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Investigation of Surface Vortex Formation at Pump · PDF file · 2018-01-10Investigation of Surface Vortex Formation at Pump Intakes in PWR ... unfavorable intake conditions lead

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  • Investigation of Surface Vortex Formation at

    Pump Intakes in PWR

    P. Pandazis1, A. Schaffrath1, F. Blmeling2

    1Gesellschaft fr Anlagen- und Reaktorsicherheit (GRS) gGmbH, Munich

    2TV NORD SysTec GmbH & Co. KG, Hamburg

    46th Annual Meeting on Nuclear Technology

    7. May 2015, BerlinNr.: 1501410

  • Outline

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 2

    Background

    Combined method to investigate surface vortices

    Applications for PWR

    Conclusions

  • Background Pump intakes

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 3

    Requires for an undisturbed long-term operation:

    avoidance of cavitation

    homogenous and non-rotational inflow

    avoidance of air entrainment

    unfavorable intake conditions lead to:

    fluctuating pump behavior

    vibrations, noise, mechanical damages

    decrease or collapse of flow rate

    Typical source of swirling or air entrainment

    surface vortices

    Surface vortices at pump intakes

    Wijdiek 1965

    Auckland

    et al. 2009

  • Background Surface vortices

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 4

    Surface vortices are generated by the pressure drop resulting from pump suction and

    disturbances in the approaching flow.

    Surface vortices can be classified in 6 types

    air core grows with decreasing submergence

    Structure of the flow field:

    vortex core: strong rotation, large gradients

    free vortex region: almost potential flow.

    Type 3

    vortex core

    free vortex

    1. Coherent surface swirl 2. Surface dimple

    3. Dye core to intake4. Vortex pulling floating

    trash, but not air

    5. Vortex pulling airbubbles to intake 6. Full air core to intake

    type 1 type 2: critical submergence

  • Background Surface vortices

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 5

    Decreasing the critical submergence:

    homogenization of the flow field

    vortex breaker devices

    vortex breaker devices -TU Budapest

    Avoidance of surface vortices sufficient submergence!

    decrease the circulation

    submergence

    swirl in intake circulation

    air inlet

    no air suction

    critical submergence

    Effect of vorticity on the submergence - Jain et al.

    Influence parameter on the critical submergence:

    suction velocity

    material properties

    circulation

  • Background Pressurized Water Reactor

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 6

    SCRAM

    isolation of containment

    coolant loss through break, refill by:

    high pressure systems

    low pressure, emergency cooling

    systems (ca. < 10 bar)

    - flooding tanks

    - containment sumps

    long term recirculation via the

    containment sump

    ( after ca. 20 min. in case of a large break)

    LOCA in a PWR containment, (e.g. break in the primary circuit)

    sump in a PWR containment

    break

    sump

    reactor pressure vessel

    pressurizer

    steam generator

    enough amount of coolant

    reliable pump operation

    requirement of a minimum sump level

    (submerge of pump intake) e.g. for

    avoiding of surface vortices

  • Background Pressurized Water Reactor

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 7

    Recommendations of the German Reactor Safety Commission (2005) concerning

    the determination of the minimum water level in the sump (critical submergence)

    large scale experiments (> 1: 20)

    application of the ANSI (American National Standard Institute) correlation

    new approach:

    Investigation of the critical submergence with numerical (CFD) method

    Results of ANSYS CFX simulations:

    efficient calculation of free vortex region

    high computational effort for the solution

    in the core region because of the strong

    gradients

    Combine the ANSYS CFX results with an analytical model

    to solve the complete flow field.

    Analytical approaches:

    efficient calculation of the whole vortex

    region

    flow parameters are necessary from the

    free vortex region

  • Outline

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 8

    Background

    Combined method to investigate surface vortices

    Applications for PWR

    Conclusions

  • Combined method Burgers & Rott vortex model

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 9

    Derived from conservation equations (mass & momentum)

    Stationary, axis-symmetrical vortices

    yields velocity field

    Extended by Ito et al. (2010)

    formula to calculate the gas-core length Lg:

    Definition of the critical submergence:

    critical gas-core length = 1 mm

    2

    4

    2ln

    g

    )(aL

    g

    ut

    r0r

    vortex-core

    Lg

    Burgers-Rott model

    Two free parameters:

    suction parameter a

    circulation To be determined with CFD simulations!

  • Perform a two-phase ANSYS CFX simulation of the pump intake.

    suction parameter a:

    deficiency of Burgers & Rott model:

    local velocity gradient is directly available from CFX results

    a is the averaged velocity gradient along the vortex core edge

    Circulation :

    definition:

    C is a closed curve around the vortex

    Integration is performed numerically by

    using the velocity field from CFX

    Critical submergence can be interpolated by using two different simulations.

    Combined method Parameter determination

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 10

    const.z

    uaconst. z

    loc

    z

    z

    u

    ,dsu

    C

    curve C

    vortex core edge utuz

    model reality

  • Validation Experiment of Moriya

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 11

    cylindrical tank, vertical pump intake(outlet diameter 50 mm)

    tangential water inlet, width 40 mm

    water is pumped in a closed loop:

    constant water level (500 mm)

    stationary vortex

    gradually increased mass flow

    gas-core length increases with mass flow

    objectives of the experiment is the deter-mination of the

    gas-core lengths

    velocity distributions experimental facility

    vortical flow

    vessel diameter (400 mm)

    outlet diameter

    ( 50 mm)

    flow inlet

    su

    bm

    erg

    en

    ce

    (50

    0 m

    m)

    inlet width

    (40 mm)

  • further sensitivity analyses:

    two-phase simulation with inhomogeneous phase model

    only momentum exchange at the interface

    SST-cc turbulence model

    flow rates: 25, 50 and 100 l/min

    Validation CFD model

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 12

    mesh sensitivity study

    horizontal mesh resolution 1.2 mm (1.8 Mio. elements)

    further refinement above the intake + wall

    mass

    flow

    velo

    city

    water

    air: 1 bar

    interface

    CFD boundary conditions

    mesh

  • Validation - Results

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 13

    combined method improves the results

    remarkably

    nearly no additional computational effort

    circulation and suction parameter are directly

    obtained from the CFD

    results

    0

    50

    100

    150

    200

    250

    300

    350

    400

    450

    500

    0 10 20 30 40 50 60 70 80 90 100

    Ga

    s-co

    re le

    ngt

    h [

    mm

    ]

    Volume flow [l/min]

    Experiment

    CFX

    Combined method

    Lg

    Next step:

    Investigation of the pump intake in a PWR sump

  • Outline

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 14

    Background

    Combined method to investigate surface vortices

    Applications for PWR

    Conclusions

  • Investigation of PWR sump

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 15

    PWR sump (vertical cross section)

    TH - intake sump grids

    coarse sump grid

    TH - 1

    TH - 2

    TH - 3

    TH - 4fine sump grid

    break positions

    PWR sump (horizontal cross section)

    Subdividing the CFD solution

    single-phase main model

    two-phase submodel

    Accident scenario: LOCA inside the containment

    PWR sump with 4 TH intake chambers, only 2 of the 4 TH-pumps are available by postulate

    concrete ceiling above the pump intake Injection of ECC water from the sump via the

    emergency core cooling system (TH)

    two cases (with different sump water level):

    case 1: 400 cm2 break, water above of concrete

    ceiling

    case 2: water level below of the concrete ceil-

    ing (1 m)

    different modeling of the break-flows in the two cases

    fine & coarse grids of the sump

  • Case 1: 400 cm2 break, water level in the sump is above the concrete

    ceiling

    P. Pandazis et al. Investigation of Surface Vortex Formation at Pump Intakes in PWR 16

    Main results:

    vortex core tends to inn

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