Key commissioning tests completed at Tianwan 7

Hot functional tests involve increasing the temperature of the reactor coolant system and carrying out comprehensive tests to ensure that coolant circuits and safety systems are operating as they should. Carried out before the loading of nuclear fuel, such testing simulates the thermal working conditions of the power plant and verifies that nuclear island and conventional equipment and systems meet design requirements.

China National Nuclear Corporation (CNNC) said the completion of hot tests on 30 December “lays a solid foundation for subsequent work such as nuclear fuel loading and grid connection”.

Cold functional tests – which are conducted to confirm whether components and systems important to safety are properly installed and ready to operate in a cold condition – were completed at Tianwan 7 in July 2025. The main purpose of those tests – which marked the first time the reactor systems were operated together with the auxiliary systems – was to verify the leak-tightness of the primary circuit.

In June 2018, Russia and China signed four agreements, including for the construction of two VVER-1200 reactors as units 7 and 8 of the Tianwan plant. Construction of unit 7 began in May 2021, with that of unit 8 starting in February 2022. The units are scheduled to be put into commercial operation in 2026 and 2027, respectively.

_{Tianwan units 7 and 8 (Image: CNNC)}

The Tianwan nuclear power plant is owned and operated by Jiangsu Nuclear Power Company, a joint venture between CNNC (50%), China Power Investment Corporation (30%) and Jiangsu Guoxin Group (20%).

The first four units at the Tianwan site – which began commercial operation between June 2007 and December 2018 – are Gidropress VVER units supplied by Russia, as will be the seventh and eighth. Units 5 and 6 both feature Chinese ACPR1000 reactors.

“Subsequently, Tianwan Nuclear Power Plant Unit 7 will proceed with nuclear fuel loading and grid connection according to plan, with commercial operation scheduled for 2026; the construction of Tianwan Nuclear Power Plant Unit 8 is also progressing smoothly according to plan,” CNNC said.