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Safety Injection System example images
The APR1400 reactor's safety systems consist of a Safety Injection System (SIS), an In-containment Refueling Water Storage Tank (IRWST), the Safety Depressurization and Vent System (SDVS), the Containment Spray System (CSS), and the Auxiliary Feed Water System (AFWS).
The main design concept of the SIS is simplification and redundancy to allow the APR1400 reactor to achieve higher reliability and better performance than conventional plants. The SIS is comprised of four independent mechanical trains without a tie line among the injection paths and two electrical divisions. Each train has one active Safety Injection Pump (SIP) and one passive Safety Injection Tank (SIT) equipped with a Fluidic Device (FD). To ensure the simplicity and independence of the SIS, the common header installed in the SIS lines of the conventional plant has been eliminated. This design allows the separation of the functions of the SIS and the Shutdown Cooling System (SCS).
The passive flow regulator, the FD, is installed in the SIT. The basic concept of the FD is vortex flow resistance. When water flows through the stand pipe, which is installed in a rectangular direction with the exit nozzle, it creates low vortex resistance and a high flow rate. When the water level is below the top of the stand pipe, the inlet flow is switched to the control ports which are installed in a tangential direction with the exit nozzle, thus leading to high vortex resistance and a low flow rate. In this light, the SIT discharges a large amount of water to fill the reactor vessel lower plenum rapidly when the water level is above the stand pipe. However, when the water level is below the stand pipe, the SIT injects a relatively small amount of water over a long period of time. The FD installed in the SIT takes the place of the low pressure SIPs, thus leading to the elimination of the low pressure SIP.
The In-containment Refueling Water Storage Tank (IRWST) is located inside the containment and the arrangement is made in such a way that the injected emergency cooling water returns to the IRWST. This design removes the operator action of switching the suction of SIP from the IRWST to the containment recirculation sump, as is required in conventional plants. This new design lowers the susceptibility of IRWST to external hazards. The IRWST provides the following functions: storing refueling water, a water source for the SIS, shutdown cooling system, and containment spray system, which is a heat sink that condenses steam discharged from the pressurizer for rapid depressurization if necessary. This prevents the emission of high pressure molten corium and enables feed and bleed operation. The IRWST also allows coolant to be supplied to the cavity flooding system which mitigates molten corium concrete interaction in case of severe accidents.
Fluidic Device example images
Through adopting the advanced features of the FD in SIT and the IRWST, the high pressure injection, low pressure injection, and recirculation modes of the conventional SIS are merged into one safety injection operation. The SIS is designed to allow safety water to be injected directly into the reactor vessel so that the discharge of injected flow through the broken cold leg is eliminated.
The Safety Depressurization and Vent System (SDVS) is a dedicated safety system designed to provide a safe means of depressurizing the Reactor Coolant System (RCS) in the event that the pressurizer spray is unavailable during plant cooldown to cold shutdown and to rapidly depressurize the RCS to initiate the feed and bleed method of plant cooldown subsequent to the total loss of feedwater. The Pilot Operated Safety Relief Valves (POSRVs) are employed for feed and bleed operation. Such a system establishes a flow path from the pressurizer steam space to the IRWST.
The Containment Spray System (CSS) consists of two trains and takes the suction of its pump from the IRWST to reduce the containment temperature and pressure during accidents occurring in the containment. The CSS is designed to be interconnected with the Shutdown Cooling System (SCS), which is also comprised of two trains. The pumps of these systems are designed to be of the same type and capacity. This design makes the CSS have a higher level of reliability compared with that of a conventional plant.
The Auxiliary Feed Water System (AFWS) consists of two divisions and four train systems, and supplies feedwater to the Steam Generators (SG)s for RCS heat removal in case of loss of main feedwater. In addition, the AFWS refills the SGs following a Loss of Coolant Accident (LOCA) to minimize leakage through pre-existing tube leaks. The reliability of the AFWS has been increased by the use of two 100% motor-driven pumps, two 100% turbine-driven pumps, and two independent safety-related emergency feedwater storage tanks located in the auxiliary building instead of a condensate storage tank as is found in a conventional plant.

Major Design Characteristics

  • Improved reliability of SIS through the design of four trains mechanical equipment
  • Simplified operation of SIS by merging high pressure injection, low pressure injection, and re-circulation modes into one safety injection mode
  • Lowered susceptibility of IRWST to external hazards by locating IRWST in the containment
  • Enhanced plant safety by adopting advanced features such as the FD in SIT, the IRWST, and the Direct Vessel Injection of SIS
  • Improved reliability of CSS through the interconnected design of the CSS and SCS
  • Increased reliability of AFWS by using two 100% motor-driven pumps, two 100% turbine-driven pumps, and two independent safety-related emergency feedwater storage tanks located in the auxiliary building