The health threat to Japanese from radiation exposure in the wake of the Fukushima nuclear accident last year is extremely low, even if certain areas near the crippled plant could be rendered off-limits for years to come, according to a panel of American radiation experts who've studied the Japanese case for the past year.

"From a radiological perspective, we expect the impact to be really, really minor," said Kathryn Higley, a professor of nuclear engineering at Oregon State University. She was part of the group that spoke...