This post has been corrected.

At its birth, nuclear power was a closely guarded national enterprise, only accessible to the most prosperous nations. But over the last 50 years it has evolved into a robust international market with a global supply chain. Not only are more countries starting or considering new nuclear plants, a great many more countries are contributing to their construction.

According to data from the International Atomic Energy Agency (IAEA) 66 nuclear reactors are under construction around the world. Dozens more are in various stages of planning.

The vast majority of new reactors are being built in China, which has invested in nuclear power in a way not seen since the United States and France first built out their capacity in the 1960’s and 70’s. China’s 2015 Five Year Plan calls for 40 reactors to be built by 2020 and as many as ten more are planned for every year thereafter. Fifteen other countries around the world are also building reactors.

The Chinese sprint toward nuclear power is along a path toward becoming a major exporter of nuclear technology and expertise. In addition to adopting western designs, China also has its own reactor designs. Plants based on those designs are also under construction both China and in Pakistan. Other countries are considering them. At the same time China has upgraded its capacity to produce pressure vessels, turbines and other heavy manufacturing components—all of which it is expected to begin exporting.

This sort of globalized manufacturing is nothing new: cars, airplanes and most other complicated machines are built in this way. However, it is new for reactors, which must be constructed on-site and rely on highly specialized parts. Those parts must be manufactured to tolerances well beyond what is required in other industries. In some cases even the equipment needed to creating them must be purpose-built.

Consider, for example, the steel pressure vessel at the heart of the most common reactor designs. These vessels can only be created in the world’s largest steel presses—some of which exert more than 30,000 pounds of force. The vessels are forged out of solid steel ingots that may weigh more than a million pounds. Until recently there were only a handful of such presses in the world. Today there are at least 23, spread across 11 countries, according to the World Nuclear Association (WNA).

Such specialization is not limited to heavy manufacturing. Nuclear reactors require thousands of other mechanical and electronic components, many of which are purpose-made. A brochure from the Nuclear Energy Institute (NEI) identifies hundreds of individual parts. (pdf) Even otherwise common products may need to meet extraordinarily fine tolerances. Standards require that steel elements relevant to safety are manufactured with exceptional “nuclear-grade steel.”

According to another NEI list, the construction of a new reactor may require a total of:

500 to 3,000 nuclear grade valves

125 to 250 pumps

44 miles of piping

300 miles of electric wiring

90,000 electrical components

According to Greg Kaser, who analyzes supply chains for the WNA, the market for nuclear components has been driven by US-based reactor companies, namely Westinghouse Electric Company. “The US can’t produce everything that’s required for a nuclear reactor anymore, so they have to go international,” Kaser told Quartz.

Reactors based on Westinghouse’s AP1000 design are under construction in both the US and China. The parts for these reactors are sourced from all over the world. Many come from European companies that were originally created to supply domestic nuclear programs, but have since become important exporters. This trade in nuclear components is difficult to measure. Despite the specific qualifications of a nuclear-grade valve, it is still a valve and doesn’t necessarily show up in trade statistics as anything more.

A great deal of trade is also in expertise. Engineers from China, Japan, South Korea and the United States frequently consult on (or lead) nuclear projects around the world. A 2014 WNA report (paywall) estimates that the total value of investments in new nuclear facilities through 2030 will be $1.2 trillion.

But this nuclear globalization has not been greeted with enthusiasm everywhere. The 2011 nuclear contamination disaster at Fukushima, Japan, briefly stalled development of some projects and prompted Germany to begin shutting down all of its reactors. A decision by the UK to allow a Chinese company to develop new nuclear reactors in England has led to both domestic and international hand-wringing over the security implications.

Others worry about about safety issues resulting from companies faking the certifications required for selling reactor components. In 2013, two South Korean nuclear reactors were shut down when it was discovered that they had installed cables with counterfeit nuclear certifications. This year the IAEA will update a procurement guide for plant operators that was published in 1996. (pdf) The new version will include a chapter specifically addressing counterfeit components.

For the moment, it’s unlikely any of these concerns will be enough to slow the resurgent growth of the global nuclear industry. Though big nuclear companies often speak of localizing the supply chain—and keeping those jobs in their home country—international competition can drive down the price of building a reactor.

In fact, the supply chain is likely to become even more important to the construction process in the future. New reactors being designed today are both smaller and more modular, and plans call for large sections of them to be assembled in factories and shipped to the site. If it sounds a lot like the assembly line at a automobile plant, that’s because it is. But of course, one small oversight or production flaw could make a much greater difference.

Correction (9:30am ET): The number of reactors currently under construction is 66. This post previously reported the number as 64.