Advanced CANDU Reactor
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The Advanced CANDU Reactor (ACR) is a Generation III+ design and is an evolutionary development of existing CANDU reactors designed by Atomic Energy of Canada Limited. It is a light-water-cooled reactor that incorporates features of both Pressurised heavy water reactors (PHWR) and Advanced Pressurized Water Reactors (APWR) technologies. It uses a similar design concept to the Steam Generating Heavy Water Reactor (SGHWR).
The design uses slightly enriched uranium (SEU) fuel, light water coolant, and a separate heavy water moderator. The reactivity regulating and safety devices are located within the low pressure moderator. The ACR also incorporates characteristics of the CANDU design, including on-power refueling with the CANFLEX fuel system; a long prompt neutron lifetime; small reactivity holdup; two fast, totally independent, dedicated safety shutdown systems; and an emergency core cooling system. The use of SEU fuel allows the reduction of coolant void reactivity coefficient to a small, negative value. The compact reactor core design reduces core size by half for the same power output over the older design.
The current size for the ACR-1000 is approximately 1200MWe. According to the AECL website, the ACR-1000 is planned to be in service by 2016. [1]
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[edit] 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. [2]
Safety Shutdown System 1 (SDS1): SDS1 is designed to rapidly and automatically terminate reactor operation. Neutron-absorbing rods (control rods that introduce negative reactivity) are stored inside of 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 90% of gross reactor heat output is reduced within 2 seconds.
Safety Shutdown System 2 (SDS2): SDS2 is also designed to rapidly and automatically terminate reactor operation. Gadolinium nitrate (GdNO3), a neutron absorbing liquid that introduces negative reactivity, is stored inside of channels that feed into horizontal nozzle assemblies. Each nozzle assembly contains high-speed electronically-controlled valves, 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 nozzle assemblies into the Calandria heavy-water moderator. The result is that 90% of gross reactor heat output is reduced within 2 seconds.
Reserve Water System (RWS): The RWS consists of a storage system located at a high elevation within the reactor building, and is designed to provide an emergency source of water for use in cooling an ACR that has suffered a Loss of Coolant Accident (LOCA). As well, the RWS can be utilized to 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 system-related functions under both operating & accident conditions. It contains seismically-qualified, redundant divisions of standby generators, batteries and distribution hardware.
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.
[edit] Operational Cost
The ACR has a planned lifetime capacity factor of greater than 93%. This is achieved by a three year planned outage frequency, with a 21-day planned outage duration and 1.5% per year forced outage. Quadrant separation allows flexibility for on-line maintenance and outage management. A high degree of safety system testing automation also reduces cost.
