Transient Analyses of sCO Cooled KAIST-Micro Modular...
Transcript of Transient Analyses of sCO Cooled KAIST-Micro Modular...
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The 5th International Symposium - Supercritical CO2 Power Cycles
Transient Analyses of sCO2 Cooled
KAIST-Micro Modular Reactor with
GAMMA+ code
Nuclear & Quantum Engineering, KAIST
Presenter: Bong Seong Oh
Yoon Han Ahn, Seong Gu Kim, Seong Jun Bae, Seong Kuk Cho
Corresponding Author: Jeong Ik Lee*
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The 5th International Symposium - Supercritical CO2 Power Cycles
Introduction
OUTLINE
Modification of GAMMA+ code
Conclusion
Code Results of MMR
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Introduction
Motivation of sCO2 cooled SMR High cycle efficiency in moderate
temperature ranges (400oC~700oC).
Compact component size→Simple layout.
CO2 is a cheap coolant, and abundant.
<SMART reactor (PWR 100MWe), KAERI> <NuScale (PWR 50MWe), NuScale Power>
<Steven A. Wright, Supercritical technologies S-CO2 overview>
Advantages of Small Modular Reactor Flexible power generation.
Better economic affordability.
Options for remote regions without
electricity grid infrastructures.
<Thermal efficiency of various cycles for range of temperature>
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Introduction
Conceptual design of MMR Simple recuperated cycle for transportability.
Printed Circuit Heat Exchanger.
Centrifugal turbo-machinery.
Air cooling system to be independent for region.
KAIST Micro Modular Reactor (MMR) One module containing reactor core,
power conversion system (PCS).
Economic benefit by shop-fabricated
construction.
Transportable modular reactor.
Supplying energy to the remote
regions.
<Ground transport> <Simple recuperated system by air cooling>
<Reactor core and power conversion system in a single containment >
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Introduction
Selection of transient code GAMMA+ code is developed for HTGR
Inexact CO2 properties near the critical point.
Turbo-machineries for ideal gas (ex. He,N2..).
Selection of scenario for safety analysis Implementation of various nuclear power plant event
Loss of Coolant Accident
Power transition event
Load rejection event
Why load rejection?
MMR would be constructed on remote regions (desert,
polar region).
These regions have tough environment and small
population →Grid could be easily damaged or unstable
Analysis of load rejection event. Analyze result of the event without any control
Build target parameters to control the cycle
Apply active control and check the result with the control
- Loss of
Coolant
- Power
transition
- Etc.
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Modification of GAMMA+ code
Original GAMMA+ code is developed for HTGR analyses. Not incorporate the exact CO2 properties especially near the critical point (Tc=304.1282 K, Pc=7.3773 MPa).
The way how to calculate thermal properties by EOS. Thermal properties can be obtained by differentiating EOS with respect to density and temperature
CO2 Properties Modeling in GAMMA+ code
<Old solution: Connection REFPROP> <Current solution: Solving EOS of CO2>
The way how to calculate transport properties. Unless state of CO2 is near critical region (240oC<T<450oC, 25kg/m3<𝜌<1000kg/m3), transport properties
are simply composed of constant coefficient and temperature of the state.
It’s too complicated to calculate transport properties of CO2 near the critical region because calculation
process includes root finding and inverse matrix →Alternative: Tabular properties proposed by N. A. Carstens.
EOS of CO2 calculator
Original GAMMA+ code
Thermal Properties
Not Critical region:
Transport properties
calculator
Transport properties
Critical region:
Tabular properties
calculator
Original GAMMA+ code
REFPROP database
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Modification of GAMMA+ code
Turbo-machinery modeling based on real gas Due to abrupt change of properties of CO2 near the critical region, real gas effect should be considered when
sCO2 turbo-machineries are modeled.
Heat rise of compressor and release of turbine could be calculated by enthalpy difference.
To obtain hideal and 𝜂comp&turb, a user has to utilize pre-generated performance maps, drawn with respect to
the corrected mass flow rate and RPM.
Performance maps of sCO2 turbo-machineries
Turbo-machinery Modeling by performance map.
( ) ideal inletcomp outlet inlet
comp
h hq h h m m
( ) ( )turb outlet inlet turb outlet idealq h h m h h m
Efficiency (a) and Pressure Ratio (b) of compressor
Efficiency (a) and Pressure Ratio (b) of turbine
<schematic diagram of modified GAMMA+ code>
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Code Results
Simplified configuration of MMR Heat of the MMR can be rejected to ambient air via cooling fan but precooler of MMR is not directly
connected with air → CO2 loop is inter-connecting the precooler and air to maintain the purity of MMR
primary cycle when even the precooler channel breaks.
However, cooling loop of MMR in GAMMA+ code is not fully modeled but simplified by prescribing the inlet
CO2 of the cooling loop.
Nodalization and modeling of MMR in GAMMA+ code.
#204
#203
Precooler
#1000#1001
CO2 Boundary volume
CO2 Boundary volume
#202
#201
Recuperator
#104 Pipe
#301
#105 Pipe
Comp Turb#302
#102
#106
# 51
# 50
CoolantChannel
Upper Plenum
: Fluid block
: External junction
: Boundary volume
: Pipe wall
#101Pipe
#103Pipe
Pipe
Pipe
#1 (Reflector)
#2 (active core)
#3 (Gas plenum)
Lower Plenum
TBV
Difference between Design parameters and code results
Reactor Power 0.00633 % Mass flow rate 0.0239 %
Compressor inlet
Pressure1.044 %
Turbomachinery
RPM0.0 %
Compressor Inlet
Temperature0.067 % Turbine Power 1.78 %
Turbine inlet
Pressure0.0654 % Compressor Power 1.835%
Turbine inlet
Temperature0.0055 % Generator Power 2.2 %
Moments of inertia modeling Moments of inertia of MMR turbomachineries are not fully
modeled yet.
Assume the inertia is proportional with reactor power ratio.
IMMR/QMMR = Irefer/Qrefer
Reference reactor is defined as2400 MWth S-CO2
cooled fast reactor developed by Pope.
NPP Generator Turbine Compressor Total
MMR
(36.2MWth)15.075 12.814 4.607 32.496
Pope
(2400MWth)1000 850 305.6 2454.7
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Code Results
Code results of load rejection event without control action
Load is rejected at 0.0 second.
Load rejection event without active control.
<Temperature of MMR components
on the event w/o control>
<Minimum and Maximum pressure
on the event w/o control >
<RPM of turbo-machinery
on the event w/o control >
<Mass flow rates on the event w/o control > <Work of turbo-machinery on the event w/o control >
0 2 4 6 8 10 12
100
200
300
400
500
600
Te
mp
era
ture
(o
C)
Time (sec)
Turb in
Comp in
Rec,h in
Rec,c in
Pre,h in
event start
0 2 4 6 8 10 12
5
10
15
20
25event start
Pre
ssu
re (
MP
a)
Time (sec)
Min P
Max P
0 2 4 6 8 10 12
100
105
110
115
120
125
130 event start
RP
M n
om
inal (%
)
Time (sec)
Turbine
Comp
0 2 4 6 8 10 12150
155
160
165
170
175
180
185
190
195
200 event start
Ma
ss f
low
ra
te (
kg
/se
c)
Time (sec)
Turb flow
Comp flow
0 2 4 6 8 10 120
10
20
30 event start
Wo
rk (
MW
)
Time (sec)
Turb W
Comp W
Grid W
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Code Results
Load rejection event without active control.
Analysis of load rejection event w/o active control Slight decreasing of temperature is due to over-expansion → lastly, temperature is again increased.
Generated heat is not converted to useful work.
The minimum pressure is declined but the maximum pressure is increasedthe pressure ratio of turbine and compressor is abruptly increased along with increasing of RPM
Rotational speed of turbine is seriously increased because load rejection could act as loss of fluid resistance so
that mass flow rate is also increased
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Code Results
Load rejection event without active control.
Bypass valve location Core inlet bypass line from the core inlet pipe to the
precooler.1. Can maximize the bypass efficiency because core inlet
fluid has quite high density.
2. Can minimize the thermal shock of precooler because core
inlet fluid has quite low temperature.
#204
#203
Precooler
#1000#1001
CO2 Boundary volume
CO2 Boundary volume
#202
#201
Recuperator
#104 Pipe
#301
#105 Pipe
Comp Turb#302
#102
#106
# 51
# 50
CoolantChannel
Upper Plenum
: Fluid block
: External junction
: Boundary volume
: Pipe wall
#101Pipe
#103Pipe
Pipe
Pipe
#1 (Reflector)
#2 (active core)
#3 (Gas plenum)
Lower Plenum
TBV
Control logic of MMR: Reducing the rotational speed
of turbine1. Reducing rotational speed of turbine → Bypass mass
flow rate at turbine inlet.
2. Since generated heat from the core isn’t converted to
the useful work → Reduce the core power.
Assumption: MMR is equipped with energy storage
system that can operate at least valve systems
air cooling fan is remaining their integrity during accident.
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Code Results
Time step control action.
Control action in load rejection event of MMR
Rotational speed of turbine is 110% nominal value at 0.845 sec and then core inlet bypass valve is opened
having 1/0.5 sec opening rate.
Time (sec) Event Setpoint or Value
0.0 Load is rejected. -
0.845 High shaft speed condition 110%
1.345 Opening of core inlet bypass -
3.5 Shutdown of reactor -
0 2 4100
110
120
Opening the bypass valve: 0.845sec
RP
M n
om
ina
l (%
)
Time (sec)
No control
Bypass control
0 2 4
0.0
0.5
1.0Finish of opening: 1.345sec
Beginning of opening: 0.845 sec
Op
en
ing
Fra
ctio
n
Time (sec)
Opening Fraction
<Setpoint of core inlet bypass valve opening> <Opening rate of core inlet bypass valve>
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Code Results
Time step control action.
Safety limitation of control parameters In general, PWR has safety limit of turbine speed as 120% nominal value.
Turbine speed of PWR is generally 1500 RPM and blade length is about 1.3m but MMR has very high rotational
speed 20200 RPM and blade diameter is about 0.16m → Turbine tip speed of MMR is much faster than
conventional PWR
Considering conservative design MMR, setpoint of opening core inlet bypass is determined as 110% nominal
value of rotational speed of turbine
Opening rate of high pressure valve is proposed as 1/0.5sec in Preliminary Safety Analysis Report of PWR.
After reactor trip signal is generated, actual time to scram a core is determined as 3.5 sec in PWR. MMR also
has falling secondary control element in center of the core and additionally devises drum type control element in
side of core as shown following figure so that this trip delay time of PWR could be again applied in MMR
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0-10
0
10
20
30
40Rod insertion: 3.5sec
He
at
(MW
)
Time (sec)
Qwall
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Code Results
Load rejection event with cycle control.
<Temperature of MMR component on the event with control>
<Minimum and Maximum pressure on the event with control >
<Heat balance of reactor core on the event with control >
0 20 40 600
5
10
15
20
25
30
35
40
Decay heat
He
at
(MW
)
Time (sec)
Qwall
Qconv
0 20 40 600
100
200
300
400
500
600
Te
mp
era
ture
(o
C)
Time (sec)
Turb in
Comp in
Rec,h in
Rec,c in
Pre,h in
0 30 60
600
660
720
Wa
ll T
em
p (
C)
Time (sec)
Wall Temp
Tw,max=717.46 C
0 20 40 605
10
15
20
P,max=21MPa
Pre
ssu
re (
MP
a)
Time (sec)
Min P
Max P
<Temperature of cladding on the event with control>
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Code Results
<RPM of turbo-machinery on the event with control > <Mass flow rates on the event with control >
<Work of turbo-machinery on the event with control > <opening fraction of TBV on the event with control >
0 20 40 600.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2 RPM,max=110%
RP
M (
rot/
min
)
Time (sec)
Turbine
Comp
0 20 40 600
50
100
150
200
250
300
Ma
ss f
low
ra
te (
kg
/se
c)
Time (sec)
Turb flow
Comp flow
0 20 40 600.0
0.2
0.4
0.6
0.8
1.0
1.2
Op
en
ing
Fra
ctio
n
Time (sec)
Opening Fraction
Load rejection event with cycle control.
0 20 40 600
10
20
Wo
rk (
MW
)
Time (sec)
Turb W
Comp W
Grid W
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Code Results
Load rejection event analysis.
Analysis of load rejection event with active control After core inlet bypass is opened, mass flow rate would be
divided into two stream lines.
From reactor core to No.103 pipe, the mass flow rate is
lower than nominal value because a portion of fluid which
would flow into reactor is bypassed to precooler.
On the other hand, the mass flow rate where stream lines
are overlapped from 203 to 202 is higher than nominal
value.
At the beginning of the event, temperatures of hot line fluid
from core to No.103 pipe is lower than nominal value but
temperatures of cold line fluid from precooler to recuperator
is higher than nominal value.
→ Hot and cold side fluid are smeared by core inlet
bypass!
Turbo-machinery work become zero or converged because
rotational speed become almost zero by rotor dynamic
equation at the end of the event.
( )tot turb comp gen gridI W W Wt
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Code Results
Safety limits.
Two safety limits of MMR
Pressure boundary limit: Pressure boundary of the system
shall not exceed 110% of nominal value from ASME code.
0 20 40 600.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2 RPM,max=110%
RP
M (
rot/
min
)
Time (sec)
Turbine
Comp
Maximum pressure is 105% of nominal value during load
rejection event with control action as shown in right figure.
Wall cladding temperature limit: Wall cladding temperature
should not exceed 800oC because previous conceptually
developed S-CO2 cooled fast reactor selects this temperature
for cladding safety criteria by Pope.
Maximum wall temperature is not exceeding 800oC during
load rejection event with control action as show in right figure
0 30 60
600
660
720
Wa
ll T
em
p (
C)
Time (sec)
Wall Temp
Tw,max=717.46 C
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Conclusions and Further Works
MMR is designed to be operable and capable of supplying energy to the remote and isolated regions Perfectly modularized.
Transported to a site via land or sea.
Load rejection event modeling The population in the remote region where MMR would be operated is small.
Grid connected to the MMR could become easily unstable due to small capacity or tough condition of the region.
Transient code and results for sCO2 power plant GAMMA+ code firstly developed by KAERI was modified to analyze the sCO2 cycle.
The steady state of the MMR is checked whether it is exactly modeled in GAMMA+ code or not.
According to transient result, load rejection event could damage to the turbine blade and let the system overheated
Consequently, core inlet bypass and reactor shutdown could lead to alleviate system on load rejection event with
satisfying limitation of 110% over-pressurization and 800 oC wall cladding temperature
Modified GAMMA+ code still requires implementation coupling with CO2 properties and turbomachinery modeling.
Further investigations on various accident scenarios are necessary to enhance the design and evaluate the safety
of developed concept
Necessity of transient analysis of MMR. The integrity of the system should be demonstrated for various selected design basis accidents.
Built control logics could be validated whether the logics are appropriate.