Progress reported at Japan nuclear plant

(CNN) — One day after black smoke prompted an evacuation, workers returned Thursday to the Fukushima Daiichi nuclear plant — employing myriad methods at the troubled facility to try and prevent more radiation from seeping into the atmosphere.

After several days of setbacks and billowing smoke, authorities talked Thursday mostly about progress in tackling issues at each of the facility’s six reactors.

“We are working to resume (operations),” Japanese Chief Cabinet Secretary Yukio Edano said. “We cannot be too optimistic, and we are still taking cautious measures.”

The smoke rising above the plant’s No. 3 reactor was nowhere to be seen shortly before 10 a.m. Thursday, said Hidehiko Nishiyama, an official with Japan’s nuclear and industrial safety agency.

He said the cause of the smoke remains unknown, speculating it may have come from burning oil or machinery nearby.

And the Japan Atomic Industrial Forum, an industry trade group, reported Thursday that — despite previous fears — the No. 3 reactor’s containment vessel was “not damaged.”

About 500 tons of seawater began being injected into that reactor shortly after 5:30 a.m. Thursday, Nishiyama said.

Authorities intend to eventually switch to fresh water, he said, without providing an explanation as to why or a timetable.

In addition, firefighters from Tokyo and Yokohoma cities are preparing to spray another 500 tons of water toward that reactor’s nuclear spent fuel pool, which Nishiyama said could happen Thursday or Friday.

These pools contain fuel rods that, if not cooled down, can overheat and, in the process, release radioactive vapors into the air.

Edano on Thursday downplayed concerns about white smoke reportedly rising from other reactors.

The “vapor” rising near the No. 1 reactor at the plant is “only natural” and not a cause for alarm, he said, especially since water is now in that unit’s nuclear spent fuel pool.

He added that the temperature at the No. 1 reactor “right now is going down.”

Nishiyama added that by decreasing the rate of water being pumped into the reactor early Thursday, authorities had also decreased pressure that had earlier been rising.

Previous buildups of hydrogen gas has contributed to at least three explosions — several of which caused injuries and coincided with spikes in radiation — at the power plant’s Nos. 1, 2 and 3 units.

Light was restored Thursday in the No. 1 reactor’s central control room, a Tokyo Electric Power Co. official told CNN.

But it was just a partial restoration, as workers continued to try to get electricity going for control panels and cooling system pumps at the reactor. Nishiyama said that the hope is to begin cooling the unit’s spent fuel pool Friday using outside power.

While describing the No. 2 unit as “quite stable,” Nishiyama did note (but did not explain) “high radiation readings” nearby.

Seawater continues to be pumped in an effort to cool down nuclear fuel rods and prevent the further emission of radioactive material into the atmosphere.

Members of Japan’s self-defense forces on Thursday doused the nuclear spent fuel pool at the No. 4 reactor. Nishiyama estimated that this effort should wrap up Friday.

And Nos. 5 and 6 reactors appear safe for now, the nuclear safety official said.

The temperatures at both units are relatively low, though that could change after their cooling system gave out on Wednesday.

Nishiyama said workers hope to get that machinery back working soon, part of a plant-wide plan to restore power gradually in the next few days.

“The power source is going to the main control room because that is the main nerve center of the entire plant,” Nishiyama said.

“Once they get that restored, then we have some instrumentation and we can figure out what’s going on in the power plant that up to this point has been almost impossible to figure out.”

Once that is done, he said that power will be sent to individual pieces of equipment and the situation will be analyzed. He estimated it could take two weeks or more to get the plant “in a stable, cold shut-down configuration.”

Lake Barrett, a nuclear engineer who led the initial cleanup and response of the Three Mile Island plant in Pennsylvania following a partial core nuclear meltdown in 1979, said there’s likely no saving the plant — though much can, and still needs, to be done to keep the crisis under control.

“It is an industrial catastrophe,” Barrett said. “It’s a huge plant, and it’s been basically destroyed internally and has high contamination levels inside. There are areas in the building where no human is going to go for a long time.”

But Barrett said the situation should be controlled and the radioactive fallout measured enough such that the long-term repercussions for the public health are relatively minimal.

“It’s also not a health catastrophe — as long as the people follow the instructions from the government, they’re going to be safe in Japan,” he said.