If it helps any... it won't be an explosion like the atom bomb... but the risk of radiation is pretty high. So long as they keep pouring water in the thing it should keep it form completely melting down. The explosions that already occurred was from super-heated steam that was under pressure...
dunno if your still checking on this but... I'd make sure that cap your replacing it with is to spec with the old.
What do you plan to use this system for? gaming? movies? Facebook?