14 nuclear near-misses

Sheriff deputies guard the entrance to the Crystal River Energy Complex Nuclear Power Plant. Workers severely damaged the nuclear plant's thick concrete reactor containment walls when they were cutting a hole to replace steam generators.

Aerial view of the Diablo Canyon Nuclear Power Plant which sits on the edge of the Pacific Ocean at Avila Beach in San Luis Obispo County, California. Some of America's nuclear power plants loom near big city populations, or perch perilously close to earthquake fault lines. Others have aged past their expiration dates but keep churning anyway. President Barack Obama has demanded that the 104 nuclear reactors at 65 sites get a second look as scientists warn that current regulatory standards don't protect the US public from the kind of atomic fallout facing quake-hit Japan.

In 2010, a botched valve repair prevented other key valves from opening. Tests after the valve repairs failed to detect the problem. The reactor operated for nearly 18 months with vital emergency systems disabled, according to the Union of Concerned Scientists.

Calvert Cliffs, MD nuclear plant

Former President George W. Bush with workers while he toured the control room of the Calvert Cliffs Nuclear Power Plant June 22, 2005 before making a speech urging Congress to pass an energy bill. A leaky roof let rainwater short out electrical equipment and one reactor automatically shut down. Also, a worn-out protective device that workers failed to replace due to cost-cutting efforts allowed the electrical problem to trigger an automatic shutdown of a second reactor.

Farley, AL

Joseph M. Farley Nuclear Generating Station/Alabama Power Company

A service water pump failed even though the company had replaced the part three years earlier. After an inspection, it was found that the installed pump failed to meet the specifications listed on the purchase order. The service water system provides cooling water to safety equipment during accidents

Fort Calhoun, NE

An auxiliary feedwater pump automatically shut down during a monthly test. The pump was subsequently found to have failed on several occasions during previous years, but the plant owner never uncovered the reason for the failures. The plant was later cited for four violations of regulatory requirements.

Davis-Besse, OH

Cracks in nozzles on the control rod drive mechanism penetrated through the head of the reactor vessel. Borated reactor cooling water leaked through some of the cracks. Workers reportedly workers did not properly account for peak temperatures inside the reactor.

Braidwood, Il.

The Exelon nuclear power generating station rises above a nearby trailer home March 17, 2006 in Braidwood, Illinois. The state of Illinois and Will County officials sued the owners and operators of the facility, claiming they failed to report leaks of radioactive tritium from the facility. Tritium is a byproduct of nuclear generation and has been linked to increased risk of cancer, birth defects and genetic damage. Problems cited included a poor design that led to repeated floods in buildings with safety equipment, a poor design that allowed vented steam to rip metal siding off containment walls, and undersized electrical fuses for vital safety equipment.

Wolf Creek

Water was found leaking from the system that cools the emergency diesel generators and other emergency equipment. A 2007 company study had predicted the leakage - in fact, such a leak did take place after a 2008 reactor shutdown, but no corrective measures had been taken to resolve the problem.

Arkansas Nuclear One

Security problems prompted an NRC special inspection. Details of what transpired are still not publicly available.

HB Robinson Florence, SC

Coincidentally, an unplanned reactor shutdown and declaration of an alert came on March 28, 2010, the 31st anniversary of the Three Mile Island accident. Twice within six months, this nuclear plant, operated by Progress Energy, was singled out for bad design, nonconforming equipment, inadequate operator performance, and poor training. Another automatic shutdown of the reactor would follow on October 7, 2010.

Brunswick, NC Nuclear One

Plant owners at the Brunswick, NC Nuclear One site declared an emergency after equipment failure. Workers reportedly were not familiar with computer systems that would have automatically notified off site workers to report immediately to emergency response facilities.

Surry, VA Power Station

An overheated electrical device caused a fire which led to a loss of power to instrumentation, causing a unit reactor to shut down automatically. A few months earlier there had been a fire caused when a similar device had overheated. In its summary of the incident, the Union of Concerned Scientists noted that pressure in the reactor vessel increased "to the point where a relief valve opened automatically, to protect the system. That relief valve opened and closed 14 times during the next 20 minutes. A similar relief valve, which stuck open the first time it opened, contributed to the partial meltdown of the Unit 2 reactor core at Three Mile Island in March 1979."

Catawba, SC nuclear plant

The nuclear plant in Catawba, SC was cited by the NRC for security-related problems. However, post-9/11 procedures prevent the public from knowing details of the report.