Staff file photo - The Tennessee Valley Authority in 2012 began raising the retaining walls near Watts Bar Dam and Watts Bar Nuclear Plant outside Spring City, Tenn. This was an early temporary fix after TVA discovered faulty early design river flow figures and the Nuclear Regulatory Commission ordered new safety features in the wake of the Fukushima nuclear plant meltdowns in Japan.

U.S. nuclear power plants weren't built for climate change.

So says the headline in April 18 Bloomberg News special online expose. The lead example, of course, is Japan's Fukushima-Daiichi reactor meltdowns after a 9.0 earthquake and consequent tsunami.

The earthquake itself, almost 81 miles offshore, did no damage. The two tsunami waves that followed were a different story. And no, earthquakes have nothing to do — that we know of — with climate change. Nor do tsunamis. But flooding certainly does, and that's why Fukushima's story illustrates this point.

When the quake hit the Fukushima plant — a near twin of TVA's Brown's Ferry plant in North Alabama, the reactors went into automatic shutdown mode, as all nuclear plants are designed to do. It's a safety feature — like a fuse blowing when your circuits are overloaded. But not even shutdown could prevent catastrophe when less than an hour later two enormous ocean waves swamped the back-up diesel generators, the seawater pumps, the back-up electrical switchgear and a series of batteries in the plant's basement. With no power, the pumped flow of cooling water to surround the hot radioactive cores ceased.

From there, the dominoes fell fast, and within three days, three of six reactor cores had melted. Explosions ripped away parts of the containment structures. Within hours, mandatory evacuations began in a radius at 1.2 miles and gradually expanded to 12.4 miles. A voluntary evacuation was requested in the 12.4-to-18.6-mile area, and 10 days later, the Japanese government set a 12.4-mile-radius "no-go" area. Some 160,000 people were evacuated from their homes. Years later, 81,000 evacuees remained displaced, as much of the nearby land is still uninhabitable. Evacuees receive the Japanese equivalent of $1,030 per month in psychological suffering compensation — money that is tax-exempt and paid unconditionally. In March, the Japan Center for Economic Research put the cost of addressing the disaster between $315 billion and $728 billion.

Japanese government officials have said there have been no harmful effects from radiation on local people, nor any doses approaching harmful levels. Even if that is true, the lives of those who lived and worked there will never be the same. Even the pro-nuclear energy group, World Nuclear Association, stresses that while no deaths were reported from the radiation exposure, "more than 1,000 premature deaths have been caused by maintaining the evacuation beyond a prudent week or so."

All over the world, and especially in the U.S., nuclear plant planners and engineers began to recheck the factors of potential earthquakes and other natural disasters used in the siting, building and maintenance of nuclear plants.

Bloomberg's Christopher Flavelle and Jeremy C.F. Lin write that as Fukushima melted down, Gregory Jaczko, the then-chairman of the U.S. Nuclear Regulatory Commission, had two immediate worries: Would radioactive fallout harm the U.S., and could a similar accident occur at any of America's 60-odd nuclear plants? The fallout didn't harm the U.S., but Jaczko's second worry "preoccupies him still."

Within days, Jaczko's NRC directed the operators of working U.S. nuclear power plants to evaluate their current flood risk (earthquake re-evaluations were already underway), using the latest weather modeling technology and accounting for the effects of climate change. Nuclear plant owners were told to compare those risks with what their plants, many almost a half-century old, were built to withstand. If there was a gap, they were told to explain how they would close it.

The process found a lot of gaps. For instance, calculations for the mother of all floods (along with the discovery of early design miscalculations) prompted TVA to begin a $17 million effort to raise the level of several dams above Watts Bar and Sequoyah.

But the nuclear industry, on the whole, fought Jaczko's recommendation of redesigning the plants. Nuclear people instead thought it would be enough to focus mainly on storing emergency generators, pumps, and other equipment in on-site concrete bunkers — a system they dubbed Flex, for Flexible Mitigation Capability. Flex was the process TVA adopted. Spokesman Jim Hopson says TVA was the first nuclear utility in the U.S. to implement and certify its FLEX facilities at Watts Bar, and among the first to certify its entire nuclear fleet.

In a sad way, we're lucky that TVA took that early approach, because in January, NRC's new majority — three commissioners appointed by President Trump — ruled that nuclear plants wouldn't have to update equipment to deal with new, higher levels of expected flooding. The commission even eliminated a requirement that plants run Flex drills.

Jaczko and others told Bloomberg the NRC already hadn't done enough to require owners of nuclear power plants to take preventative measures — and that the risks will only increase as climate change worsens.

Jaczko said the new ruling nullified the work done following Fukushima. "It's like studying the safety of seat belts and then not making automakers put them in a car."

Using data from the Union of Concerned Scientists, Bloomberg mapped the plants expected to flood an average of at least twice a month by 2060. Some 90% of the current 59 operating plants were shown as having a minimum of one to four flood risks for which the facilities were not designed. TVA's Brown's Ferry in North Alabama, Watts Bar in Spring City, Tennessee, and Sequoyah in Soddy-Daisy all made that risk list.

Should we worry? We'll take a deeper look Monday.