Korea's oldest nuclear reactor, the Kori No. 1, resumed operation on Sunday after an extensive safety check up followed by approval to restart.
The Kori reactor is located in the country's southeastern coastal town of Gori in Busan.
It was shut down last month due to malfunction of electric circuits.
Then, it underwent an inspection especially with rising safety concerns regarding nuclear power plants following Japan's latest nuclear crisis.
The Korean government plans to continue running the 33-year-old reactor through 2017 which is long past its original 30-year lifespan despite opposition from local civic groups.
Meanwhile, the Seoul government also plans to spend one trillion won or about 920 million US dollars for the next five years on improving safety of all atomic power reactors in the country.