AFTER THE MELTDOWNS at Japan’s Fukushima Daiichi nuclear complex this year, it was sensible to ask how safe are America’s nuclear plants. The federal watchdog Nuclear Regulatory Commission (NRC) ordered a report on the vulnerabilities of nuclear power stations and what regulators should do to improve them. The commissioners will hold a meeting on the findings of a preliminary assessment this week. The takeaway: America’s plants are safe. But they could be safer.

The investigators found that a series of calamitous failures similar to what happened at Fukushima Daiichi just isn’t likely to occur in America, for a variety of reasons. The NRC regularly updates its rules according to everything from new seismic studies to updated analysis of hypothetical threats. The reaction to the Sept. 11 terrorist attacks among regulators and industry, for example, tightened preparedness to cope with massive explosions, the loss of off-site electrical power and similar events. Unlike Japan, America doesn’t have nuclear reactors on a coastline abutting a major subduction zone fault, which can produce earthquakes and tsunamis much larger than, say, the San Andreas can.

Still, there’s room to learn from Japan’s stricken reactors. Some NRC regulations differ from plant to plant depending on when they were built; others were designed specifically with terrorism in mind but not other threats. The commission can develop and apply some of its rules more coherently. In that effort, the report argues, the NRC should require nuclear power stations to be able to cope for at least 72 hours without power from their reactors or from outside. Backup generators should be impervious to earthquakes, extreme weather and other threats, and preparations for a sudden blackout should ensure emergency power sufficient to keep nuclear waste cool and contained and to illuminate control-room instrumentation. It was the loss of backup power at Fukushima that crippled the plants. Regulators can also require improvements to prevent the dangerous buildup of gas, which might have caused explosions at the Fukushima complex.

In some cases, new rules would require measures that plant operators already have taken voluntarily. In others, the NRC would have to impose new demands.

The NRC should use this review not merely to respond to a single event but to ensure that it is actively assessing low-probability but high-consequence risks. Polls show that Americans largely haven’t lost confidence in their nuclear plants. Government regulators should give them every reason not to.