The top section of the steel inner containment vessel has been installed at unit 4 of China’s Haiyang NPP in Shandong province. The steel containment vessel consists of six modules: a bottom head, a cylindrical shell (comprising rings one to four), and a top head. It is a key barrier to prevent the release of radioactive material and is part of the passive safety system.
The top head of the containment vessel – manufactured by CNNC Equipment Corporation – was lifted and positioned precisely on top of the containment structure. The entire process took 3 hours and 22 minutes. The 658-tonne top head is about 40 metres in diameter and 11 metres in height.
“With this step, the initial shape of the reactor building has been realised, and construction of the nuclear island has shifted from civil engineering to installation,” said State Power Investment Corporation (SPIC). A steel and concrete outer dome will now be installed over the inner dome.
The Haiyang NPP hosts two AP1000 reactors (units 1&2), which entered commercial operation in 2018 and 2019, with two CAP1000 reactors (units 3&4) – the Chinese version of the Westinghouse AP1000 – under construction. Unit 1 of the Haiyang plant entered commercial operation in October 2018, with unit 2 following in January 2019. Construction of units 5&6 received official approval in April.
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 several construction activities can take place at the same time, reducing the time taken to build the 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’,” SPIC said. “It prefabricates relevant sub-modules in the production workshop, and completes the assembly, hoisting and installation of the modules at the site, greatly improving the efficiency of project construction.”
