The chances of a leakage of radiation from an incident are so small though, that the hype doesn't come anywhere near the risk. The flasks that carry the waste have to be able to stand very serious incidents such as being dropped onto a totally unyielding surface from a certain height and placed in a fire for a considerable amount of time. The often mentioned set up collision between a Class 46 and a Nuclear flask was actually nothing like as bad as what the flasks are designed to withstand, yet was set up so that the flask was most vulnerable (the loco struck the corner of the lid of the flask). Basically, there is nothing to fear from common railway accidents such as derailments, collisions etc (including derailments into the path of another train). As far as deliberate action goes, a deliberate train crash has already been disounted, this leaves bombing and hijacking. The strength of the flasks means that a bomb would be very unlikely to cause a release of radioactive material. It's important to remember that if a bomb was placed right against the flask, only a small amount of the energy (I think about 30%) would be absorbed by the flask, the rest would head outwards away from the flask. You'd need a very powerful bomb to damage the flask enough to cause a realease of radiation. Getting a large enough bomb near to the flask would be near impossible though, and the further away it is the more the blast fades before it hits the flask. Of cource, they could vaporise the flask, a nuke would be the only thing able to do this, but then the material in the flask would be only a small part of the worry. You might be able to damage one seriously with an armour piercing type weapon or a "bunker buster" bomb, but terrorists don't tend to have these sorts of things, or the capability to deliver them (driving a tank or flying a plane to central London to attack a flask isn't going to happen). In all cases, the worst case scenario is really a small, contained leak of radioactive material, effecting the imediate area around the flask, probably no more than the freight yard or the station. Anyone near enough to recieve a lethal dose of radiation would probably be killed or seriously injured by the bomb anyway. As far as hyjacking goes, I can't think hyjacking a train is a feasable option, since trains travel on fixed paths, making them easy to intercept, and with the above knowledge of hoe sturdy flasks are, I'd say derailing the train or bombing the locos would be a good option. The only real way to hyjack the flask would be to transfer it to a road vehicle, but of cource if it's already going by road (as some would like) that's one problem solved anyway. The time and equipment needed to transfer to a road vehicle would make discovery very likely, and again I'd say that the ultimate option of "taking out" the vehicle would be perfectly feasable. Even were they to steal one, there is the question of what to do with it, since you can't exactly hide on easily, and getting one out of the country surely isn't an option.