Moisseytsev #45 Recent SCO2 Cycle Analysis at...

Recent Developments in S-CO2

Cycle

Dynamic Modeling and Analysis at ANL

Anton Moisseytsev and Jim Sienicki

Argonne National Laboratory, USA

The 4th International Symposium - Supercritical CO2

Power Cycles

Pittsburgh, PA

September 9-10, 2014

Contents

� The presentation provides an update on recent analyses of the S-CO2

Brayton

cycle at ANL

– Since the last S-CO2

Symposium in 2011

– The majority of the results has been already presented at various conferences

� The analysis presented is this paper has been carried out using the Plant Dynamics

Code (PDC) developed at ANL

– Most of the S-CO2

cycle control analysis carried out at ANL and presented here has been

done in application of the cycle as an energy converter for Sodium-Cooled Fast Reactors

(SFRs)

� Recent Progress

– Coupling of the PDC with the SAS4A/SASSYS-1 code

– Dynamic simulation and control of the S-CO2

cycle

– S-CO2

cycle control with active reactor control

– ANL Plant Dynamics Code validation

"Recent Developments in S-CO2 Cycle Dynamic Modeling and Analysis at ANL" by A. Moisseytsev, 4th S-CO2 Symposium, Pittsburgh, PA, September 9-10, 2014

2

ANL Plant Dynamics Code (PDC)

� Specifically developed for analysis of S-CO2

cycle

– One-dimensional system level transient analysis code

– Targets the specific features of the cycle

• Operation close to the critical point

• Recompression cycle (if needed)

– Real CO2

properties

• Properties variation in HX’s and turbomachinery

• No ideal gas assumptions

• Compressibility effects

� Incorporates S-CO2

cycle control mechanisms and logic

� Incorporates steady-state design code to determine cycle initial conditions

� Integrated “semi-automatic” turbomachinery design

– Design and performance subroutines for both turbine and compressor

� Fast solution scheme runs efficiently on a PC

– Taylor series

– Almost real time (for slow transients)


3

Coupling of the PDC with the SAS4A/SASSYS-1 Code


4

SAS4A/SASSYS-1 Code

� Developed by Argonne National Laboratory

� Leading capability for analysis of liquid-metal-cooled reactors at system level

– Primary use: safety analysis

� Incorporates detailed reactor as well as primary and intermediate loop thermal

hydraulics

– Forced and natural circulation, pump models, heat exchangers

� Reactivity coefficients specific to fast reactors

– Core axial and radial expansions, control rod expansion, coolant density, etc.

– Radial-, axial-, and temperature-dependent distributions in transients

� Includes balance-of-plant model

– Currently limited to steam cycles

� Coupling PDC with SAS4A/SASSYS-1 would combine analysis capabilities for the

reactor and S-CO2

BOP

– Covering the entire plant


5

Coupling PDC with SAS4A/SASSYS-1 code

� Coupling PDC with SAS4A/SASSYS-1 would combine analysis capabilities for the

reactor and S-CO2

BOP

– Covering the entire plant

� However, the access to SAS4A/SASSYS-1 source code is restricted (Export

Controlled)

– Previously, the two codes were run separately with iterative update of input files

� New coupling scheme uses SAS4A/SASSYS-1 PC executable file

– Does not require access to the SAS4A/SASSYS-1 source code

– Utilizes Fortran capabilities to work with EXE files

– Takes advantage of SAS4A/SASSYS-1 restart capability

� The data transfer between PDC and SAS4A/SASSYS-1

– Occurs at each SAS4A/SASSYS-1 time step

– Is done by reading SAS4A/SASSYS-1 output files and writing input files

– Involves intermediate sodium conditions at RHX inlet and outlet


6

PDC-SAS4A/SASSYS-1 Coupling

� New coupling scheme uses

SAS4A/SASSYS-1 PC executable file

– Does not require access to the

SAS4A/SASSYS-1 source code

– Utilizes Fortran capabilities to work

with EXE files

– Takes advantage of SAS4A/SASSYS-1

restart capability

– Could be applied to other heat source

codes

� The data transfer between PDC and

SAS4A/SASSYS-1

– Occurs at each SAS4A/SASSYS-1 time

step

– Is done by reading SAS4A/SASSYS-1

output files and writing input files

– Involves intermediate sodium

conditions at RHX inlet and outlet


7

SAS4A/SASSYS-1 – Reactor Side

PDC – S-CO2 Side

Run steady-state calculations

Use steady-state sodium RHX-outlet

temperature Update restart

input file

Run one time step transient calculations

Sodium RHX-inlet temperature and

flow rate

Run transient calculations

Current time = SAS4A/

SASSYS-1 time

No

Sodium RHX-outlet temperature

Extrapolate sodium

RHX-outlet temperature

Run steady-state calculations

Maximum time

reached

End

Start

No

Update input tables for sodium temperature and flow rate

Yes

Yes

Dynamic Simulation and Control of the S-CO2Cycle


8

S-CO2Cycle Control Analyses

� Load Following

– Goal: to show that the cycle can be controlled to change power level

– Investigate and optimize control mechanisms

� Decay heat removal

– Goal: demonstrate that the cycle can be used in low power regime

– Investigate and optimize control mechanisms


9

S-CO2Cycle Control

� Included into transient PDC equations

� Relies on combination of control mechanism

– Turbine bypass [17]

• Fastest power control (on pressure and flow)

• Least efficient

– Inventory control [18]

• The most efficient (preserves TM velocity triangles

for ideal gas)

• Slow (introduce disturbance to compressor conditions)

• Limited by tank volume

• Decreases compressor surge margin

– Turbine throttling [16]

• More efficient than TBP, but less efficient than INV

• Introduces an extra pressure rise with valve closing (not good for full pressure)

– Cooler bypass [19]

– Cooling water flow rate [14]

– Compressor surge control


10

S-CO2Cycle Control: Control Strategy

� Use inventory control when possible

– Subject to storage tank volume limitation

� Turbine throttling

– Outside INV range

� Turbine bypass for small

load changes and

fine-tuning

� Minimum temperature

control

– Always

� Shaft speed control

– For decay heat removal

– After disconnection from

the grid

� Compressor surge control

– When needed

– Low power


11

Demonstration of S-CO2Cycle Control with PDC


12

� Simulation in two stages

– First stage: Load following from 100% down to 0%

– Second Stage: Transition to decay heat removal

First Stage

� The electrical grid demand was set to reduce linearly at 5%/min rate from 100% to

0%

– 1,200 s transient time

– The only external input

� S-CO2

cycle automatic controls adjust the conditions on the BOP side to maintain

balance between the net generator output and the grid demand

� Autonomous reactor operation is assumed

– Sodium-cooled fast reactor (ABR-1000)

– No reactor power control by control rods

• Only rely on reactivity feedbacks

– No control of primary and intermediate pumps

Results of Transient Simulations: Load Following

� Grid demand decreases linearly to 0 (external input)

� Net generator output follows the grid demand very closely

– Achieved by control actions on S-CO2

side


13

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 200 400 600 800 1000 1200

W,

FRA

CT

ION

OF N

OM

INA

L G

EN

ER

ATO

R P

OW

ER

TIME, s

TURBINE AND COMPRESSORS WORK AND GENERATOR OUTPUT

W_Turb

W_Comp1

W_Comp2

W_gen

W_grid

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000 1200

VA

LV

E O

PEN

FLO

W A

REA

, %

TIME, s

VALVES CONTROL ACTION

f_TBPv

f_INViv

f_INVov

f_TINv

f_C2Ov


� Reduced heat removal by CO2

affects the temperatures on the sodium side of

Na-CO2

HX

– Sodium inlet temperature is defined by heat balance on the reactor side

� On the reactor side, changing intermediate and then primary loop temperatures

introduce reactivity to the core


14

300

350

400

450

500

550

0 200 400 600 800 1000 1200

TEM

PER

AT

UR

E, oC

TIME, s

BRAYTON CYCLE TEMPERATURES: RHX

Hot_i

Hot_o

Cold_i

Cold_o

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0 200 400 600 800 1000 1200

REA

CT

IVIT

Y, $

TIME, s

CORE REACTIVITY

NET EXTERNAL DOPPLER AX. EXP.

RAD. EXP. CRDL EXP. COOLANT


� The net effect of reactivity feedbacks is reduction of reactor power

– Which closely follows the heat removal by CO2

side

– Even without active reactor power control

� The peak reactor temperatures stay below the nominal values

– Result of strong negative reactivity feedbacks of ABR-1000 SFR core


15

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800 1000 1200

NO

RM

ALIZ

ED

PO

WER O

R F

LO

W

TIME, s

CORE POWER AND FLOW

POWER DECAY POWER PEAK CHANNEL FLOW

300

350

400

450

500

550

600

650

700

750

0 200 400 600 800 1000 1200

TEM

PERAT

URE, oC

TIME, s

PEAK CORE TEMPERATURES

PEAK FUEL PEAK CLAD

PEAK COOLANT INLET

Transition to the Decay Heat Removal Mode


16

� Goal: find S-CO2

cycle control which would allow plant operation at low reactor

power

– 6% or less

� Simulation was continued after the generator power reached 0% level

– Same transient, Stage 2 starts at 1,200 s

� Generator is assumed to be disconnected from the grid

– Zero grid demand

– Ideally, the control system would maintain zero net generator output

• If there is enough reserve power in turbine to drive the compressors

– Turbomachinery shaft speed is assumed to reduce linearly to 20%

� No other changes in external input

– Still autonomous reactor operation

� Minimum temperature control is no longer required to maintain minimum

temperature at design point

– As long as the temperature stays above the critical value

Results of Transient Simulations: Transition to Decay Heat

� Slowing down shaft reduces both turbine and compressors work

– Still, turbine provides sufficient power to drive the compressors

– Zero net generator output is maintained

� The automatic cycle control maintains zero generator power

– To match zero load demand


17

-1%

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

1200 1500 1800 2100 2400 2700

W,

FR

AC

TIO

N O

F N

OM

INA

L G

EN

ER

ATO

R P

OW

ER

TIME, s

TURBINE AND COMPRESSORS WORK AND GENERATOR OUTPUT

W_Turb

W_Comp1

W_Comp2

W_gen

W_grid

0

10

20

30

40

50

60

70

80

90

100

1200 1500 1800 2100 2400 2700

VA

LV

E O

PEN

FLO

W A

REA

, %

TIME, s

VALVES CONTROL ACTION

f_TBPv

f_INViv

f_INVov

f_TINv

f_C2Ov

� Compressor surge/stall approach is detected at about 2,100 s

– Triggering surge control flow

– Still, the flow is not too high to increase the compressor work significantly


18


0%

10%

20%

30%

40%

50%

60%

70%

80%

1200 1500 1800 2100 2400 2700

STA

LL M

ARG

IN

TIME, s

COMPRESSORS STALL MARGIN

Comp1

Comp2

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

1200 1500 1800 2100 2400 2700

m,

RELAT

IVE T

O N

OM

INA

L T

UR

BIN

E

TIME, s

BRAYTON CYCLE FLOW RATES: SURGE CONTROL

Comp1

Comp2

� Temperatures above the critical point are maintained

– Even with disabled cooler bypass control

� The heat removal rate by the cycle reduces to about 3% nominal


19


30.9

31.4

31.9

32.4

32.9

33.4

33.9

34.4

34.9

1200 1500 1800 2100 2400 2700

TEM

PERATU

RE, oC

TIME, s

COMPRESSOR #1 INLET TEMPERATURE

T_c_i

T_crit

0%

5%

10%

15%

20%

25%

30%

35%

1200 1500 1800 2100 2400 2700

PO

WER,

FRA

CTIO

N O

F F

ULL R

EA

CTO

R P

OW

ER

TIME, s

HEAT BALANCE IN RHX

Q_RHX_Rx

Q_RHX_CO2

S-CO2Cycle Control with Active Reactor Control


20

Active Reactor Control in PDC-SAS4A/SASSYS-1 Codes

� In load following transients, the changes start on BOP side

– E.g., turbine bypass valve opening in response to reducing grid load

– Reactor “sees” changes through CO2

heat removal variation (reduction) in the

intermediate sodium-to-CO2

reactor heat exchanger (RHX)

� To maintain intermediate sodium temperatures, sodium flow rate needs to be

adjusted (reduced)

– IHTS pump control

� This will affect IHX

temperatures

– Primary pump control

� With changed (low) primary

coolant flow, reactor power

needs to be changed

– To maintain core-outlet

temperature

– By means of the control rod

movements


21

6

5

3

4

2

Reactor Control Logic

Controllable Parameter Measured Value Controlled By Control

Intermediate loop cold-

side temperatures

RHX-outlet Na

temperature

Intermediate sodium

flow rate

Intermediate sodium

pump torque

Primary loop cold-side

temperatures

IHX-outlet primary Na

temperature

Primary sodium flow

rate

Primary sodium

pump torque

Hot-side temperaturesCore-average outlet

temperatureCore power (reactivity)

External core

reactivity


22

� Active reactor control logic was implemented in the PDC

– Control action is communicated to SAS4A/SASSYS-1

� In ideal world, the temperatures will be maintained at steady-state levels

everywhere

– Power/flow=1

� In reality, system delays (and other limitations) will prevent that

– Are there S-CO2

cycle limitations?

Results of Active Reactor Control (40% linear load reduction)

� Active control showed better results

– Less temperature variation

– Better power-to-flow ratio

– Higher cycle efficiency

� However, these results were

obtained for only 40% load

reduction

– What happens below 60%

load?


23

320

325

330

335

340

345

350

0 200 400 600 800 1000 1200

TEM

PER

AT

UR

E, oC

TIME, s


Hot_o Cold_i

CO2Temperature at RHX Inlet

� In highly-recuperated S-CO2

cycle, RHX-

inlet temperature is defined by HTR

performance

� When flow rate increases, heat

transfer in HTR is reduced, RHX-inlet

temperature ↓– During turbine bypass

• 0-120 s

� With decreasing flow rate, RHX-inlet

temperature ↑– With inventory control

� When CO2

temperature at RHX cold

end reaches steady-state value for

sodium temperature, ability to

maintain that temperature is lost


24

320

325

330

335

340

345

350

0 200 400 600 800 1000 1200

TEM

PER

AT

UR

E, oC

TIME, s


Hot_o Cold_i

CO2Temperature at RHX Inlet

� Several approaches to control the temperature (prevent from increasing) were

investigated

– Reduced inventory control action

– Recuperator bypass

– Relaxed sodium temperature requirements

– Reduced core-outlet temperature

� Control on S-CO2

cycle side resulted in too low cycle efficiency

– Plus, there are additional limits

� Results with relaxed temperature limits are acceptable

– If high structure temperatures (say, 400 oC) can be tolerated

� Reduced core-outlet temperature is recommended as a preferred option

– All temperature limits are satisfied

• There are short-term effects

– Cycle efficiency drop from lower turbine-inlet temperature is not significant


25

ANL Plant Dynamics Code Validation


26

ANL Plant Dynamics Code V&V History

� S-CO2

cycle has never been commercially operated

� Earlier V&V was limited to benchmark calculations against similar codes elsewhere

� Later, limited code validation on individual components

– Heat exchangers (PCHE test loop at ANL)

– Turbomachinery (Ideal gas loop at SNL)

– Small-scale S-CO2

compressor test loop at Barber-Nichols Inc.

� Recently, Barber-Nichols, Inc. (BNI) and Sandia National Labs (SNL) constructed

and operated small-scale closed split-flow S-CO2

cycle loop

– SNL Loop will provide a configuration for PDC testing and validation of modeling

• CO2

working fluid

• Equipment designed to operate close to the critical point

• Recompression cycle configuration

– Recent PDC validation effort is focused on simulating the SNL Loop and data


27

July 14, 2011 SNL Loop Setup

� Single TAC

� Two recuperators

– HTR is “overdesigned” for this setup -> very little, if any, heat transfer in LTR

– Only HTR is simulated in the PDC

� 4 heaters

– 390 kW input limit at

BNI facility


28

SNL Loop Data and Modeling

� Some specifics of the experimental setup (for model validation purposes) were

identified

– Significant heat loss in pipes and in turbine

• The heat loss in turbine volute is not measured

– The loop could not be run for a long time to achieve “perfect” heat balance

• Required for steady-state initialization in the PDC

– Lack of information on PCHE internal configuration

– No water flow rate measurements

– Temperature measurement uncertainty (1.1 oC) is significant

� Some features were dealt with modeling assumptions


29

Transient Simulation: Assumptions

� The LTR was excluded from the PDC model

� The electrical heaters are simulated with shell-and-tube heat exchangers

– Sodium flow on the hot side for the steady-state model

– Direct heat input into the HX “tubes” in transients

� All of the heat losses in the system were simulated to occur in the HTR-heater pipe

– Including turbomachinery heat loss

– The amount of the heat loss was determined to achieve a heat balance throughout the

system at steady-state conditions

– In a transient, the heat loss is scaled with the changing CO2

temperatures in the pipe

� Other than the heat loss, no heat transfer is simulated in the pipes in the PDC

– Also includes the absence of heat exchange between the CO2

and the pipe walls

� The TAC drain flow is not included into the PDC steady-state and transient models


30

Steady-State Calculations

� Good agreement was achieved for

steady-state

– Required significant heat loss

simulation (19 kW) at heater inlet

• Simulates all heat losses in the

cycle

• Also compensates for not

achieving perfect heat balance in

HTR by 3356 s

– Skipping LTR did not affect

temperatures much


31

Time 3355.6 s1.779 kg/s T, °C

31.3 P, MPa232.7 231.3 7.4639.712 9.611 RPM

31.5 28.07.465 #N/A

210.7 46.3142.2 7.724 9.8679.751

207.2 45.4 45.6 46.1 45.9 33.97.464 9.784 9.772 9.893 7.496 #N/A

#N/A kg/s145.1 45.7 45.5 45.79.540 7.523 7.512 7.482

35,000

Heater

Alt

Cooler

CT

HTRLTR

1.859 kg/s T, °C0.0 31.5 P, MPa

232.2 232.1 7.451 Q, kW9.786 9.759 RPM192.20 35,000

31.7 28.07.475 0.228

16.50210.3 46.0 153.0

145.4 7.803 9.8509.794

209.5 45.9 45.8 33.07.532 9.838 7.487 0.101

7.301 kg/s-19.0 153.8 46.2

9.834 7.527

0.00

PDC Steady-State Results

33.30

15.00

401.2

Heater

Alt

Cooler

CT

HTRLTR

PDC

Data

Dynamic Simulation of SNL S-CO2Loop with the PDC

� Transient is defined by the experimental data through the external input:

� Initial conditions: “steady-state” at 3356 s


32

34,000

36,000

38,000

40,000

42,000

44,000

46,000

48,000

50,000

52,000

54,000

0 500 1000 1500 2000 2500

SHA

FT R

OTA

TIO

NA

L SP

EED

, R

PM

TIME, s

SHAFT SPEED

RPM A

PDC (Input)

200

220

240

260

280

300

320

340

360

0 500 1000 1500 2000 2500

TEM

PER

ATU

RE,

oC

TIME, s

HEATER OUTLET TEMPERATURE

Target Inlet Temp

PDC Input

27

27.5

28

28.5

29

29.5

0 500 1000 1500 2000 2500

TEM

PER

ATU

RE,

oC

TIME, s

WATER INLET TEMPERATURE

T900

PDC Input

0.998

1

1.002

1.004

1.006

1.008

1.01

0 500 1000 1500 2000 2500

TEM

PER

ATU

RE,

NO

RM

ALI

ZED

TO

ST

EAD

Y ST

ATE

VALU

E

TIME, s

COOLER OUTLET TEMPERATURE

Experimental Value

PDC Input

Shaft Speed Water Inlet Temperature

Target Heater Outlet TemperatureTarget Cooler Outlet Temperature

Transient Results Presentation


33

T600

PDC

� Compare all available experimental measurements with the corresponding PDC

predictions

– Temperatures, pressures, density, flow rates

� The following slides show such comparisons for each individual parameter

� Few results are presented here

– Differences are briefly discussed

– See the paper for more detailed comparison

Measured data (e.g., Temperature at point 600)

Corresponding code results

Transient Results Comparison

� Heater outlet temperature is predicted very accurately

– Results of the automatic control

– Short-term behavior is achieved by control’s PID coefficients optimization

– In some cases, there is not enough reserve capacity in the heater

• Discussed below

� Turbine inlet temperature is very close to the heater outlet

– There is, however, a somewhat noticeable time delay in the experimental data

• Not showing in the PDC – result of not simulating pipe heat capacity


34

200

220

240

260

280

300

320

340

360

0 500 1000 1500 2000 2500

TEM

PER

AT

UR

E, oC

TIME, s

HEATER OUTLET TEMPERATURE

T600

PDC

200

220

240

260

280

300

320

340

360

0 500 1000 1500 2000 2500

TEM

PERATU

RE, oC

TIME, s

TURBINE INLET TEMPERATURE

T100A

PDC

T600

PDC

1

2

3

4

1

2

3

4

40

45

50

55

60

65

0 500 1000 1500 2000 2500

TEM

PER

AT

UR

E, oC

TIME, s

HTR HOT SIDE OUTLET TEMPERATURE

T202

PDC


� Turbine outlet temperature is predicted accurately earlier in the transient

– But diverges with higher turbine speed

• Overprediction of turbine performance at higher speeds

� HTR hot side outlet temperature is slightly overpredicted by the PDC

– Overprediction of HTR performance

– Maximum difference is only 1.5 oC

• Measurement ΔT = 1.1 oC


35

1

2

3

200

220

240

260

280

300

320

0 500 1000 1500 2000 2500

TEM

PER

AT

UR

E, oC

TIME, s

TURBINE OUTLET TEMPERATURE

T200A

PDC

12

3


� Cooler outlet temperature is very close

– Maximum difference is only 0.3 oC

– Measured temperature was an input for PDC

• Verifies control performance, not necessarily cooler model

� Compressor outlet temperature is predicted very accurately

– Maximum difference is only 1 oC

• Within the measurement uncertainty


36

31

31.5

32

32.5

33

33.5

34

34.5

0 500 1000 1500 2000 2500

TEM

PER

AT

UR

E, oC

TIME, s

COOLER OUTLET TEMPERATURE

T399

PDC

40

45

50

55

60

65

0 500 1000 1500 2000 2500

TEM

PERATU

RE, oC

TIME, s

COMPRESSOR OUTLET TEMPERATURE

T500A

PDC


� Compressor outlet pressure is predicted accurately earlier and late in the

transient

– Pressure is overpredicted in the middle section

• High rotational speeds

� Turbine inlet pressure is consistently overpredicted by the code

– In part, due to compressor performance overprediction

– Also, underprediction of the pressure drops

• LTR


37

1

2

9

9.5

10

10.5

11

11.5

12

12.5

13

13.5

0 500 1000 1500 2000 2500

PR

ESSU

RE,

MPa

TIME, s

COMPRESSOR OUTLET PRESSURE

P500A

PDC1

2

1

9

9.5

10

10.5

11

11.5

12

12.5

13

13.5

0 500 1000 1500 2000 2500

PR

ESSU

RE,

MPa

TIME, s

TURBINE INLET PRESSURE

P100A

PDC


� Low side pressures show much better agreement

– Especially, for the compressor inlet

� Compressor inlet density prediction is close

– The only density measurement in the loop

– Some difference at later stages are possibly due to difference in the cooler-outlet

temperature


38

1

2

7.2

7.4

7.6

7.8

8

8.2

8.4

8.6

8.8

9

0 500 1000 1500 2000 2500

PR

ESSU

RE,

MPa

TIME, s

BRAYTON CYCLE PRESSURES: LOWP200A

Turb-out

(PDC)

P400A

Comp-in

(PDC)

1

340

350

360

370

380

390

400

410

420

0 500 1000 1500 2000 2500

DEN

SIT

Y, k

g/m

3

TIME, s

COMPRESSOR INLET DENSITY

DensityA

PDC

2


� CO2

flow rate is overpredicted by the code for most of the transient

– By about 5%

– Consistent with steady-state results

• Flow rate was calculated from the heat balance

• Perfect heat balance was not achieved at 3356 s

– Also, code predicts much faster change in the flow rate

• Possibly, due to heat capacity of turbomachinery, which is ignored in the PDC by virtue of using

the turbomachinery maps


39

1.7

1.8

1.9

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

0 500 1000 1500 2000 2500

FLO

W R

AT

E,

kg/s

TIME, s

BRAYTON CYCLE FLOW RATES

MassFlowA

Turb

(PDC)

Comp

(PDC)

Lessons Learned from SNL Loop Simulation (So Far)

� The PDC transient results are close to the experimental data

– The existing modeling capabilities may be sufficient

� Lack of information on PCHE internal configuration

– E.g., channel diameter, zigzag angle

� The loop could not be run for a long time to achieve “perfect” heat balance

– Required for steady-state initialization in the PDC

– “Steady-state” at supercritical conditions is highly recommended

� Heat loss in pipes, recuperators, and turbine is difficult to account for

– The heat loss in turbine volute is not measured

� Water flow rate measurements are needed for cooler model validation

� Complete understanding of the control action is required for modeling

� Temperature measurement uncertainty (1.1 oC) is significant

– Density is only measured at the compressor inlet

� Turbomachinery performance is overpredicted at higher speeds

– Need loss correlations better suited for small-scale TM

� Note that all of these effects are specific to the SNL small-scale loop and become

negligible for commercial-scale S-CO2

cycles


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Summary

� Plant Dynamics Code is developed at ANL for analysis of S-CO2

cycles

– Addresses specific features of the cycle

� A new approach was developed to couple the PDC with SAS4A/SASSYS-1

– Coupled reactor-BOP calculations

� A control strategy for the S-CO2

Brayton cycle has been developed

– Combination of various control mechanisms

– Enables load following from 100% to 0% and transition to decay heat removal mode

� Active reactor control is implemented in the coupled PDC-SAS4A/SASSYS-1 codes

– Aspects of S-CO2

cycle operation on the reactor control are discovered and investigated

� PDC validation is ongoing

– Effort is concentrated on modeling the SNL S-CO2

Loop

– Lessons learned regarding simulation of the experimental facilities


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Moisseytsev #45 Recent SCO2 Cycle Analysis at...

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