NukeWorker Forum
Career Path => Training, Tests & Education => Topic started by: bhg on Jun 22, 2016, 09:17
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Can anyone help me with the term turbine run back? Another student said the turn run back only deals with the reactor is this true? Thanks .
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No. Run back means the turbine gets a signal to reduce load to a certain power and the reactor follows it. (PWR)
In a BWR the reactor gets the run back signal and the turbine follows.
In either case they are linked
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No. Run back means the turbine gets a signal to reduce load to a certain power and the reactor follows it. (PWR)
In a BWR the reactor gets the run back signal and the turbine follows.
In either case they are linked
This. We have signals, at my station, specifically called turbine run back.
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Runback in the original question.
Yes. Reactor Power is reduced quickly by "running back" Recirculation Flow.
In old BWRs, Recirc Pump Speed is reduced. In BWR 5s and 6s, Recirc Flow Control Valve is throttled in the closed direction.
In both cases, core flow is reduced which lowers reactor power.
The turbine sees lowering pressure at its throttle and closes down on Control Valves. So Turbine load lowers too.
Most common is feedwater generated signals, a concurrent low water level with evidence of a tripped pump usually triggers a runback to lower Reactor Power to within the remaining feedwater capacity. We call that a Level 4 Runback. (Low RPV Water Level). Plants that tend to survive a feed pump trip without scramming have a good L4 runback function. Obviously, I'm implying some don't.
Not to confuse you, but BWR Turbine Generators ALSO have protective features that lower Load Set. Some folks call these Generator Runbacks.
If cooling is threatened or some other initiator triggers load reduction, Bypass Valves open to lower Generator Load. There's a "failure to runback" trip waiting on you there. If load doesn't get low enough, fast enough (and it generally doesn't) - a Turbine Generator Trip occurs. The reason for my learned pessimism is, Recirculation can get a full power reactor down to 65% or so. That's all you're doing quickly. Rod insertion to lower power takes time you don't have with generator protection circuits activated. So don't fight it. Give a good brief and scram it.
Tell 'em I told you. That ought to work.