INES-event
INES 1

NOT FULLY INSERTED CONTROL RODS

After last year's control rod problems at Ringhals 4, extra tests are required with more stringent acceptance criteria concerning insertion time. During the recent control rod test, some of the rods had exceeded the newly required shorter insertion time. It was decided to stop the reactor. The reactor was shut down and during the normal cool down process, under subcritical conditions, with the primary coolant borated to 2000 ppm, at 175 degree C due to steam generator level deviation scram was called upon. Three control rods did not reach their bottom position but stopped a few centimeters less than their fully inserted position.
IES level 1.
Justification:
Table II. Severity classification criteria for degradation of defence-in-depth with an initator.
Initiator frequency/initiator probability; High/expected
Safety function availability; within operational limits and conditions

Location: RINGHALS-3
Event date: Sun, 12-02-1995
Nuclear event report
Legenda & explanation