Cooled by the Gulf of Tonkin on a tropical island 1,100 megawatts from the mainland, a Hainan reactor entered commercial power for the first time and gave China its 61st operating nuclear plant
Palm fronds bend over a coastal headland where a concrete dome rises against the haze.
Below it, warm seawater pulls steadily through intake pipes built for a climate most reactor engineers never plan around.
This is the Gulf of Tonkin shoreline on a subtropical island far south of China’s industrial belt.
The reactor’s double containment shell and the island’s relative seismic stability shaped the site selection years before first concrete.
Inside that dome, a machine just finished a ten week climb from cold steel to full load.
What actually happens inside a reactor during those ten weeks before it earns the right to call itself commercial?
How a pressurized water reactor climbs from first heat to full commercial load
The journey from cold steel to commercial power follows a fixed physical sequence, and Changjiang Unit 3 ran the full course in roughly ten weeks. First criticality, the moment a sustained chain reaction is confirmed inside the reactor vessel, was logged on July 10, when neutrons from splitting uranium atoms begin sustaining the reaction without outside help, though output is still a tiny fraction of design power.
From there, operators raise power gradually, diverting steam into the turbines and watching every sensor before each step up.
On August 1, the unit was “successfully connected to the grid, and the first kilowatt-hour of clean electricity was generated here, flowing into thousands of homes,” the plant’s co-owner announced. That statement added that “stable parameters and good operating condition” had moved the reactor into its load bearing trial phase, where operators must show the reactor sustains rated output reliably and safety systems respond correctly before regulators sign off. The unit cleared that process and was declared in commercial operation on September 17, 2026, just 47 days after grid connection.
A tropical island site that changes every maintenance calculation
Hainan sits in the South China Sea, separated from the mainland by the Qiongzhou Strait, with a climate unlike the temperate provinces where most of China’s reactor fleet operates. Seawater temperature in the Gulf of Tonkin runs warmer than the Yellow Sea or Bohai Bay, which affects steam cycle efficiency and forces condenser systems built for sustained warm water intake, while humidity and salt air drive corrosion strategies that differ from inland or northern coastal plants.
Two older CNP-600 reactors have run at the Changjiang site since 2015 and 2016. That decade of data now belongs to a machine nearly twice as powerful as either predecessor.
Changjiang-3 is also the first large scale power reactor the plant’s controlling operator has built and run as lead stakeholder, giving the commissioning sequence weight beyond the megawatt count.
The numbers behind a 40 billion yuan island commitment
First concrete was poured for Unit 3’s nuclear island base slab in March 2021, with Unit 4 following that December. The two Hualong One units together represent an estimated 40 billion yuan investment, equivalent to roughly $5.9 billion, a substantial commitment for an island grid that has long relied on undersea cables and local gas generation.
Together the two Phase II units are expected to generate 18 billion kilowatt hours of clean electricity annually. That output replaces more than 6.32 million metric tons of standard coal and cuts carbon dioxide emissions by about 11.6 million metric tons a year, according to the plant’s general manager as reported by World Nuclear News.
Before this milestone, the International Atomic Energy Agency counted 60 commercial reactor units in operation and 37 under construction in China, far more than any other country. With Changjiang-3 online, those figures moved to 61 in commercial operation and 36 under construction.
The Hualong One design and what it means for Hainan’s grid
The Hualong One carries 177 fuel assemblies, each roughly 12 feet long, with an 18 to 24 month refueling interval. It runs three coolant loops, double containment and active safety systems with some passive elements, backed by a 60 year design life.
At 1,100 MW net output, the unit delivers roughly 80 percent more power than each of the two older CNP-600 machines already on site, from a footprint that does not grow proportionally with that jump. The Hualong One is now China’s flagship reactor technology, making up about half of all reactor new build projects nationwide, and its arrival on Hainan marks the design’s spread across every type of Chinese grid geography.
The reactor’s double containment shell and the island’s relative seismic stability shaped the site selection years before first concrete. Also sharing the site is China’s demonstration ACP100 small modular reactor, the Linglong One, now in pre-commissioning tests, which would make Hainan the only place running both a commercial scale Hualong One and the world’s first land based small modular reactor on one grid connection.
What comes next for the site and for the fleet behind it
Unit 4, an identical Hualong One, broke ground in December 2021 and is scheduled to follow Unit 3 into operation in early 2027. Combined output at Changjiang will then push past 3,000 MW across all four units, turning a modestly sized provincial plant into one of southern China’s more powerful nuclear stations.
For the broader nuclear workforce, the skills pipeline behind these commissioning runs is itself becoming strategic. A trained operator pool that can bring a 1,100 MW machine from cold steel to commercial load in ten weeks reflects decades of accumulated knowledge, and new training partnerships are gaining urgency wherever reactor construction is accelerating.
The fuel supply chain matters just as much, since new fuel plant capacity is being built out because reactor timelines are tightening worldwide and fuel lead times cannot be compressed the way a construction schedule sometimes can.
Back on Hainan, the simpler question is whether the Gulf of Tonkin’s warm water and salt air, already navigated by the older units for a decade, will prove just as manageable for a machine nearly twice their size. Ten weeks of commissioning data is a promising start, but a 60 year design life is a long test, and the island has only just begun it.
Hugo is an engineer with strong technical expertise. Multilingual from an early age, his writing combines technical clarity with a strong interest in science and energy.
