DOE publishes review of criticality accidents by Bob Felton Updated edition of report describes 60 accidents worldwide. In every case there were multiple causes, but equipment failure or malfunction played a negligible role in all of the incidents. The primary causes, always, were human.
Humans err, but they also learn from error.
Though there was an average of one accident per year in both Russia and the U.S. between the late 1950s and the mid-'60s, accidents then declined in each country to approximately one accident per 10 years. Second, facility managers dedicated personnel to developing and implementing criticality safety processes and standards. Additionally, no process accident resulted in significant radiation effects on either persons or the environment outside the limits of the facility. Further, neither faulty calculations nor previously unobserved physical phenomena played a role in any of the incidents. It is one thing to have written procedures that are intended to be followed in order to provide for safe operations.