Fukushima

Tepco: Bent rod found in spent fuel pool — Nuclear fuel rods touching — “Serious fuel failure accident” risked at Japan plant

Asahi Simbun,

13 December, 2012

Tokyo Electric Power Co. said Dec. 12 a bent water rod caused two fuel rods to come into contact inside a fuel rod assembly stored in a spent fuel storage pool for the No. 5 reactor of the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture.

No damage to nuclear fuel or other anomalies have been reported, but the two fuel rods may have been in contact with each other when they were burning inside the reactor.

The situation had the potential to cause a serious fuel failure accident.

A fuel rod assembly is a bundle of 60 fuel rods. A water rod, or a passage for coolant water, runs through its center.

Water rods were found to be bending in 18 fuel rod assemblies in the storage pool. Closer studies found that in one fuel rod assembly, the bending water rod pushed one nearby fuel rod into contact with another.

At the Kashiwazaki-Kariwa plant, a number of unspent fuel rod assemblies had been exposed to excessive loads due to sloppy work procedures when they were encased in metal covers.

The two fuel rods in question may have come into contact during such work procedures, TEPCO officials said.

The fuel rod assembly was encased in a cover in 1994 and burned in the nuclear reactor from 1995 to 2000.

Gundersen: I’m sure there’s a lot of damaged nuclear fuel in Fukushima spent fuel pools — The tubes are cracked — May be completely severed

Fairewinds,
9 December

 Nuclear Expert Arnie Gundersen, Fairewinds Energy Education: We know though that the fuel is damaged. And the reason we know that is that the radioactivity in the fuel pool water is extraordinarily high and it hasn’t really come down over the last 18 months.

Originally, people thought that maybe it was deposition from the explosions and it settled on the water, but they’ve been running these fuel pool cooling systems now for months and months and months and we still see high levels of radiation in the spent fuel pools.

So that tells me that the fuel bundles themselves have been damaged either by the earthquake, or the explosion, or by a prompt moderated criticality, or by the aftershocks.

Host: So there’s exposed fuel in the pool right now?

Gundersen: If you think of this thing like long tubes of spaghetti, tubes of zircoloy, those tubes are cracked…. The fuel rods, the individual fuel rods are cracked, from either the seismic motion, or the explosion, or the rattling of the building from the explosion. They may be completely severed, but there’s certainly cracks, we call it a weeper. Depending on the length of the crack, the bigger the weep.

I’m sure you’re going to find when they start pulling that spent fuel that they’ll have a lot of weepers, a lot of damaged fuel.

And it’s compounded because it’s not clean water, its salt water. This stuff was never designed to be in salt water so you have hot warm zircoloy in boron and salt water and there’s all sorts of chemical reactions going.