loads on rpv internals in a pwr due to loss-of-coolant ... · jahrestagung kerntechnik 2012 –...

Loads on RPV Internals in a PWR due to Loss -of-Coolant Accident consideringFluid -Structure InteractionDr. P. Akimov, Dr. M. Hartmann, L. ObereisenbuchnerFluid DynamicsStuttgart, May 24, 2012

Jahrestagung Kerntechnik 2012 – Loads on RPV Internals in a PWR due to LOCA considering Fluid-Structure Interaction – Dr. P. Akimov – May 24, 2012 - p.3

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Content

Motivation

Fluid-structure interaction

Introduction of computer codes used� STRAC / HAUPT

� LOCAFLEX

Sample LOCA calculations

Summary



Motivation

In the case of a LOCA (e.g. break at themain coolant line):

Allowable deformations of Control Rod Guide Tubes must not be exceeded

� ensure safe reactor shutdown

Integrity of the RPV internals(e.g. Core Support Barrel,Support Plates, Support Columns)

� ensure sufficient core cooling

RPV and internals

Core SupportBarrel

UpperSupport

Plate(USP)

UpperCore Plate

(UCP)

LowerSupport Plate

UpperSupportColumns

Control RodGuide Tubes

CoreDowncomer

Upper Plenum

Take into account the main effects of the fluid-structure interaction in the computational models



Fluid -structure interaction (FSI)FSI effects with regard to the

Core Support Barrel (CSB):FSI effects in the Upper Plenum:

buckling of the CSB

deflection of the CSB

bending of the tubularstructures in the Upper Plenum

HotNozzle

Core

Upper Support Plate

Upper Core Plate

Zone ofreducedpressure

Postulatedbreak

Downcomer

RPV

CSB

ColdNozzle

Strong reduction of incoming pressure waves due to FSI



Sequential vs. coupled FSI approaches

Fluid

Structure

Fluid Forces

Displacement &Stresses

Fluid Structure

Fluid Forces

Displacements

Stresses fromdisplacements

Assessment of the results

No FSI effects!

Sequential approach: FSI approach:

Covering global loads,not realistic

More realistic, load reduction effects due to structural reaction



Computer codes

Upper plenum internals

� Code STRAC / HAUPT

Lower internals, RPV, and FuelAssemblies (FAs)

� Code LOCAFLEX

RPV and internals

Core withFAs

Upper Plenum

Core SupportBarrel

Lowerinternals

Code STRAC / HAUPT(upper plenum internals)



STRAC / HAUPTMain features

1D and 3D componentsPIPE, TEE, VALVE, PUMP,STGEN, VESSEL, CORE

Non-homogeneous,non-equilibrium modelling2 fluid flow, 2 phase flow

Modifications and model extensionsEvaluation of forces, valve models,interface to structure programs, e.g., HAUPT

Fluid-structure interaction of the upper plenum internals is considered

STRAC is based on code TRAC (Transient Reactor Analysis Code) Loop 1

(hot)Loop 2(hot)

Loop 2(cold)

Loop 3(cold)

Loop 3(hot)

Loop 4(hot)

Loop 4(cold)

Loop 1(cold)

CSB RPV

Guide Tube forMeasurement

SupportColumn

Control RodGuide Tube

3D grid for the RPV(horizontal cross section)

Code LOCAFLEX(RPV, the core, and RPV internals)



LOCAFLEXMain features

Fluid: The whole primary coolant volume is included.Modeled are: the RPV with internals, the core,steam generators, pumps, etc

1D, 2 phase flow

Structure: The model consists of the RPV, the core, and the RPV internals (except for the upper plenum internals)

New object-oriented developments allow for complex structural models generated by ANSYS software with nonlinear couplings

Fluid-structure interaction in the downcomer is considered



LOCAFLEXFluid model of the RPV

RPV and internals

LowerSupport Plate

Down-comer

UpperSupport

Plate

UpperCore Plate

Core

= 2D Network

ColdNozzle

HotNozzle

Upper SupportPlate

Upper CorePlate

Lower SupportPlate

Downcomer

Core

R309

R308

R307

R306

R305

R300

R299

R298

R297

R9 – R144

R8 – R143

R7 – R142

R6 – R141

R5 – R140

R4 – R139

R3 – R138

R2 – R137

R1 – R136

R289 – R296R386 – R393

Cor

e B

ypas

s

R303

R302

R304

R310R328R346R364

R327R345R363R381

Loop Level

R301



LOCAFLEXStructural model (RPV)

Rigid beam model of the RPV

1

10

2

3

15

4

5

11

6

7

12

8

13

14

9 26

27

28 29 30 31

32

33

18

19

20 21 22 23 24

25

17

Parts of the RPV and internals that are in this model

Coupling to the Lower Support Plate

Coupling of the RPV supportto the building fixpoint

Coupling to the CSB Flange



UCP

USP

CRGA-C

USP

UCP

Controlassemblies

LOCAFLEXStructural model (Lower internals)

Extended FE-model with over 2000 MDOFs *)

Parts of the RPV and internalsthat are in this model*) MDOFs = Master Degrees of Freedom

CB

HR

UCP

CRGA-C

USP

HOLD-DOWN-SPRING

Coreschroud

LSP

CSB

UCP

USP

Hold-Down Spring

Hold-DownSpring

Controlassemblies



LOCAFLEXStructural model (Upper plenum internals)

RPV and internals

UpperSupport

Plate

UpperCore Plate


Fluid forceson the tubular

structures

The fluid forces due to the pressure waves (from STRAC/HAUPT) are applied in LOCAFLEX directly to the tubular structures

Realistic coupling mechanism between the UCP and the USP thanks to the detailed FE models of the upper plenum internals

UCP

USP

CRGA-C

USP

UCP

Controlassemblies



LOCAFLEXStructural model (Core)

Horizontal row models of Fuel Assemblies (FAs)(5 row models for 1 direction are shown with colors)

Loop 1(cold)

Loop 2(cold)

Loop 2(hot)

Loop 1(hot)

Loop 3(hot)

Loop 4(hot)

Loop 4(cold)

Loop 3(cold)

Core-X

Core-Y

Core-X

Core-YCoupling to UCP

Couplingto LSP

Impact couplings Shroud / FA and FA / FA



LOCAFLEXCoupling between fluid & structure models

RPV and internals

Core SupportBarrel

UpperSupport

Plate

UpperCore Plate

LowerSupport Plate

UpperSupportColumns


CoreDowncomer

CoreShroud

Fixpoint

► Downcomer

► Downcomer

► inside CSB

► …

CSB

RPV

CSB

► CSB Flange

► LSP

► UCP

► RPV

► …

RPV

FAs

FAs

Building fixpoint

By means of

Structure

By means of

Fluid

Sample LOCA calculations



0.0 0.1 0.2 0.3 0.4 0.5 0.6TIME (S)

-1.0

-0.5

0.0

0.5

Sca

led

forc

e (C

SB

/CS

Bm

ax)

without FSI

Y directionX direction

LOCA calculation: Cold leg breakResults

Total Force on the CSB

Deflection of the CSB due torapid decompression

RPV with 4 loops

X

Y

Loop 1(cold)

CSBRPV

Loop 4(cold)

Loop 4(hot)

Loop 3(hot)

Loop 3(cold)

Loop 2(cold)

Loop 1(hot)



LOCA calculation: Cold leg breakFSI effects

With FSI � more realistic analysisas to peak loadings & frequencies

0.0 0.1 0.2 0.3 0.4 0.5 0.6TIME (S)

-1.0

-0.5

0.0

0.5

Sca

led

forc

e (C

SB

/CS

Bm

ax)

without FSI



0.0 0.1 0.2 0.3 0.4 0.5 0.6TIME (S)

-1.0

-0.5

0.0

0.5

Sca

led

forc

e (C

SB

/CS

Bm

ax)

with FSI



Summary

Accurate and reliable numerical tools —STRAC / HAUPT and LOCAFLEX — for loads analyses in the assessment of safety for nuclear power reactors

Allowing for Fluid-Structure Interaction and a complete consideration of dynamics lead to more realistic analyses of loads on the RPV internals

New developments in LOCAFLEX allow for more realisticand accurate calculations



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Loads on RPV Internals in a PWR due to Loss -of-Coolant Accident consideringFluid -Structure InteractionDr. P. Akimov, Dr. M. Hartmann, L. ObereisenbuchnerFluid DynamicsStuttgart, May 24, 2012

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loads on rpv internals in a pwr due to loss-of-coolant ... · jahrestagung kerntechnik 2012 –...

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