CFD simulation of fibre material transport in a PWR core ... · permeability to the coolant flow is...

Text optional: Institutsname � Prof. Dr. Hans Mustermann � www.fzd.de � Mitglied der Leibniz-GemeinschaftDr. Thomas Höhne | Institut für Sicherheitsforschung | http://www.hzdr.de

CFD simulation of CFD simulation of fibrefibre material material

transport in a PWR core under loss transport in a PWR core under loss

of coolant conditionsof coolant conditions

T. Höhne, A. Grahn, S. Kliem

Forschungszentrum Dresden- Rossendorf (FZD)

Institut für Sicherheitsforschung

Postfach 51 01 19, D-01314 Dresden

Seite 2Dr. Thomas Höhne | Institut für Sicherheitsforschung | http://www.hzdr.de

Transport of Transport of fibrefibre materialmaterial

Leckstörfall mit Freisetzung von Mineralwolle

Transport of fibre material in a German PWR

Status in German NPPs :

- Back flushing procedures,

implementation of differential

pressure measurements,

modifications of the insulation, the

strainer size and the mesh size at

the strainers

- But: Still possible, that a small

amount of smaller fractions of the

fibre material can be transported

into the RPV

- Core coolability must be

guaranteed all the time!

Szenario, Assumptions :

- LOCA, SCRAM, ECCS hot leg injection, after 1600s switch to sump cooling

mode with 150 kg/s per loop, decay heat 80 MW, leak in cold leg, no stable

natural circulation


During hot leg ECC injection, the fibres enter the upper plenum and can accumulate

at the fuel element spacer grids, preferably at the uppermost grid level

General Aim: calculation of break-through channels and of the distribution of

mineral wool fibres across the grid spacers (local mass load, pressure)

SzenarioSzenario

Source. AREVA NP

(1) upper support

plate,

(2) control rod guide

tubes,

(3) fuel element,

(4) RPV,

(5) core wall,

(6) lower support

plate,

(7) perforated drum,

(8) hot leg ECC

injection of

colder fluid

Measurements at UPTF: Establishment of

downwards directed break-trough channels at the

core


Previous CFDPrevious CFD--Calculations: Calculations:


Boundary Conditions, Model AssumptionsBoundary Conditions, Model Assumptions

Boundary conditions:

- RPV pressure at cold leg 2.5 bar,

averaged coolant temperature 380 K,

- ECC water 150 kg/s per loop,

temperature 330 K,

Model assumptions:

- Fluid: two phase, incompressibel

- Water & Fibre material

- Turbulence model: SST

- Automatic wall funtions

- uppermost spacer grid plane collects

all the fibres that arrive there: 3 D

subdomain for strainer model

implementation

- Initial state: inner circulationfuel element

uppermost

spacer

grid plane


StrainerStrainer Model Model -- Accumulation of fibre Accumulation of fibre

materialmaterial


StrainerStrainer ModelModel

� implementation of strainer model for the

spacer grid, which completely retains the

insulation material carried by the coolant

� accumulation of the insulation material

� rise to the formation of a compressible

fibrous cake

� permeability to the coolant flow is

calculated in terms of the local amount of

deposited material and the local value of

the superficial liquid velocity.

� porosity distribution due to streamwise

increase of compacting pressure

� pressure drop in fibrous layers according

to Davis and Ergun

� self compaction under pk

(experiments, TH Zittau) strainer model for the

spacer grid


Results Results 4 4 LoopsLoops 5kg 5kg FibreFibre Material Material InjectionInjection


4 4 LoopsLoops 5kg 5kg FibreFibre Material Material InjectionInjection

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80

Zeit / s

ak

ku

mu

lie

rte

Fa

se

rn [

kg

]

Time / s

Mass load fibres [kg/m²] 68 s after startMass load fibres [kg/m²] 40 s after start

Accum

ula

ted fib

res

[kg]


Further improvement of the Further improvement of the

modellingmodelling

VGB Project: VGB Project: "Qualifizierung "Qualifizierung

von von CFDCFD--ProgrammenProgrammen ffüür r

Fragestellungen der Fragestellungen der

Reaktorsicherheit Reaktorsicherheit

(FZD/SA"AT" 41/09 B)(FZD/SA"AT" 41/09 B)


CAD Geometry- real Konvoi structures in the upper plenum

- ECC injection nozzle (“Hutze”), SG bottom

- Core geometry as porous body, horizontal flow components are

possible

Decay Heat Distribution- 3D extraction of node-wise heat source from DYN3D

- import into CFX and interpolation

ImprovementsImprovements -- NextNext StepsSteps

Steam Production- three phase flow, injection of steam via volumetric source

- re-suspension of the insulation material with upwards flow


New Grid New Grid -- KonvoiKonvoi GeometryGeometry

PWR Konvoi – Modular Grid 19

Mio. Cells


New Grid New Grid -- KonvoiKonvoi GeometryGeometry


Mio. Cells

Core: spacer grid levels, FE head, bottom

Hot leg incl. Hutze, SG Bottom

Upper plenum incl. structures, SSFE

Hot leg

SG

Bottom

Cold leg incl. ECCS pipe


New GridNew Grid


Mio. Cells

Core: Porous Media


CoreCore ModellingModelling and and DecayDecay HeatHeat

DistributionDistribution


New: Full Core: Porous Media

- Core Permeability β= 0.537- Flow Resistance: Directional Loss Model

STREAMWISE LOSS:

Option = Permeability and Loss Coefficient

Resistance Loss Coefficient = 3.38 [m^-1]

TRANSVERSE LOSS:

Option = Streamwise Coefficient Multiplier

Streamwise Coefficient Multiplier = 10.

- Core Support Plate Permeability = 0.229 [m2]- Resistance Loss Coefficient = 9.8 [m^-1]


New: Full Core: Porous Media

- Volumetric Heatsource:

DYN3D – CFX coupling

Nodewise calculation of decay heat with

DYN3D (10x193 Nodes):- Begin of Cycle of a generic Konvoi reactor

core,

- coolant mass flow rate 400 kg/s from bottom

to top,

- no crosswise mixing,

- decay power 80MW (approx. 2% of the

nominal power, 1600s after SCRAM),

- no boiling

- Extraction of 1930 Volumetric

Heatsource Points of Decay Heat

calculation in DYN3D

- Transformation and use of interpolation

algorithm in ANSYS CFX

- Calbration algorithm with overall Decay

Heat Value

Heatsources @Core(spacer planes)

CFX (Heatsources)


ResultsResults of Inner of Inner CirculationCirculation withwith ECC ECC

injectioninjection


ResultsResults of Inner of Inner CirculationCirculation

RPV, upper

spacer grid

indicated,

ECC water

injection

over 120 s


Preliminary Results: Preliminary Results:

ECC ECC waterwater injectioninjection in 4 in 4 loopsloops --

5kg 5kg FibreFibre Material Material InjectionInjection


4 4 LoopsLoops 5kg 5kg FibreFibre Material Material InjectionInjection

RPV, inlet

nozzle

plane, ECC

water

injection with

fibre material

(5kg ), 25 s,

isosurface at

750 ppm


SteamSteam productionproduction


SteamSteam ProductionProduction –– SimplifiedSimplified ModelModel

- Simplified RPV model (5 Mio. nodes, 14 Mio. Elements) consists of Hot leg,

Upper Plenum, Core, spacer grids

- 3 phase flow (solid, gas, liquid), multiphase flow models, strainer model

- Steam injection via volumetric sources into subdomain core (0.95 [kg m-3 s-1],

410 [K])

- Start of ECC injection with 1.25 kg isolation material (150 kg/s)

Grid model

Steam.vf @ nozzle plane 0-9s after ECC injection


PreliminaryPreliminary ResultsResults -- FibreFibre Material Material InjectionInjection

RPV, upper

spacer grid,

ECC water

injection with

fibre material

(1.25 kg ), 9

s, isosurface

at 750 ppm


SummarySummary

Major modeling improvements were done for:

• Geometry (use of original Konvoi geometry)

• Decay heat simulation

• Steam production

Preliminary Results:

- the fiber material at the uppermost spacer grid plane isnot evenly distributed

- first, it is accumulated at the positions of the break-

through channels- steam production makes the flow in the upper plenum

situation more complex


AcknowledgmentsAcknowledgments

The project was funded by the Nuclear Special Committee “Plant engineering” of

VGB PowerTech (Germany).

ThankThank youyou!!

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CFD simulation of fibre material transport in a PWR core ... · permeability to the coolant flow is...

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