INES-event
INES 0

Reactor trip due to the malfunction of optical isolator

Yonggwang unit 4 was operated at the rated power. During normal operation, reactor was tripped due to the dropping of control rods. Investigation revealed that CEAC (Control Element Assembly Calculator) no.1 caused reactor trip because one of the optical isolator had been gone out and it generated wrong control rod position signal.
There was no release of radioactive materials outside the reactor building and no unplanned exposure to employees.
Justification: As full safety functions were available, the event is rated at level "0" as per User's Manual Part III, Table II, A1

Location: YONGGWANG-4
Event date: Wed, 19-06-1996
Nuclear event report
Legenda & explanation