Fox News reported a few minutes ago:
“Repairs to monitoring equipment … showed that the water level in the core of Unit 1 at the Fukushima Dai-ichi plant is much lower than previously thought, leaving the portion of the fuel rods still intact … fully exposed. Other fuel has slumped to the bottom of the pressure vessel and is thought to be covered in water.
Fox also reported more details about the leak in the reactor’s containment vessel:
Nuclear Industrial and Safety Agency officials said the new data indicates that it is likely that partially melted fuel had fallen to the bottom of the pressurized vessel that holds the reactor core together and possibly leached down into the drywell soon after the March 11 quake and tsunami that struck Japan’s northeastern coast.
While officials said it was unlikely that the chunks of fuel were still dangerously hot or that they could melt through the concrete base of containment vessel, they acknowledged that the level of damage could complicate plans detailed in April to bring the plant to a cold shutdown within nine months. Further examination was needed to ascertain the full extent of damage, they said.
First mention I’ve heard of the China Syndrome: an uncontained meltdown burning through concrete till the fuel reaches groudwater….
The new information also puts a crimp into TEPCO’s plans for cooling down the reactor:
TEPCO had adopted an unorthodox method of trying to cool Unit 1’s reactor by trying to fill the drywell with water leaking from the core, but the possibility that chunks of melted fuel had fallen and damaged part the containment vessel raised questions about how successful this method would be. It also called into question the utility’s timeline for stabilizing the reactor.
TEPCO announced that the temperature readings were now fairly low, and also inadvertently gave us an idea of how hot the fuel got early in the disaster:
Recent temperatures inside Unit 1’s core were at the most 237 degrees Fahrenheit (114 Celsius), well below the normal operating temperature of about 570 Fahrenheit (300 Celsius). Zirconium fuel rod casing begin to break down at 2,200 Fahrenheit (1,200 Celsius) and melt at 3,900 Fahrenheit (2,200 Celsius).
Since the company has admitted that fuel rods melted in the accident, that must mean that temperatures were above 3,900 degrees, and means that we were extremely lucky that the water they used to cool the fuel did not suffer a steam explosion, like Chernobyl. Some of the water may, however, have been split by the heat into oxygen and hydrogen, the latter gathering in the reactor buildings and leading to the explosions that destroyed the structures.
If you have the stomach to read more, here’s a link: http://www.foxnews.com/world/2011/05/12/greater-expected-damage-seen-japan-reactor/