The same crowd that trains to be suicide bombers.
Sorry Pecos. I don’t care how willing you are to die it can’t be done. These research reactors are basically a very deep pool of water with a reactor core setting at the bottom.
The reactor is controlled by moving neutron absorbing control rods into or out of the core using remote controlled motors.
It requires special equipment to handle the fuel because if the fuel is raised to with in a few feet of the surface of the water anyone that can see the fuel will receive a lethal dose of radiation in a few seconds.
If someone wanted to remove the fuel from the reactor pool and take it away they would have to bring special transport cask to the reactor building lower this cask that weighs around 20 tons in to the pool. Then load the cask with the irradiated fuel using the remote controlled machines. Then seal the cask again with remote controlled tools raise the cask out of the pool and place it on a specially built trailer and drive away with the irradiated fuel.
Now this whole process takes weeks to perform by people trained to do it and we are to believe that terrorist will be able to do it in a couple of hours without causing enough of a ruckus to draw the attention of the police that they will fail in stealing weapons grade reactor fuel.
Now the idea that reasonably intelligent terrorist would even attempt such a mission is laughable. Especially when there are so much more easy soft targets available.