Children and women who are pregnant are at most immediate risk from any radiation released by nuclear reactors in Japan, a US radiation expert says。

America is the world's largest producer of nuclear energy, but has not approved a single new plant since a scary (but non-lethal) nuclear accident at Three Mile Island in 1979.

The cooling problems at the Japanese plant raised fears of a repeat of 1979's Three Mile Island accident, the most serious in the history of the U.S. nuclear power industry.