The whole industry, despite using vastly different reactor designs, has devised a standard for hose fittings, pump types and other basic backup equipment.

It is an unusual level of coordination for a fragmented industry.

Many of the changes to hardware built into the plant, like pipes and cables, will be made this spring and fall, when reactors around the country shut down for refueling. Plumbers and electricians will swarm over the reactors’ innards to allow the new portable hardware to work. Plumbers will install connection points where emergency pumps could force water into critical spots if the permanent pumps failed because of loss of electricity, as happened at Fukushima Daiichi after the tsunami, leading to the triple meltdown. Electricians will create connections where portable generators could be used.

“Fukushima woke up the world nuclear industry, not just the U.S.,” said the chairwoman of the Nuclear Regulatory Commission, Allison M. Macfarlane, in an interview. “It woke everybody up and said: ‘Hey, you didn’t even think about these different issues happening. You never thought about an earthquake that could create a tsunami that would swamp your emergency diesel generators and leave you without power for an extended period. You never planned for more than one reactor going down at a site, you have to think about that now.’ ”

At Peach Bottom, though, the plant’s designers did prepare for some situations, like a flood. Plant officials here proudly show off the “submarine doors,” at the entry to the emergency diesel generators. These open with a turn of a giant crank, like an old bank vault, and would let the diesel generators continue running even if the river’s water level somehow rose 20 feet. Diesel fuel tanks, which sat in front of the reactors at Fukushima Daiichi and were washed away by the tsunami, are buried here and would continue to function if submerged.

Still, big fixes are needed.

Even before Fukushima, the United States Geological Survey updated its earthquake risk estimate for the eastern and central United States, and the nuclear plants have until the end of this month to say whether the new estimates predict a ground motion above what they are designed for.

Several are also reanalyzing for flood risk, including the chance of failure of an upstream dam. At Peach Bottom, tour guides show off a series of gray boxes that played a crucial, and tragic, role at Fukushima: these are the electrical devices that eventually move valves, power motors or perform other essential functions. At Fukushima, all were flooded with seawater, rendering them useless even if the plant still had electricity. Here, they are too high to flood, engineers say.