Bursts of smoke Monday from the buildings housing the No. 2 and No. 3 reactors forced repair crews to evacuate the crippled Fukushima No. 1 nuclear plant, but no rise in radiation levels was detected at the compound, the government and Tokyo Electric Power Co. said.

Tepco officials said they believed the smoke from the No. 2 reactor was actually water vapor and probably did not originate from the reactor itself or the spent fuel pool.

Around 9 p.m., a Tepco official in Tokyo told reporters that radiation levels around the No. 2 reactor had not changed.

Earlier in the day, gray smoke seen emanating from reactor No. 3 at around 3:55 p.m. prompted firefighters to evacuate, but had stopped by shortly after 6 p.m., the Nuclear and Industrial Safety Agency said.

The two incidents nevertheless prompted the Tokyo Fire Department to temporarily evacuate the facility and halt efforts for the day to spray the spent fuel pool with water.

NISA also said radiation levels did not change significantly at the compound on Monday afternoon and that the temperature and pressure inside the No. 3 reactor were also unchanged.

Chief Cabinet Secretary Yukio Edano told a news conference that “there are various inflammable materials” in the damaged building housing reactor No. 3.

On Sunday, a Self-Defense Forces helicopter flew over the plant to measure the surface temperatures of the six reactors there. All were below 100 degrees above where the six spent fuel pools are situated, indicating they all contained cooling water.

“The figures are reassuring to all the people” of Japan, Defense Minister Toshimi Kitazawa said Sunday.

Meanwhile, the focus of the operation continued to center on restarting the cooling systems at each reactor to keep the cores and the spent fuel in the unprotected storage pools from melting down. The entire plant lost power after it was doused by the tsunami on March 11.

Tokyo Electric Power Co. is in the process of checking out the electrical system of the No. 2 reactor, which was the first of the six to have its power center re-connected Sunday from cables Tepco laid outside the plant.

According to NISA, power to the air conditioning and monitoring equipment at reactor No. 2 might be restored by the end of Monday.

Power cables were connected to reactor No. 4 as well. Workers were busy checking whether cooling pumps and other key safety equipment were damaged by the quake and tsunami.

The spent fuel pool at No. 3 contains highly dangerous MOX, earlier reports said.

On Monday afternoon, Prime Minister Naoto Kan said slow but steady progress was being made to contain the crisis at the plant.

“Thanks to the desperate efforts of related parties, progress is being made, although the pace is slow,” Kan told the emergency headquarters at the prime minister’s office.

“Now we have started seeing some hope of getting out of this crisis situation,” he said.

Kan also said his administration was gearing up for Tohoku region reconstruction efforts.

Two 74-type tanks from the Ground Self-Defense Force arrived at the plant shortly after 6 a.m. Monday tasked with clearing away contaminated debris blocking access to key installations. The tanks’ heavy armor can block some radiation.

The Fire and Disaster Management Agency’s hyper-rescue team poured 1,137 tons of water from 8:39 p.m. Sunday to 3:58 a.m. Monday into the pool of spent fuel rods at the No. 3 reactor, and the Self-Defense Forces sprayed an additional 90 tons of water from 6:37 a.m. to 8:41 a.m.

NISA also said one worker at the plant had been exposed to more than 150 millisieverts of radiation in total but was not in need of medical attention.

Government regulations had set the maximum allowable radiation dose at 100 millisieverts in total, but the ceiling has been raised to 250.

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