Inner containment dome in place at Haiyang 4

The steel containment vessel of the CAP1000 - the Chinese version of the Westinghouse AP1000 - consists of six modules: a bottom head, a cylindrical shell (comprising rings one to four), and a top head. It serves as a crucial barrier to prevent the release of radioactive material and is a key component in implementing passive safety functions.

On 6 September, the top head of the containment vessel for Haiyang 4 - manufactured by CNNC Equipment Corporation - was hoisted and precisely positioned on top of the containment structure. The entire process to install the top head - measuring about 40 metres in diameter, 11 metres in height and weighing 658 tonnes - took 3 hours and 22 minutes.

"With this, the initial shape of the reactor building has been realised, and the nuclear island construction has shifted from civil engineering to installation," State Power Investment Corporation (SPIC) said. A steel and concrete outer dome will next be installed over the inner dome.

_{(Image: SPIC)}

The CAP1000 reactor design uses modular construction techniques, enabling large structural modules to be built at factories and then installed at the site. This means that more construction activities can take place at the same time, reducing the time taken to build a plant as well as offering economic and quality control benefits.

"As the contractor of the steel containment vessel, CNNC Equipment Corporation fully implements the concept of 'factory prefabrication and modular construction', prefabricates relevant sub-modules in the production workshop, and completes the assembly, hoisting and installation of the modules at the nuclear power site, greatly improving the efficiency of project construction," SPIC said.

The construction of two CAP1000 reactors at Haiyang - which is already home to two AP1000 units - was approved by China's State Council in April 2022. 

The first safety-related concrete was poured for the nuclear island of Haiyang unit 3 in July 2022. Construction of Haiyang 4 began in April last year. The planned construction period for Haiyang 3 and 4 was 56 months, with the two units scheduled to be fully operational in 2027.