TOKYO — Clouds of superheated, radioactive steam forced four workers to retreat from a damaged nuclear reactor Wednesday in the latest setback in attempts to control radiation spewing from the hobbled Fukushima power plant.
While the government and Tokyo Electric Power Co. (Tepco), a privately run utility in charge of the Fukushima Dai-ichi plant, have publicly reaffirmed that they are on track to shut down the plant's six nuclear reactors by the end of the year, conditions appear to be worsening at units 1, 2 and 3, with officials and experts increasingly indicating that a "meltdown" is indeed under way.
Workers entering unit 2 on Wednesday for the first time since a March 15 explosion were unable to withstand the high heat and humidity inside the building housing the reactor, Tepco officials said. They stayed inside for only 14 minutes.
Vapors in the building, likely caused by water evaporating off pools containing spent nuclear fuel rods, could hamper efforts to install equipment needed to recycle contaminated water through damaged reactors.
High levels of radiation also have forced workers, who briefly entered reactor unit 1 for the first time earlier this month, to delay plans to install a new cooling system there.
Critics have long accused Tepco and the government of withholding information from the public. Tepco this week began releasing some 2,000 pages of documents that describe versions of events immediately after the March 11 earthquake and tsunami.
Tepco officials now say the initial 9.0 magnitude earthquake, not just the 50-foot high tsunami, may have damaged vital equipment needed to activate cooling systems either by back-up electricity or by workers who tried to open valves manually.
Though Tepco officials have made several promises over the past two months to restore cooling systems "within days," no progress has been reported. Officials have been saying they still lack a clear picture of actual conditions at the plant because of damaged or malfunctioning gauges. No journalists or independent outside observers have been allowed near the plant, and the government has sealed off a 12-mile radius around the buildings.
Tepco also is not releasing information about an estimated 1,900 workers at the site. They have refused to provide the name or many details about a worker who died earlier this week. Police are investigating the cause of death.
Goshi Hosono, special adviser to Prime Minister Naoto Kan, told reporters Monday that "we have to assume that meltdowns have taken place" at reactors 1, 2 and 3.
At a separate news conference the same day, Haruki Madarame, chairman of the Nuclear Safety Commission, also used the word "meltdown," which most officials have been avoiding until now.
"When highly contaminated water was found at the No. 2 reactor building in late March, we recognized that a meltdown had taken place. So I informed the government," he said.
"As for No. 1 and No. 3 reactors, we recognized that, given the processes that led to the accidents there, the same thing had occurred."
Mr. Kan said Wednesday that Japan needs to increase the independence of its nuclear regulators, who until now have been working in the same ministry as plant operators, unlike most other nations.