 4. ULTIMATE HEAT SINK AND RESIDUAL HEAT TRANSFER SYSTEMS
  • Ultimate heat sink
  • Residual heat transfer systems
    • Residual heat transfer in operational states
    • Residual heat transfer for design basis accidents
    • Residual heat transfer for design extension conditions
• 5. SPECIFIC CONSIDERATIONS IN DESIGN OF THE REACTOR COOLANT SYSTEM
  • Structural design
  • Design basis loads and load combinations
  • Control of cooling conditions in operational states
  • Pressure control and overpressure protection
  • Isolation of the reactor coolant pressure boundary
  • Postulated initiating events
  • Internal hazards
  • External hazards
  • Layout
  • Design limits
  • Safety classification
  • Environmental qualification
  • Pressure tests
  • Venting
    • For pressurized water reactors
    • For boiling water reactors
    • For pressurized heavy water reactors
  • Specific design aspects
    • Reactor pressure vessel
    • Reactor pressure vessel internals (for PWRs and BWRs)
    • Fuel channel assemblies (for PHWRs)
    • Reactor coolant pumps (for PWRs and PHWRs) and reactor recirculation pumps (for BWRs)
    • Relief and safety valves (for PWRs and PHWRs) or safety relief valves (for BWRs)
    • Steam generators (for PWRs and PHWRs)
    • Piping system
    • Leak before break or break preclusion piping
    • Leak detection system
    • Insulation materials
• 6. SPECIFIC CONSIDERATIONS IN DESIGN OF THE ASSOCIATED SYSTEMS FOR PWR TECHNOLOGY
  • Systems for control of coolant inventory and core reactivity in operational states
    • Control of the coolant inventory
    • Control of core reactivity
  • Systems for heat removal in operational states
    • Heat removal in power operation and hot shutdown modes
    • Residual heat removal mode
  • Systems for core cooling and residual heat removal in accident conditions (excluding design extension conditions with core melting)
    • Core cooling in accident conditions
    • Residual heat removal in hot shutdown modes for design basis accidents
    • Long term removal of residual heat in design basis accidents
    • Residual heat removal in hot shutdown modes for design extension conditions without significant fuel degradation
    • Fast depressurization of the reactor coolant system in design extension conditions with core melting
  • Systems for control of core reactivity in accident conditions
    • Specific design aspects
• 7. SPECIFIC CONSIDERATIONS IN DESIGN OF THE ASSOCIATED SYSTEMS FOR BWR TECHNOLOGY
  • Systems for control of coolant inventory and core reactivity in operational states
    • Reactor water cleanup
  • Systems for heat removal in operational states
    • Isolation condensers (if included in the design)
  • Systems for core cooling and residual heat removal in accident conditions
    • Core cooling in design basis accidents
    • Residual heat removal in design basis accidents
    • Core cooling in design extension conditions
    • Reactor coolant system fast depressurization in design extension conditions with core melting
  • Systems for control of core reactivity in accident conditions
• 8. SPECIFIC CONSIDERATIONS IN DESIGN OF THE ASSOCIATED SYSTEMS FOR PHWR TECHNOLOGY
  • Systems for control of core reactivity in operational states
  • Systems for heat removal in operational states
    • Steam and feedwater system
    • Shutdown cooling system (residual heat removal system)
    • Auxiliary feedwater system
  • Systems for control of core reactivity in accident conditions
    • Reactor shutdown systems
  • Systems for core cooling and residual heat removal in accident conditions
    • Emergency core cooling system
    • Enhanced emergency heat removal system
    • Heat transfer in design extension conditions
    • Moderator system in design extension conditions without significant fuel degradation
    • Provisions for fast depressurization of the primary heat transport system (crash cooldown)
• REFERENCES
• CONTRIBUTORS TO DRAFTING AND REVIEW