A UN scientific panel on Tuesday confirmed a previous finding that radiation from the 2011 Fukushima disaster in Japan was unlikely to raise cancer rates discernibly, and said a jump in thyroid cancer in children was due to "ultrasensitive" screening methods.

Fukushima was the worst nuclear accident since Chernobyl, the 1986 Soviet reactor explosion that sent radioactive dust across much of Europe. A 9.0-magnitude quake and tsunami crippled the Fukushima Dai-ichi plant, and more than 160,000 residents had to flee as radiation spewed into the air.

After Chernobyl, people living close to the plant were exposed to...