Super module installed at Haiyang 3

The tank, which holds up to 500,000 gallons - nearly 2 million litres - of borated water, is positioned above the reactor, and relies on gravity as the only driving force needed to release water to keep the reactor core cool should the reactor experience an unexpected shutdown.

The CA02 and CA03 structural steel modules are known as super modules because they are too large to transport and require on-site assembly. The CA03 module - assembled from 17 sub-modules - is more than 35 metres long, 12 metres tall and weighs about 228 tonnes. The CA02 is about 12 metres tall and weighs over 50 tonnes.

The CA03 module of Haiyang 3 was installed on 31 May - 31 days ahead of schedule, China National Nuclear Corporation announced.

The CA03 module in place within unit 3's containment building (Image: CNNC)

The first safety-related concrete was poured for the nuclear island of Haiyang unit 3 in July 2022. It marked the official start of construction of the first of two CAP1000 pressurised water reactors - the Chinese version of the Westinghouse AP1000 - planned as Phase II of the site, which is already home to two AP1000 units. Construction of Haiyang 4 began in April this year.

The Shanghai Nuclear Engineering Research and Design Institute noted that the planned construction period for Haiyang 3 and 4 was 56 months, so the two units "are scheduled to be fully operational in 2027".