Energy Northwest's Hanford plant in Washington state, USA underwent an emergency shutdown on 30 July.
It is reported that a false indication of a valve malfunction triggered an unsuccessful automatic shutdown which was completed manually. A fault in the shutdown system meant that two control rods failed to enter the reactor core and had to be inserted manually.
The shutdown led to a state-wide alert for emergency services that lasted two hours. Once the control rods been inserted, operators could have cancelled the alert but decided to err on the side of caution, according to Energy Northwest's Heather McMurdo.