To this day it remains one of the worst reactor accidents, with design and operational mistakes on the scale of Chernobyl. It's enormously fortunate that the reactor was fairly small.
Not exactly -- the reactor did shut down "safely", just not fast enough to avoid a steam explosion. Chernobyl was dangerous because it had a positive "void coefficient": the more the coolant boils, the more reactive the core becomes. It's easy to see why this is a bad thing.
SL-1 had a negative void coefficient: as the coolant boils off, fewer neutrons are slowed down to speeds where they can be readily captured by fuel and the reaction slows down, creating a negative feedback loop. This type of passive safety is all but mandatory in modern reactor designs. SL-1 blew up because the feedback loop lagged behind the pressure buildup by a few milliseconds, and it spontaneously disassembled (kaboom). No meltdown, no china syndrome -- just a bunch of fuel all over the place and a guy impaled on the ceiling.
http://en.wikipedia.org/wiki/SL-1
To this day it remains one of the worst reactor accidents, with design and operational mistakes on the scale of Chernobyl. It's enormously fortunate that the reactor was fairly small.