Washington ( CNN ) -- U.S. regulators are directing 31 nuclear reactors similar in design to the Fukushima Daiichi plant in Japan , where an earthquake and tsunami caused a meltdown two years ago , to take additional steps to help contain radiation and other damage from any accident that is not quickly halted . The Nuclear Regulatory Commission directive on Thursday requires enhancements to systems for venting accumulated pressure from containment structures during an emergency . Vents must also be able to safely handle rising temperatures , hydrogen concentrations and radiation levels . The changes also aim to ensure that plant personnel can continue to operate vents safely if a reactor core melts down , the agency said . Plants in the United States were ordered last year by the NRC to take other steps to upgrade their `` hardened '' venting systems after the 2011 disaster in Japan that crippled three reactors and released radiation into the atmosphere . It was the worst nuclear accident since Chernobyl in 1986 . `` Strengthened vents will help these plants continue to protect the public and the environment even if emergency systems ca n't immediately stop an accident , '' NRC Chairman Allison Macfarlane said in a statement . `` By safely releasing built-up pressure and hydrogen , the plants will preserve the buildings that contain radioactive material , '' she said . U.S. plants covered under the directive are older , boiling-water reactors mainly similar in design to the Fukushima facility . During the meltdown in Japan , containment pressure exceeded twice the design limit , and there was no power or air to vent systems , according to an overview of the disaster by the Institute of Nuclear Power Operators . The goal for completing venting improvements in the United States is 2014 , depending on refueling schedules . Additional steps would take longer , if deemed necessary . The directive covers scenarios for structures meant to condense steam generated during an accident and control pressure and for the larger structures that surround the reactor . The NRC also plans to develop a rule to improve the filtering of radioactive material from any vented gases and to improve procedures for preserving the integrity of containment systems . An industry group said the new order is in line with its assessment of the `` most effective means '' to address venting . `` Venting to protect containment integrity and to mitigate the impact of a serious event is among the long-established training responses that are part of these facilities ' severe accident mitigation guidelines , '' according to a statement from the Nuclear Energy Institute , a trade group for the industry . The organization said the timetable is achievable but it did not provide a cost estimate . Plant operators may have to spend nearly $ 3.6 billion over the next three to five years on modifications to the nation 's 102 nuclear facilities in response to the Fukushima accident , according to a Platts survey released on Thursday . This includes costs for government mandates to handle threats from flooding and earthquakes as well as related engineering studies , Platts , an energy industry information service , said .
Nuclear Regulatory Commission requires changes at 31 plants . NRC wants enhancements to help contain damage from any accident . They are similar in design to Fukushima accident in Japan . Nuclear , which caused meltdown at Fukushima in Japan .