It had been a while since we had a factual update (as opposed to just lies and spin) from Fukushima. Courtesy of Kyodo, we now know that what was speculated by some as true, and rebutted by most as mere scaremongering, is in fact, fact. "Some of the spent nuclear fuel rods stored in the No. 4 reactor building
of the crisis-hit Fukushima Daiichi power plant were confirmed to be
damaged, but most of them are believed to be in sound condition, plant
operator Tokyo Electric Power Co. said Wednesday." Naturally, in one month we will learn that most of them are damaged, and in two months, that each and every one has been demolished. "The firm known as TEPCO said its analysis of a 400-milliliter water
sample taken Tuesday from the No. 4 unit's spent nuclear fuel pool
revealed the damage to some fuel rods in such a pool for the first time,
as it detected higher-than-usual levels of radioactive iodine-131,
cesium-134 and cesium-137." These confirm an ongoing fission reaction. In a tremendously ironic development, the No. 4 reactor, halted for a regular inspection before last month's
earthquake and tsunami disaster, had all of its 1,331 spent fuel rods
and 204 unused fuel rods stored in the pool for the maintenance work. Unfortunately, the entire pool ended up being damaged following the quake and the subsequent explosion, in essence nullifying any protection that the containment dome would have provided. As the picture from the Asahi Shimbun below shows, the damage from overhanging structures which have subsequently fallen into the fuel pool likely means that there could well be an uncontrolled, if weak, fission reaction currently going on in the reactor 4 SFP (where the water temperature is currently 90 degrees) unprotected by the elements due to the complete destruction of the Reactor 4 shell.
(picture via of saposjoint)
More from Kyodo:
The cooling period for 548 of the 1,331 rods was shorter than that for others and the volume of decay heat emitted from the fuel in the No. 4 unit pool is larger compared with pools at other reactor buildings.
According to TEPCO, radioactive iodine-131 amounting to 220 becquerels per cubic centimeter, cesium-134 of 88 becquerels and cesium-137 of 93 becquerels were detected in the pool water. Those substances are generated by nuclear fission.
The government's Nuclear and Industrial Safety Agency said the confirmed radioactive materials were up to 100,000 times higher than normal but that the higher readings may have also been caused by the pouring of rainwater containing much radioactivity or particles of radiation-emitting rubble in the pool.
The roof and the upper walls of the No. 4 reactor building have been blown away by a hydrogen explosion and damaged by fires since the disaster struck the plant. The water level in the spent fuel pool is believed to have temporarily dropped.
In the meantime the latest drywell readiation reading in Reactor 1 is still "out of commission"
And lastly, a demonstration from Fairewinds' Arnie Gunderson who shows how the Zircalloy uranium pellets mostly likely melted and shattered, possibly penetrating through the floor of reactors 2 and 3.