Major nuclear power company Westinghouse, a U.S. subsidiary of Japan's Toshiba, filed for Chapter 11 bankruptcy on Wednesday in a massive blow to the industry.

The filing marked "a defining moment in the decades-long downward spiral of the global nuclear power industry," wrote Greenpeace Japan in a statement.

"Toshiba/Westinghouse is responsible for building more nuclear reactors worldwide than any other entity," the group observed. "With the financial meltdown of Westinghouse, Toshiba also recently announced its plans to withdraw from foreign construction projects—a move that has far-reaching implications outside Japan and the U.S., such as the construction of three reactors in the U.K. at Moorside."

"We have all but completely pulled out of the nuclear business overseas," Toshiba president Satoshi Tsunakawa said at a news conference, according to the New York Times.

The Times further reports:

The filing comes as the company's corporate parent, Toshiba of Japan, scrambles to stanch huge losses stemming from Westinghouse's troubled nuclear construction projects in the American South. Now, the future of those projects, which once seemed to be on the leading edge of a renaissance for nuclear energy, is in doubt.

"This is a fairly big and consequential deal," said Richard Nephew, a senior research scholar at the Center on Global Energy Policy at Columbia University. "You've had some power companies and big utilities run into financial trouble, but this kind of thing hasn't happened."

"Toshiba/Westinghouse find themselves a victim of their own hubris and a nuclear industry where financial prudence was never a strong point," Greenpeace Germany added in a brief (pdf).

It's underscoring the global meltdown of the nuclear power industry, argued Greenpeace Japan energy campaigner Ai Kashiwagi. "If we look at how nuclear stacks up against renewables, it's clearly in freefall," Kashiwagi said. "An estimated 147 gigawatts  of renewable power was added in 2015, compared to just 11 gigawatts for nuclear power in the same year."

"For too long the nuclear industry has locked away huge amounts of capital at the expense of developing increasingly affordable renewable energy and updating energy grids," Kashiwagi added. "The future of energy in Japan and globally will be renewables and it's time governments get on board."