Complex sentence: Combined with the much larger than expected yield and an unanticipated wind shift radioactive fallout was spread eastward onto the inhabited Rongelap and Rongerik Atolls.
Split into simpler sentences: Combined with the much larger than expected yield and an unanticipated wind shift radioactive, fallout spread into unanticipated areas. The fallout spread eastward onto the inhabited Rongelap and Rongerik Atolls.