One of the Japanese nuclear reactors experienced a total meltdown, but we're only finding out two months after the accident
The No. 1 nuclear reactor at Fukushima Daiichi melted down in the first day after the massive quake and tsunami cut power to the plant, the Tokyo Electric Power Company admitted Sunday.
As Nature News' Geoff Brumfiel reports, workers went into the unit recently "to recalibrate some of the sensors on the reactor." Much to their surprise and dismay, they found that the core experienced a total meltdown. The zirconium alloy tubes that hold the uranium fuel pellets during normal operation all warped and the uranium is now lying at the bottom of the pressure vessel, or possibly even outside of it in the basement below or outside the concrete containment building. With all the fuel piled up at the bottom, there is some danger that the nuclear reaction could have restarted. As of now, engineers on the scene aren't sure what happened.
The revelation that the reactor experienced a total meltdown doesn't change the situation at Fukushima that much. The temperatures inside the reactor now appear to be low enough that whatever happened to the fuel is not continuing. The same cooling and cleanup operations must happen.
But what the information does highlight is that when a nuclear reactor gets damaged, the people in charge have to make a lot of decisions with imperfect information. The scary thing about a nuclear disaster like this is that here we are two months later and new (and very important) news about what happened is still coming out.