The 1,000-MW nuclear power plant at Kudankulam stopped generation on Thursday night following a steam leak, Power System Operation Corporation Ltd (POSOCO) said.
The unit was restarted only on January 30 after nearly seven months of maintenance shutdown.
According to POSOCO, the atomic power plant outage happened at around 8.35 p.m. due to steam leak in the secondary side.
On Thursday, the power generation touched the day's peak of 757 MW while the average generation for the day was 582 MW.
"A minor steam leak in the feed water system in turbine building from 14 mm impulse line is being attended," R.S. Sundar, site director at Kudankulam Nuclear Power Project (KNPP) told IANS on Friday.
The unit is expected to restart operation on February 7.
India's atomic power plant operator Nuclear Power Corporation of India Ltd (NPCIL) is setting up two 1,000 MW atomic power plants at Kudankulam in Tirunelvelli district, around 650 km from here, at an outlay of over Rs.17,000 crore.
The first unit attained criticality, which is the beginning of the fission process, in July 2013.
Subsequently it was connected to the southern grid in October 2013.
However, commercial power generation began only on December 31, 2014.
The unit also experienced breakdowns after commercial production started.
The unit was shut down in June 2015 for 60 days for refuelling and annual maintenance in June 2015.
Operating at full capacity, the unit supplies power to Tamil Nadu (562.5 MW), Puducherry (33.5 MW), Kerala (133 MW), Karnataka (221 MW) and Andhra Pradesh (50 MW).
The NPCIL skipped several deadlines in restarting the first unit and finally on January 21, 2016 the reactor restarted the fission process and was connected to the southern grid on January 30.
According to the official position, the second 1,000 MW unit at Kudankulam is expected to go critical, or start the fission process, for the first time sometime this year.
However, sources told IANS that the unit may go critical early next year.
The second unit has to get some parts from Russia as some of its components have been used in the first unit so that the latter could start operating fast.
The fuel has to be loaded into the second reactor.
A senior official in the Atomic Energy Regulatory Board (AERB) recently told IANS that the results of the second unit's commissioning and inspection reports are being studied.
"After the reports are studied, AERB might lay down some conditions which have to be completed before NPCIL applies for the permission to load the fuel," he had said.
Meanwhile the AERB has given its nod for site preparation work for building the third and fourth units at Kudankulam. The two units would cost around Rs.40,000 crore.