GFR-He/CO2 AnalysisUsing RELAP5/ATHENATheron D. Marshall, PhD
August 26, 2004
Idaho National Engineering and Environmental Laboratory
Slide 2
Outline of Presentation
• Gen-IV, Gas-cooled Fast Reactor concept– Looking beyond the Next Generation Nuclear
Plant• Impetus for Safety Analysis
– Is passive safety inherently safe?• The Large-Break LOCA
– One of the most severe GFR challenges• RELAP5/ATHENA Input Model• Modeling Predictions
– What the numbers imply• Conclusions
Idaho National Engineering and Environmental Laboratory
Slide 3
What is the Gen-IV GFR Reactor Concept?
• Has design specifications of:– being inherently safe– using direct Brayton
cycle energy conversion with the He option
– featuring high outlet temperatures, which increase thermal efficiency and suggest H2 production
Background
Idaho National Engineering and Environmental Laboratory
Slide 4
GFR – Looking beyond the NGNP
• Anticipated deployment: 2025• Neutron flux of 1 x 1014 n/cm2-s• Power density of 55 MW/m3 to 100 MW/m3
• Reference core configuration and fuel:– Plate/block, UC with SiC matrix
• Optional core configuration and fuel:– pin, U-Zr CERMET
• Reference core coolant:– He at 7 MPa [490 °C {in}, 842 °C {exit}]
• Optional core coolant:– CO2 at 20 MPa [400 °C {in}, 550 °C {exit}]
Background
Idaho National Engineering and Environmental Laboratory
Slide 5
GFR, NGNP – a difference in flow direction
NGNP with concentric inlet/outletand downward flow through core
GFR with concentric inlet/outletand upward flow through core
Background
Idaho National Engineering and Environmental Laboratory
Slide 6
Impetus for Safety Analysis
• Gen-IV reactor concepts have the directive of having enhanced safety systems
• Ideally the reactors will circumvent an accident scenario with minimal operator intervention
• The high power density of the GFR will effectively challenge any Decay Heat Removal System (DHRS)
• A passively-safe GFR DHRS may require innovative components and engineering design
• Safety analyses and experiments are necessary to validate any DHRS designs
Define Research Task
Idaho National Engineering and Environmental Laboratory
Slide 7
Challenge of the Large-Break LOCA
• A double guillotine break of the inlet and outlet legs• Decay Heat: 13% [SCRAM], 1.5% [1 hr], 1.2% [2 hr] of
600 MW• Gen-IV Objective:
– Complete decay heat removal with a passive DHRS
– DHRS should maintain temperature limits for a minimum time period of three days
• Maximum matrix temperature limit < 2000 °C
Define Research Task
Idaho National Engineering and Environmental Laboratory
Slide 8
ATHENA Model: GFR Specifications
• Coolants: He and S-CO2• Fuel: UC with SiC matrix• TiN radial reflector and BC neutron shield• Overview of system parameters:
600 MWth20 MPa400 ºC550 ºC
3260 kg/s8.35 m2
6.42 m2
GA-MHR
600 MWth7 MPa490 ºC850 ºC
330 kg/s8.35 m2
6.42 m2
GA-MHR
Power LevelCoolant PressureInlet TemperatureOutlet TemperatureMass Flow RateInlet Flow AreaOutlet Flow AreaReactor Cavity Cooling System (RCCS)
S-CO2HeSystem Parameter
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 9
ATHENA Model: GFR Core Cross Section
600 MWth50 MW/m3
1.251.7 m127
20 cm91
40 %
Thermal PowerAverage Power DensityAxial Power PeakingCore HeightFuel AssembliesWidth of Fuel AssemblyCoolant Holes/AssemblyCoolant Void Fraction
ValueCore Parameter
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 10
ATHENA Model: Unit Cell Heat Structure
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 11
ATHENA Model: Hydraulic Nodalization
Containment
Dow
ncom
er
Inlet Plenum
ShldShld Shld
Refl
Shld Shld
Refl Refl Refl Refl
Cor
e-1
Cor
e-2
Cor
e-3
Ref
lect
or
Shi
eld
Shld
Refl
Shld
Refl
Shld
Refl
Shld
Refl
Shld
Refl
Outlet Plenum
Head Plenum
RV Head
RV
Wal
l
Outlet
Inlet
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 12
ATHENA Model: Conduction Circuit
Neutron Shield
Reflector
Core
Core Support
Outlet Plenum
Inlet Plenum
1002
1003-01
1000-01
Reactor Head Dome
Reactor Vessel
Upper and Lower Head
1401-01
1401-02
1401-03
1401-04
1401-05
1401-06
1401-07
1401-08
1401-09
1401-10
1401-11
1401-12
1401-13
1401-14
1401-15
1401-16
Core Barrel
1001-01
1001-02
1001-03
1001-04
1001-05
1001-06
1001-07
1001-08
1001-09
1001-10
1001-11
1001-12
1001-13
1001-14
1001-15
1001-16
1001-17
Reactor Vessel
Cylindrical Wall
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 13
ATHENA Model: Core Nodalization
Core
5000-21
5000-22
5000-23
5000-24
5000-25
5000-16
5000-17
5000-18
5000-19
5000-20
5000-11
5000-12
5000-13
5000-14
5000-15
5000-06
5000-07
5000-08
5000-09
5000-10
5000-01
5000-02
5000-03
5000-04
5000-05
5002-21
5002-22
5002-23
5002-24
5002-25
5002-16
5002-17
5002-18
5002-19
5002-20
5002-11
5002-12
5002-13
5002-14
5002-15
5002-06
5002-07
5002-08
5002-09
5002-10
5002-01
5002-02
5002-03
5002-04
5002-05
5004-21
5004-22
5004-23
5004-24
5004-25
5004-16
5004-17
5004-18
5004-19
5004-20
5004-11
5004-12
5004-13
5004-14
5004-15
5004-06
5004-07
5004-08
5004-09
5004-10
5004-01
5004-02
5004-03
5004-04
5004-05
Reflect
6000-01
6000-02
4000-01
4000-02
6002-01
6002-02
4002-01
4002-02
6004-01
6004-02
4004-01
4004-02
6006-01
6006-02
5006-09
5006-10
5006-07
5006-08
5006-05
5006-06
5006-03
5006-04
5006-01
5006-02
4006-01
4006-02
Shield
7000-01
7000-02
3000-01
3000-02
7002-01
7002-02
3002-01
3002-02
7004-01
7004-02
3004-01
3004-02
7006-01
7006-02
3006-01
3006-02
7008-01
7008-02
6008-01
6008-02
5008-09
5008-10
5008-07
5008-08
5008-05
5008-06
5008-03
5008-04
5008-01
5008-02
4008-01
4008-02
3008-01
3008-02
Core Support
2010-05
2000-01
2000-02
2002-01
2002-02
2004-01
2004-02
2006-01
2006-02
2008-01
2008-02
2010-01
2010-02
2010-03
2010-04
Core Barrel
1401-01
1401-02
1401-03
1401-04
1401-05
1401-06
1401-07
1401-08
1401-09
1401-10
1401-11
1401-12
1401-13
1401-14
1401-15
1401-16
1401-17
1401-18
1401-19
1401-20
1401-21
1401-22
1401-23
1401-24
1401-25
1401-26
1401-27
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 14
ATHENA Model: Radiation Circuit
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 15
ATHENA Model: Core, Containment, RCCS
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 16
ATHENA Model: Input Deck Specifics
• Heat Structures: 134• Mesh Points: 725• Hydrodynamic Volumes: 144• Volume:
– Coolant (He/CO2): 6,608 m3
– RCCS (air): 816 m3
• Mass:– He Coolant: 9,348 kg– CO2 Coolant: 44,402 kg– RCCS 947 kg
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 17
ATHENA Model: Boundary Conditions
• Specified:– coolant inlet temperature [490°C, He] [400°C, CO2]– coolant outlet temperature [842°C, He] [550°C, CO2]
• Calculated:– coolant flow rate calculated during steady state to
provide desired outlet plenum temperature• Assumed:
– SCRAM curve of PWR– No gamma/neutron heating in reflector/shield– Containment pressure maintained [~0.8 MPa, He]
[~1.8 MPa, CO2]– RCCS is the DHRS (baseline case)
Bound Research Task
Idaho National Engineering and Environmental Laboratory
Slide 18
• Steady-State Analysis– determined by constant containment temperature– volumetric heat capacity decreased by factor of 100– problem time of 4,200 s
Overview of ATHENA Steady-State Analysis
Perform Research Task
Idaho National Engineering and Environmental Laboratory
Slide 19
• LB-LOCA Transient– problem time reset to
0 s– valves open coolant
loop to containment at 10 s
– SCRAM starts at 10 s and finishes at 14 s
– Problem time: 180,000 s (50 hrs)
Overview of ATHENA Transient Analysis
Perform Research Task
Idaho National Engineering and Environmental Laboratory
Slide 20
He Case Approaches Matrix Temp. Limit*
CO2 He
*Containment pressure maintained
Understanding the Results
Idaho National Engineering and Environmental Laboratory
Slide 21
Containment Pres. Enhances Heat Transfer
Containment Volume: 6,063 m3
PQ m C T
m A Vρ
•
•
= ⋅ ⋅
= ⋅ ⋅
�
Understanding the Results
Idaho National Engineering and Environmental Laboratory
Slide 22
Containment Temp. Means More Design Work
Understanding the Results
Idaho National Engineering and Environmental Laboratory
Slide 23
Vessel Temperature Is A Design Challenge
Understanding the Results
Idaho National Engineering and Environmental Laboratory
Slide 24
CO2 Downcomer Flow Shows Flow Reversal
CO2 He
Understanding the Results
Idaho National Engineering and Environmental Laboratory
Slide 25
Conclusions and Future Work
• The RELAP5 results compare well with expected temperature and pressure trends
• The temperature limit of the core matrix material may be reached when He is the coolant
• The densities of the two coolants play an important part in the DHRS performance
• Future work will include:– sensitivity studies on containment transient pressure– CO2 injection for the He DHRS– Analysis with CERMET fuel pins
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