TOKYO — Japanese officials and safety workers struggled to reassert control over badly damaged nuclear reactors and avert calamity on Tuesday, after the situation at the stricken Fukushima plant appeared to verge towards catastrophe. Radiationn levels shot up at the plant after a new explosion and fire.
Though the situation remained dangerous, there were signs that workers had, at least for the moment, contained some of the danger: The escalated radiation levels of earlier in the day — possibly from a fire in the No. 4 reactor — stabilized and then declined towards evening, according to Japanese authorities.
Engineers at the plant, working at tremendous personal risk, on Tuesday continued efforts to cool down the most heavily damaged unit, reactor No. 2, by pumping in seawater. According to government statements, most of the 800 workers at the plant had been withdrawn, leaving 50 or so workers in a desperate effort to keep the cores of three stricken reactors cooled with seawater pumped by firefighting equipment, while crews battled to put out the fire at the No. 4 reactor, which they claimed to have done just after noon on Tuesday.
But late Tuesday, Japan’s nuclear watchdog said a pool storing spent fuel rods at that fourth reactor had overheated and reached boiling point and had become unapproachable by workers at the plant. The fire earlier Tuesday morning was sparked by a hydrogen explosion generated by rising temperatures at the fuel pool, which released radioactivity directly into the atmosphere. The government said late Tuesday that radiation levels at the Fukushima plant also appeared to be falling sharply from levels earlier in the day.
The fourth reactor had been turned off and was under refurbishment for months before the earthquake and tsunami hit the plant on Friday. But the plant contains spent fuel rods that were removed from the reactor. If these rods had run dry, they could overheat and catch fire. That is almost as dangerous as the fuel in working reactors melting down, because the spent fuel can also spew radioactivity into the atmosphere.
In a brief morning address to the nation Tokyo time, Prime Minister Naoto Kan pleaded for calm, but warned that radiation that had leaked earlier had already spread from the crippled reactors and there was “a very high risk” of further leakage.
The sudden turn of events, after an explosion Monday at one reactor and then an early-morning explosion Tuesday at yet another — the third in four days at the plant — already made the crisis at the Fukushima Daiichi Nuclear Power Station the worst nuclear accident since the Chernobyl reactor disaster a quarter century ago. It had already become impossible for workers to remain at many areas within the plant for extended periods, the nuclear watchdog said.
Shigekatsu Oomukai, a spokesperson for the Nuclear and Industrial Safety Agency, said the substantial capacity of the pool meant that the water in the pool was unlikely to evaporate soon. But he said workers were having difficulty reaching the pool to cool it, because of the high temperature of the water.
Worryingly, temperatures appeared to be rising in the spent fuel pools at two other reactors at the plant, No. 5 and No. 6, said Yukio Edano, the chief cabinet secretary.
Earlier Tuesday, the Japanese government told people living within about 20 miles of the Daiichi plant to stay indoors, keep their windows closed and stop using air conditioning.
Mr. Kan, whose government was extraordinarily weak before the sequence of calamities struck the nation, told the Japanese people that “although this incident is of great concern, I ask you to react very calmly.” And in fact, there seemed to be little panic, but huge apprehension in a country where radioactivity brings up memories of Hiroshima and Nagasaki, the haunting images of post-war Japan.
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