Modeling of steam generators of

nuclear power plants (SGEN)

Timo Pättikangas • Ville Hovi • Sampsa Lauerma • Ismo Karppinen

VTT Technical Research Centre of Finland Ltd

Tommi Rämä • Timo Toppila

Fortum Power and Heat Oy

Main Steam Line Break (MSLB) transient in a

VVER-440 steam generator

Conclusions CFD method for the simulation of steam generators has

been developed. The method has been validated against

available (scarce) data on a VVER-440 steam generator

and experiments performed with the steam generator of

the PWR PACTEL facility. Main Steam Line Break

transient in a VVER-440 steam generator has been

successfully simulated. Loss Of Offsite Power transient in

an EPR steam generator has been calculated.

Introduction Steam generators of nuclear power plants are modeled with

three-dimensional Computational Fluid Dynamics (CFD)

calculations. The behavior of the primary circuit is first modeled

with the Apros code. The outer wall temperatures of the primary

tubes are used as the boundary condition for the CFD

calculation of the secondary side. In the CFD model, the

primary tubes are described as porous media. The boiling and

condensation models are implemented as user-defined

functions in the ANSYS Fluent CFD code.

Contacts Timo Pättikangas

Tel. +358 40 595 1968

timo.pattikangas@vtt.fi

Timo Toppila

Tel. +358 50 453 2364

timo.toppila@fortum.com

Figure 8. Contours of void fraction (left) and evaporation rate (right) during the

Loss Of Offsite Power (LOOP) transient in an EPR steam generator.

Loss Of Offsite Power (LOOP) transient in an

EPR steam generator

Time (s) Event

5.0 Loss of offsite power. Pumps start to coastdown, main feedwater

closure, isolation of the steam lines.

8.6 Reactor trip from low RCP speed.

9.0 Turbine trip.

9.1 Maximum primary pressure is reached.

14.4 Opening of the main steam relief train.

54 Full closure of the steam relief control valves.

Time (s) Event

−10 Plant in normal operation.

0 Main steamline of one of the steam generators has a 2100%

guillotine break.

0...200 Fast pressure decrease occurs on the secondary side.

12 Reactor scram and turbine trip.

87 Stoppage of the main circulation pump.

5.0 s 7.5 s 10.0 s 12.5 s 15.0 s 17.5 s

20.0 s 25.0 s 30.0 s 40.0 s 50.0 s 60.0 s

[-]

5.0 s 7.5 s 10.0 s 12.5 s 15.0 s 17.5 s

20.0 s 25.0 s 30.0 s 40.0 s 50.0 s 60.0 s

[kg/m3s]

Figure 6. CFD model of an EPR steam

generator.

Figure 7. Pressure on the secondary

side of an EPR steam generator during

LOOP transient.

tube

bundle

dryer unit

feedring

swirl vane

separator

Figure 3. An overview of a VVER-440

steam generator.

Figure 4. CFD model of a VVER-440

steam generator.

Figure 5. Surface temperature of the heat transfer tubes (left) and void fraction at

the operational state (top right) and 50 seconds after the MSLB of the steam

generator (bottom right).

[°C] [-]

Figure 1. Pressure on the primary and

secondary side during MSLB transient.

Figure 2. Steam production rate of the

affected steam generator during MSLB

transient.