The safety systems that will be employed in the CANDU-SCWR will be based on those employed in the ACRTM design [3]. However, an additional passive safety system that utilizes the separation between moderator and coolant in the CANDU design will also be used with enhancements that are expected to significantly reduce the probability of core damage.

IX — 2.1. ACR Passive safety systems

These systems are described elsewhere in this document for the ACR-1000 design. Differences between the CANDU-SCWR and the ACR-1000 will be taken into consideration when selecting which of these systems will be selected in the reference CANDU-SCWR design. For example, the reserve water system (RWS) will not be used to provide cooling via the steam generators since the CANDU-SCWR uses a direct cycle. Implementation of the following ACR passive safety systems in the CANDU-SCWR is currently under evaluation:

™ ACR™ (Advanced CANDU Reactor™) is a trademark of Atomic Energy of Canada Ltd (AECL).

a) Two independent shutdown systems: these consist of shutoff rods and liquid injection shutdown systems. Both systems are located in the low pressure moderator system and are driven either by gravity (spring-assisted shutoff rods) or pressurized gas (poison liquid injection).

b) Emergency coolant injection (ECI) system: the ECI system consists of accumulator tanks filled with make-up water and pressurized by compressed gas to provide emergency cooling when the core pressure falls below the pressure of the accumulators.

c) Reserve water system (RWS): this system provides gravity-driven cooling water from the reserve water tank (RWT) to several systems such as the containment spray cooling system and the moderator cooling system.

d) Containment cooling system: this system consists of containment cooling spray and is actuated automatically for any event resulting in pressures or temperatures that challenge the integrity of the containment. Once actuated, operation of the sprays relies only on gravity to deliver water from the RWT to the spray headers, which are located at a high elevation in the reactor building. Spray nozzles connected to the spray headers diffuse the cooling water into fine droplets, which fall through the containment atmosphere [3].