Advanced CANDU Reactor
Encyclopedia
The Advanced CANDU Reactor (ACR) is a Generation III+
nuclear reactor design and is a further development of existing CANDU reactors designed by Atomic Energy of Canada Limited
. The ACR is a light-water-cooled reactor that incorporates features of both Pressurised Heavy Water Reactors (PHWR) and Advanced Pressurized Water Reactor
s (APWR) technologies. It uses a similar design concept to the Steam Generating Heavy Water Reactor (SGHWR).
The design uses lightly enriched uranium (LEU)
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; a long prompt neutron
lifetime; small reactivity holdup; two fast, totally independent, dedicated safety shutdown systems; and an emergency core cooling system (although all generation 2, 3, and 3+ designs have this feature). The compact reactor core
reduces core size by half for the same power output over the older design.
The fuel bundle is a variant of the 43-element CANFLEX design (CANFLEX-ACR). The use of LEU fuel with a neutron absorbing centre element allows the reduction of coolant void reactivity coefficient
to a nominally small, negative value. It also results in higher burnup operation than traditional CANDU designs.
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.
The reactors are intended for use in nuclear power plant
s to produce nuclear power
from nuclear fuel
.
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.
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.
.
AECL was marketing the ACR-1000 as part of the UK's Generic Design Process but pulled out in April 2008. CEO Hugh MacDiarmid is quoted as stating, ""We believe very strongly that our best course of action to ensure the ACR-1000 is successful in the global market place is to focus first and foremost on establishing it here at home."
Generation III reactor
A generation III reactor is a development of any of the generation II nuclear reactor designs incorporating evolutionary improvements in design developed during the lifetime of the generation II reactor designs...
nuclear reactor design and is a further development of existing CANDU reactors designed by Atomic Energy of Canada Limited
Atomic Energy of Canada Limited
Atomic Energy of Canada Limited or AECL is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory...
. The ACR is a light-water-cooled reactor that incorporates features of both Pressurised Heavy Water Reactors (PHWR) and Advanced Pressurized Water Reactor
Advanced Pressurized Water Reactor
Westinghouse Electric Company's AP1000 reactor design is the first Generation III+ reactor to receive final design approval from the U.S. Nuclear Regulatory Commission ....
s (APWR) technologies. It uses a similar design concept to the Steam Generating Heavy Water Reactor (SGHWR).
The design uses lightly enriched uranium (LEU)
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...
fuel, light water coolant, and a separate heavy water
Heavy water
Heavy water is water highly enriched in the hydrogen isotope deuterium; e.g., heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction...
moderator. The reactivity regulating and safety
Nuclear safety
Nuclear safety covers the actions taken to prevent nuclear and radiation accidents or to limit their consequences. This covers nuclear power plants as well as all other nuclear facilities, the transportation of nuclear materials, and the use and storage of nuclear materials for medical, power,...
devices are located within the low pressure moderator. The ACR also incorporates characteristics of the CANDU design, including on-power refueling with the CANFLEX
CANFLEX
CANFLEX; the name is derived from its function: CANDU FLEXible fuelling, is an advanced fuel bundle design developed by Atomic Energy of Canada Ltd. , along with the Korean Atomic Energy Research Institute for use in CANDU design nuclear reactors...
fuel; a long prompt neutron
Prompt neutron
In nuclear engineering, a prompt neutron is a neutron immediately emitted by a nuclear fission event, as opposed to a delayed neutron decay which can occur within the same context, emitted by one of the fission products anytime from a few milliseconds to a few minutes later.-Principle:Using U-235...
lifetime; small reactivity holdup; two fast, totally independent, dedicated safety shutdown systems; and an emergency core cooling system (although all generation 2, 3, and 3+ designs have this feature). The compact reactor core
Nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...
reduces core size by half for the same power output over the older design.
The fuel bundle is a variant of the 43-element CANFLEX design (CANFLEX-ACR). The use of LEU fuel with a neutron absorbing centre element allows the reduction of coolant void reactivity coefficient
Void coefficient
In nuclear engineering, the void coefficient is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids form in the reactor moderator or coolant...
to a nominally small, negative value. It also results in higher burnup operation than traditional CANDU designs.
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.
The reactors are intended for use in nuclear power plant
Nuclear power plant
A nuclear power plant is a thermal power station in which the heat source is one or more nuclear reactors. As in a conventional thermal power station the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.Nuclear power plants are usually...
s to produce nuclear power
Nuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
from nuclear fuel
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...
.
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
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....
) 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
Gadolinium nitrate
Gadolinium nitrate is an inorganic compound of gadolinium. It is used as a water-soluble neutron poison in nuclear reactors. Gadolinium nitrate, like all nitrates, is an oxidizing agent.-Use:...
(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.
Operational Cost
The ACR has a planned lifetime capacity factorCapacity factor
The net capacity factor or load factor of a power plant is the ratio of the actual output of a power plant over a period of time and its potential output if it had operated at full nameplate capacity the entire time...
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.
Future Prospects
The ACR-1000 has been submitted as part of Ontario's request for proposal (RFP). Bruce Power, which has acquired Alberta Energy, is also considering it for deployment in Western Canada, both for power generation, or for steam generation (used in processing oil sands). The province of New Brunswick has accepted a proposal for a feasibility study for an ACR-1000 at Point LepreauPoint Lepreau Nuclear Generating Station
Point Lepreau Nuclear Generating Station is a Canadian nuclear power station located 2 km northeast of Point Lepreau, New Brunswick. The facility was constructed between 1975-1983 by NB Power, the provincially-owned public utility....
.
AECL was marketing the ACR-1000 as part of the UK's Generic Design Process but pulled out in April 2008. CEO Hugh MacDiarmid is quoted as stating, ""We believe very strongly that our best course of action to ensure the ACR-1000 is successful in the global market place is to focus first and foremost on establishing it here at home."