For the second time in two weeks, Entergy’s Pilgrim nuclear reactor experienced an “event” requiring notification to the NRC. The scram discharge volume valve failed on February 18, 2013, and again on March 1, 2013.
According to the Union of Concerned Scientists, “The scram discharge volume is a large metal tank that collects the water vented from the control rod’s hydraulic pistons during a scram. It is sized to contain all the water vented during a scram. [The valve that failed] is one of the valves on the drain line from the scram discharge volume. When a scram signal occurs, this valve automatically closes (or is designed to do so, whether it does so is another matter).”
The NRC requires Entergy to make sure this valve is operating as designed because it is a mechanical system that is critical to Pilgrim’s safe operation. The valve is part of the reactor shutdown system, and must be able to operate during a “scram”. A scram means for some reason Entergy has to stop the nuclear reaction (the fission that splits the atoms) from happening.
During the February 2013 blizzard (Nemo) Pilgrim had to shut down twice. What if the valve had failed during Nemo – instead of a mere 9 days later, on Feb. 18?
The U.S. NRC says that the valves only have a one in a million chances of interfering with reactor shut down. But, according to the Union of Concerned Scientists, in June 1980, that is exactly what happened at the Brown’s Ferry nuclear plant in Alabama: that one in a million chance happened and almost caused a nuclear disaster.
Pilgrim is old and worn out. It exceeds industry averages for automatic shutdowns and unplanned power outages. It presents an unacceptable risk to our region – this valve failure is just one more example of that.