Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer.
Another major earthquake rocked northeastern Japan again Monday evening at 5:16 local time, and was followed by a number of strong aftershocks. The 7.0-magnitude quake caused some cities to lose power, and there were reports of a mudslide and the collapse of houses that had been weakened by previous shocks. The quake was felt as far away as Tokyo. Shinkansen bullet trains in the region were halted and bullet train services between the capital and Osaka in the southwest were also suspended for a short time.
Off-site power at the crippled Fukushima Dai-1 nuclear plant was lost immediately following the quake, but was restored again at 6:05 p.m. local time. During the power outage, water injections into reactors 1, 2, and 3 were halted for about 50 minutes. Though back-up diesel generators and power trucks were on hand to provide power for pumping water, a tsunami warning issued by the Meteorological Agency caused workers to evacuate from the vicinity of reactors 1 through 4, leaving no time to manually switch over to the back-up systems, according to NHK, Japan’s national broadcaster.
Tokyo Electric Power Co. (TEPCO) said that when workers returned to the site once the tsunami warning was lifted, monitoring systems showed no signs of radiation increases, and no other significant problems were found. However, as of 9 p.m. local time there was no word on when workers would resume pumping nitrogen into the No. 1 reactor, after the operation was halted by the quake. The nitrogen injections reduce the likelihood of another explosion happening through a buildup of hydrogen and oxygen in the reactor.
The quake was almost the same magnitude as the 7.1 aftershock that struck the area last Thursday night, which caused problems for other nuclear plants in the region. But this time around, the Nuclear and Industrial Safety Agency (NISA) announced that the quake had caused no serious problems at nuclear stations.
Yukio Edano, Japan's Chief Cabinet Secretary, told reporters in an afternoon press conference that the government will extend the 20-kilometer evacuation zone around the Fukushima Dai-1 nuclear plant. Until now, people living between 20 and 30 km from the plant were told they could evacuate voluntarily; the new evacuation orders will apply to some towns in the 20-to-30-km zone and beyond. Because radiations levels are relatively high in these areas, Edano said that health officials are worried about the cumulative impact of radiation on residents living there for the next six to twelve months. The government will work with the concerned municipalities on evacuating residents over the next four weeks. Edano added that the government would also designate certain areas in the 20-to-30-km zone the "emergency preparation evacuation zone," where residents would be asked to be prepared to evacuate in case of an emergency.
Meanwhile, work continued over the weekend on emptying storage tanks, a mission that included dumping thousand of tons of slightly radioactive water into in the ocean. The tanks were cleared to make storage room for highly radioactive water that had pooled in the No. 2 reactor's turbine building and outside trench. The water needs to be removed from these locations, as well as the turbine basements and trenches of reactors 1 and 3, to give workers access to the reactors' crucial cooling systems, which have been offline since the tsunami. Restoring the reactors' cooling functions would allow TEPCO to end the current stopgap efforts of constantly injecting water into the reactors to keep the fuel rods covered with cooling water. TEPCO has estimated the total amount of pooled water at 60 000 tons, so the company has made arrangements to have additional storage tanks brought to the site.
There is little time to lose, because some water levels are rising. Experts believe the most highly radioactive water was contaminated by the No. 2 reactor core, where the fuel rods are thought to have been damaged through overheating. That water has gradually been edging up the No. 2 building's trench shaft since TEPCO managed to stem a leak of contaminated water, which was gushing into the ocean via a cracked concrete pit. Nishiyama said on Sunday that water in the trench shaft had risen 12 centimeters and was now less than a meter away from spilling over the top.
IMAGE: JAPAN METEOROLOGICAL AGENCY