evaluation of two phase natural circulation flow in the ... using the relap5/mod3 contents – to...

ERMSAR 2015, Marseille March 24 – 26, 2015

Evaluation of Two Phase Natural Circulation Flow

in the Reactor Cavity under IVR-ERVC

for Different Thermal Power Reactors

Rae-Joon Park, Kwang-Soon Ha, Hwan-Yeol Kim

Severe Accident & PHWR Safety Research Division

Korea Atomic Energy Research Institute


CONTENTS

Introduction

– IVR-ERVC Concept

– Research Needs & Backgrounds

– Objectives

RELAP5 Input Model

RELAP5 Results & Discussion

Conclusions

2


Introduction (1)

In-Vessel corium Retention through External Reactor Vessel

Cooling

– Design Feature for SA Mitigation

AP600 & AP1000 in USA

Loviisa in Finland

KERENA in Germany, and so on

– As a part of SAMG Strategies

APR1400 & OPR1000 in Korea

Current Operating Plants, and so on

3

Schematic Diagram of IVR-ERVC


Introduction (2)

IVR-ERVC

– The strategy of the APR1400 for severe accident mitigation aims at retaining molten core in-vessel first and ex-vessel cooling of corium second in case the reactor vessel fails, reinforcing the principle of defense-in-depth.

– IVR-ERVC was adopted as one of severe accident management strategies. In IVR-ERVC condition, the cavity will be flooded from IRWST by the SCP and the BAMP to the hot leg penetration bottom level.

4

M M

M

Cavity

Containment Building

HVT

IRWST IRWSTM

M

Aux. Building

SCP (5000 gpm)

BAMP (200 gpm)

CVCS

RCS

M

M M

M

M

SteamGenerator

SteamGenerator

ReactorVessel

Reactor CavityFlooding System

External Reactor VesselCooling System

IVR-ERVC in the APR1400 : Active

system (Not passive) & non severe

accident design feature

Schematic Diagram of the APR1400(Advanced Power Reactor)


Introduction (3)

To evaluate IVR-ERVC

– Thermal load

– Heat removal rate (CHF)

– Success Criteria

CHF > Thermal Load

In general, an increase in natural circulation coolant mass flow rate in cooling channel leads to increase in the heat removal rate at the reactor vessel wall.

To Increase natural circulation flow rate

– Gap configuration to form streamline flow

– Optimal coolant inlet/outlet design

– Steam venting to prevent pressure build-up in annular gap between reactor vessel and insulation

5

Thermal Loading

- Accident Sequence

- Melt Configuration

- Melt Composition

Cooling Water

Circulation Features

Wall CHF

- Geometry

- Flow Condition

100 1000

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

CH

F [

MW

/m2]

Mass Flow Rate [kg/sec]

Q = 20 MW

Subcooling 70oC Saturated Cond.

s = 5 cm

s = 10 cm

s = 15 cm

SULTAN Experimental Results

on CHF in CEA/France

Natural circulation flow feature should be evaluated.


Introduction (4)

Design features of OPR1000 and APR1400

To enhance heat removal rate(increase natural circulation flow)

– APR1400 : Optimal insulation design

– OPR1000: Not yet

6

Design Parameters OPR1000 APR1400

Core Thermal Power (MW) 2815 3983

Fuel(UO2) Mass (ton) 85.6 120.0

Mass for Active Core Zircaloy-4 (ton) 23.9 33.6

Bottom Head Inner Diameter (m) 4.2 4.7

Bottom Head Thickness (cm) 15.2 16.5

Number of ICI Nozzle in the Lower Head 45 61


7

Introduction (5)

Objective:

– Analysis of two phase natural circulation mass flow rate in the

annular gap between the outer reactor vessel wall and the

insulation using the RELAP5/MOD3

Contents

– To analyze the coolant circulation coolant mass flow rate in

APR1400 & OPR1000

– To analyze the effects of the coolant injection temperature and

water level on the coolant mass flow rate


RELAP5 Input Model (1)

RELAP5/MOD3

– This system thermal hydraulic computer code was developed at the INL(Idaho National Laboratory) for the USNRC.

– This 1-D best estimate transient simulation computer code uses six equations on mass, momentum, and energy equations.

– This computer code includes analyses required to support rulemaking, licensing audit calculations, evaluations of accident mitigation strategies, evaluations of operator guidelines, and experiment planning analyses.

– This computer code can be used for the simulation of a wide variety of hydraulic and thermal transients in both nuclear and non-nuclear systems involving mixtures of steam, water, non-condensable, and solute.

8



9

SV20

SV15

SV10

Annulus100(50 Vols,

Cavity Volume)

SJ 21

SJ11

SJ 111

30-1,2

30-3,4

30-5,6

30-7,8

Annulus30-9,10

SJ 16

TDV106

TDJ105

SJ 41

Annulus40-7,10

40-4,7

40-1,3

Annulus 50 (5)

SJ 61

Annulus 60 (10)

SJ 91

SV92

SJ 51

TDV104

SJ 103

SJ63

SJ93

SJ 31

Annulus70(10)

SJ 81

Annulus90(2)

SJ 71

Annulus80(2)

100-1,2

100-3,4

100-5,6

100-7,8

Ht St100-9,10

Ht St100-17,20

100-14,17

100-11,13

Ht St100-21,25

Ht St200-23,24

Ht St200-21,22

Ht St200-11,20

Ht St200-1,10

No. Description

Heat Structure 100 Spherical Reactor Vessel

Heat Structure 200 Cylindrical Reactor Vessel

Single Volume 20 Volume Between the Reactor Vessel

Bottom and the Insulation

Annulus 30, 40 ,50 Volume Between the Spherical

Reactor Vessel and Insulation

Annulus 60,70, 80, 90

Single Volume 92

Volume Between the Cylindrical

Reactor Vessel and Insulation

Annulus 100 Reactor Vessel Outside Cavity

Volume

Single Volume 10 Bottom Side Cavity Volume

Single Volume 15 Bottom Cavity Volume under the

Reactor Vessel

Time Dep. Volume 104 Containment Atmosphere

Time Dep. Volume 106 Water Source (CFST)

Single Junction 16 Water Inlet

Single Junction 63 Water Outlet

Single Junction 93 Steam Outlet



10

Input Conditions OPR1000

(Assumed) APR1400

Water Inlet Area (m2) 1.765 1.765

Water Outlet Area (m2) 1.486 1.672

Steam Outlet Area (m2) 0.372 0.372

Water Outlet Position from the

Reactor Vessel Bottom (m) 5.69 6.14

Steam Outlet Position from the


Distance Between Insulation and


Insulation design for natural circulation flow



Annular gap area

11

Minimum Gap Area Water Inlets

4.50

210.76

42.37

4.50

47.79

56.6 deg

317.17

8.06

3.50

ICI Penetrations

R86.34

3.0 - 6.0

4.50

R99.915

14.51

Shear Key38.69

Steam Venting Slots

R101.34

8.50

I.D. 42.0

Water Level

36.00

Hot Leg

60 deg

120 deg

60 deg

120 deg

Shear Key

Height (m)

0 1 2 3 4 5 6

Are

a (

m2)

0

2

4

6

8

10

12

14

APR1400

OPR1000


12

MAAP4 Results for the APR1400

(from KHNP)

Reduced Results

for the OPR1000

0 20 40 60 80 1000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 Zone4

Zone3

Zone2Zone1

Heat

Flu

x (

MW

/m2)

Angle (degree)


Thermal load

Angle (degree)

0 20 40 60 80

He

at

Flu

x (

MW

/m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

APR1000

APR1400

OPR


Time (sec)

5000 6000 7000 8000 9000 10000

Ma

ss F

low

Ra

te (

kg

/s)

0

200

400

600

800

1000

1200

1400

Water Inlet

Water Outlet

Steam Outlet

Time (sec)

5000 6000 7000 8000 9000 10000

Ma

ss F

low

Ra

te (

kg/s

)

0

200

400

600

800

1000

1200

1400

Water Inlet

Water Outlet

Steam Outlet

13

RELAP5 Results & Discussion (1)

Temporal coolant circulation mass flow rate

– Oscillatory Flow, APR1400 > OPR1000(Annular Gap Area, Thermal Load)

– Some water circulates through the steam outlet because two phase water level increases in the annular gap

APR1400 OPR1000


14

Temperature (OC)

40 60 80 100

Ma

ss F

low

Ra

te (

kg/s

)

0

500

1000

1500

2000

APR1400

OPR1000


Coolant injection temperature effect

– An increase in coolant injection temperature leads to an increase in the coolant circulation mass flow rate.



Local pressure and averaged void fraction (OPR1000)

– Coolant Injection Temp ↑ Bubble Generation ↑ Coolant Circulation Mass Flow Rate ↑

15

Height (m)

0 2 4 6 8 10

Lo

cal P

ressu

re (

bar)

0.8

1.0

1.2

1.4

1.6

1.8

Coolant Injection Temp. = 25 oC




Height (m)

0 2 4 6 8 10

Lo

ca

l V

oid

Fra

ctio

n

0.0

0.2

0.4

0.6

0.8

1.0






Level (m)

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Mass F

low

Rate

(kg/s

)

0

200

400

600

800

1000


Water level effect in the reactor cavity (OPR1000)

– If water level is lower than the outlet, an decrease in water level

leads to an rapid decrease in the coolant circulation mass flow

rate.

16



Local pressure and averaged void fraction (OPR1000)

– If water level is lower than water outlet,

Water level ↓ Local pressure ↓ Challenging distance in gap to flow out ↑ Circulation Mass Flow Rate ↓

17

Height (m)

0 2 4 6 8 10

Lo

ca

l P

ressu

re (

ba

r)

0.8

1.0

1.2

1.4

1.6

1.8

Water Level = 6.95 m





Height (m)

0 2 4 6 8 10

Lo

ca

l V

oid

Fra

ctio

n0.0

0.2

0.4

0.6

0.8

1.0








Driving mechanism of circulation flow

– Circulation flow = driving force – pressure loss

– Driving force = pressure difference in gap and pool

To increase driving force (higher void fraction)

– higher wall heat flux

– Higher coolant temperature

– Pressure loss = gap pressure, form & friction loss

To decrease pressure loss

– Lower two-phase level in gap

– Larger gap size (minimum gap region)

– Uniform gap (reductions of form loss)

18


Conclusions (1)

Natural circulation flow features of APR1400 and OPR1000

were examined by RELAP5 code.

– The coolant circulation mass flow rate at high power of the

APR1400 is higher than that at low power of the OPR1000.

– The increase of the coolant injection temperature leads to an

increase in the steam generation rate, which leads to an increase

in the coolant circulation mass flow rate.

– The coolant injection temperature is not effective on the local

pressure, but is effective on the local average void fraction.

– A decrease in the water level in the reactor cavity leads to a

decrease in the local pressure at the lower region and an

increase in the challenging distance in gap, which leads to a

decrease in the coolant circulation mass flow rate.

19


Conclusions (2)

It is concluded from the RELAP5 results that the present

design of the reactor vessel insulation in the APR1400 and the

OPR1000 is suitable for the IVR-ERVC.

Verification experiments and a more detailed analysis are

necessary to evaluate the IVR-ERVC in OPR1000.

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Thank you for your attention!

Toward the Robust and Resilient Nuclear System for the Highly Improbable Event

evaluation of two phase natural circulation flow in the ... using the relap5/mod3 contents – to...

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