Advanced CANDU Reactor - Safety Systems

Safety Systems

The ACR-1000 design currently calls for a variety of safety systems, most of which are evolutionary derivatives of the systems utilized on the CANDU 6 reactor design. Each ACR requires both SDS1 & SDS2 to be online and fully operational before they will operate at any power level.

Safety Shutdown System 1 (SDS1): SDS1 is designed to rapidly and automatically terminate reactor operation. Neutron-absorbing rods (control rods that shut down the nuclear chain reaction) are stored inside isolated channels located directly above the reactor vessel (Calandria) and are controlled via a triple-channel logic circuit. When any 2 of the 3 circuit paths are activated (due to sensing the need for emergency reactor trip), the direct current-controlled clutches that keep each control-rod in the storage position are de-energized. The result is that each control-rod is inserted into the Calandria, and the reactor heat output is reduced by 90% within 2 seconds.

Safety Shutdown System 2 (SDS2): SDS2 is also designed to rapidly and automatically terminate reactor operation. Gadolinium nitrate (GdNO₃) solution, a neutron-absorbing liquid that shuts down the nuclear chain reaction, is stored inside channels that feed into horizontal nozzle assemblies. Each nozzle has an electronically controlled valve, all of which are controlled via a triple-channel logic circuit. When any 2 of the 3 circuit paths are activated (due to sensing the need for emergency reactor trip), each of these valves are opened and liquid GdNO₃ is injected through the nozzles to mix with the heavy-water moderator liquid in the reactor vessel (Calandria). The result is that the reactor heat output is reduced by 90% within 2 seconds.

Reserve water system (RWS): The RWS consists of a water tank located at a high elevation within the reactor building. This provides water for use in cooling an ACR that has suffered a Loss of Coolant Accident (LOCA). The RWS can also provide emergency water (via gravity-feed) to the steam generators, moderator system, shield cooling system or the heat transport system of any ACR.

Electrical power supply system (EPS): The EPS system is designed to provide each ACR unit with the required electrical power needed to perform all safety functions under both operating & accident conditions. It contains seismically qualified, redundant standby generators, batteries and distribution switchgear.

Cooling water system (CWS): The CWS provides all necessary light water (H₂O) required to perform all safety system-related functions under both operating & accident conditions. All safety-related portions of the system are seismically qualified and contain redundant divisions.