It's quite disturbing how many misconceptions and misunderstandings there are here. Let's try and set the record straight.
1. A nuclear power reactor cannot explode like a nuclear weapon. The material in use is too full of impurities, not densely packed enough and not enriched with enough fissile content to work like a nuclear weapon. Even in a meltdown, (which is a fancy name for everything gets too hot and melts, nothing more) you wouldn't get close. What you might get in a meltdown is hydrogen gas production from a reaction between the fuel rod metal (that encases the uranium) and steam. The hydrogen gas can then explode (hydrogen has a tendency to do this, see Hindenburg etc. [yes I know about the paint..]). A hydrogen gas explosion is what happened at Fukushima following a meltdown. It's also what they feared might happen at Three Mile Island, though it never did because they managed to stop it going that far.
2. He was using DEPLETED Uranium 238. The clue is in the question people, DEPLETED. That's like trying to start a fire by using ashes instead of wood, it's not going to happen. The useful bit is already gone, refined away in the enrichment process. Depleted Uranium is considerably less radioactive than natural Uranium in the ground, although it is still toxic and poisonous, like other heavy metals such as lead.
3. His 'meltdown' was a chemical reaction, other people have already explained this well so I wont bother repeating them.
4. He should go to prison. Stupidity can be, and often is, criminality. The Deepwater Horizon guys in the Gulf of Mexico were criminally stupid and should go to jail. This guy is criminally stupid and should too. The radiation risk is minimal, cause he was too dumb to get far on that front. But he was still playing around in his kitchen with a whole bunch of toxic substances that could have reacted chemically, potentially killing him. Additionally, he could have poisoned neighbours and his local environment as it seems likely he would have also been too stupid to clear up safely once he was done. 2 years might be a bit much, but 30 days might give him a nudge in the correct, safer, direction.