Work to restore key equipment at the Fukushima No. 1 nuclear plant’s crippled reactors continued Thursday, despite reports of smoke rising from reactors No. 1 through 4.

The lights were turned back on in the central control room of reactor 1 at 11:30 a.m., following Tuesday’s news that the lighting was back in the reactor 3 control room.

Workers were preparing to test-run possibly by late Thursday a cooling pump to inject fresh water into reactor 3, instead of seawater that could damage components.

Meanwhile, three workers were exposed to relatively strong radiation on the basement floor of the No. 3 reactor’s turbine building Thursday, and two were sent to a hospital because part of the skin on their legs was contaminated with radioactive materials, according to the Nuclear and Industrial Safety Agency.

Later in the day, Tokyo Electric Power Co. ordered workers at the No. 3 unit’s basement floor and first floor to evacuate.

It was not immediately known how serious the condition of the two workers was. According to Chief Cabinet Secretary Yukio Edano, their legs were soaked in water that was contaminated with radioactive materials.

The two had been setting up cables inside the No. 3 unit building, Edano said.

Tepco said radioactive water may have seeped through their protective clothing. The injuries were caused by direct exposure to beta rays, the utility added.

The radiation exposure was between 170 to 180 millisieverts, it said.

The health ministry has raised the maximum allowable total radiation exposure for a worker to 250 millisieverts from the original level of 100, given the seriousness of the crisis at the crippled nuclear plant.

According to Tepco, none of the three workers has been exposed to a total radiation dose of 250 millisieverts or more, despite the accident.

By Thursday, 17 workers, including the three involved in the accident, had been exposed to 100 millisieverts or more in total.

White smoke was seen billowing out of reactors 1 through 4 as of 10 a.m. Thursday, but NISA said efforts to restore the facilities were not stalled.

Edano said he believed the smoke was most probably water vapor emanating from the reactors’ spent fuel pools, and said the situation is being monitored closely. “We are dealing with the situation with extreme caution,” he said.

On Wednesday, dark gray smoke was seen rising from reactor 3, forcing workers to evacuate temporarily.

But Tepco officials said Thursday that while they were uncertain what caused the smoke, it had anyway vanished by the time Tepco workers checked the site early Thursday, and pumping of seawater to its spent fuel pool resumed.

Efforts are currently under way to reactivate the cooling pumps in reactors 3 and 4, and engineers will also be checking whether the same could be done with reactors 1 and 2.

Tepco said a test-run of the cooling pump in reactor 3 would be conducted once it can be determined whether there was water left in the water storage tank, as an empty tank would risk damaging the pump.

A NISA spokesman said Thursday that reactivating the cooling pump will enable fresh water, rather than seawater, to flow through the reactor, which would be less damaging to the reactor facilities.

Information from Kyodo added

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