Mitsubishi Heavy Industries delivers steam generators for Cruas 2

Mitsubishi Heavy Industries has completed delivery of three replacement steam generators to EDF for installation at Unit 2 of the Cruas nuclear power station in southeastern France. The major components are intended to replace existing equipment within the 900 MWe pressurised water reactor during a future maintenance outage.

The company announced the delivery on 15 October 2026. Manufacturing of the generators was completed at its Kobe facilities in January 2024, and the equipment subsequently obtained the required French conformity certification in February 2026 before being transported to France.

EDF ordered the equipment in 2019 from Mitsubishi Heavy Industries and Onet Technologies. The wider programme covers nine replacement steam generators, of which the three delivered for Cruas Unit 2 constitute the first group. Six additional units remain under manufacture for delivery from 2028 onwards.

The delivery milestone should not be confused with installation or commissioning. Reaching the customer and obtaining conformity documentation are prerequisites for subsequent work, but neither establishes that the equipment has entered operation at Cruas.

Each generator is approximately 21 metres tall and weighs about 330 tonnes. It contains around 4,500 heat transfer tubes made from TT690 alloy, a material selected for resistance to corrosion mechanisms relevant to pressurised water reactor steam generator service.

A steam generator transfers heat from the reactor’s primary coolant system to a separate secondary circuit. This arrangement allows a pressurised water reactor to generate steam for its turbine while keeping the primary and secondary coolant circuits physically separated.

Water in the primary circuit passes through the reactor and absorbs heat produced by nuclear fission. It is maintained under high pressure to prevent bulk boiling under normal operating conditions, then circulates through the steam generator tubes where thermal energy moves through the tube walls.

Water in the secondary circuit receives this heat and produces steam that can drive the turbine. The turbine converts the energy in the steam into rotational mechanical energy, which drives an electrical generator connected through the plant’s electrical systems.

The separation of the circuits makes tube integrity particularly important. A defect in a steam generator tube can compromise the barrier between the reactor coolant system and the secondary water, requiring inspection, assessment and appropriate remedial measures.

The approximately 4,500 tubes provide a large heat transfer surface within each vessel. Heat transfer depends on surface area, tube material, temperature differences and fluid conditions, while the mechanical design must accommodate high pressures and thermal changes during operation.

TT690 is a heat-treated nickel-based alloy used in steam generator tubing to improve resistance to certain forms of corrosion. Its selection does not eliminate the need for routine inspection or establish an unrestricted service life for the replacement equipment.

MHI reports that the main vessel uses low-alloy steel. Fabrication of components of this size involves demanding welding, dimensional control and inspection procedures, together with documented conformity to the requirements applicable to nuclear pressure equipment.

The French certification obtained in February 2026 concerns the conformity of the supplied steam generators. It is not a statement that all future installation work has already been approved or that Cruas Unit 2 can return to service without further checks.

EDF has described transport of the steam generators to the Cruas-Meysse site following their arrival at Fos-sur-Mer. Moving vessels weighing hundreds of tonnes requires specially planned handling and transport arrangements, including assessments of route geometry and structural loading.

The generators are scheduled for installation during the fourth ten-year inspection of Cruas Unit 2, expected to begin in early 2027. EDF has indicated that the replacement operation is expected to take approximately four months and involve about 400 people working in shifts.

These timings and workforce numbers describe planned activities. They should not be used to imply that the three components were installed or tested inside the reactor building during 2026.

Replacement of a steam generator requires careful management of the interfaces with the primary coolant system and secondary steam and feedwater pipework. The plant must first be placed in the appropriate condition for equipment isolation, removal and installation.

Once the existing equipment has been removed, the replacement components must be positioned and connected to the relevant circuits. Mechanical installation must then be followed by inspections and tests appropriate to the pressure boundaries, associated equipment and operating arrangements.

The power station’s subsequent return to service will depend on completion of the outage programme and the requirements applying to its continued operation. No operating performance benefit from the new units can yet be measured, because they have not been reported as installed and commissioned.

France’s pressurised water reactor fleet requires periodic inspection and renewal of major components as plants age. Steam generator replacement is a significant undertaking because the equipment is closely integrated with both the reactor coolant circuit and the turbine steam system.

MHI reports that its cumulative steam generator orders exceed 130 units across domestic and international markets. That manufacturing background establishes experience in supplying such equipment, but is distinct from the project-specific acceptance and installation requirements for Cruas 2.

The next milestone for the three delivered generators will be their replacement of existing equipment during the planned 2027 outage. The six remaining units under the wider EDF order are on a separate manufacturing and delivery timetable beginning in 2028.