In late January, by a 3-to-2 vote, NRC commissioners rejected a recommendation from their own senior staff to require reactor owners to recognize new climate reality and fortify their plants against real-world natural hazards such as flooding and seismic events. Most, if not all, of those reactors were engineered, built and maintained with highly optimistic assumptions rooted in the late 1960s and 1970s.

For those keeping tabs, March is nuclear accident month. Three Mile Island occurred 40 years ago; Fukushima Daiichi, eight.

In the aftermath of Japan’s Fukushima disaster, the NRC asked its staff to scrutinize U.S. reactor operations and identify ways to prevent a similar accident. The experts crafted a list of 12 sweeping recommendations. The underlying theme: Prepare for the unexpected.

High on the list was a recommendation that plant owners be required to reevaluate the seismic and flooding hazards at their sites “consistent with the current state of knowledge and analytical methods,” and update buildings and equipment to reflect actual risks — not projections formulated back when “Laugh-In” was must-see TV.

The 12 recommendations were delivered to the NRC commissioners in July 2011. A draft of new rules implementing the recommendations was finally hammered out in 2016. Lobbyists for the industry pushed back, arguing existing rules provide adequate protection. That’s not surprising. After the Three Mile Island accident, when safety enhancements were ordered, the price tag was steep. The industry set out to ensure that didn’t happen again.

Heeding the NRC’s initial calls to conduct hazard assessments, plant operators performed “walkdowns” at their facilities, evaluating critical safety systems for vulnerabilities, with varying degrees of thoroughness. In 2012, Florida Power & Light reported that its St. Lucie plant was prepared for disaster, but two years later, heavy rainfall sent 50,000 gallons of water through flood barriers that had been missing the proper seals for decades. Duke Energy underestimated peak storm-surge heights at its Brunswick plant near Wilmington, North Carolina, by about 8 feet.

Flooding is a particular threat. Because nuclear reactors require access to water for cooling, many sit in locations vulnerable to severe coastal storms or rising rivers. Hurricane Florence last fall threatened 16 reactors in North Carolina, South Carolina and Virginia. The year before, Florida’s two nuclear facilities, Turkey Point and St. Lucie, sat in the path of Hurricane Irma barreling toward the coast. Thirty-four reactors at 20 sites around the United States are downstream from large dams. Possible failure of the dams, and the tsunami of water unleashed after a collapse, was ignored or not adequately taken into consideration when the plants were designed. Nor was the threat of increasingly severe storms and resultant flooding.

When the results of the “walkdowns” were tabulated, 55 of the 61 U.S. nuclear sites were found to confront flooding hazards beyond what they were designed to withstand.

Identifying the problems was Part I of that NRC staff recommendation. Ordering fixes was Part II.

“This decision is nonsensical,” Baran wrote.”Instead of requiring nuclear power plants to be prepared for the actual flooding and earthquake hazards that could occur at their sites, NRC will allow them to be prepared only for the old, outdated hazards typically calculated decades ago when the science of seismology and hydrology was far less advanced than it is today,” he wrote.

Burns added: “The accident at Fukushima was a direct result of the operator and regulator failing to take action to account for new scientific knowledge related to natural hazards, especially flooding hazards. … In the United States, there exists incontrovertible evidence that the current design bases for some plants do not address a flood hazard identified by the licensees’ (plant operators’])own analyses.”

The new regulations aren’t scheduled to even go into effect for at least two years, probably longer. We’ll just have to wait to learn who’s right — the world’s climate experts or three members of the NRC.

Susan Stranahan is a journalist who covered the Three Mile Island accident and is a co-author of “Fukushima: The Story of a Nuclear Disaster.” She wrote this column for the Washington Post.

In January, the majority of commissioners said, in effect, forget Part II.

The commission dropped the new natural hazard upgrades, saying they were not “necessary for adequate protection” or did not provide “a cost- justified, substantial safety benefit.” Other rules contained in the regulatory package would protect public health and safety, said chairman Kristine L. Svinicki, in a statement on behalf of the majority.

That prompted strong dissents from commissioners Jeff Baran and Stephen Burns.