Tokyo Electric Power's (Tepco) Fukushima power plants were thrust back into the spotlight on Tuesday, after an earthquake hit the region, reviving memories of 2011's tragic nuclear disaster.
A 7.4 magnitude quake shook the coast of Fukushima at about 6 a.m. local time, producing a tsunami with 3-meter high waves on the northern Pacific coast, Japan's Meteorological Agency (JMA) said. American quake monitoring agency USGS later downgraded the magnitude to 6.9, from its initial measure of 7.3, and tsunami warnings were lifted by 12.50 p.m. local time.
Tuesday's quake was actually an aftershock of the 9.1 magnitude earthquake in 2011 that hit the same region, according to the JMA. Back then, the deadly quake and subsequent tsunami destroyed the cooling system at Tepco's Daiichi nuclear plant, resulting in a massive meltdown and the release of radioactive material that continues to contaminate the area.
Following Tuesday's quake, Tepco's Daini plant—separate from the Daiichi unit—said that a system designed to keep atomic fuel cool at one reactor was halted. But after around 90 minutes, Tepco announced that it had restarted the cooling system. Even when plants are shut, fuel needs to be kept cool to prevent overheating, which could lead to meltdown, as occurred in 2011.
Experts were quick to praise the firm's quick technical response and communication.
"Tecpco did much better this time than in 2011...As someone who is chairing their reform committee, I always want them to improve but they did well today," remarked Dale Klein, associate vice chancellor for research at the University of Texas System.
For the past five years, all of Tepco's plants in Fukushima have remained shut since and no problems were announced at other plants on Tuesday.
Lake Barrett, a nuclear engineer and former executive at the U.S. Nuclear Regulatory Commission, told CNBC's "Squawk Box" that Tuesday's quake couldn't inflict serious harm on any of Tepco's plants.
"In the five years since those plants were operating, the amount of [generated] heat is very small, it's the same as a car engine. It would take a while to get to a serious situation and because there's plenty of time for the auxiliary power supply and pumps to add cooling water, there's no significant risk," he said.
Tepco said on Tuesday that temperatures in Daini's nuclear fuel rod pool would take a full week [of heating] before reaching dangerous levels, local media reported.
Tuesday's scare didn't last long but it was still enough to generate fear in a country still reeling from the 2011 disaster.
"These events do reinforce the idea that there are issues with having nuclear power in Japan. So there could be another rise in the sentiment against nuclear power," said Takuji Okubo, principal and chief economist at Japan Macro Advisors.
Social media commentators echoed the same sentiment.
Last year, Kyushu Electric became the first utility company to bring its nuclear reactors back online after new, post-disaster safety rules were implemented. This month, regulators cleared the way for the firm to restart two more reactors.
The ruling Liberal Democratic Party wants Japan to return to nuclear power in order to lower electricity costs, with Prime Minister Shinzo Abe hoping for nuclear power to make up 22 percent of Japan's energy mix by 2030, versus more than a quarter before the 2011 tragedy.
But the public remains opposed to the idea of active nuclear plants, according to opinion polls. And the victory of Ryuichi Yoneyama in Niigata's gubernatorial elections in October seemed to confirm that. Yoneyama's promise to ensure the prefecture's nuclear plant—the seven-reactor Kashiwazaki-Kariwa complex, the world's biggest nuclear power station—would remain closed helped the political outsider defeat the LDP-backed Tamio Mori, local media said.
It remains to be seen if Tuesday's incident will derail Abe's nuclear hopes.
"It all depends if the public views this as a glass half-full or half-empty situation. In terms of safety, Tepco demonstrated they were better prepared so that should give the public more confidence [in nuclear plants]," said Klein.
There were still steps Abe could take to further reassure the public, he added.
Nuclear plants store radioactive water in storage tanks so in order prevent any accidents in the face of future quakes, the government should undertake a controlled release of the contaminated water in a safe and environmentally sound manner, Klein said.