The world’s first Hualong One nuclear reactor has been completed in south China’s Fujian province after the installation of its dome-shaped containment structure, chinanews.com reported on Thursday.

The 70.48-meter pilot nuclear reactor, codenamed “No. 5 Reactor Unit,” in the nuclear power plant in Fuqing, Fujian, uses Hualong One technology, a domestically developed third-generation reactor design.

It took 17 hours to finish the containment structure, which consists of a main body and a dome. Sealing the dome marked important progress, a person in charge of the construction said.

Fuqing has plans to build six pressurized water reactor units with megawatt capacity. Units 1-4, using second-generation technology, have been finished and started commercial operations. Construction on Units 5-6, which use the self-developed third-generation Hualong One design, started in 2015.

China has the largest proportion of nuclear power units under construction, and the country is expected to be the world’s second most number of nuclear units in 2020, according to its national plan.