Generation III+ unit features passive containment cooling system
The three steel rings forming the walls of the main containment vessel have been hoisted into place at Unit 3 of the Sanmen nuclear power station in Zhejiang province, eastern China.
Sanmen-3 is the first CAP1000 nuclear plant under construction in China. The CAP1000 is China’s version of the Westinghouse AP1000.
Generation II pressurised water reactor unit containment buildings had a double wall with a steel liner inside and the concrete protection structure outside. Containment buildings for the Generation III+ AP1000 and CAP1000 have seen some significant changes.
According to the US Nuclear Regulatory Commission, one of the main changes is that the liner is not attached to the concrete walls in the portion above 40 metres.
The space between the inner steel vessel – made of stainless steel with a wall thickness of about 4.5 centimetres in most sections – and the outer reinforced concrete protection wall is reserved for air flow in exchange with the outside environment and a water film flow that cools the steel containment through natural convection and evaporation in case of a severe accident.
This system, called the passive containment cooling system, is designed to work in a similar way as a wet cooling tower works. It was developed by Westinghouse for the AP1000.
Installation of the three rings was completed on 5 June, the Shanghai Nuclear Engineering Research and Design Institute announced. The total hoisting weight was about 826 tonnes.
The Sanmen station is already home to two commercially operational Westinghouse AP1000 units – Sanmen-1 and Sanmen-2. They began commercial operation in 2018.
First concrete was poured for Sanmen-3 in June 2022. In March 2023, first concrete was poured for the nuclear island of Sanmen-4, also a CAP1000 unit.
According to International Atomic Energy Agency data, China has 25 nuclear plants under construction. It has 56 plants in operation that generated a 4.9% share of electricity production in 2023.
