Washington ( CNN ) -- The chairman of the Nuclear Regulatory Commission said Tuesday that the situation in the wake of the Japanese nuclear reactor crisis is static but not yet stable . On the day that Japan bumped up the seriousness of its nuclear accident from a Level 5 to a Level 7 priority , on par with the Chernobyl disaster , a Senate committee heard from U.S. environmental officials , scientists and NRC Chairman Gregory Jaczko . `` From the information we have , we believe the situation currently is static , namely we do n't see significant changes on a day-to-day basis with the reactors , '' Jaczko told the Senate Committee on Environment and Public Works . `` It is not yet , however , what we believe to be stable : namely that given additional events or other circumstances ... there would not be the potential for significant additional problems at the reactors . '' Thus , Jaczko said , the focus is `` on these efforts to transition from static to stable to ensure ( the ) long-term ... ability to cool the reactors and to provide cooling for the spent fuel pools . '' California Sen. Barbara Boxer 's state has a number of nuclear plants in areas with high seismic activity near millions of people . She pressed Jaczko for reassurances that enough is being done to protect people in the United States , especially California residents . `` We 've got to move beyond talk and get to the serious question ( of ) what do we do , to do everything in our power to make it safe , '' Boxer said . Boxer pointed out that officials once said it was `` very unlikely '' Japan would ever face the kind of crisis it finds itself in today . Questions were raised at the hearing about how far to extend evacuation zones in the United States in the event of a nuclear incident . The NRC has recommended that Americans in Japan stay at least 50 miles away from the damaged reactors . The current standard in the United States is a 10-mile evacuation zone . `` As we 've seen in Japan , nuclear events tend to develop over a long period of time , '' said Jaczko . `` This is three weeks into this event , and we 've had the time and the ability to make protective action recommendations , and to update and modify them as conditions of the plant changed . So that 10 miles is really based around the idea of what do you need to have prepared right away so that if you have an event that develops quickly , you can address that and have prestaged and prepared what to do , '' he said . Boxer pointed out that two of the nuclear plants in California were built to withstand a certain level of earthquake , pointing out in Japan it was 7.5 but the devastating quake was much more powerful . She said nuclear regulatory officials are being too conservative . `` It 's eerie to me , because I do n't sense enough humility from all of us here . You know , as some great scientists once said , we think we have all the answers , but Mother Nature may not agree with us . So a lot of what you 're saying is the same thing that they said , '' Boxer pointed out . `` You ca n't know for sure what 's going to happen , '' she said . Lisa Jackson , administrator for the Environmental Protection Agency , reassured senators that air and water sampling for radiation contamination continue in the United States and that so far there is nothing to worry about . `` Let me be clear , EPA has not seen and does not expect to see radiation in our air or water reaching harmful levels in the United States , '' said Jackson . `` All of the data that we have seen , which we continue to make public and available on our website , indicates that while radiation levels are slightly elevated in some places , they are significantly below problematic levels . ''
NRC Chairman Gregory Jaczko speaks to members of Senate public works panel . `` We do n't see significant changes on a day-to-day basis with the reactors , '' Jaczko says . Sen. Barbara Boxer seeks assurances on safety of U.S. reactors in seismic zones . TL;DR The Nuclear Regulatory Commission is expected to vote Thursday on whether to approve construction of two new nuclear power plants at Indian Point and Oyster Creek.