By Kevin Krolicki and Kiyoshi Takenaka
FUKUSHIMA, Japan (Reuters) - Japanese officials said on Saturday the unprecedented effort to remove spent fuel rods from one of the crippled Fukushima nuclear reactors was on track despite lingering concerns about the structure's vulnerability to another earthquake.
"I don't think the situation is unstable," said Goshi Hosono, Japan's minister in charge of the response to the nuclear crisis. He was speaking to reporters after his first tour of the twisted and partly destroyed building that houses Fukushima's No. 4 reactor.
The visit marked an effort by Japanese officials to show they are addressing international concerns about the risk of a second accident at Fukushima, and a group of reporters were allowed to accompany Hosono on his tour of the plant while clean-up operations were suspended for the day.
Hosono said he expected workers to begin removing fuel from the No.4 reactor's storage pool next year. Work began last month to raise what amounts to a giant tent over the building to keep radioactive dust from scattering during the transport of the fuel rods.
"We want to move as quickly as possible," Hosono said.
Tokyo Electric Power, the utility that operates the Fukushima Daiichi plant, says its analysis shows the No.4 reactor building would hold up in a strong earthquake even after being badly damaged by a hydrogen explosion last March when three nearby reactors suffered meltdowns.
Japanese safety regulators on Friday ordered Tepco to recheck its findings after measurements showed the west wall of the reactor building was buckling out by about 3 centimeters (1.2 inches).
Hosono said the government accepted Tepco's estimate that the No.4 reactor could withstand an earthquake measuring a "strong 6" on the Japanese scale.
The magnitude 9 quake last March that triggered a tsunami and overran Fukushima's back-up power systems was measured at 7 on the Japanese scale north of the plant in Miyagi prefecture.
Some environmental critics charge the No.4 reactor presents a particular risk of a knock-on disaster if a subsequent earthquake were to topple it or puncture its fuel storage pool and allow the 20 meters (65 feet) of water now covering and cooling 1,535 uranium fuel assemblies to drain away.
Such an accident, they say, could release far more radiation than the leaks of radioactive water Tepco has battled since improvising a system for cooling reactor cores last year.
Hosono, who was accompanied by aides and bodyguards on his tour of the plant, climbed a narrow and dark staircase built with scaffolding to take workers to the top of the No.4 building where the fuel pool has been covered with a tarp.
Tepco has taken steps to shore up support for the pool, which measures 10 meters by 20 meters across, by adding a cement column underneath.
Officials from the utility demonstrated how they were using water in the pool as a kind of level to confirm the building was not tipping. They also showed a grid of floats holding up the tarp they said could support a person if a worker fell in.
Hosono said his biggest concern was ensuring Japan could secure the labour and talent to finish the decommissioning of the Fukushima reactors over the coming decades.
"This may take 30 or even 40 years to complete and extremely difficult work is still ahead of us," he told Tepco workers.
(Editing by Sophie Hares)