Koji Okamoto, is a professor of nuclear engineering at the University of Tokyo. “I also calculated the amount of xenon from the data that TEPCO released and found it was about the same as the amount produced due to spontaneous fission,” Okamoto said.
“They injected boric acid solution, but the amount of xenon did not change. It is likely that the xenon was the result of spontaneous fission, not of criticality,” Sumita said.
The fuel rods in the No. 2 reactor are believed to have melted, forming a misshapen lump at the bottom of the pressure vessel. But how the fuel has melted or whether it has leaked through to the containment vessel remains unknown.
High radiation levels have prevented TEPCO workers from installing gauges and other equipment that could more accurately determine the internal conditions of the reactors.
TEPCO, for now, is depending largely on computer simulations based on temperatures and pressure levels in the reactors to estimate what is going on inside.
“The problem is that TEPCO pointed to the possibility of ‘criticality’ taking place, if only temporarily,” said Fumiya Tanabe, director of the Institute of Nuclear Safety System Inc. “It eventually showed that the utility failed to predict the situation of fuel rods or the present internal state of the reactor. It should imagine the worst possible situation and deal with it for the recovery.”
Source: AJW Asahi