Followup letter to NRC about industry proposal to rely on "leak-before-break" scheme (04/2010)
In September 1996, the NRC intiated a "high priority" safety issue affecting two-thirds of the US nuclear power reactors. If a pipe ruptured inside the containment building at one of these reactors, the emergency systems' initial response would be to pump water from a large outdoor tank to the reactor vessel to cool the nuclear core. Before this tank emptied, the emergency systems would swap to take water collecting in the containment basement and recycle it through the reactor vessel for continued core cooling.
But the water jetting out from the broken ends of the ruptured pipe would scour insulation off piping, coatings off equipment, and even paint off walls and carry this debris down to the basement where it could clog the screens protecting the emergency pumps. The NRC required owners of the vulnerable reactors to ensure their emergency pumps would function during emergencies.
The NRC reviewed the steps taken by the owners and found that about half of the owners had taken shortcuts that raised questions about whether their systems could cool the reactor core during an emergency. These owners wanted the NRC to accept their shortcuts. These owners wanted the NRC to instead allow them to take credit for "leak before break," a belief that pipe ruptures will be preceded by leaking pipes allowing time for reactors to be shut down before the catastrphic rupture occurs.
In two letters to the NRC, UCS expressed concerns about this notion, citing numerous times when leakage was detected but reactors continued to operate for days, months, and even years.
