FUKUSHIMA REACTOR 1: FULL MELTDOWN, REACTOR VESSEL BREACHED

May 13th, 2011
Via: Reuters:
One of the reactors at Japan’s crippled Fukushima nuclear power plant has a hole in its main vessel following a meltdown of fuel rods, leading to a leakage of radioactive water, its operator said on Thursday.
The disclosure by Tokyo Electric Power Co (TEPCO) is the latest indication that the disaster was worse than previously disclosed, making it more difficult to stabilize the plant.
…
Based on the amount of water that is remaining around the partially melted and collapsed fuel, Matsumoto estimated that the pressure vessel had developed a hole of several centimeters in diameter.
The finding makes it likely that at one point in the immediate wake of the disaster the 4-meter-high stack of uranium-rich rods at the core of the reactor had been entirely exposed to the air, he said. Boiling water reactors like those at Fukushima rely on water as both a coolant and a barrier to radiation.
U.S. nuclear experts said that the company may have to build a concrete wall around the unit because of the breach, and that this could now take years.
“If it is assumed the fuel did melt through the reactor, then the most likely solution is to encapsulate the entire unit. This may include constructing a concrete wall around the unit and building a protective cover over it,” W. Gene Corley, senior vice president of CTL Group in Skokie, Illinois, said on Thursday.
“Because of the high radiation that would be present if this has happened, the construction will take many months and may stretch into years,” Corley said.
TEPCO should consider digging a trench around reactors 1-3 all the way down to the bedrock, which is about 50 feet below the surface, said Arnie Gundersen, Chief Engineer at Fairewinds Associates Inc of Burlington, Vermont, who once worked on reactors of similar design to the Fukushima plant.
He said this should be filled with zeolite, which can absorb radioactive cesium to stop more poisons from leaking into the groundwater around the plant.
“TEPCO seems to be going backwards in getting the situation under control and things may well be slowly eroding with all the units having problems,” said Tom Clements with Friends of the Earth, a U.S.-based environmental group.
“At this point, TEPCO still finds itself in unchartered waters and is not able to carry out any plan to get the situation under control,” he said.

True radiation spread to North America: