What are the primary causes of accidents in nuclear power plant?

  1. Operator error due to inadequate understanding (usually a training problem)
  2. Operator error due to misreading instruments (sometimes a design error, sometimes a training problem)
  3. Operator error due to management error ("just following orders" syndrome)
  4. Reactor malfunction.
  5. Reactor damage due to external events (e.g. earthquake & tsunami as in Japan)

TMI was as follows: 4 (stuck valve), 2 (thinking light on control panel said valve was closed), 1 (turning off emergency cooling water, letting core run out of coolant).

Chernobyl was as follows: 3 (management ordered all emergency systems disabled to allow retry of test), 5 (power demand in Kiev delayed test), 1 (new shift proceeded with test without adequate understanding of marked up procedure), 3 (when operators hesitated to proceed due to safety issues management threatened to replace them), 1 (operator pressed SCRAM with too many rods removed for design, triggering steam explosion instead of shutting down reactor).

Japan 2011 was as follows: 5 (quake), 5 (tsunami), (need to wait and see rest of sequence after failure analysis report is written).