Besides the SL-1 incident, there have been criticality accidents associated with nuclear technology development. There were a couple in the Manhattan Project. There was one a few years ago in Japan. There have been a couple of fatalities associated with commercial irradiators that use radioactive sources or accelerators. In general, these are exceedingly rare accidents, especially compared with risks we accept on a daily basis (driving cars, climbing ladders, etc.) that have higher fatality rates.