Japan declared an atomic power emergency Friday, ordering the evacuation of thousands of residents living nearby the Fukushima nuclear power plant, which was damaged in that country's magnitude 8.9-magnitude earthquake. This marks the first time that Japan has issued such a warning for one of its nuclear facilities.
The New York Times reports that a continuing major concern at the Fukushima 1 nuclear power plant, northeast of Tokyo, is over its cooling system. In a separate AP dispatch, Japanese officials announced their plan to release "slightly radioactive" vapor that had built up in the system since the quake disabled normal cooling functions. Pressure in one of the plant's six cooling towers had increased to a level 1.5 times what's considered normal, the wire service reported.
The plant's cooling facility requires an uninterrupted supply of electricity to cool the heat from radioactive fuel rods even after engineers have taken the remainder of the plant offline. As Times reporter Matthew L. Wald explains:
<p style="padding:0 0px 1em; font-style:italic;">Heat from the nuclear fuel rods must be removed by water in a cooling system, but that requires power to run the pumps and to align the valves in the pipes. So the plant requires a continuous supply of electricity even after the reactor stops generating its own power. […]</p>
<p style="padding:0 0px 1em; font-style:italic;">Civilian power reactors are designed with emergency diesel generators to assure the ability to continue cooling even during a blackout. …It was not immediately clear how many there are at Fukushima, but the operators reported earlier in the day that they were not working, prompting the evacuation.</p>
<p style="padding:0 0px 1em; font-style:italic;">Fukushima 1, which was designed by General Electric and entered commercial service in 1971, was probably equipped to function for some hours without emergency diesel generators, according to David Lochbaum, who worked at three American reactor complexes that use General Electric technology. …</p>
<p style="padding:0 0px 1em; font-style:italic;">If the cooling system remains inoperative for many hours, the water would eventually boil away, he said, and the fuel would begin to melt. That is what happened at Three Mile Island, the reactor near Harrisburg, Pa., that suffered a partial core melt in March 1979. In that case the cause was not an earthquake, but mechanical failure, operator error and poor design, government investigators later found.</p>
<p style="padding:0 0px 1em; font-style:italic;">Mr. Lochbaum, who now works for the Union of Concerned Scientists, a group that is very often critical of nuclear safety standards, said that if the cooling water in the vessel was boiling away, the process of boiling enough to expose the fuel would take "hours, not minutes."</p>
Meanwhile, an analyst with the international nuclear power group, the World Nuclear Association, told Reuters that water was now being pumped into the cooling system at Fukushima, describing the situation as "under control."
(The Fukushima No. 1 plant in Fukushima Prefecture, northern Japan, in October 2008. Kyodo, via AP.)