Advanced CANDU reactor
The Advanced CANDU reactor (ACR-1000) is a Generation III+ pressurized water reactor design developed by Atomic Energy of Canada Limited (AECL), evolving from the established CANDU technology to deliver approximately 1,200 megawatts of electrical power through a compact core using slightly enriched uranium (SEU) fuel bundles, light water coolant, and a heavy water moderator within a horizontal pressure tube configuration that enables on-power refueling.[1][2] This design incorporates enhanced economic performance via reduced heavy water inventory, improved thermal efficiency, and a smaller footprint compared to earlier CANDU models, while preserving inherent safety traits such as low-pressure operation and two independent shutdown systems.[3][4] Key advancements in the ACR-1000 include a 520-channel core with optimized fuel management for higher burnup and capacity factors exceeding 90%, alongside modular construction to shorten build times and costs, positioning it as a bridge technology for utilities transitioning from fossil fuels amid rising energy demands.[5][6] Safety features emphasize passive cooling, robust containment, and probabilistic risk assessments aligning with international standards, building on decades of CANDU operational data from over 20 reactors worldwide that demonstrate low void reactivity coefficients and rapid shutdown capabilities.[7][8] Development progressed through pre-licensing reviews by the Canadian Nuclear Safety Commission, culminating in a successful design certification in 2011, yet the project faced challenges from AECL's privatization uncertainties and shifting global market preferences toward alternative reactor types, leading to its shelving without commercial deployment.[9][10] Despite this, the ACR-1000's technical innovations influenced subsequent Canadian nuclear R&D, including advanced fuel cycles and small modular reactor concepts, underscoring its role in sustaining expertise for future heavy-water-based systems.[11][12]Historical Development
Origins in CANDU Technology
The CANDU (CANada Deuterium Uranium) reactor design emerged from Canadian nuclear research initiated in the late 1940s at Chalk River Laboratories, building on heavy water moderation technology developed during World War II collaborations and early prototypes like ZEEP (1945) and NRX (1947).[13] This approach prioritized natural uranium fuel to avoid costly enrichment, leveraging heavy water's superior neutron economy for efficient fission without light water's parasitic absorption. The foundational pressure tube architecture—horizontal zirconium-alloy tubes housing fuel bundles, separated from the calandria vessel containing the heavy water moderator—enabled compact cores and on-power refueling, a capability demonstrated in NRU (1957) and formalized in the Nuclear Power Demonstration (NPD) prototype, which achieved first criticality in 1962 and generated 20 MWe commercially from 1963.[13] Subsequent milestones included Douglas Point (200 MWe, operational 1968) and the Pickering Generating Station (four 500 MWe units, 1971–1973), establishing CANDU-6 as a standardized 600+ MWe design exported internationally by the 1980s.[13] The Advanced CANDU Reactor (ACR), exemplified by the ACR-1000, directly inherits these CANDU hallmarks while addressing economic limitations through targeted evolution, drawing on over 450 reactor-years of operational data from 33 units worldwide by the mid-2000s.[2] Core retentions include the horizontal pressure tube calandria with 520 fuel channels in a square lattice, heavy water moderation for neutron efficiency, dual independent shutdown systems (poison and mechanical), and on-power refueling via modular fuel handling, which supports capacity factors exceeding 90% without outages.[1] These features ensure inherent safety via defence-in-depth and low-pressure moderation separated from high-pressure coolant loops, validated empirically across CANDU fleets with zero core melt accidents attributable to design flaws.[1] Key advancements stem from substituting heavy water coolant with pressurized light water, slashing inventory costs by 90% and enabling slightly enriched uranium (SEU) fuel bundles (CANFLEX-ACR design, ~2.4% U-235 enrichment) for higher burnup (~20,000 MWd/tU versus CANDU's ~7,500 MWd/tU natural uranium), thus reducing refueling frequency and waste volume while preserving compatibility with CANDU's fuel cycle infrastructure.[2] Development commenced in the early 2000s under Atomic Energy of Canada Limited (AECL), with basic engineering completed by 2008 targeting 1,100–1,200 MWe output per unit, modular construction for 54-month builds, and enhanced thermal margins informed by CANDU physics modeling and thermal-hydraulics R&D at Chalk River.[1] This progression aligns with Generation III+ standards, incorporating four-quadrant spatial separation of safety systems and modern instrumentation, yet remains grounded in proven CANDU materials like Zr-2.5Nb pressure tubes for corrosion resistance and seismic robustness.[2]Evolution to ACR-1000 Design
The Advanced CANDU Reactor (ACR-1000) represents an evolutionary progression from the established CANDU-6 design, developed by Atomic Energy of Canada Limited (AECL) to address economic pressures in global nuclear markets while preserving core CANDU advantages such as pressure-tube architecture, heavy-water moderation, and on-power refueling capability.[2][1] Drawing on over four decades of operational feedback from CANDU plants, the ACR-1000 incorporates refinements aimed at reducing capital costs by approximately 30% compared to prior generations through minimized heavy water inventory and simplified systems.[1] This evolution was motivated by the need to compete with light-water reactor designs, positioning the ACR-1000 as a Generation III+ reactor with a net output of about 1,100 MWe per unit in a two-unit configuration.[2] A primary design shift involved replacing heavy-water coolant with pressurized light water, which lowers deuterium oxide requirements by over 90% and enables compatibility with conventional steam cycles for higher thermal efficiency.[1][2] Fuel transitioned to slightly enriched uranium (approximately 2.4 wt% U-235) in CANFLEX-ACR bundles, supporting higher burnup rates up to 20,000 MWd/tU and reducing refueling frequency, thereby enhancing fuel cycle economics without sacrificing the natural uranium flexibility inherent to CANDU technology.[1] The core features 520 modular horizontal fuel channels, a more compact arrangement than CANDU-6's vertical bundles, which facilitates shorter construction timelines—targeted at 48-54 months for initial units—and improved seismic resilience through separated calandria and pressure tubes.[1][2] Safety enhancements built on CANDU precedents include two independent shutdown systems, gravity-driven emergency core cooling, and a robust containment structure with a leak rate below 0.2% per day, achieving a core damage frequency of 9.5 × 10^{-8} per reactor-year.[1] These features emphasize defense-in-depth with passive elements like the moderator as a heat sink, while maintaining low-pressure operation to minimize accident escalation risks.[2] Development milestones encompassed pre-licensing reviews by the Canadian Nuclear Safety Commission (CNSC), with Phase 1 completed in February 2009, Phase 2 in August 2009, and the final phase in February 2011, alongside international assessments by the UK and US regulators.[14][9] However, despite basic engineering completion around 2010, the design was not advanced to commercial deployment due to funding constraints and market shifts.[1]Key Milestones and Prototyping Efforts
The Advanced CANDU Reactor (ACR-1000) design emerged in the early 2000s from Atomic Energy of Canada Limited (AECL) as an evolutionary step beyond the CANDU-6, incorporating light-water cooling while retaining heavy-water moderation and pressure-tube architecture to enhance economic viability and fuel efficiency.[2] Development leveraged operational data from over 30 CANDU units, focusing on modular construction and slightly enriched uranium fuel to achieve higher burn-up rates.[1] By 2005, AECL had advanced preliminary engineering, including core optimization for a 1,165 MWe output per unit, with plans for two-unit stations.[2] A pivotal regulatory milestone occurred in 2010 when Canada's Nuclear Safety Commission (CNSC) granted pre-project design approval, confirming the ACR-1000 met fundamental Canadian safety and licensing requirements for new nuclear plants without identified barriers.[15] This followed phases assessing fundamental design principles, safety analyses, and compliance with regulatory expectations. In January 2011, the CNSC completed all three phases of the vendor pre-project design review—the first such full completion for any Generation III+ reactor in Canada—verifying the design's acceptability against national standards.[9] Prototyping efforts emphasized component-level validation rather than full-scale reactor construction, drawing on existing CANDU infrastructure at sites like Chalk River Laboratories. Fuel qualification for the ACR-1000's slightly enriched bundles involved out-reactor performance tests, in-reactor irradiation experiments in operational CANDU reactors, and supporting analyses to confirm behavior under extended burn-up conditions.[16] AECL issued contracts to Canadian manufacturers for prototype components, such as pressure tubes and calandria elements, to support design verification, though no integrated prototype reactor was built.[17] Development stalled post-2011 amid AECL's financial restructuring and lack of firm orders, with the design shelved without advancing to construction or further physical prototyping.[15]Technical Design
Core and Pressure Tube Architecture
The core of the Advanced CANDU Reactor (ACR-1000) utilizes a horizontal pressure tube architecture, an evolutionary feature from earlier CANDU designs that replaces a large reactor pressure vessel with individual Zr-2.5 Nb alloy pressure tubes to contain pressurized light water coolant and fuel bundles. This modular approach facilitates on-power refueling, distributed heat generation, and enhanced fault isolation, as a breach in one tube does not compromise the entire core boundary. The pressure tubes are arrayed within a low-pressure calandria vessel filled with heavy water moderator, which slows neutrons for efficient fission in natural uranium or slightly enriched fuel without requiring a large, high-pressure vessel typical of light water reactors.[1][4] Each fuel channel assembly comprises a central pressure tube, approximately 103 mm in diameter with wall thicknesses optimized for higher operating pressures up to 10 MPa associated with light water cooling, enclosed by a larger Zircaloy-2 calandria tube. Garter springs position the pressure tube centrally within the calandria tube, maintaining a 10-13 mm annular gap filled with helium or CO2 gas for thermal insulation, reducing heat transfer to the moderator, and enabling annulus gas monitoring for early leak detection via radiolytic gas or coolant ingress signals. End fittings seal the channel while permitting fuel handling, and the reduced lattice pitch—approximately 28.6 cm between channels—compacts the core volume by about 40% compared to traditional heavy-water-cooled CANDU units, boosting power density to around 50 kW/L while preserving negative reactivity coefficients.[18][3][19] Advancements in the ACR-1000 pressure tube design include thicker walls (up to 4.5 mm) and improved material properties for delayed hydride cracking resistance, extending operational life beyond 60 years under cyclic loading and neutron fluence up to 10^21 n/cm². The calandria tube, with enhanced corrosion resistance, contains any pressure tube rupture within the moderator boundary, preventing coolant-moderator mixing and maintaining separation of the high-pressure (10 MPa, 310°C) coolant loop from the low-pressure (0.1 MPa, 70°C) moderator. This architecture inherently limits the energy release from a channel failure to the inventory of a single tube—about 0.3 m³ of coolant—minimizing pressure spikes and enabling passive decay heat removal via conduction and radiation across the annulus.[3][18][1]Fuel and Moderation Systems
The fuel for the ACR-1000 consists of uranium dioxide (UO₂) pellets with low-enriched uranium (LEU) at a reference level of 2.4 wt% ²³⁵U, clad in zirconium alloy tubes and assembled into 43-element CANFLEX-ACR bundles.[2][20] This bundle design evolves from the CANFLEX-Mk4 tested in CANDU-6 reactors, incorporating modifications for higher burnup targets of 20,000 MWd/tU and compatibility with light water coolant, while retaining the modular, short-length (approximately 50 cm axial) format for on-power refueling.[2][21] The core holds 520 horizontal pressure tubes, each loaded with 12 bundles, enabling axial shuffling and discharge without reactor shutdown via paired fuelling machines on a bridge system at both reactor faces.[2] Fuel verification processes, including irradiation testing at facilities like the NRU reactor, confirm performance under ACR-specific conditions such as higher coolant density and optimized element spacing to minimize fission gas release and achieve negative coolant void reactivity.[22][18] The moderation system utilizes heavy water (D₂O) in a low-pressure (approximately 0.1 MPa), low-temperature (around 70°C) calandria tank that envelops the fuel channels via concentric calandria tubes, providing neutron thermalization while isolating the moderator from the higher-pressure light water coolant loop.[1] Heavy water's superior moderating efficiency—due to deuterium's lower thermal neutron absorption cross-section (0.0005 barns vs. 0.33 barns for hydrogen)—supports effective neutron economy with LEU fuel, allowing reduced moderator-to-fuel volume ratios compared to natural-uranium designs.[4] The system features a recirculating loop for active cooling and purification, achieving a half-life of under one hour for impurity removal to limit activity buildup, with instrumentation for density, temperature, and level control integrated into the reactor regulating system.[23][24] This dual-fluid approach reduces heavy water inventory by over 60% relative to heavy-water-cooled CANDU predecessors, primarily through tighter lattice spacing enabled by LEU's higher fissile content and light water's higher density, which offsets moderation needs while enhancing core compactness and economic viability.[25] The design maintains separation of moderator and coolant for independent response in transients, with heavy water's thermal capacity aiding heat removal in postulated accidents.[1]Coolant and Heat Transfer Mechanisms
The Advanced CANDU Reactor (ACR-1000) employs light water as the primary coolant, which circulates through horizontal pressure tubes containing slightly enriched uranium fuel bundles, while heavy water functions separately as the moderator within the calandria vessel.[26] This dual-fluid approach leverages the superior moderating properties of heavy water for neutron economy alongside the lower cost and availability of light water for heat removal, reducing overall heavy water inventory by approximately two-thirds compared to traditional CANDU designs.[27] The heat transport system (HTS) features a two-loop configuration in a figure-of-eight arrangement, similar to the CANDU-6 but optimized for higher coolant pressures (approximately 11.1 MPa) and temperatures to enhance thermodynamic efficiency and core power density.[24] Centrifugal pumps drive forced convection flow through the primary circuit, where subcooled light water absorbs fission-generated heat from fuel cladding via single-phase convective heat transfer, maintaining a minimum 1°C subcooling margin to prevent boiling and ensure thermal-hydraulic stability.[18] Coolant velocity and flow distribution are tailored to minimize pressure drops across feeders and headers while maximizing heat extraction from the compact core. Downstream of the core, heated primary coolant enters vertical U-tube steam generators, where it transfers energy across Alloy 800 tubing walls to the secondary-side feedwater via conduction and two-phase boiling convection, producing high-pressure steam (around 6 MPa) for the turbine cycle without direct contact between circuits.[28] [4] This shell-and-tube exchanger design incorporates features like optimized tube bundles and fouling margins to sustain efficient heat transfer coefficients under operational transients, with primary-to-secondary isolation preventing cross-contamination.[26] Overall, the system's reliance on pressurized, single-phase primary flow and latent-heat secondary boiling aligns with proven pressurized water reactor principles, adapted to the pressure-tube architecture for enhanced refueling flexibility.[27]Safety Engineering
Inherent and Passive Safety Features
The ACR-1000 design emphasizes inherent safety characteristics intrinsic to its physics and architecture, which prevent or mitigate accidents without reliance on active intervention or external power. These include a negative power coefficient of reactivity that ensures self-limiting power excursions during loss-of-coolant accidents (LOCAs), thereby capping peak fuel cladding temperatures, alongside a minimized coolant void reactivity effect that balances nuclear feedback mechanisms.[1] The pressure tube configuration, with individual horizontal tubes separated from the low-temperature, low-pressure heavy water moderator, inherently limits the consequences of localized failures, as the moderator system serves as a decoupled thermal sink capable of absorbing decay heat through conduction and natural convection even in severe scenarios.[2] This separation enhances overall stability, drawing from established CANDU principles while adapting to light water coolant for improved neutron economy and reduced heavy water inventory.[1] Passive safety features in the ACR-1000 leverage natural forces such as gravity, buoyancy, and stored thermal capacity to achieve core cooling, shutdown, and containment integrity without electrical power or operator action. Natural circulation drives coolant flow in the heat transport system (HTS) for post-trip cooldown, core refilling after a LOCA, and sustained fuel cooling, complemented by gravity-fed emergency coolant injection from dedicated tanks.[29] [1] Key heat sinks include the heavy water moderator tank, which passively removes decay heat via the calandria tubes, and the light water-filled reactor vault and shield tank, providing extended thermal mass for beyond-design-basis events; these are augmented by the Reserve Water System (RWS), which supplies gravity-driven makeup water to steam generators, containment sprays, and ECC subsystems.[2] [29] Shutdown capabilities incorporate two independent, fast-acting systems classified under the design's defence-in-depth strategy: Shutdown System 1 (SDS1) deploys gravity-dropped neutron-absorbing rods into the moderator upon trip signal from 2-out-of-4 channels, while Shutdown System 2 (SDS2) injects gadolinium nitrate poison into the moderator via high-pressure vessels, ensuring rapid reactivity suppression with diverse physical principles and minimal common-mode vulnerabilities.[2] [1] Emergency core cooling (ECC) relies on passive high-pressure injection followed by long-term recirculating cooling through natural circulation loops, while containment employs a steel-lined concrete structure with passive spray systems for pressure and hydrogen management, achieving a design leak rate of 0.2% volume per day at peak pressure.[1] These elements, integrated with four-quadrant physical separation of safety trains, yield probabilistic risk assessments indicating core damage frequencies below 10^{-7} per reactor-year for at-power and shutdown states.[1]Shutdown and Containment Systems
The Advanced CANDU Reactor (ACR-1000) employs two independent, diverse, and fast-acting shutdown systems (SDS1 and SDS2) to achieve rapid reactor shutdown under both normal and accident conditions. SDS1 drives solid shut-off rods into the reactor core via gravity-assisted deployment triggered by electromagnetic release, while SDS2 injects a gadolinium-based neutron-absorbing liquid poison directly into the moderator using high-pressure pumps.[30][5] These systems are physically separated, with dedicated instrumentation, power supplies, and control logic to prevent common-mode failures, and both can be initiated automatically by trip parameters or manually from the main control room.[1] Hard-wired voting logic ensures deterministic operation without reliance on software, enhancing reliability during transients.[1] For sustained post-shutdown control, the ACR-1000 design includes a Guaranteed Shutdown State (GSS) mechanism using dedicated long-term shutdown rods inserted into the core, maintaining subcriticality even under assumed failures of the primary SDS. This rod-based GSS supplements the liquid injection capabilities of SDS2, providing diversity in shutdown modes and ensuring core reactivity remains negative for extended periods without operator intervention.[31] Empirical modeling confirms that poison injection in SDS2 achieves shutdown within seconds, with distribution verified through computational fluid dynamics simulations accounting for moderator flow dynamics.[32] The containment system comprises a steel-lined, pre-stressed concrete reactor building designed to withstand internal pressures from design-basis accidents, such as a large-break loss-of-coolant event, without exceeding leak-tightness criteria.[19] Automatic isolation valves and dampers seal all penetrations upon containment isolation signals, with fail-safe positioning to close in the event of power loss or support system failure.[1] Building air coolers facilitate post-accident pressure and temperature reduction through natural circulation, while access airlocks maintain structural integrity during maintenance. Probabilistic safety assessments indicate core damage frequencies below 10^{-7} per reactor-year, attributable in part to the robustness of this containment envelope integrated with emergency core cooling.[33]Empirical Safety Performance Data
The Advanced CANDU Reactor (ACR-1000), having never progressed beyond the design and pre-licensing stages, lacks any operational empirical safety performance data from actual deployment. Its safety projections derive from probabilistic safety assessments (PSAs) and simulations building on the parent CANDU technology, rather than real-world incident records.[1][34] Commercial CANDU power reactors, operational since 1971, have accumulated over 2,000 reactor-years across approximately 20 units in Canada and additional exported designs in countries including Argentina, India, Romania, and South Korea, without any core damage accidents or significant off-site radiological releases attributable to reactor failure.[35] This record contrasts with global nuclear incidents like Three Mile Island (1979 partial meltdown) and Chernobyl (1986 explosion), neither of which involved CANDU designs. Minor events, such as pressure tube inspections or feeder pipe inspections in the 1990s at Ontario stations, were addressed through regulatory-mandated retrofits without impacting public health or plant integrity.[36][37] Canadian Nuclear Safety Commission (CNSC) oversight data indicate that CANDU units maintain safety performance metrics comparable to or exceeding international benchmarks, with forced outage rates due to safety systems averaging below 1% annually and no Level 4+ events on the International Nuclear Event Scale (INES) for power reactors.[37] Critics, including environmental groups, have highlighted potential vulnerabilities like feeder cracking or tritium releases during routine operation, but empirical evidence shows these managed within design limits, with tritium emissions below regulatory thresholds (e.g., annual public dose <0.1 mSv from Canadian stations).[38][34] Overall, the technology's two independent shutdown systems and separate moderator/coolant loops have contributed to this low incident profile, informing ACR design enhancements like improved emergency core cooling.[39]Economic Analysis
Capital Investment Requirements
The Advanced CANDU Reactor (ACR-1000), developed by Atomic Energy of Canada Limited (AECL), incorporated design modifications aimed at reducing capital investment relative to predecessor CANDU-6 units, which had an overnight capital cost estimated at approximately $2,972 per kW in 2005 assessments for new builds.[40] AECL projected capital cost reductions of 25% or more for nth-of-a-kind (NOAK) ACR-1000 units through optimizations such as a compact core with higher power density (1.8 MWe per fuel channel versus 1.5 for CANDU-6), elimination of heavy water coolant in favor of light water to minimize inventory expenses, and modular construction enabling shorter critical paths.[3] These features were intended to yield an overall overnight cost competitive with contemporary Generation III reactors, potentially in the $2,000–$2,500 per kW range for serial production, though exact figures varied by site-specific factors like labor and regulatory approvals.[41] Construction timelines were a key lever for capital efficiency, with first-of-a-kind (FOAK) schedules projected at 54 months from first concrete to commercial operation, compressing to 48 months for NOAK units via prefabricated modules and simplified systems like CANFLEX-ACR fuel bundles supporting higher burnup and fewer refuelings.[1] Additional savings stemmed from reduced heavy water requirements (4.4 MWe per Mg versus 1.5 for CANDU-6) and enhanced steam parameters for better thermodynamic efficiency, lowering the total plant investment for a nominal 1,200 MWe output.[3] Some analyses suggested up to 40% cost abatement versus CANDU-6 baselines, positioning the ACR-1000 as economically viable for emerging markets with lower domestic engineering overheads.[42] These projections, however, relied on unproven serial deployment and assumed learning curve benefits not realized, as AECL's ACR program faced development impairments totaling $205 million by 2011 due to commercialization uncertainties.[43] Independent critiques highlighted risks of underestimating indirect costs like extended regulatory reviews or supply chain dependencies, common in heavy-water reactor evolutions, rendering actual capital requirements speculative absent built prototypes.[44] No firm contracts materialized to validate the estimates, contributing to the program's suspension in 2011.[45]Operational and Fuel Cycle Costs
The ACR-1000 design incorporated light water as the primary coolant, replacing the heavy water used in conventional CANDU reactors, which was projected to significantly lower operational costs by reducing the inventory and leakage makeup requirements for expensive heavy water and minimizing tritium production and associated handling expenses.[1] Enhanced automation in monitoring, testing, and control systems further supported reduced staffing needs and maintenance downtime, with features enabling on-power access for inspections and repairs to achieve refueling outages limited to once every three years, thereby improving capacity factors toward 90% or higher.[3][18] These elements were intended to yield operation and maintenance (O&M) costs competitive with Generation III+ pressurized water reactors, though exact per-MWh figures remained vendor estimates without operational validation prior to the program's suspension in 2011.[1] The fuel cycle for the ACR-1000 utilized a once-through approach with 37-element bundles of slightly enriched uranium (SEU) at 1.2-1.5% U-235 enrichment, enabling fuel burnup of approximately 18-20 GWd/tU—more than double that of natural uranium CANDU-6 bundles at 7-8 GWd/tU—and resulting in fewer bundles processed annually (about 3,500 versus 4,000 for equivalent CANDU output).[30][1] This higher efficiency offset the added upfront enrichment costs (estimated at low tails assays for economic viability) by reducing overall uranium requirements by up to 20% per unit energy output and generating 30% less spent fuel volume per MWth, which in turn lowered interim storage and disposal burdens.[1] While traditional CANDU natural uranium cycles avoided enrichment entirely, AECL projections indicated the ACR's SEU approach would achieve net fuel cycle costs below those of heavy-water-cooled predecessors through optimized bundle design and reduced handling operations, with potential flexibility for recycled uranium or thorium cycles in future adaptations.[3][4] Vendor analyses positioned the combined O&M and fuel cycle contributions to levelized unit energy cost at around 1-1.5 cents/kWh, subordinate to capital expenses in overall economics.[46]Comparative Economic Metrics
The Advanced CANDU Reactor (ACR-1000) featured design elements intended to align its capital costs more closely with those of light-water reactors, including light-water cooling and slightly enriched uranium fuel to minimize heavy-water inventory expenses. Early estimates placed overnight capital costs at $1,000–$1,500 per kWe for standardized twin-unit deployments.[47] However, Ontario Power Generation's assessments escalated these figures to approximately $2,500/kWe in 2005 and $3,000/kWe by 2007, reflecting site-specific factors and supply chain realities; unconfirmed Atomic Energy of Canada Limited bids for Darlington New Build later approached $10,800/kWe for two units.[48] In comparison, Gen III+ pressurized water reactors like the Westinghouse AP1000 saw initial overnight estimates of $1,000–$2,000/kWe but experienced realizations exceeding $10,000/kWe at U.S. sites such as Vogtle due to regulatory delays and construction inefficiencies, while projected future builds aim for $2,900–$8,300/kWe. The AREVA EPR, another contemporary design, quoted over $7,000/kWe in bids, highlighting that ACR-1000 projections remained within the lower-to-mid range of advanced light-water reactor estimates before program suspension.[48] Operational and maintenance costs for the ACR-1000 were projected to benefit from CANDU heritage features like online refueling, enabling capacity factors above 90% in mature CANDU-6 plants, compared to 85–90% for pressurized water reactors.[49] Fuel cycle economics favored the ACR design, with costs estimated at $4.00/MWh for the related ACR-700 variant versus higher enriched-uranium expenses for pressurized water reactors, where fuel constitutes up to 70% more of total unit energy costs despite lower volume needs.[50][51] This stemmed from the ACR's use of slightly enriched uranium, reducing fabrication and enrichment outlays relative to standard 3–5% enriched fuel in PWRs, while retaining flexibility for natural uranium. Overall levelized unit energy costs for CANDU systems, including advanced variants, were deemed competitive with PWRs when fuel represents 30% of total expenses, though capital-intensive builds amplified financing sensitivities in both technologies.[51]| Metric | ACR-1000 Estimate | AP1000 (Projected/Realized) | Key Notes |
|---|---|---|---|
| Overnight Capital ($/kWe) | $1,000–$3,000 (early); up to $10,800 (late bids) | $2,900–$8,300 (future); >$10,000 (Vogtle) | ACR aimed for LWR parity via reduced heavy water; escalations common across designs due to FOAK risks.[47][48] |
| Fuel Cost ($/MWh) | ~$4.00 (ACR variant) | Higher by ~70% relative | ACR leverages SEU/natural U efficiency; PWRs offset by burnup gains.[50][51] |
| Capacity Factor (%) | >90 (projected from CANDU ops) | 85–90 | Online refueling advantage for ACR/CANDU.[49] |