NE 405/505 Exam 2 Spring 2016

Transcription

1 NE 405/505 Exam 2 Spring 2016 (30% 1 A WR with U-ube Steam Generators is operating at 100 % with all control systems in their normal automatic control mode. he operator initiates a ramp decrease in load to 90% at the warranted ramp rate. Describe all control system actions leading to steady state at the new power level. You may use up/down arrow logic indicators as appropriate to reduce verbage in your answer. Repeat your analysis for WRs operating with Once hrough Steam Generators and for Boiling Water Reactors operating with jet pumps. WR with U SOLUION (W ( DEM imp he turbine demand sets the reference impulse pressure. During the ramp decrease, the control system response would be: Control Rods ( CV W (Elec. wr imp imp imp REL ( imp > ( (Rx wr > (Elec. wr REL REL CR (Rx wr REL As the demand and reference impulse pressure go to their steady state values at the end of the ramp, the control system response will bring the system parameters to their new steady state according to ( imp imp ( imp CV imp W (Elec. wr REL ( CV W (Elec. wr imp imp imp REL imp (

2 E -( 1 E (Rx wr - (Elec. wr 2 REL REL E=G E +G E > E 0 CR (Rx wr REL < E=0 CR (Rx wr REL Steam Generator Level imp (Level During the ramp CV m (Level imp Once the ramp terminates, then CV m (Level imp In general, E m - m 1 E Level - (Level 2 E=G E +G E > E 0 FCV m < E=0 FCV m Feed ump Speed FCV RM FCV F ressurizer Level (Level RZ In addition (Level RZ

3 During the ramp, (Level RZ Level RZ Once the ramp terminates and the system goes to steady state (Level RZ Level RZ In general Level (Level m RZ RZ charging RZ RZ charging Level (Level m ressurizer ressure (Level rz ress RZ During the ramp, Level rz ress RZ Once the ramp terminates and the system goes to steady state Level rz ress RZ In general rz ress (rz ress Q m HR Q m HR spray spray rz ress (rz ress Q m HR spray

4 WR with O (W (m DEM he turbine demand sets the reference flow rate. During the ramp decrease, the control system response would be: Control Rods m (m FCV m m < m Level UA > ( CR (Rx wr REL (- UA Q (m < m g gen < ( CV CV m W imp As the demand and impulse pressure go to their steady state values at the end of the ramp, the control system response will bring the system parameters to their new steady state according to W (W DEM (m m (m FCV m m m Level UA ( CR (Rx wr REL ( UA Q (m g gen m

5 ( CV CV m W imp he system stabilizes when Q RX = Q m m W = (W DEM Steam Generator Level Steam generator level (boiling length is not controlled and floats Feed ump Speed Feed ump Speed control is the same as in the U case ressurizer ressure and Level Control ressurizer ressure and Level Control is the same as in the U case.

6 BWR (W (m DEM he turbine demand sets the reference flow rate. During the ramp decrease, the control system response would be: Control Rods Control Rods would not move during this maneuver. Reactivity control is by the recirculation valves. Recirculation Valves m (m Recirc Valve m Rx m ( Rx wr Rx g Rx wr (+ = 0 Rx wr Rx Rx wr (m < m g gen < ( CV CV m W imp As the demand and impulse pressure go to their steady state values at the end of the ramp, the control system response will bring the system parameters to their new steady state according to W (W DEM (m m (m Recirc Valve m Rx m ( Rx wr Rx g Rx wr ( = 0 Rx wr Rx Rx wr (m g gen m ( CV CV m W imp

7 Reactor Vessel Level Reactor Vessel level is controlled in the same manner at level in Us Feed ump Speed Feed ump Speed control is the same as in the U case ressurizer ressure and Level Control here is no pressurizer.

8 (30% 2 For the maneuver and three reactor types in problem 1, indicate whether the following system parameters are Directly Controlled (DC, Indirectly Controlled (IC, or not applicable (NA a urbine Impulse ressure b urbine/generator Speed c urbine Control Valve osition d urbine Output e Steam ressure f Steam Generator Level g Reactor Vessel Level h Steam Flow Rate i Feed Flow Rate j Feed Control Valve osition k Average Coolant emperature l Core Flow Rate m rimary System ressure n Control Rod osition o Core ower Level SOLUION U O BWR urbine Impulse ressure DC IC IC urbine/generator Speed DC DC DC urbine Control Valve osition NA NA NA urbine Output IC IC IC Steam ressure IC DC DC Steam Generator Level DC NA NA Reactor Vessel Level NA NA DC Steam Flow Rate NA IC DC Feed Flow Rate NA DC IC Feed Control Valve osition NA NA NA Average Coolant emperature DC DC IC Core Flow Rate NA NA NA rimary System ressure DC DC DC Control Rod osition NA NA NA Core ower Level IC IC IC

9 (20% 3 A potential accident in WRs with U-ube Steam Generators is a controller failure resulting in all control valves failing open. a A safety engineer chooses to analyze this accident making the following assumptions, why? i EOC ii Rods in manual iii Reactor at 102 % power iv Feed ump Speed Controller in Manual v ressurizer Heaters Disabled SOLUION i EOC: his is an overcooling accident. he moderator temperature coefficient is most negative at EOC, leading to the greatest positive reactivity insertion. ii Rods in manual: he reactor is assumed to be at full power with all rods out. he rods can not withdraw any further. Since (Rx wr REL > (Elec. wr REL, even if < ( the rods could insert mitigating the reactivity insertion. iii Reactor at 102 % power: As this event leads to a positive reactivity insertion, power will increase. DNB and CHF are a concern. his puts the reactor at the upper end of the measurement band and closer to thermal limits at the beginning of the accident. iv Feed ump Speed Controller in Manual: If the FCV is nearly full open at full power, then increasing the flow rate through the valve increases the pressure drop across the valve and the pump speed controller would reduce RMs reducing the flow rate. One could also argue that opening the valve might reduce the pressure drop across the valve resulting in the pump speed controller increasing RMs making the accident worse, so the speed controller should be in AUO. v ressurizer Heaters Disabled: Since DNB is a concern for this event, the reduction in will result in a reduction in ressurizer level and consequently pressurizer pressure, thus lowering critical heat flux and the DNBR. Disabling the heaters prevents the heaters from returning the pressure to its set point. b Assuming all other control systems operate in their normal automatic mode, sketch the following system parameters up to the point of reactor trip and explain the shape of your graphs. i ave ii Reactor ower and Heat Flux iii Reactor Fuel emperature iv ressurizer Level v Steam Generator Level

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12 c Given the attached trip logic diagram, what potential trips protect against this accident and what is the primary trip protection function (e.g. over pressurization of containment? i High power trip (DNB and fuel centerline melt ii Low pressurizer pressure (DNB iii kw/ft (fuel centerline melt iv DNB (CHF (20% 4 Short Answer SOLUION a Why can WRs with Once hrough Steam Generators operate with a constant ave program and constant pressure? ANSWER: UA is not constant, so for sat constant and Q = UA ( - sat, - UA Q sat b What are the trade offs between operating a Once hrough Steam Generator with a constant ave program and a ave program that increases with power? ANSWER: A constant implies a smaller pressurizer volume at the expense of a longer generator. An increasing with power allows for a smaller generator, but at the expense of a larger pressurizer volume. c If control rods move to control ave, why are reactor power and turbine output inputs to the rod speed controller? ANSWER: he difference between the relative electric power and relative reactor power provides an anticipatory signal to begin rod motion prior to changes in. d Why is generator shrink/swell a greater control problem at low power levels? ANSWER: At low powers, control is based purely on the level error signal. Shrink/swell generates a level error signal that moves opposite of the flow/ flow error and causes the FCV to move in the wrong direction. e What is meant by a linear control valve? How are linear control valves utilized in water control? ANSWER: he flow through the valve is linear with valve position if the pressure drop across the valve is constant. Variable speed pumps are used in conjunction with linear control valves to maintain a constant pressure drop across the valve and maintain the linear valve behavior. f Why do essentially all power reactors run at the same, fixed urbine/generator speeds? ANSWER: o match the grid electrical frequency. g If the bundle side of a U-ube generator is always full to the moisture separators during normal operation, why is the liquid level in the downcomer used to infer generator inventory? ANSWER: he bundle mixture density increases and decreases with inventory. he downcomer density is essentially constant. Since the bundle height is constant L H L BD BD DC BD DC DC h A pressurizer is operating a 100% power when a controller error causes the backup heaters to energize. What is the impact on the system dynamic behavior? Assuming the heaters remain fully energized, and sprays are

13 disabled, what will terminate this event? ANSWER: he is no impact on the system dynamic behavior. High pressurizer pressure will eventually trip the reactor. i Give a brief description of the control algorithm for WRs with Once hrough Steam Generators. ANSWER: Reference flow rate is approximately proportional to electric demand. For a change in load, the reference flow rate will follow the demand. If the measured flow rate is less than the reference flow rate, the FCVs are opened. If the measured flow rate is greater than the reference flow rate, the FCVs are closed j Briefly describe the system response of a BWR to a boron dilution accident. ANSWER: None.