Back in November right before they started removing fuel assemblies from the Spent Fuel Pool of Reactor 4, TEPCO announced (again) that there were three spent fuel assemblies in the pool that had been deformed.
The company released the photos of one of the assemblies on December 27, 2013, whose protective case (channel box) is cracked in several locations. According to the incident report filed with Nucia (Nuclear Information Archive maintained by Japan Nuclear Safety Institute), the incident happened in 1982 when workers not thoroughly familiar with the fuel removal procedure made a series of mistakes.
From TEPCO's photos and videos library (12/27/2013):
A fuel assembly is about 4.5 meters long; of that, the channel box is about 4.2 meters long.
If you care to know what TEPCO has to say about the fuel assembly removal operation in Reactor 4, here's their PDF presentation in English.
One of several workers who have been tweeting from Fukushima I Nuclear Power Plant, "Sunny", says:
It's not that TEPCO hid the fuel assembly damage. It's been reported on official sites like Nucia. It just shows how uninterested people were in nuclear power [until the Fukushima accident].
I didn't even know there were 54 nuclear reactors dotting the scenic coastlines in Japan.