The No. 4 reactor at Kansai Electric Power Co.'s Oi plant in Fukui Prefecture in western Japan was taken off-line late Sunday, making it the second time the country has been without nuclear power since an earthquake and tsunami in March 2011 destroyed the Fukushima-Daiichi nuclear plant.
The country's other 49 reactors went offl-line earlier.
Kyodo News reported that with the halting of the 50th reactor the government, under the new nuclear regulations that took effect in July, will likely keep all the reactors off-line until the end of the year while regulators decide which ones would be safe enough to restart.
Public sentiment against resumption of any of the nuclear power plants remains strong even though many utilities, forced to resort to thermal power generation, have increased electricity rates.
About 8,000 people marched on Tokyo streets during the weekend to show their opposition to restarting any nuclear plant, Kyodo reported.
"We want to keep telling what is happening at Fukushima even though everybody is talking about the Olympics," said Nobel literature laureate Kenzaburo Oe, who organized the anti-nuclear rally. Last week, Tokyo was picked as the venue for the 2020 Summer Olympics.
There have been reports the crippled Fukushima plant is still leaking contaminated water despite massive efforts to shut down the facility permanently.
Before the March 2011 disaster, nuclear power supplied about 30 percent of Japan's electricity.
Kyodo said a dozen reactors, including the Oi plant's No. 3 and No. 4 units, are awaiting safety confirmation from the Nuclear Regulation Authority.
Prime Minister Shinzo Abe's government, which wants to pull the country's economy out of 15 years of deflation, has said nuclear power will play a key role in meeting the country's energy demand.