It will be the first to do so since reactors went offline due to safety concerns after the Fukushima accident last year.

Operator Kansai Electric Power Company plans to start lifting control rods in the No.3 reactor at 9:00 PM and the reactor is expected to reach criticality, starting a self-sustaining chain reaction, early on Monday.

The reactor will start generating power on Wednesday, and begin operating at full capacity four days later.

Although a growing group of protestors has blocked a road leading to the plant since Saturday, preventing workers' access, the utility expects there will be no impact on Sunday's work as it has already secured enough workers for the job.

The Ohi plant has been under around-the-clock monitoring since June 16th.

The Kyodo news agency reported earlier in the day a small amount of radioactive cesium has been detected in the urine samples of 141 children in Japan’s Fukushima prefecture, where the crippled nuclear power plant is still leaking radiation.

A total of 2,022 infants and young children were surveyed by a Japanese research group. Three urine samples contained more than 10 becquerels of cesium per kilogram, including a case with 17.5 becquerels. Ten becquerels or less of cesium was found in the samples of the other 138, the Yokohama-based Isotope Research Institute said. The urine samples also contained about an average 64 becquerels of radioactive potassium.