One of the ways scientists study the CMB is by subjecting the warm and cold spots in the radiation to a detailed statistical analysis, examining the deviations in temperature as a function of their size on the sky - their angular scale.
The guidance, once again, was that after careful analysis of data, radiation levels and damage assessments to all units at the plant, our independent experts at the NRC are in agreement with the response and measures taken by Japanese technicians, including their recommended 20-kilometer radius for evacuation and additional shelter-in-place recommendations out to 30 kilometers.