China's Candu reactor sets new record

The first unit of the Qinshan III nuclear power plant, located near Shanghai in China's Zhejiang province, was shut down as planned on 1 May after 738 days of uninterrupted operation. The plant set a new record for the longest continuous operation of a power reactor in China and a world record for the operating duration of a Candu-6 reactor.

During its latest operating campaign, which began on 24 April 2023, Qinshan III unit 1 supplied more than 12.5 TWh of electricity. The amount of electricity supplied is equivalent to reducing standard coal consumption by 3.8 million tonnes and cutting carbon dioxide emissions by 9.97 million tonnes, according to the plant's majority owner, China National Nuclear Corporation (CNNC).

Global use of Candu-6 reactors

A total of nine Candu-6 reactors are in operation worldwide. They are located at the Cernavoda plant in Romania (units 1 and 2), the Embalse plant in Argentina, Canada's Point Lepreau plant, China's Qinshan III plant (units 1 and 2), and South Korea's Wolsong plant (units 2-4).

Candu reactors are pressurised heavy water reactors (PHWRs). They are designed so that some fuel assemblies can be replaced without shutting down the entire reactor. The world record for continuous nuclear reactor operation is currently held by Darlington 1 in Canada, also a PHWR design, which was shut down on 5 February 2021 after 1106 days of operation.

History and future of the Qinshan III units

Units 1 and 2 at the Qinshan III plant use Candu-6 heavy water reactor technology. Atomic Energy of Canada Limited (AECL) was the main contractor for the turnkey project. Construction of the plant began in 1997. The first unit started up in September 2002 and the second in April 2003.

Both reactors are now nearing the end of their original 30-year design life. The operator, Third Qinshan Nuclear Power Company, has therefore launched a refurbishment programme for the reactors and their associated fuel channels. The extensive maintenance work is intended to extend the units' operation by a further 30 years.

Candu reactors have a large horizontal vessel called a calandria, containing 480 tubes through which high-temperature coolant flows. Each tube is fitted with two end fittings that allow the fuel bundles to be separated and replaced without shutting down the entire reactor. Refurbishment to extend the plant's operating life requires the complete removal of these components and thousands of other auxiliary parts.