The Advanced CANDU reactor (ACR), or ACR-1000, was a proposed Generation III+ nuclear reactor design, developed by Atomic Energy of Canada Limited (AECL). It combined features of the existing CANDU pressurised heavy water reactors (PHWR) with features of light-water cooled pressurized water reactors (PWR). From CANDU, it took the heavy water moderator, which gave the design an improved neutron economy that allowed it to burn a variety of fuels. It replaced the heavy water cooling loop with one containing conventional light water, reducing costs. The name refers to its design power in the 1,000 MWe class, with the baseline around 1,200 MWe. [1]
The ACR-1000 was introduced as a lower-priced option compared to a larger version of the baseline CANDU which was being designed, the CANDU 9. ACR was slightly larger but less expensive to build and run. The downside was that it did not have the flexibility of fuels that the original CANDU design offered, and would no longer run on pure unenriched uranium. This was a small price to pay given the low cost of enrichment services and fuel in general.
AECL bid the ACR-1000 on several proposals around the world but won no contests. The last serious proposal was for a two-reactor expansion of the Darlington Nuclear Generating Station, but this project was canceled in 2009 when the price was estimated to be three times what the government was budgeting. With no other sales prospects, in 2011 the AECL reactor design division was sold to SNC-Lavalin to provide services to the existing CANDU fleet. Development of the ACR ended. [2]
The original CANDU design used heavy water as both the neutron moderator and the coolant for the primary cooling loop. It was believed that this design would result in lower overall operating costs due to its ability to use natural uranium for fuel, eliminating the need for enrichment. At the time, it was believed there would be hundreds and perhaps thousands of nuclear reactors in operation by the 1980s, and in that case the cost of enrichment would become considerable.
Further, the design used both pressurized and unpressurized sections, the latter known as a "calandria", which it was believed would lower construction costs compared to designs that used highly pressurized cores. In contrast to typical light-water designs, CANDU did not require a single large pressure vessel, which was among the more complex parts of other designs. This design also allowed it to be refuelled while it was running, improving the capacity factor, a key metric in overall performance.
However, the use of natural uranium also meant the core was much less dense compared to other designs, and much larger overall. It was expected this additional cost would be offset by lower capital costs on other items, as well as lower operational costs. The key trade-off was the cost of the fuel, in an era when enriched uranium fuel was limited and expensive and its price was expected to rise considerably by the 1980s.
In practice, these advantages did not work out. The high expected fuel costs never came to be; when reactor construction stalled at around 200 units worldwide, instead of the expected thousands, fuel costs remained steady as there was ample enrichment capability for the amount of fuel being used. This left CANDU in the unexpected position of selling itself primarily on the lack of need for enrichment and the possibility that this presented a lower nuclear proliferation risk.
ACR addresses the high capital costs of the CANDU design primarily by using low-enrichment uranium (LEU) fuel. This allows the reactor core to be built much more compactly, roughly half that of a CANDU of the same power. Additionally, it replaces the heavy water coolant in the high-pressure section of the calandria with conventional "light" water. This greatly reduces the amount of heavy water needed, and the cost of the primary coolant loop. Heavy water remains in the low-pressure section of the calandria, where it is essentially static and used only as a 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, independent, safety shutdown systems; and an emergency core cooling system.
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 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. [3]
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 (Gd(NO3)3) 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 Gd(NO3)3 solution 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.
Emergency 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. [ citation needed ]
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.
Bruce Power considered ACR in 2007 for deployment in Western Canada, both for power generation, or for steam generation to be used in processing oil sands. In 2011, Bruce Power decided not to move forward with this project. [4]
In 2008, the province of New Brunswick accepted a proposal for a feasibility study for an ACR-1000 at Point Lepreau. This led to a formal bid by Team Candu, consisting of AECL, GE Canada, Hitachi Canada, Babcock & Wilcox Canada and SNC-Lavalin Nuclear, which proposed using a 1085 MWe ACR-1000. Nothing further came of this bid. It was later replaced by a mid-2010 bid by Areva, a bid that also lapsed. [2]
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." [5]
The ACR-1000 was submitted as part of Ontario's request for proposal (RFP) for the Darlington B installation. Ultimately, AECL was the only company to place a formal bid, with a two-reactor ACR-1000 plant. The bids required that all contingencies for time and budget overruns be considered in the plans. The resulting bid was $26 billion for a total of 2,400 MWe, or over $10,800 per kilowatt. This was three times what had been expected, and called "shockingly high". As this was the only bid, the Ministry of Energy and Infrastructure decided to cancel the expansion project in 2009. [6]
In 2011, with no sales prospects remaining, the Canadian government sold AECL's reactor division to SNC-Lavalin. In 2014, SNC announced a partnership with the China National Nuclear Corporation (CNNC) to support sales and construction of the existing CANDU designs. Among these was a plan to use their two CANDU-6 reactors in a recycling scheme under the name Advanced Fuel CANDU Reactor (AFCR). [7] [8] However, these plans did not proceed. SNC and CNNC subsequently announced collaboration on a Heavy Water Reactor, also based on legacy CANDU technology, and unrelated to the Advanced Heavy Water Reactor being developed in India. [9]
The CANDU is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide moderator and its use of uranium fuel. CANDU reactors were first developed in the late 1950s and 1960s by a partnership between Atomic Energy of Canada Limited (AECL), the Hydro-Electric Power Commission of Ontario, Canadian General Electric, and other companies.
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. When a fissile nucleus like uranium-235 or plutonium-239 absorbs a neutron, it splits into lighter nuclei, releasing energy, gamma radiation, and free neutrons, which can induce further fission in a self-sustaining chain reaction. The process is carefully controlled using control rods and neutron moderators to regulate the number of neutrons that continue the reaction, ensuring the reactor operates safely, although inherent control by means of delayed neutrons also plays an important role in reactor output control. The efficiency of nuclear fuel is much higher than fossil fuels; the 5% enriched uranium used in the newest reactors has an energy density 120,000 times higher than coal.
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants. In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms. The heated, high pressure water then flows to a steam generator, where it transfers its thermal energy to lower pressure water of a secondary system where steam is generated. The steam then drives turbines, which spin an electric generator. In contrast to a boiling water reactor (BWR), pressure in the primary coolant loop prevents the water from boiling within the reactor. All light-water reactors use ordinary water as both coolant and neutron moderator. Most use anywhere from two to four vertically mounted steam generators; VVER reactors use horizontal steam generators.
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely more susceptible than fast neutrons to propagate a nuclear chain reaction of uranium-235 or other fissile isotope by colliding with their atomic nucleus.
NRX was a heavy-water-moderated, light-water-cooled, nuclear research reactor at the Canadian Chalk River Laboratories, which came into operation in 1947 at a design power rating of 10 MW (thermal), increasing to 42 MW by 1954. At the time of its construction, it was Canada's most expensive science facility and the world's most powerful nuclear research reactor. NRX was remarkable both in terms of its heat output and the number of free neutrons it generated. When a nuclear reactor such as NRX is operating, its nuclear chain reaction generates many free neutrons. In the late 1940s, NRX was the most intense neutron source in the world.
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons, as opposed to slow thermal neutrons used in thermal-neutron reactors. Such a fast reactor needs no neutron moderator, but requires fuel that is relatively rich in fissile material when compared to that required for a thermal-neutron reactor. Around 20 land based fast reactors have been built, accumulating over 400 reactor years of operation globally. The largest was the Superphénix sodium cooled fast reactor in France that was designed to deliver 1,242 MWe. Fast reactors have been studied since the 1950s, as they provide certain advantages over the existing fleet of water-cooled and water-moderated reactors. These are:
Atomic Energy of Canada Limited (AECL) is a Canadian Crown corporation and the largest nuclear science and technology laboratory in Canada. AECL developed the CANDU reactor technology starting in the 1950s, and in October 2011 licensed this technology to Candu Energy.
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. Net reactivity in a reactor depends on several factors, one of which is the void coefficient. Reactors in which either the moderator or the coolant is a liquid will typically have a void coefficient which is either negative or positive. Reactors in which neither the moderator nor the coolant is a liquid will have a zero void coefficient. It is unclear how the definition of "void" coefficient applies to reactors in which the moderator/coolant is neither liquid nor gas.
The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reactors are the most common type of nuclear reactor, and light-water reactors are the most common type of thermal-neutron reactor.
ZED-2 is a zero-power nuclear research reactor built at the Chalk River Laboratories in Ontario, Canada. It is the successor to the ZEEP reactor. Designed by AECL for CANDU reactor support, the unit saw first criticality on 7 September 1960. The reactor is still operating at Chalk River where it is used for reactor physics and nuclear fuel research.
The supercritical water reactor (SCWR) is a concept Generation IV reactor, designed as a light water reactor (LWR) that operates at supercritical pressure. The term critical in this context refers to the critical point of water, and should not be confused with the concept of criticality of the nuclear reactor.
The Steam Generating Heavy Water Reactor (SGHWR) was a United Kingdom design for commercial nuclear reactors. It uses heavy water as the neutron moderator and normal "light" water as the coolant. The coolant boils in the reactor, like a boiling water reactor, and drives the power-extraction steam turbines.
The Douglas Point Nuclear Generating Station was Canada’s first full-scale nuclear power plant and the second CANDU pressurised heavy water reactor. Its success was a major milestone and marked Canada's entry into the global nuclear power scene. The same site was later used for the Bruce Nuclear Generating Station.
Nuclear power in Canada is provided by 19 commercial reactors with a net capacity of 13.5 gigawatt (GW), producing a total of 95.6 terawatt-hours (TWh) of electricity, which accounted for 16.6% of the country's total electric energy generation in 2015. All but one of these reactors are located in Ontario, where they produced 61% of the province's electricity in 2019. Seven smaller reactors are used for research and to produce radiopharmaceuticals for use in nuclear medicine.
The Whiteshell Reactor No. 1, or WR-1, was a Canadian research reactor located at AECL's Whiteshell Laboratories (WNRL) in Manitoba. Originally known as Organic-Cooled Deuterium-Reactor Experiment (OCDRE), it was built to test the concept of a CANDU-type reactor that replaced the heavy water coolant with an oil substance. This had a number of potential advantages in terms of cost and efficiency.
Carolinas–Virginia Tube Reactor (CVTR), also known as Parr Nuclear Station, was an experimental pressurized tube heavy water nuclear power reactor at Parr, South Carolina in Fairfield County. It was built and operated by the Carolinas Virginia Nuclear Power Associates. CVTR was a small test reactor, capable of generating 17 megawatts of electricity. It was officially commissioned in December 1963 and left service in January 1967.
A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for a pressurized water reactor (PWR). While heavy water is very expensive to isolate from ordinary water (often referred to as light water in contrast to heavy water), its low absorption of neutrons greatly increases the neutron economy of the reactor, avoiding the need for enriched fuel. The high cost of the heavy water is offset by the lowered cost of using natural uranium and/or alternative fuel cycles. As of the beginning of 2001, 31 PHWRs were in operation, having a total capacity of 16.5 GW(e), representing roughly 7.76% by number and 4.7% by generating capacity of all current operating reactors.
Candu Energy Inc. is a Canadian wholly owned subsidiary of Montreal-based AtkinsRéalis, specializing in the design and supply of nuclear reactors, as well as nuclear reactor products and services. Candu Energy Inc. was created in 2011 when parent company SNC-Lavalin purchased the commercial reactor division of Atomic Energy of Canada Limited (AECL), along with the development and marketing rights to CANDU reactor technology.
An organic nuclear reactor, or organic cooled reactor (OCR), is a type of nuclear reactor that uses some form of organic fluid, typically a hydrocarbon substance like polychlorinated biphenyl (PCB), for cooling and sometimes as a neutron moderator as well.
The IPHWR-700 is an Indian pressurized heavy-water reactor designed by the NPCIL. It is a Generation III reactor developed from earlier CANDU based 220 MW and 540 MW designs. It can generate 700 MW of electricity. Currently there are two units operational, 6 units under construction and 8 more units planned, at a cost of ₹1.05 lakh crore (US$13 billion).
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