Cold functional tests are carried out to confirm whether components and systems important to safety are properly installed and ready to operate in a cold condition. The main purpose of these tests is to verify the leak-tightness of the primary circuit and components - such as pressure vessels, pipelines and valves of both the nuclear and conventional islands - and to clean the main circulation pipes. The tests mark the first time the reactor systems are operated together with the auxiliary systems.

"The primary circuit pressure boundary of the unit was intact and well sealed, marking the full transition of the nuclear power unit from the installation stage to the commissioning stage," CGN said.

In May 2015, the National Energy Administration approved the project to carry out site protection and related demonstration work at San'ao. On 2 September 2020, the executive meeting of the State Council approved the construction of units 1 and 2 as the first phase of the plant. China's National Nuclear Safety Administration issued a construction permit for the two units on 30 December that year and first concrete for unit 1 was poured the following day. The first concrete for San'ao 2 was poured on 30 December 2021.

San'ao 1 and 2 are scheduled to begin supplying electricity in 2026 and 2027, respectively.

The San'ao plant is the first nuclear power project in China's Yangtze River Delta region to adopt the Hualong One reactor design. A total of six Hualong One units are planned for the San'ao site. In August this year, China's State Council approved the construction of San'ao Phase II (units 3 and 4).

"After all of them are put into commercial operation, they will provide more than 54 billion kilowatt-hours of clean energy each year to Zhejiang Province and even the Yangtze River Delta region, which is close to the annual electricity consumption of Wenzhou City in 2023," CGN noted. "It can reduce standard coal consumption by more than 16 million tonnes and carbon dioxide emissions by more than 44 million tonnes each year, which is equivalent to afforestation of 110,000 hectares."

The San'ao project marks the first Chinese nuclear power project involving private capital, with Geely Technology Group taking a 2% stake in the plant. China General Nuclear (CGN) holds 46% of the shares of the project company Cangnan Nuclear Power, with other state-owned enterprises holding the remainder.