* Operator KHNP says non-critical data over plants leaked
* KHNP to hold drills against cyberattaks on Monday-Tuesday (Adds nuclear plants drills against cyberattacks, and graphics)
SEOUL, Dec 21 - Seoul prosecutors have launched an investigation of a leak of non-critical data at South Korea's nuclear power operator, the prosecutors' office said on Sunday, as worries mount about nuclear safety and potential cyberattacks from North Korea.
TOKYO, Dec 20 - A 5.9 magnitude earthquake hit Japan's Honshu island on Saturday, the U.S. Geological Survey said, shaking Fukushima where crippled nuclear power plants are located, but local media said there was no tsunami warning.
Dec 19 - In a disappointment to environmentalists, the U.S. Environmental Protection Agency issued rules on Friday labeling coal ash, a byproduct of coal-based power production containing toxic materials such as arsenic and lead, as non-hazardous waste.
No related earnings announcements are currently scheduled within the next 7 days.