Key commissioning tests completed at Changjiang 4

Such 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 cold functional 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 cold test involves progressively increasing the pressure of the primary loop system, successively completing systematic assessments at pressure levels of 2.7 MPa, 7.0 MPa, 10.0 MPa, 15.4 MPa, 17.13 MPa, and 22.3 MPa.

"As a milestone in the construction of the Hualong One units, the successful completion of this cold test marks the official entry of Unit 4 into the commissioning phase, laying a solid foundation and clearing key obstacles for subsequent hot testing, fuel loading, and grid connection," CNNC said.

Hot functional tests involve increasing the temperature of the reactor coolant system and carrying out comprehensive tests to ensure that coolant circuits and safety systems are operating as they should. Carried out before the loading of nuclear fuel, such testing simulates the thermal working conditions of the power plant and verifies that nuclear island and conventional equipment and systems meet design requirements.

Changjiang units 3 and 4 (Image: CNNC)

Two Hualong One reactors are being constructed in the second phase of the Changjiang plant. First concrete was poured for the base slab of unit 3's nuclear island in March 2021, with that of unit 4 being poured in the December of that year. Changjiang Phase II - units 3 and 4 - represents a total estimated investment of CNY40 billion (USD5.9 billion), according to China Huaneng, which holds a 51% share in the project. Changjiang unit 3 achieved first criticality - a sustained chain reaction - on 10 July and was connected to the grid on 1 August. Both units are scheduled to be fully operational in early 2027.

The Changjiang nuclear site is already home to two operating CNP-600 pressurised water reactors (PWRs) - Changjiang 1 and 2 - which entered commercial operation in 2015 and 2016, respectively. In 2021, CNNC also began construction of a demonstration ACP100 small modular reactor at the site. The multi-purpose 125 MWe PWR - also referred to as the Linglong One - is designed for electricity production, heating, steam production or seawater desalination. It is currently undergoing pre-commissioning tests.

The island province of Hainan is China's southernmost point. Energy policies published in 2019 by Hainan Province Development and Reform Commission specify that nuclear power will become the primary source of electricity for the island, which has a population of close to 10 million.