Washington ( CNN ) -- The Nuclear Regulatory Commission told Congress on Thursday that the likelihood of a Fukushimi Daiichi-type event in the United States is `` very , very small . '' However , it said an ongoing study of the Japanese disaster will probably lead to changes to increase safety at the nation 's 104 commercial power plants . The commission said , in a nutshell , it expects to require nuclear plants to be prepared for bigger natural disasters , to survive longer power outages and to consider the possibility of simultaneous disasters affecting multiple reactors , as happened in Japan . Commissioner George Apostolakis said one of the lessons of Fukushima is `` humility . '' `` I believe that , as a community of safety analysts , we were pretty confident that there would be no new surprises , '' Apostolakis said . `` Fukushima has challenged that belief . '' Commissioners said the commission 's core safety concept , a belts-and-suspenders policy called `` Defense in Depth , '' is sound . The policy requires power plant designers and operators to have multiple , redundant layers of defense to respond to failures so that no single layer of response is relied on . They also endorsed support for regulations that require plants to be designed to withstand the strongest natural disasters on record for that location , with an added margin of safety . But while voicing support for both concepts , some commissioners said `` Defense in Depth '' needs to be deeper and margins of safety wider . Currently , emergency plans for most U.S. nuclear reactors envision one nuclear reactor being in danger . At Fukushima , all four operating reactors were affected by the tsunami that followed an earthquake in March . The Nuclear Regulatory Commission also requires plans to evacuate a 10-mile zone around power plants , but U.S. authorities recommended that U.S. citizens within 50 miles of Fukushima evacuate . Japan to hand out radiation meters to children . `` If there 's an overall lesson we can learn from this , I think that is you ca n't ... predict everything that will happen in the future . You ca n't predict every earthquake , every tsunami , but ... you have to be able to recover from whatever happens , '' Commissioner William Magwood IV said . Currently , a Nuclear Regulatory Commission task force is midway through a 90-day review of the Fukushima incident , searching for lessons that can quickly be applied to U.S. plants . The 90-day study , to be released July 19 , will be followed by a lengthier study involving more long-term changes . At a hearing before the Senate Environment and Public Works Committee , commissioners discussed some of the lessons learned . They include : . -- The commission needs to evaluate its `` station blackout '' rule concerning how power plants deal with the loss of electrical power , Commissioner William Ostendorff said . `` I think that the commission will probably receive from the task force perhaps some recommendations in this area , '' he said . -- Backup batteries used to power control room functions during blackouts are insufficient , Apostolakis said . `` Clearly , the main message from Fukushima is that four hours , or sometimes eight , is not sufficient , '' he said . `` Interestingly enough , when the requirement of four or longer hours was put in place , it was actually a conservative estimate . ( Regulators ) looked at the time it took to recover AC power ( during a blackout ) . The average was about two hours , so to be conservative , they doubled it . And now we have this accident that shows its very inadequate , so that 's certainly something we have to look into . '' -- The commission needs to consider the impact that spent-fuel pool problems can have during a larger event , Chairman Gregory Jaczko said . `` I think we 've had a singular focus , perhaps , on reactor safety in the event of accidents and not put enough attention into considering the impact of spent fuel pools ( on the response ) , '' he said . -- The commission needs to consider staging of emergency and back-up equipment . After the September 11 terrorist attacks , the commission required plants to stage auxiliary diesel generators near nuclear plants , Magwood said . `` We require those units to be just a very short distance away from , say , reactor buildings . Clearly , if we had those procedures in place and had experienced a Fukushima-type event , that equipment would have been wiped out along with a lot of the other side equipment . That was a significant revelation for me and something I think we have to address , '' he said . -- The commission needs to review first-responder communication capabilities . `` It 's always very difficult to have communication in a crisis situation , and I think that 's an area that we can always be exercising and improving , '' Commissioner Kristine Svinicki commission . Commissioners also said the agency must study what led to the hydrogen explosions that plagued Fukushima but said not enough is known about the incident to recommend changes . `` We 've always asked ourselves the question , 'Are the plants still safe ? Is there anything we need to do today to address that ? ' And the answer continues to be 'No , ' `` Jaczko said . `` We want to get good information , ( and ) we have time to do that . `` The likelihood of something like this happening in the United States is still very , very small , because these are really very , very unlikely types of events , '' he said . Jaczko said the current 90-day review `` may seem like a very long time , ( but ) to the people doing the review , it 's going by in a millisecond . '' `` But it 's important that we get it right , and I think that so far , they are looking at all the right things , '' he said .
Commissioners tell them of potential changes to power plants . ` ` is '' among highlights of Japan 's history , commissioner says . They say the present Japanese electricity concept is sound .