ohh i think i get the picture. the ball is encased in bricks except for the top. then he lays a brick over the ball, and zap!
Yeah, maybe. Or maybe, he gets the bricks stacked up around the core, and he's got a little "fort" of bricks stacked up (like a kid would make a "fort" out of toy blocks), and the geiger counters are really starting to sing, and he thinks "I'll just lower this piece by hand down through the middle of the 'fort' and see what happens with the radiation count." And then there's a sudden blue flash (just like the glow you see in those pictures of nuclear fuel elements under 25 feet of ultra-pure water in storage at nuclear power plants around the country). And maybe he hears something too... an alarm klaxon suddenly goes off, or the reaction itself makes a sound. And he jumps in alarm, and drops the brick (which is damn heavy, WC is really dense). The blue glow gets brighter, and he reaches in and grabs that sucker and pulls it the hell out of there.
Then he called his boss. He was worried, but not really scared.
(steely)