TOKAI, Ibaraki Pref. -- While facts continued to trickle out about the nation's worst radiation leakage, which occurred at the nuclear fuel reprocessing plant here last week, officials of the governmental Power Reactor and Nuclear Fuel Development Corp. (PNC) kept claiming the leak posed no serious bodily or environmental harm.

By the weekend, all 37 workers believed exposed to radiation at the PNC-run Tokai plant had returned to normal duties, and PNC officials said none has shown symptoms of abnormalities. Experts agree that the amount of exposure -- if the PNC-released data are correct -- is not large enough to pose any immediate risk to the workers' health. But some say longer-term effects cannot be ruled out.

Radiation first leaked after a fire broke out at the bituminization facility at 10 a.m. Still more leaked following an explosion 10 hours later. The 37 were among 112 workers who were known to have been in and around the facility at the time. The PNC has announced that a total of 22,600 becquerels of alpha rays -- including those from highly toxic plutonium, which can cause cancer -- and 58.3 million becquerels of beta rays -- including those from cesium, which can pose a genetic hazard -- were released into the air after the accident. A becquerel is a unit for measuring radioactive decay and shows the number of atoms that disintegrate per second.