nuclear-news

INADVERTENT CRITICALITY    “There is a risk of an inadvertent criticality if the bundles are distorted and get too close to each other,” Gundersen said.  He was referring to an atomic chain reaction that left unchecked could result in a large release of radiation and heat that the fuel pool cooling system isn’t designed to absorb.

“The problem with a fuel pool criticality is that you can’t stop it. There are no control rods to control it,” Gundersen said. “The spent fuel pool cooling system is designed only to remove decay heat, not heat from an ongoing nuclear reaction.”

The rods are also vulnerable to fire should they be exposed to air, Gundersen said.

The fuel assemblies are situated in a 10 metre by 12 metre concrete pool, the base of which is 18 metres above ground level. The fuel rods are covered by 7 metres of water, Nagai said.

The pool was exposed to the air after an explosion a few days after the quake and tsunami blew off the roof. The cranes and equipment normally used to extract used fuel from the reactor’s core were also destroyed. Tepco has shored up the building, which may have tilted and was bulging after the explosion, a source of global concern that has been raised in the US Congress……….

Under normal circumstances, the operation to remove all the fuel would take about 100 days. Tepco initially planned to take two years before reducing the schedule to one year in recognition of the urgency. But that may be an optimistic estimate.

“I think it’ll probably be longer than they think and they’re probably going to run into some issues,” said Murray Jennex, an associate professor at San Diego State University who is an expert on nuclear containment and worked at the San Onofre nuclear plant in California.

“I don’t know if anyone has looked into the experience of Chernobyl, building a concrete sarcophagus, but they don’t seem to last well with all that contamination.”  Corrosion from the salt water will have also weakened the building and equipment, he said….. http://www.stuff.co.nz/world/asia/9041215/The-deadliest-part-of-Japans-nuclear-clean-up