The China Syndrome refers to a scenario in which a molten nuclear reactor core could could fission its way through its containment vessel, melt through the basement of the power plant and down into the earth. While a molten reactor core wouldn't burn "all the way through to China" it could enter the soil and water table and cause huge contamination in the crops and drinking water around the power plant. It's a nightmare scenario,the stuff of movies. And it might just have happened at Fukushima.
Last week, plant operator Tepco sent engineers in to recalibrate water level gauges in reactor number 1. They made an alarming discovery: virtually all the fuel in the core had melted down. That means that the zirconium alloy tubes that hold the uranium fuel and the fuel itself lies in a clump---either at the bottom of the pressure vessel, or in the basement below or possibly even outside the containment building. Engineers don't know for sure, though current temperature readings suggest that fission inside the reactor core has definitely ceased for good (i.e. there will be no further melting).
Anecdotal evidence doesn't bode well for how far the fuel melted: Tepco has been pumping thousands of tons of water onto reactor 1 to try to cool it—yet the water level in the containment vessel is too low to run an emergency cooling system. That means the water is escaping somewhere on a course cut by molten fuel--probably into the basement of the reactor building, though it's also possible it melted through everything into the earth.
Many experts say a full-blown China syndrome is unlikely in large part because the fuel from the type of reactors at Fukushima is designed in such a way that it probably won't sustain "recriticality" once meltdown occurs. What's more, boron, which slows nuclear reactions, was pumped into the cooling water of the reactor after the initial accident to prevent the core from going "critical" again.
But assuming a worst case scenario hasn't occurred, having so much highly radioactive water sloshing around the basement is going to make cleanup even more difficult...
Was Fukushima a China Syndrome?
Monday, May 16, 2011