TOKYO—Japan unveiled its plan to clean up the Fukushima Daiichi nuclear plant and return the surrounding region to normal, a 40-year process that represents one of the most ambitious such efforts in history. 
 
 The plan lays out a timetable to completely dismantle the plant, where reactors overheated dangerously following the March 11 earthquake and tsunami. It includes the development of robots to decontaminate the reactor buildings and technology to seal leaks in walls submerged in radioactive water. 
 
 The path laid out is arduous and slow: Officials estimate they won't finish plugging Fukushima Daiichi's leaky reactor buildings until 2018. Removing the melted fuel rods from three reactors will take 25 years, or until about 2036. 
 
 Plant operator Tokyo Electric Power Co. has estimated the decommissioning process will cost roughly ¥1 trillion ($12.8 billion), although that figure is expected to rise. 
 
 The decommissioning plan follows a proposal announced earlier this week, to start—as early as April—to return to their homes some of the 88,000 evacuees from areas nearest the plant, and to spend at least ¥1 trillion on decontaminating towns, parks and roads. It comes as the government also considers tightening food-safety standards to permit only one-fifth of the radioactive cesium that current rules allow. 
 
 Together, those proposals form the backbone of Japan's plan to deal with the long-term repercussions of the world's second-worst nuclear accident, following Chernobyl in 1986. Experts say the program will be extremely challenging to implement, in part because they aim to bring the region back, as much as possible, to the way it was before the accident. 
 
 "There is a strong call for us to put a lot of effort into decontamination, into restoring everything that can be restored, so people can live there again," said Goshi Hosono, Japan's minister overseeing the nuclear crisis, in an interview with The Wall Street Journal. "In order to restore things, we need to work on developing the technology, and devote plenty of money to whatever else is needed.'' 
 
 In many ways, Japan's cleanup and restoration plans are more ambitious and challenging than those following the nuclear accidents at Three Mile Island in the U.S. and Chernobyl in the former Soviet Union. 
 
 The 1979 accident at Three Mile Island was much smaller in scale, and emitted far less radioactive material into the atmosphere. The reactor's fuel rods were damaged, but the vessels in which they were contained were intact. 
 
 That is a very different situation than at Fukushima Daiichi, where the fuel in three reactors is thought to have burned holes in their immediately surrounding pressure vessels, and in one case to have fallen all the way through to the bottom of the outer containment vessel. The reactor buildings and equipment at Fukushima Daiichi also are damaged and leaking radioactive water, something that didn't happen at Three Mile Island. 
 
 Experts say those differences present huge technological challenges—particularly in figuring out how to get to the bits of melted fuel. Those bits are likely scattered around the piping and other equipment at the bottom of the reactors' containment vessels "like bird droppings,'' says Tadashi Narabayashi, a professor of reactor engineering at Hokkaido University. 
 
 According to the government's blueprint for dismantling Fukushima Daiichi, engineers will first have to repair the reactor building leaks, which could take six years, then drain the buildings of radioactive water, which could take an additional two years. 
 
 Those estimates themselves are iffy, since nobody knows yet where the leaks are, says Hajimu Yamana, a professor of nuclear engineering at Kyoto University and head of a government panel studying how to dismantle the plant. "It's a bit of a stretch to say you'll do something in [a certain number of] years, when you don't know what it is you have to do,'' he said. 
 
 Not until 2022 does the plan foresee beginning the process of removing the melted fuel. 
 
 Japan's cleanup plans also are more ambitious than those in place at Chernobyl, but for different reasons, experts say. In that accident, the lack of a containment vessel surrounding the reactor meant radioactive materials from the accident were spread far and wide. Japanese officials point out that radiation released from Fukushima Daiichi is still only about 15% of what was emitted at Chernobyl. 
 
 But the Chernobyl cleanup plans were also simpler, experts say: Build a thick concrete container around the shattered reactor and move people away permanently. That won't work in Japan, where land is scarce and attachments to it are strong, says Mr. Hosono, the nuclear-crisis minister. "In this small country, people won't accept it if there is a big area where nobody is able to live,'' he says. 
 
 That means Japan is prepared to spend a lot of time, energy and money cutting up the contaminated plant and cleansing the site, so that people feel safe moving back near it. The government also has released ambitious plans to decontaminate surrounding areas to radiation levels that—while still many times what they were before the accident—are considered well below levels that scientists have found to be dangerous. 
 
 "We're trying to restore the land, even if living there doesn't raise health concerns,'' says Mr. Yamana. "That is very difficult.'' 
 
 —Juro Osawa contributed to this article. 
 
 Write to Phred Dvorak at phred.dvorak@wsj.com and Mitsuru Obe at mitsuru.obe@dowjones.com ||||| TOKYO (Reuters) - Japan on Tuesday approved an increase in compensation payments for the Fukushima crisis to 7.07 trillion yen ($57.18 billion), as tens of thousands of evacuees remain in temporary housing more than four years after the disaster. 
 
 Tokyo Electric Power Co (Tepco), the operator of the wrecked Fukushima Daiichi nuclear station, will receive 950 billion yen more in public funds on top of the 6.125 trillion agreed earlier, the utility and the government said. 
 
 The increase, agreed after a request by Tepco, adds to the bill for taxpayers for the disaster in March 2011, when three reactors melted down after an earthquake and tsunami, in the worst nuclear crisis since Chernobyl in 1986, destroying businesses and livelihoods. 
 
 Tepco has face a stream of legal cases seeking compensation over the disaster. 
 
 Electricity bills for Japanese households have also risen 25 percent since the catastrophe as the country resorted to importing more fossils fuels with the gradual shutdown of all nuclear reactors for safety checks and upgrades. 
 
 Prime Minister Shinzo Abe's government and Tepco, which was bailed out by taxpayers in 2012, are undertaking an unprecedented cleanup to lower radiation levels in towns closest to the plant, although some areas will likely remain off limits for decades. 
 
 Inside the plant, Tepco has struggled to bring the situation under control and it is estimated removing the melted fuel from the wrecked reactors and cleaning up the site will cost tens of billions of dollars and take decades to complete. 
 
 The government plans to revoke evacuation orders for most people forced from their homes by the disaster within two years as part of a plan to cap compensation payouts and speed up reconstruction. 
 
 (Reporting by Osamu Tsukimori; Editing by Aaron Sheldrick and Ed Davies) ||||| TOKYO — Decommissioning the wrecked reactors at the Fukushima Daiichi nuclear plant will take 40 years and require the use of robots to remove melted fuel that appears to be stuck to the bottom of the reactors’ containment vessels, the Japanese government said on Wednesday. 
 
 The predictions were contained in a detailed roadmap for fully shutting down the three reactors, which suffered meltdowns after an earthquake and tsunami struck the plant on March 11. The government had previously predicted it would take 30 years to clean up after the accident at Fukushima, the world’s worst nuclear disaster since Chernobyl in 1986. 
 
 The nuclear crisis minister, Goshi Hosono, acknowledged that no country has ever had to clean up three destroyed reactors at the same time. Mr. Hosono told reporters the decommissioning faced challenges that were not totally predictable, but “we must do it even though we may face difficulties along the way.” 
 
 The plan’s release follows last week’s declaration by Prime Minister Yoshihiko Noda that the plant had been put into the equivalent of a “cold shutdown,” a stable state that suggested the runaway reactors had finally been brought under control. Critics, however, immediately challenged that statement, saying it was impossible to call the reactors stable when their fuel had melted through the inner containment vessels, and appeared to be attached to the concrete bottom of outer containment vessels. 
 
 Still, the government appears ready to move ahead with the next stage of the cleanup. According to Wednesday’s roadmap, the plant’s operator, Tokyo Electric Power, will spend the next two years removing spent fuel rods from storage pools located in the same buildings as the damaged reactors. At least one of those pools, which are highly radioactive, was exposed by hydrogen explosions that destroyed the reactor buildings in the first days of the accident. 
 
 The most technically challenging step will be removing the melted fuel, a process that the government said will take 25 years and require new types of robots and other new technologies that have not even been developed yet. After the removal, fully decommissioning the reactors will take another 5 to 10 years, according to the roadmap.
– It's going to take decades to completely decommission the Fukushima nuclear power plant, but a critical step in that process began in earnest today, reports NBC News. One of the six 136-foot covers draped over one of the plant's nuclear reactors to keep radioactive materials from seeping out is being painstakingly removed. Tepco officials say it will take till the end of 2016 to pry all six covers off, and till at least 2020 to remove the nearly 300 spent fuel rods lurking underneath. The project, which was supposed to commence last July, was previously postponed because of fears of radiation escaping. "For the safety of Fukushima's residents, we would like the work to proceed with extra care," says the chief of a group of monitors overseeing the project. The total cost and time for the entire decommissioning assignment: tens of billions of dollars over 30 years or so, NBC notes. Meanwhile, the Japanese government today approved an increase in compensation payments to Tepco to a total of $57.2 billion, Reuters reports. That's $7.7 billion added onto the $49.5 billion in taxpayer-funded aid that Tepco had previously been approved to receive. (Check out more details about the decommissioning project on Tepco's dedicated website.)