Perhaps an interruption of power to the field windings of the affected control rods. Could be as simple as a control cabinet fried unexpectedly or some other electrical gremlin.
3 rods inserted into the core out of the many available would have disrupted the neutron flux profile away from what the reactor is intended to operate against in steady-state, so manual shutdown is the right answer until the cause of the control rod being dropped can be figured out, repaired, tested and then the reactor restarted.
But while not typical, this kind of event has happened many times before and will again. Pretty boring IMO, which is why I agree with the non-emergency declaration by NRC.
This could be an intentional design feature regarding power loss to critical reactor control systems.
Rig N+2 control rods with an actively powered electromechanical retaining mechanism. In any kind of serious electrical issue occurs on the protected circuit, all 3 drop automatically.
Yeah, on one of the reactor designs I was familiar with, control rods were bundled into groups which were managed as a set and were intended to be operated in different sequences over core life.
So when I read "3 control rods hit the bottom" what I hear is "there was an unexpected group scram", but I don't know enough about this reactor design to know if that's actually what happened, or whether it was 3 unrelated control rods instead.
Perhaps an interruption of power to the field windings of the affected control rods. Could be as simple as a control cabinet fried unexpectedly or some other electrical gremlin.
3 rods inserted into the core out of the many available would have disrupted the neutron flux profile away from what the reactor is intended to operate against in steady-state, so manual shutdown is the right answer until the cause of the control rod being dropped can be figured out, repaired, tested and then the reactor restarted.
But while not typical, this kind of event has happened many times before and will again. Pretty boring IMO, which is why I agree with the non-emergency declaration by NRC.
This could be an intentional design feature regarding power loss to critical reactor control systems.
Rig N+2 control rods with an actively powered electromechanical retaining mechanism. In any kind of serious electrical issue occurs on the protected circuit, all 3 drop automatically.
Yeah, on one of the reactor designs I was familiar with, control rods were bundled into groups which were managed as a set and were intended to be operated in different sequences over core life.
So when I read "3 control rods hit the bottom" what I hear is "there was an unexpected group scram", but I don't know enough about this reactor design to know if that's actually what happened, or whether it was 3 unrelated control rods instead.
I was unable to find the NRC filling, if someone finds the link to it, please drop a reply with it.
This is potentially interesting as this reactor recently had its operating license extended earlier in the year.
https://www.nrc.gov/reading-rm/doc-collections/event-status/...
Event 58408, 'manual reactor trip'.