This April 9, 2012 file photo shows construction well underway for two new nuclear reactors at the V.C. Summer Nuclear Station in Jenkinsville, S.C. Photo: Jeffrey Collins, AP

Two nuclear power units that were under construction in South Carolina will be abandoned, the utility announced this week.

The economic and financial reasons behind the abandonment plan highlight the pressures in developing nuclear power, once a great hope of the 20th century, but tainted by a series of disasters and near-misses over the last half-century.

The South Carolina Electric and Gas Company announced Monday that additional costs to complete the two units at the V.C. Summer Nuclear Station in Jenkinsville, including the uncertainty of tax credits, made the nuclear facility “prohibitively expensive” – and forced their hand financially.

“Based on these factors, SCE&G concluded that it would not be in the best interest of its customers and other stakeholders to continue construction of the project,” they announced.

The main driver of the decision was the bankruptcy of the primary construction contractor, Westinghouse, said Kevin Marsh, chairman and CEO of the SCAN Corporation, the parent company of SCE&G. That bankruptcy eliminated the fixed-price contract – and made the numbers untenable, he added in a prepared statement.

“Many factors outside our control have changed since inception of this project,” said Marsh. “Ceasing work on the project was our least desired option, but this is the right thing to do at this time.”

According to the filing before the Public Service Commission of South Carolina, the forecasted cost for the two units was originally $6.3 billion – but had ballooned to $7.7 billion in the most recent estimates.

One report indicates that some $5 billion had already been spent on the project.

Nuclear power has lost portions of its worldwide market over successive decades. Most recently, Switzerland voted in May to get rid of its entire nuclear palette – a power source accounting for more than a third of the European nation’s portfolio.

The slowdown in the nuclear market began with an intermittent series of incidents – the first of which was the meltdown at Three Mile Island in 1979.

The U.S. Nuclear Regulatory Commission concedes the panic and anxiety of that incident “permanently changed both the nuclear industry and the NRC.” But that total meltdown was narrowly averted, with no fatalities reported. Other incidents were much more serious – most notably the Chernobyl disaster of 1986 in the Ukraine, and the Fukushima incident in Japan in 2011.

Together, the crises have stalled the development of nuclear energy, the NRC explained.

“Public fear and distrust increased, NRC’s regulations and oversight became broader and more robust, and management of the plants was scrutinized more carefully,” the agency has said.

Indeed, nuclear’s growth tailed off considerably in the U.S. after 1979. It did reach a peak generation of 23 percent of all U.S. electricity in December 1999 – but that total fell to 18 percent by summer 2015. In the same time frame, natural gas’s portion of the American power generation portfolio rose from 11 percent to 35 percent.

Some experts hold that economics, and not disasters, are what have curtailed the use of nuclear in the U.S.

Ninety-nine nuclear plants are currently in use in the U.S. today, the NRC says. The most recent performance analysis of the plants found only 85 met all safety and security objectives, the NRC found.