(CNN) -- U.S. nuclear power plants keep plans for dealing with a severe accident close at hand, but many of them need updating and nearly half the plants don't include them in regular drills, regulators said Monday.
Those findings are part of the Nuclear Regulatory Commission's safety review of U.S. reactors launched after the triple meltdown at Japan's Fukushima Daiichi plant in March. Nearly all the 104 U.S. plants had secured copies of their "Severe Accident Management Guidelines" in their reactor control rooms, emergency operations centers and technical support centers, NRC inspectors found.
But only 42% of those plants regularly update their guidelines, the NRC found. And while nearly all of them train operators on the guidelines when hired, "There is a notable gap in regularly training on these guidelines," NRC spokesman Scott Burnell said.
Only 61% regularly conduct drills on the procedures, which the U.S. nuclear industry voluntarily adopted in the 1990s, the NRC reported Monday. Since the measures are voluntary, the NRC can't force changes, Burnell said -- but he added, "We would expect that the plants that have fallen slightly behind their peers would do what is necessary to keep up with them."
The agency has already ordered American utilities to confirm that they have equipment "in place and available" to prevent a catastrophe like the one at Fukushima Daiichi, the worst nuclear accident since Chernobyl. Plant managers must submit detailed statements, under oath, by July 11.
NRC officials are scheduled to present their findings to the five-member commission July 19, Burnell said.
All three operating reactors at Fukushima Daiichi melted down after the plant was swamped by the tsunami that followed northern Japan's magnitude 9 earthquake in March, Japanese authorities confirmed Monday.
Previous assessments had indicated a full meltdown only in the plant's No. 1 reactor, though the cores of units 2 and 3 were believed to have suffered significant damage.
The Japanese government said Monday's announcement won't change the plans for stabilizing the plant, a process that the Tokyo Electric Power Company expects to complete between October and January 2012. More than 100,000 people in the surrounding area have been displaced by the disaster, which Japan declared a top-scale nuclear accident in April.
CNN's Matt Smith contributed to this report.