OVERVIEW - RELAP/SCDAPSIM Presented Dr. Chris Allison.

OVERVIEW - RELAP/SCDAPSIM

Presented Dr. Chris Allison

Outline

• General modeling approaches

• Primary differences between RELAP/SCDAPSIM and– RELAP/MOD3.3– MAAP and MELCOR codes

RELAP5 and SCDAP WERE ORIGINALLY DEVELOPED BY US NRC

• RELAP5 developed for DBA analysis (Late 1970s)– SCDAP (Severe Core Damage Analysis

Package) added in 1980s for SA analysis)

• RELAP/SCDAPSIM developed by ISS/SDTP for commercial applications– Advanced numerics and programming – Standard RELAP5/MOD3.2/3.3 and

SCDAP/RELAP/MOD3.2 models

• Non-equilibrium, two fluid models for hydrodynamics including transport of non-condensable gases

• 2D/3D capability provided through “cross-flow” options• Convective and radiative heat transfer • 1D heat conduction in system structures• Point reactor kinetics

– External 3D kinetics provided through link to user supplied reactor kinetics packages

• Control system, trip logic, and special system components such as valves and pumps

RELAP/MOD3.2 and RELAP/MOD3.3 models used for system TH analysis

• Detailed LWR core components

• Upper plenum structures

• Core debris and molten pools

• Lower plenum debris and vessel structures

SCDAP components/models used for detailed vessel and core behavior

User selects representative fuel rod, control rod/blade and other components for LWR core

• Bundle convective and radiative heat transfer – Radiation absorption by fluid– Bundle deformation/blockage/grid spacer effects on

flow patterns

• 2D heat conduction• Grid spacer heating and melting• Bundle deformation/blockage formation• Liquefaction and failure of core components• Debris/void formation

User defines representative assembly for each flow channel in core

Fuel Rod 1

Control rod

Fuel Rod 2

Water Rod

Representative components can have different power levels

SCDAP fuel rod components use 2D models to predict temperature (r,z), deformation, chemical

interactions and melting

Zr Cladding

UO2 Fuel Pellet

Gap

SCDAP fuel rod components consider failure due to spacer grid interactions, metallic and ceramic

melt relocation, and fragmentation

• 2D heat conduction• Fission product buildup and release• Cladding deformation and rupture• Cladding oxidation and hydrogen production

– Effects of steam availability and vapor diffusion considered

• Zr – spacer grid interactions• UO2 dissolution by molten Zr• Zr melting and relocation• UO2/ZrO2 melting and relocation

SCDAP control rod components use 2D models to predict temperature (r,z), deformation, chemical


Zr Guide Tube

Ag-In-Cd/B4C Absorber

Gap

SS Sheath

SCDAP BWR control components use 3D models to predict temperature (r,z), deformation, chemical


Zr Guide Tube

B4C Absorber

Gap between absorber tube and sheath

SS Sheath

Interstitial Gap

SCDAP Ag-In-Cd or B4C control rod/blade models consider early failure of control

structures

• 2D heat conduction• Cladding oxidation and hydrogen production

– Effects of steam availability and vapor diffusion considered

• Zr/SS – control material interactions• Guide tube, cladding, control material melting

and relocation

SCDAP general 2D shroud model tracks behavior of other core components

• LWR SCDAP general shroud model used to model core walls, experimental facility structures– 2D heat conduction– Zr layer oxidation and hydrogen production

• Effects of steam availability and vapor diffusion considered

– Melting and relocation

SCDAP upper plenum models describe heating and melting

• Oxidation– Parabolic rate– Steam starvation

• Heat conduction– Lumped parameter

• Relocation of upper plenum structures into core or lower plenum

SCDAP in-core debris/model pool models describe later stages of core

failure

• Oxidation– Parabolic rate– Steam starvation

• Heat conduction– Lumped parameter (in rubble)– 1D (in metallic blockages)– 1D (molten pool crust perimeter)

SCDAP in-core debris/molten pool models describe formation, growth, and

failure of in-core molten pools• Molten pool behavior

– Radial and axial spreading

– Crust thinning and mechanical failure

• Side wall versus top surface

– Transient natural circulation

– Interactions with shroud wall

SCDAP in-core debris/model pool models describe formation, growth, and

failure of in-core molten pools• Material relocation

– Void formation– Molten pool upper

crust collapse• Mixing of debris/molten

pool

– Relocation of upper plenum structures into core

– Molten pool slumping

SCDAP uses a detailed 2D model to describe behavior of lower plenum

debris/vessel• Heat conduction

– 2D finite element– gap resistance

(solid/melt)– 1D model at crust

boundary perimeter

• Molten pool behavior– Transient natural

circulation– Interactions with vessel

wall

SCDAP uses detailed 2D model to describe behavior of lower plenum

debris/vessel• Creep rupture failure

of vessel wall• Material relocation

– Relocation of upper plenum structures

– Relocation of core component materials

– Molten pool slumping• Ex-vessel flooding

Primary differences between RELAP/SCDAPSIM and RELAP/MOD3.3

• RELAP5/MOD3.3 limited to transients that will not result in core damage– Peak fuel cladding temperatures < 1500 K

(2200 oF)– Limited cladding oxidation (< embrittlement)

• RELAP5/MOD3.3 radiation exchange heat transfer model neglects absorption by fluid


• RELAP/SCDAPSIM has detailed core component models for typical LWR/HWR designs– LWR fuel rod– Ag-In-Cd/B4C control rod– BWR control blade model– Electrically-heated fuel rod simulator

• RELAP/SCDAPSIM has upper and lower plenum models for typical LWR designs– Detailed 2D finite element model to describe lower head

• RELAP5/MOD3.3 uses general 1D heat structure model to describe all structures including core and vessel


• RELAP5/MOD3.3’s 1D heat conduction model to ignores important phenomena for fuel elements or electrically heated fuel element simulators– Axial conduction – Temperature-dependent electrical resistivity changes on power profile – Burnup/thermal cycling influence on thermal properties – Influence of changes in gap dimensions, fuel rod internal pressure, and

fission product release on fuel-cladding gap conductance – Steam starvation and vapor diffusion limits for cladding oxidation– Zircaloy cladding embrittlement– Fission product release

Note: Boiloff.i sample problem demonstrates differences between RELAP5 and SCDAP fuel rod models (plot)


• RELAP5/MOD3.3’s 1D heat conduction model to ignores important phenomena for fuel elements or electrically heated fuel element simulators– Axial conduction – Temperature-dependent electrical resistivity changes on power profile – Burnup/thermal cycling influence on thermal properties – Influence of changes in gap dimensions, fuel rod internal pressure, and

fission product release on fuel-cladding gap conductance – Steam starvation and vapor diffusion limits for cladding oxidation– Zircaloy cladding embrittlement– Fission product release

Note: See boiloff example in “Practical Examples of Severe Accident Analysis” for demonstration of differences between RELAP5 and SCDAP fuel rod models

Primary differences between RELAP/SCDAPSIM and more simplified SA integral codes

• RELAP/SCDAPSIM limited to in-vessel behavior– Source term and containment provided through links to

IMPACT/SAMPSON Modules from NUPEC– RELAP/SCDAPSIM/MOD4 being extended for integrated source

term and containment response

• RELAP/SCDAPSIM computation times are longer than MAAP and comparable to MELCOR– DBA transients typically run 10-20 times faster than real time– Typical SA transients run 1-5 times faster than real time

RELAP/SCDAPSIM allows much more detailed representation of RCS/vessel

• RCS/Vessel nodalization more detailed than historical DBA analysis using RELAP/TRAC– 2D/3D core/vessel – 2D lower plenum/vessel– Detailed 2D core component modeling

• Typical SA input models use– Several hundred TH volumes and RCS heat structures– Five representative assemblies with 2 or more SCDAP

components– Several hundred volumes in 2D lower plenum/vessel mesh

417

418

419

420

409

411

407

413 317 313

324 305

326

303 302

327

602

328

341340

301

342 343

831

HPI

833

LPI

836

ACC

611

CG

612832

834

RCP

601

401402

403

405

404

406

410

422 424 426 428 430 432 434 436 438421

423 425 427

429 431 433 435 437 439

471

470451

MSSV

450

441

MSRV

440MSIV

T/D-AFW-STM

T/D-AFW

MFW

M/D-AFW

416

314316414

306323408412

315

325 304BD

LD

217

218

219

220

209

211

207

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124105

126

103102

127

128

141 140

101

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611

CG

811

HPI

813

LPI

816

ACC

910RCP

Broken Loop

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203

205

204

206

210

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223225227

229231233235237239

271

270251

MSSV

250

241

MSRV

240MSIV

T/D-AFW-STM

T/D-AFW

MFW

M/D-AFW

216

902116

123 208212

125104BD

702 704

MSV

710

GV

701

Turbine705

700

745751

TBV

750

741

Steam Generator

215

114SGTR

106

614LOCA

911

415

541

PRV

540

551

PSV

550

561

A-SPRY

560

510

SPRYP

ress

uriz

er

502

503

501

511

Reactor Pressure Vessel

(See Next Page)

Steam Generator

901

Intact Loop

MAAP4 Nodalizationof RCS

SCDAP/RELAP5 Nodalization of RCS

TML with AM and HPI

13: Cold Leg

12: Crossover Leg

9: Hot Leg

10: Tubes Up Flow

11: TubesDown Flow

5: Tubes Down Flow

4: Tubes Up Flow

3: Hot Leg

Pre

ssur

izer

7: Cold Leg

6: Crossover Leg8: Downcomer

Broken LoopIntact Loop

2: UpperPlenum

1:Core

12

1 16 14

13

FROM COLD TO HOT LEGS 10 LEGS

2

75 74 73 72 71

6

83

5

49 39 29 19 59

584

583

582

581

580

RELAP/SCDAPnodalization of4-Loop RPV

2D connections allow for cross flow due to natural circulation or loss of geometry

RELAP/SCDAPSIM models generally more detailed

• 6 equation, non-equilibrium hydro

• 2 D heat conduction• Relocation of Zr-In, Zr-U-

O, (U-Zr)-O2• Grid spacer interactions• Molten pool (U-Zr)-O2

formation, growth, and relocation– Radial, axial (bypass lower

metallic layers)

• quasi-equilibrium hydrodynamics

• 1D lumped parameter• Relocation of Zr-U-O

– –

• Core slumping (user defined temperature)– Axial– User defined (MAAP)

RELAP/SCDAPSIM MAAP/MELCORVS

SCDAP will predict melting over wide range of temperatures

Liquefaction of Structural and Control

Material

Liquefaction of Zr-O-U

Melting of (U-Zr)-O2

MAAP/MELCOR will predict core slumping at user specified temperature

TMI-2 End State

SCDAP can predict molten pool relocation into lower plenum even if core plate

and lower core intact

MAAP/MELCOR

Lower core and plate must slump before upper material can relocate


• Reflood– Oxide spalling

• Accelerated heating, oxidation, melting

• Reflood– Oxide spalling

(MELCOR) • Accelerated heating,

oxidation, melting

– MAAP does not consider oxide spalling


Oxide spalling during reflood critical to predict

H2 and melt formation


• Reflood– Debris formation– Exterior cooling of molten

pool crusts

• Transient 2D lower plenum debris/vessel heat conduction and molten pool convection– Stratified formation– Homogenous molten pool

• Reflood– Debris formation (user)– Exterior cooling of debris

beds (user)

• Steady state analytic/lumped parameter lower plenum debris/vessel– Stratified formation– Stratified metallic/ceramic

(MAAP)


Assumptions on lower plenum debris will impact vessel failure

SCDAP

MELCOR

MAAP

Molten pool (mixture)

Layers formed by debris/melt relocation

Layers formed by debris/melt relocation

Structural material

Corium

Gap cooling

RELAP/SCDAPSIM user defined parameters are intentionally limited

• System defined through TH nodalization, selection of representative core and plenum components and nodalization– RELAP5 and SCDAP user guidelines and training

• RELAP5 modeling parameters used to control flow regimes– Established through RELAP5 validation activities

• SCDAP modeling parameters limited to critical areas of modeling uncertainties– Recommended defaults set through validation

activities

MAAP/MELCOR make extensive use of modeling parameters to

adjust basic processes

• Extensive use of user defined parameters make evaluation of trends very difficult

• Scaling of code-to-data comparison results to plant behavior is unclear– Modeling parameters are unique to facility– Conservatism or non-conservatism may be

influenced by user choices

OVERVIEW - RELAP/SCDAPSIM Presented Dr. Chris Allison.

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Transcript of OVERVIEW - RELAP/SCDAPSIM Presented Dr. Chris Allison.