Patent Number: 055286399
Section: claims

1. A method of protecting against transient overpower in a boiling water nuclear reactor, comprising the steps of: operating a boiling water nuclear reactor in a permissible operating range which is above a cavitation region, below a maximum operating line and bounded by a minimum normal flow line and a maximum normal flow line;  monitoring the operating power level of said reactor during said operating step;  automatically adjusting a first (primary) setpoint to maintain said first setpoint at a first selected margin above said monitored operating power level during a planned change in said operating power level and not automatically adjusting said first setpoint during an unexpected change in said operating power level;  limiting the upper and lower values of the variation of said first setpoint; and  activating systems which automatically scram (shutdown)the reactor when the level of said monitored operating power level rises unexpectedly above said first setpoint.  automatically adjusting a second setpoint to maintain said second setpoint at a second selected margin above the level of said monitored operating power level during said planned change in said operating power level and not automatically adjusting said second setpoint during an unexpected change in said operating power level;  limiting the upper and lower values of the variation of said second setpoint; and  activating an alarm which alerts an operator and automatically initiates selected action to counteract an unplanned disturbance and to avoid full trip of said reactor when said monitored operating power level rises unexpectedly above said second setpoint.  means for monitoring the operating power level of said reactor;  means for automatically adjusting a first (primary) setpoint while the operating power level is in a permissible operating range to maintain said first setpoint at a first selected margin above said monitored operating power level during a planned change in said operating power level and not automatically adjusting said first setpoint during an unexpected change in said operating power level; and  means for activating systems which automatically scram (shutdown) the reactor when the level of said monitored operating power level rises unexpectedly above said first setpoint.  means for automatically adjusting a second setpoint to maintain said second setpoint at a second selected margin above the level of said monitored operating power level during said planned change in said operating power level and not automatically adjusting said second setpoint during an unexpected change in said operating power level;  means for activating an alarm which alerts an operator and automatically initiates selected action to counteract an unplanned disturbance and to avoid full trip of said reactor when said monitored operating power level rises unexpectedly above said second setpoint.  means for automatically adjusting said first setpoint while the operating power level is in a permissible operating range to maintain said first setpoint at a first selected margin above said monitored operating power level during a planned change in said operating power level and not automatically adjusting said first setpoint during an unexpected change in said operating power level.  an alarm trip unit which initiates automatic action to counteract an unplanned disturbance and to avoid full trip of said reactor;  means for automatically adjusting a second setpoint to maintain said second setpoint a second selected margin above said monitored operating power level during said planned change in said operating power level and not automatically adjusting said second setpoint during an unexpected change in said operating power level; and  means for activating said alarm trip unit when the level of said monitored operating power level rises unexpectedly above said second setpoint.  monitoring the level of reactor recirculation flow; and  utilizing said monitored reactor recirculation flow level to further adjust one of said first and second setpoints.  monitoring a reactor parameter; and  utilizing said reactor parameter to further adjust one of said first and second setpoints,  wherein said reactor parameter is selected from the group consisting of reactor vessel pressure, reactor core temperature, reactor feedwater temperature, reactor feedwater flowrate and reactor steam flowrate.  means for monitoring the level of reactor recirculation flow; and  means for utilizing said monitored reactor recirculation flow level to further adjust one of said first and second setpoints.  means for monitoring a reactor parameter; and  means for utilizing said reactor parameter to further adjust one of said first and second setpoints,  wherein said reactor parameter is selected from the group consisting of reactor vessel pressure, reactor core temperature, reactor feedwater temperature, reactor feedwater flowrate and reactor steam flowrate.  means for monitoring the level of reactor recirculation flow; and  means for utilizing said monitored reactor recirculation flow level to further adjust one of said first and second setpoints.  means for monitoring a reactor parameter; and  means for utilizing said reactor parameter to further adjust one of said first and second setpoints,  wherein said reactor parameter is selected from the group consisting of reactor vessel pressure, reactor core temperature, reactor feedwater temperature, reactor feedwater flowrate and reactor steam flowrate. 2. The method as defined in claim 1, wherein said first setpoint automatically activates alternate reactor protection system action. 3. The method as defined in claim 1, wherein said step of monitoring the operating power level of said reactor is performed by forming a filtered signal representing the operating power level of said reactor. 4. The method as defined in claim 1, further comprising the steps of: 5. A protection system for protecting against transient overpower in a nuclear reactor, comprising: 6. The protection system as defined in claim 5, wherein said first setpoint automatically activates alternate reactor protection system action. 7. The protection system as defined in claim 5, wherein said monitoring means comprises means for forming a filtered signal representing the operating power level of said reactor. 8. The protection system as defined in claim 5, further comprising: 9. In a system for protecting against transient overpower in a nuclear reactor including a first trip unit that when tripped automatically initiates an action to mitigate a transient event, means for monitoring the operating power level of said reactor and means for activating said first trip unit when the level of said monitored operating power level rises unexpectedly above a first (primary) setpoint, the improvement comprising: 10. The system as defined in claim 9, wherein said monitoring means comprises means for forming a filtered signal representing the operating power level of said reactor. 11. The system as defined in claim 9, wherein said first trip unit is a scram trip unit and said first setpoint is a scram setpoint that when tripped automatically shuts down the reactor. 12. The system as defined in claim 11, further comprising: 13. The method as defined in claim 4, further comprising the steps of: 14. The method as defined in claim 4, further comprising the steps of: 15. The protection system as defined in claim 8, further comprising: 16. The protection system as defined in claim 8, further comprising: 17. The system as defined in claim 12, further comprising: 18. The system as defined in claim 12, further comprising: