- - Thursday, May 5, 2011

TOKYO | Outfitted like scuba divers, workers on Thursday entered a reactor building for the first time since an explosion crippled the Fukushima nuclear power plant in March and began releasing radiation.

A team of workers donned masks and heavy oxygen tanks, then took turns inside Unit 1 for 10 minutes at a time, officials for Tokyo Electric Power Co. (Tepco) said. The workers set up hoses for a ventilation system that they hope will filter 95 percent of dangerous radioactive elements out of the air.

If the ventilation system succeeds, workers will be able to spend more time inside to set up a cooling system, which is needed to achieve a cold shutdown of the reactor, one of four stricken units at the plant.

If the operation fails, workers could face higher radiation levels inside, or they might not be able to go near the damaged reactors, which could explode again if they overheat.

“We have completed work to place eight ducts inside the facility for the air-cleaning system,” Tepco spokesman Taisuke Tomikawa said. “The operation went smoothly, with no major troubles today, and the radiation the workers were exposed to was, so far, lower than originally expected.

“We plan to operate the system for a few days so that we can reduce radiation to around one-twentieth of the current level inside the facility,” he said.

Tepco then will begin building a new cooling system outside the reactor, with water pipes connecting it to heat exchange equipment inside, Mr. Tomikawa said.

The nuclear safety agency said the filters and ventilators were running.

“We will operate the [ventilators] for about two or three days. After that we plan to start work on actually installing the cooling system,” spokesman Naoyuki Matsumoto said.

Hydrogen explosions at four of the plant’s six reactors blew apart some of their walls and roofs and scattered radioactive debris, forcing some 80,000 residents within a 12-mile radius to evacuate.

Since workers could not safely approach the reactors, a remote-controlled robot, made in the United States, has been recording levels of radiation. Data last Friday showed a drop in levels, and the operator decided to send workers in, Mr. Tomikawa said.

On Thursday, workers set up a tent around the building’s entrance to prevent radioactive air from seeping into the outside atmosphere. Entering in small teams at intervals, workers were exposed to levels of radiation just below the legal limit, Mr. Tomikawa said.

Little is known about the workers. Neither media nor independent analysts have not been allowed near the site since the March 11 tsunami wiped out the plant’s electrical systems, causing reactors to overheat.

At Tepco headquarters in Tokyo, government officials, company scientists and nuclear regulators have been joining together to give extensive press conferences that many local and foreign reporters say lack context, analysis of human health risks and independent views.

Many executives have worked in Tepco and the government’s regulatory agency, raising concerns over what local media calls a “culture of complicity” in a “nuclear village” where criticism or whistle-blowing is discouraged or punished.