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Section 4.5.9, Safety systems and safety support systems

The information submitted in the application should demonstrate that the safety systems (as defined in REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9]) ensure the safe shutdown of the reactor or the residual heat removal from the core, or limit the consequences of AOOs and DBAs. The application should describe how the safety support system supports the operation of one or more safety systems.

Means of shutdown

The application should describe the means of reactor shutdown, reducing reactor power to a low value, and maintaining that power for the required duration, when the reactor power control system and the inherent characteristics are insufficient or incapable of maintaining reactor power within the requirements of the SOE.

Systems and components supporting emergency core cooling functions

The application should describe the systems and components that support the emergency core cooling functions. Systems that supply electrical power or cooling water to equipment used in the operation of emergency core cooling should be considered as a safety support system.

The applicant should ensure that, if injection of emergency coolant is required, an operator cannot easily prevent the injection from taking place.

The application should demonstrate that reactor facility safety would not be affected even if all or part of emergency core cooling was operated inadvertently.

Systems and components supporting emergency heat removal functions

The application should describe the systems and components that support the emergency heat removal functions, which provide for removal of residual heat in order to meet fuel design limits and reactor coolant boundary condition limits in accordance with section 8.8 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

If emergency heat removal is required to mitigate the consequences of a DBA, then the emergency heat removal functions should be designed as a safety system.

The applicant should demonstrate that, during DECs, the emergency heat removal systems and components will function as required.

Systems and components supporting confinement and containment functions

The application should describe the systems and components supporting confinement and containment functions in place to minimize the release of radioactive materials to the environment during operational states and DBAs. The confinement and containment functions should also assist in mitigating the consequences of design-extension conditions (DECs). Confinement or containment functions should be part of the safety system and may include complementary design features. The application should cover the full spectrum of operational states and accident conditions and should include applicable codes and standards, in accordance with section 8.6 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The description should describe, as appropriate, the following information about the systems and components supporting confinement and containment functions:

  • heat removal system 
  • functional design of the secondary containment
  • isolation system
  • ventilation system
  • penetrations
  • protection against overpressure and under-pressure
  • control of combustible gas
  • venting provisions
  • spray system
  • leakage testing system

The application should address the design basis requirements for each of the systems identified above. It should also include a schematic presentation of the containment envelope showing the containment boundary for each operational state.

Safety support system

The information submitted should demonstrate that the safety support systems ensure the fundamental safety functions are available in operational states, DBAs and DECs. The design should include emergency safety support systems to cope with the possibility of loss of normal service and, where applicable, concurrent loss of backup systems.

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