gfr-he/co2 analysis using relap5/athena documents/marshall.pdfathena model: gfr specifications •...

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


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


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


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


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


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


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


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


Slide 10

ATHENA Model: Unit Cell Heat Structure

Bound Research Task


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


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

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1401-14

1401-15

1401-16

Core Barrel

1001-01

1001-02

1001-03

1001-04

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1001-07

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1001-10

1001-11

1001-12

1001-13

1001-14

1001-15

1001-16

1001-17

Reactor Vessel

Cylindrical Wall

Bound Research Task


Slide 13

ATHENA Model: Core Nodalization

Core

5000-21

5000-22

5000-23

5000-24

5000-25

5000-16

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5000-20

5000-11

5000-12

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5000-15

5000-06

5000-07

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5000-10

5000-01

5000-02

5000-03

5000-04

5000-05

5002-21

5002-22

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5002-24

5002-25

5002-16

5002-17

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5002-11

5002-12

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5002-14

5002-15

5002-06

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5002-10

5002-01

5002-02

5002-03

5002-04

5002-05

5004-21

5004-22

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5004-24

5004-25

5004-16

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5004-11

5004-12

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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

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1401-27

Bound Research Task


Slide 14

ATHENA Model: Radiation Circuit

Bound Research Task


Slide 15

ATHENA Model: Core, Containment, RCCS

Bound Research Task


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


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


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


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


Slide 20

He Case Approaches Matrix Temp. Limit*

CO2 He

*Containment pressure maintained

Understanding the Results


Slide 21

Containment Pres. Enhances Heat Transfer

Containment Volume: 6,063 m3

PQ m C T

m A Vρ

•

•

= ⋅ ⋅

= ⋅ ⋅

�



Slide 22

Containment Temp. Means More Design Work



Slide 23

Vessel Temperature Is A Design Challenge



Slide 24

CO2 Downcomer Flow Shows Flow Reversal

CO2 He



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

gfr-he/co2 analysis using relap5/athena documents/marshall.pdfathena model: gfr specifications •...

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