Thermal hydraulic behavior of feeding SG

in severe SGTR accident

Youngsu Na* and Sung Il Kim

Accident Monitoring and Mitigation Research Team

*Corresponding author: ysna@kaeri.re.kr

Transactions of the Korean Nuclear Society Autumn Meeting

Online, December 16-18, 2020

Preliminary analysis of aerosol behavior in secondary SG shell

2/8

Containment

building

1962 TID-14844

Experts’ opinions

(Conservative approximation)

Auxiliary

building

1995 NUREG-1465

Code for severe accident

(Experiments + phenomena)

2012 SOARCA

Code with detailed models

Core

degradation

Fission

products

Assessment of accident source term

(1) Release rate of radioactive nuclide

(2) Mitigation effect during release

Best-estimated source term

of SGTR

Bypass through

inter-system

Bypass through

SG tube rupture

3/8

Containment buildingOPR1000

(1) SBO → Reactor/RCP trip

(2) SRV open/close → Fluctuating P

(5) SGTR → Discharging Fission products

(3) CET > 923 K → SAMG

Sequence(KAERI/TR-7852/2019)

Environment

CV500

CV600

CV

610

FL260

FL351

FL352

FL610

FL616

CV316

CV312

CV315

CV510

CV

331 CV

332

CV

333

CV

341

CV

340

CV344

CV345

CV

347

CV

348

CV350

FL316

FL311

FL315FL333

FL332

FL313

FL312

CV311

FL331

FL335

FL341

FL342

FL

340

FL

345

FL

348

FL

344

FL510

FL513

FL320

Surge line

Hotleg

FL9

Pressurizer

FL512

FL522

Safety Depressurization System

Safety Relief Valve(2)

Inlet

plenum

FL1(9.6 mm d)

FL347

FL350

Outlet plenum

Steam generator

secondary loop(6)

CV740

Turbine

FL611

FL612

FL2

FL3

FL4

Atmospheric Dump Valve(4)

Main Steam Safety Valve

SG tube

rupture(5)

(4) ADV open → △P &T btw. SG & Env.

(6) Feeding secondary SG shell

CV600

Mass sourceCF1000

CF1001

T: CF1002

F: 0

L-A-IFTESGTR

start

CF1003

T: CF1004

F: 0

L-A-IFTELimit of

feeding*

Time of

feeding****~3000 s after SGTR, 35 kg/s

*until water level of 5.58 m

Assume feeding conditions

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Pressure and Temperature

SRV open/close → Fluctuating P

Pressure w/o feeding SG Pressure when

feeding SG

Feeding

ADV open

SGTR start

Lower head

penetration

Vapor temp. in SG tube

SG tubeSG shell

Vapor temp. in SG shell

Feeding

Feeding

SG tube

SG shell

Feeding SG

No feeding

Feeding SG

No feeding

5/8

Flow rate and Water level

Fluid passing through SGTR Flows at inlet and outlet of SG shell

w/o feeding SG

Feeding SG

SGTR start

Lower head

penetration

ADV(outlet)

SGTR(inlet)Feeding SG

Water level in SG shell

Feeding SG

w/o feeding SG

Limit of

feeding

level

Temp. in SG shell when feeding SG

Vapor

Liquid

Feeding SG

(3) Turbulence = f (dp)

(2) Diffusion(∇C, T)

Aerosol dynamics Iodine pool chemistry

Pool scrubbing in SG shell

Size(mass) distribution(t) =

Source ± Condensation/Evaporation

±Agglomeration - Deposition

gas↔particle

combination removalMAEROS code

Deposition velocity

(1) Gravity = f (dp)

Deposited aerosol on pipelines

DF = DF1 x DF2 x DF3 x DF4

vent exit swarm riseSPARC-90 code

condensation

inertial

impaction(dp)

gravity(dp),

diffusion,

centrifugal

condensation,

gravity,

diffusion,

centrifugal

DFCS = DF1 x DF2,d x DF3,d x DF4,d

DFI2 = DF1 x DF4 in early accident

[I2,atm] = f ([I2,aq], PCI2(T))

I-, OH-, H+... in late pool

= f (dp)

Chemical eqs. ~#200

A + B C + D

Radiolysis, reactionI2, CH3I

1

2

3

generation

→ Iodine chemistry(CsOH)3

= f (pH, dose rate)

vent exit

swarm rise

HNO3

in pipe

db(z)

z

vb, db

→ Pool

scrubbing

2

6/8

→ DF

7/8

Aerosol behavior in SG shell

CS aerosol in SG shell when feeding

Pool

Atmosphere

CS aerosol in outside environment

Feeding SG SGTR

w/o feeding SG

Feeding SG

75% down

Before feeding After feeding

Pressure(MPa) 0.15 1.54

Vapor temp.(K) 892 667

Pool temp.(K) - 460

Water level(m) - 4.1*

Flow rate(m/s) 487** 606**

ADV

SG shell

Pool formed

by feeding

TH conditions in SG shell from gap release to vessel failure

SGTR

*from elevation

of SGTR**Choke flow

Atmosphere

Environment

Conclusion and Future work

Thermal hydraulic analysis → Pool in SG shell(1)

This work was supported by National Research Foundation of Korea(NRF) grant funded by the Korea

government(Ministry of Science and ICT) (No. NRF-2017M2A8A4015280).

(1)KAERI/TR-8356/2020

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“Development of evaluation technologies on radioactive material releases by

steam generator tube rupture under severe accident”

2020(4th year)

Behavior of fission products in SG shell

2021(5th year) Sensitivity analysis of mitigation action → CS, I2, ...

▪ Feeding time/rate: 34,000~41,000 s/1~30 kg/s

Validation of calculation of pool scrubbing

▪ Jet regime experiments in THEMIS project