Tokyo - Japanese officials said yesterday that the nation's worst nuclear accident may be upgraded to the same level as America's 1979 Three Mile Island accident, but added they saw no increased impact on health or the environment. Also yesterday, a nuclear power company said it had found that a small amount of radiation had leaked from two barrels of low-level nuclear waste transported last month to a disposal facility in northern Japan. Tokyo Electric Power Co Inc said it was investigating the cause of those leaks but added the amount was too small to cause harm.