The restart of the Sendai plant is viewed with suspicion by much of the public. The nearby volcanic activity does not help with this.
Japanese utility Kyushu Electric Power said on Monday that it was monitoring activity at a volcano near its Sendai nuclear plant, but did not need to take any special precautions after authorities warned of the risk of a larger-than-usual eruption.
The reactor is the first to be restarted under new safety standards put in place since the meltdowns at Fukushima in 2011.
The possibility of a significant eruption of Sakurajima, located about 50 km (30 miles) from Sendai, is a reminder of the volatile geology of Japan, which has 110 active volcanoes.Some residents within 3 km of the volcano have been evacuated in advance of the expected eruption.
"We are not currently taking any particular response," Kyushu Electric spokesman Tomomitsu Sakata said by phone.
"There is no impact in particular to the operations" of the Sendai plant, Sakata said. "We will continue to pay close attention to information from the Japan Meteorological Agency."
The 890-megawatt-reactor had reached 50 percent of its output by Sunday and the operator expects full power to be achieved around Aug. 24, Sakata said.
Critics of the nuclear industry say that new safety measures are insufficient, particularly for plants such as Sendai, which is located near five giant calderas, crater-like depressions formed by past eruptions, with the closest one about 40 km away.
The precautions by Japan's Nuclear Regulation Authority for volcanic eruptions were "wanting in a number of important respects" and did not meet international standards, said John Large, chief executive of Large & Associates, a nuclear engineering consultancy.
Large wrote a report this year on the Sendai plant's ability to withstand being hit by volcanic ash and has testified in court about the issue.
Sakurajima is one of Japan's most active volcanoes and erupts almost constantly. There was a risk of larger than usual eruption, an official at the Japan Meteorological Agency said on Saturday.