Olkiluoto 3 is operating at half power – The control rod fell into the reactor

The Olkiluoto 3 plant unit operates at half capacity. The reason is the reactor control rod falling into the reactor.

On Wednesday, Olkiluoto 3 was in normal production when one of the control rods unexpectedly fell into the reactor.

Industrial Power (TVO) communications manager Johanna Aho says that the function of the control rods is to protect the nuclear power plant in emergency situations.

Olkiluoto 3 has 89 adjustment rods. They adjust the power of the reactor and, if necessary, stop the reactor.

When the reactor detects a malfunction in the plant, the control rods automatically fall into the reactor, as a result of which the production power of the plant decreases and the nuclear reaction stops.

“There are two tasks with these adjustment rods,” says Aho.

Unexpected disruption

On Wednesday, an unexpected disturbance occurred at the OL3 production facility, which triggered the safety mechanism.

TVO announced on Wednesday early evening that the fall of the control stick was caused by a failure of the control stick drive mechanism. Earlier, the cause of the disturbance was investigated.

The plant’s production capacity was automatically reduced to approximately 1,220 megawatts on Wednesday. In order to find out the cause of the disturbance and fix the fault, electricity production was further reduced to 750 megawatts.

TVO estimated on Wednesday afternoon that Olkiluoto 3 will run at a low power level until 6 p.m. Aho said that the schedule depends on how quickly the cause of the malfunction is found and the fault is repaired.

Duration varies

After a disturbance situation, the output of the production plant is usually increased gradually.

Aho says that after the previous partial power reduction, it took about a day to raise the production power to the usual level. However, the schedule always depends on the situation.

“We make our own plan for how to get back out of it,” says Aho.

“It completely depends on whether, for example, tests need to be done between power increases.”

A disturbance situation does not affect nuclear safety.