KYIV, Jan 12 - Reactor No. 3 of South-Ukrainian nuclear power plant (NPP) automatically reduced output to 590 MW at 22:45 local time on January 11 as a result of the shutdown of main circulation pump No. 1 by the automatic protection system, the State Nuclear Regulatory Inspectorate of Ukraine reported on its website.

In keeping with the International Nuclear Events Scale (INES), this event is rated as "below the scale/level 0," the inspectorate said.

"The protection system has responded flawlessly; a commission has been set up to investigate into the causes of the event. The radiation background on Yuzhnoukrainsk NPP's site is unchanged, physical protection works in usual mode," it said.