Apparently Homer Simpson was not just doing safety inspection at the Springfield Nuclear Power Plant - he was also on the job at Diablo Canyon:
For 18 months, operators at the Diablo Canyon nuclear plant near San Luis Obispo didn't realize that a system to pump water into one of their reactors during an emergency wasn't working.
It had been accidentally disabled by the plant's own engineers...
The problem...involved a series of valves that allow water to pour into one of the plant's two reactors during emergencies, keeping the reactor from overheating...
Engineers at Diablo Canyon inadvertently created the problem while trying to solve another issue, according to the report.
A pair of remotely operated valves in the emergency cooling system was taking too long to move from completely closed to completely open. So engineers shortened the distance between those two positions, according to the report.
Unfortunately, two other pairs of valves were interlocked with the first. They couldn't open at all until the first pair opened all the way. No one noticed until the valves refused to open during a test in October 2009, 18 months after the engineers made the changes.
more...
Good thing that there's 70,000 tons of deadly radioactive waste material being stored at more than 100 nuclear plants across the U.S., dependent on such cooling systems to keep it from catastrophically melting down.
And good thing that the nuclear power industry only has very limited liability in the case of accidents, leaving taxpayers on the hook for the hundreds of billions of dollars in costs in the case of a major nuclear accident.