The plant shut down in the middle of the night on July 23, 2015 after several control room alarms went off. . . .
Callaway is a nuclear plant (PWR) located near Fulton, Missouri and owned by the Ameren Corporation. It’s a single-unit plant that produces 1,190 MW of power.
RCS operational LEAKAGE shall be limited to:
a. No pressure boundary LEAKAGE,
b. 1 gpm unidentified LEAKAGE,
c. 10 gpm identified LEAKAGE, and
d. 150 gallons per day primary to secondary LEAKAGE through any
one steam generator (SG).
This was an occasion of unidentified leakage. The plant detected 1.6 gallons per minute, which exceeded the TS limit of 1.5. So, they shut down the plant:
On July 22, 2015 at 9:09 p.m. control room operators received alarms indicating elevated containment radiation, humidity, temperature, and sump levels. At 9:39 p.m. operators diagnosed unidentified reactor coolant system leakage of approximately 1.6 gallons per minute.
On July 23, 2015, at 1:15 a.m. (all times CDT), Callaway Plant operators commenced a reactor shutdown from 100 percent power in response to reactor coolant system leakage…
The culprit was a leaky gasket:
At 5:02 p.m. the licensee entered the containment building and determined the source of the leak to be from a gasket on a blind flange on a 3/4 inch drain valve off of the auxiliary pressurizer spray line.
The plant repaired the leak, along with a few other items:
The licensee repaired the gasket leak while in Mode 3, and addressed other equipment issues associated with the B main feedwater pump, and an auxiliary feedwater pump flow control valve.
They quickly resolved the issues and restarted just two days later:
After successful resolution of these issues, the licensee commenced a reactor startup on July 25, 2015, and achieved approximately 100 percent power on July 27.