I’m guessing that this is a bad thing, but Reuters doesn’t feel the need to really say so.
No expert, but I used to work at Comanche Peak Nuclear Power Plant in Glen Rose, Texas. Basically you insert the rods into the reactor to slow down the fission reaction, and withdraw them to speed up the fission reaction.
Yes, yes, very bad, there is much more radioactivity in the rods in these storage ponds than in the reactor itself. If you can keep them cool and shielded (water is an excellent shield), fine, otherwise don't buy fish from Japan for 300 years.