mdsolar writes: A group of engineers in the U.S. Nuclear Regulatory Commission say they have identified a design flaw in nearly all nuclear reactors in the country that should result in their mandatory shutdown unless operators fix the problem, Reuters reports. In late February, the engineers petitioned the NRC to order immediate enforcement actions to correct the design flaw, which they say could result in damage to cooling systems and ultimately lead to an emergency situation. The filing asks the agency to respond by March 21 and is a part of a standard NRC process, according to the news outlet. The filing stems from an incident in January 2012, when Exelon's Byron 2 unit in Illinois experienced an automatic reactor trip from full power after an undervoltage condition was detected. The unit was shut down for a week, in what is known as an open phase condition created by an unbalanced voltage. The NRC engineers say such an event could cause an electrical short, reducing the abilituy of cooling systems to operate.