Today a travel "alert" was issued by the U.S. State Dept. to replace the travel "warning" of March 31, 2011. Here it is (I tried to put all the important bits in bold)
The assessment of technical and subject matter experts across U.S. govt agencies is that while the situation at the Fukushima Daiichi plant remains serious and dynamic, the health and safety risks to areas beyond the 50 mile evacuation zone, and particularly to Tokyo, Nagoya (Aichi Prefecture), Yokohama (Kanagawa Prefecture) nearby U.S. military facilities and the prefectures of Akita, Aomori, Chiba, Gunma, Iwate, Nagano, Niigata, Saitama, Shizuoka, Tochigi, and Yamanashi, and those portions of Fukushima, Ibaraki, Miyagi and Yamagata prefectures which are outside a 50 mile radius of the Fukushima Daiichi nuclear power plant are low and do not pose significant risks to U.S. citizens.
This analysis takes into consideration both various age groups and the classification of the severity of the situation at Fukushima Daiichi as a Level 7 event by the Government of Japan, which reflects what has transpired since the initial incident and the potential long-term effects in the area surrounding the plant.
This assessment reflects inputs from our national laboratories as well as the unanimous opinion of the U.S. scientific experts on the ground in Japan.... Based on the much reduced rate of heat generation in the reactor fuel after one month of cooling and the corresponding decay of short-lived radioactive isotopes, even in the event of an unexpected disruption at the Fukushima Daiichi plant, harmful exposures to people beyond the 50 mile evacuation zone are highly unlikely, and there would be a significant amount of time to best assess any steps that might have to be taken.
The situation at the plant is dramatically different today than it was on March 16, when we saw significant ongoing releases of radioactivity, the loss of effective means to cool the reactor cores and spent fuel, the absence of outside power or fresh water supply for emergency management, and considerable uncertainty about the condition of the site. Today, while the situation remains serious, and there is still a possibility of unanticipated developments, cooling efforts are ongoing and successful, power, water supply, and back-up services have been partially or fully restored, and planning has begun to control radioactive contamination and mitigate future dangers. Our coordination with the Japanese is regular and productive, and we have a greatly increased capacity to measure and analyze risks.
The Department of State has lifted Voluntary Authorized Departure, allowing dependents of the U.S. government employees to return to Japan.
We continue to recommend that U.S. citizens avoid travel within the 50-mile radius of the Fukushima Daiichi Nuclear Plant. U.S. citizens who are still within this radius should evacuate or shelter in place.
Japan is one of the most seismically active places in the world. Tokyo and areas to the Northeast continue to experience strong aftershocks related to the March 11 earthquake. Aftershocks following an earthquake of this magnitude can be expected to continue for more than a year. Identifying potential hazards ahead of time and advance planning can reduce the dangers of serious injury or loss of life from an earthquake. See the Embassy Website for detailed information on earthquake safety: