Massachusetts Institute of Technology Department of Nuclear Science and Engineering 22 06 Engineering of Nuclear Systems Dynamic Behavior of BWR 1 The control system of the BWR controls the reactor pressure power and water level as follows The reactor pressure is controlled by the turbine control valves The reactor power reactivity is controlled by the recirculation pumps via void reactivity feedback and the Control Rods CRs The level is controlled by the Feed Water FW flow Why do we want to control level A schematic of the BWR control system is shown below Pressure Control System Sensed Steam Flow Sensed Level Feedwater Control System Steam Rate Bypass Valves Turbine Valves Pressure Control System Sensed Feedwater Flow Feedwater Pump Sensed Turbine Inlet Pressure Load Demand Error Manual Controls Turbine Load Reference Sensed Flux Control Rod Sensed Flow Recirculation Flow Control System Manual Controls Core Flow Control Rod Drive System Rod Drive Manual Controls Courtesy of GE Hitachi Nuclear Systems Used with permission How does the BWR respond to a change in CR position e g CR withdrawal P pressure density Fuel q power Control rod m flow h subcooling Control rod withdraw Fewer absorptions Higher power higher heat flux q Density decrease less moderation more leakage reaches new steady state Courtesy of GE Hitachi Nuclear Systems Used with permission 2 How does the BWR respond to a change in core flow e g flow increase P pressure density Fuel q power Control rod m flow h subcooling m Flow increase more heat removal Density increase better moderation less leakage Higher power higher heat flux q Density decrease less moderation more leakage reaches new steady state Courtesy of GE Hitachi Nuclear Systems Used with permission In both cases the void reactivity feedback takes the system back to a different steadystate condition Predict the response of the BWR to i an increase in coolant subcooling at the core inlet for example this could be caused by a decrease in the feedwater temperature ii an increase in reactor pressure for example this could be caused by partially closing the turbine valve iii an increase in turbine load Without the control system would the BWR naturally follow the turbine load 3 IAEA Simulator Quick Reference Guide The IAEA BWR simulator simulates an Advanced Boiling Water Reactor ABWR ABWR has no external recirculation loops and pumps uses internal pumps instead The LB LOCA is eliminated by design BWR 6 ABWR Steam dryer Steam nozzle Steam separator Feedwater nozzle Fuel assemblies Pressure vessel Vessel support skirt Recirculation pump Control rod guide tubes Control rod drives source unknown All rights reserved This content is excluded from our Creative Commons license For more information see http ocw mit edu fairuse SIMULATOR STARTUP Select program BWR for execution the executable file is BWR exe Click anywhere on BWR simulator screen Click OK to Load Full Power IC The simulator will display the Plant Overview screen with all parameters initialized to 100 Full Power At the bottom right hand corner click on Run to start the simulator SIMULATOR INITIALIZATION If at any time you need to return the simulator to one of the stored initialization points do the following Freeze the simulator Click on IC Click on Load IC Click on FP 100 IC for 100 full power initial state Click OK to Load C BWR Simulator FP 100 IC Click YES to Load C BWR Simulator FP 100 IC Click Return Start the simulator operating by selecting Run LIST OF BWR SIMULATOR DISPLAY SCREENS 1 BWR Plant Overview 2 BWR Control Loops 3 BWR Power Flow Map Controls 4 BWR Reactivity Setpoints 5 BWR Scram Parameters 4 6 BWR Turbine Generator 7 BWR Feedwater Extraction Steam 8 BWR Trends GENERIC BWR SIMULATOR DISPLAY COMMON FEATURES The generic BWR simulator has 8 interactive display screens or pages Each screen has the same information at the top and bottom as follows The top of the screen contains 21 plant alarms and annunciations these indicate important status changes in plant parameters that require operator actions The top right hand corner shows the simulator status The window under Labview this is the proprietary graphical user interface software that is used to generate the screen displays has a counter that is incrementing when Labview is running if Labview is frozen i e the displays cannot be changed the counter will not be incrementing The window displaying CASSIM this is the proprietary simulation engine software that computes the simulation model responses will be green and the counter under it will not be incrementing when the simulator is frozen i e the model programs are not executing and will turn red and the counter will increment when the simulator is running To stop freeze Labview click once on the STOP red Stop sign at the top left hand corner to restart Labview click on the symbol at the top left hand corner To start the simulation click on Run at the bottom right hand corner to Stop the simulation click on Freeze at the bottom right hand corner The bottom of the screen shows the values of the following major plant parameters Reactor neutron power Reactor thermal power Turbine generator output power Gross Reactor pressure kPa Core flow kg s Reactor water level m Balance of plant BOP steam flow kg s that means steam flow after the main steam isolation valve Feedwater flow kg s Average fuel temperature Deg C The bottom left hand corner allows the initiation of two major plant events Reactor trip or reactor scram Turbine trip These correspond to hardwired push buttons in the actual control room The box above the trip buttons shows the display currently selected i e plant overview by clicking and holding on the arrow in this box the titles of the other displays will be shown and a new one can be selected by highlighting it The remaining buttons in the bottom right hand corner allow control of the simulation one iteration at a time Iterate the selection of initialization points IC insertion of malfunctions Malf and calling up the Help screen online hyperlinked Help is not 5 available yet As a general rule all dynamic display values shown in display boxes on the screens follow the following conventions All pressure values are designated as P next to the display box and have units of kPa All temperature values are designated as T next to the display box and have values of deg C All flow values are designated as F next to the display box and have values of kg s Steam qualities are indicated as