ATMEA1 main features

3D View of the ATMEA1 Nuclear Island


The ATMEA1 reactor was designed with the aim to develop a medium-power reactor that is safer and more reliable than others available on the market today. Its generation III+ design combines proven technology used in the EDF Group EPR and MHI APWR models with our improvements in current design features and specifications.

A next-generation design built on proven technology

The ATMEA1 reactor encompasses the following design features:

  • Thermal output: 3,300 MWth
  • Electrical output: ~1,200 MWe (net)
  • Design availability factor: 92% throughout plant lifecycle (target)
  • Core: 157 fuel assemblies
  • Primary system: three-loop configuration
  • Safety injection: three independent safety trains with 100% capacity and passive advanced accumulators
  • Safety Cooling Chain Systems: additional diversified safety train (Div X) with 100% capacity
  • Severe accident mitigation: core catcher, dedicated cooling system and hydrogen re-combiners for long-term containment integrity
  • Emergency power supply: three independent systems + one backup train + one diversified additional alternative AC power system
3D View of the ATMEA1 reactor

A wide range of economic and environmental benefits

The ATMEA1 design maximizes pressurized water reactor (PWR) performance to deliver the following benefits:

  • Fuel economy and waste reduction
  • High thermal efficiency (up to 37%)
  • Reduced decommissioning burden thanks to a 60-year service life
  • Long fuel cycles and short refueling outages for a high availability factor (>92% over plant lifecycle)
  • Advanced operational flexibility (load follow and frequency control capability)
  • Adaptability to different grid requirements (50 or 60Hz)
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The reactor building is protected by a 1.8-meter-thick reinforced, pre-stressed concrete shell with an internal steel liner. An annular space in the lower part collects all potential leakages from containment penetrations. Redundant mechanical and electrical safety systems with 100% capacity are strictly separated into three divisions. An additional backup train enables on-power maintenance for all other trains, providing the following systems:

  • Essential service water
  • Component cooling water
  • Emergency power system
  • Corresponding support systems
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The three-loop configuration constitutes the reactor’s coolant system. The reactor coolant system is comprised of the following:

  • Reactor pressure vessel
  • Steam generator (one per loop)
  • Pressurizer
  • Reactor coolant pumps (one per loop)
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The reactor pressure vessel integrates all the latest design improvements from EDF Group and MHI, including the following:

  • Top-mounted, in-core instrumentation
  • Enhanced mechanical characteristics of vessel material, including brittle fracture resistance
  • Flow distribution device to homogenize flow at the core inlet
  • Baffling structure equipped with a heavy neutron reflector that improves fuel economy and ensures reactor pressure vessel over a 60-year service life
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The vertical shell and natural circulation heat exchangers fitted with an axial economizer provide increased steam pressure. This steam generator:

  • Enhances heat exchange efficiency,
  • Increases outlet steam pressure,
  • Resists primary stress corrosion by using alloy 690 TT tubes,
  • Increases time available to counteract water loss due to larger water volume stored.
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The pressurizer comprises a series of control systems designed to maintain system pressure. This system provides the following:

  • Controls to accommodate positive and negative pressure surges
  • Pressure relief valves to depressurize the reactor coolant system in the event of an accident
  • Extended time to counteract any abnormal operating situation thanks to the pressurizer’s larger size
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Driven by air-cooled, three-phase induction motors, these vertical assemblies consist of the following:

  • Motor
  • Seal assembly
  • Stand Still seal against station black out
  • Hydraulic unit
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Reactor coolant pipes connect the reactor pressure vessel, steam generators, pressurizer and reactor coolant pumps. Cooling pipes are made of forged austenitic stainless steel with integrated nozzles and designed to minimize the number of welds. Instruments are installed to monitor the following:

  • Flow
  • Temperature
  • Pressure
  • Chemical composition
  • Radiation
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The control modes and control channels allow for a high amount of flexibility in normal operation, including the following:

  • Frequency control (up to 15% variation)
  • Load following capability between 25% and 100% of power (normal escalation rate of 1% to 3% per minute, and up to 5% per minute to reach 100% power in case of emergency need)
  • House load operation capability without reactor trip in case of degraded grid conditions
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The core design enables various fuel management systems to best fit operator needs. Fuel cycle length is from 12 to 24 months. Fuel options range from uranium to full MOX cores. The ATMEA1 design is compliant with international regulations.

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