The power production is expected to resume in the next two or three days after the problem is fixed KNPP Site Director, R S Sundar stated.
"The power generation from KNPP's first unit stopped at 12.41 pm on December 3 as the reactor stopped functioning while we were carrying out some routine checks," Sundar said.
The unit was generating around 400 MW of power before the reactor stopped functioning, the KNPP Site Director added.
KNPP's Unit 1 has been considerably contributing to the power-starved southern state of Tamil Nadu, since the last week of October this year.
Nuclear Power Corporation of India Ltd (NPCIL) is collaborating with Russia to set up two new 1,000 MW reactors at Kudankulam, in Tirunelveli district of Tamil Nadu.
While the first unit attained criticality in July 2013, the second unit is nearing completion and should be operational in the early months of 2014.