### Abstract

Fossil-fueled power plants have been operated with water
at supercritical pressures for
decades due to the high thermal efficiency achievable by
increasing the system pressure
above the critical point. During the recent years, there
has been a renewed interest to
develop also water-cooled nuclear reactors which work
under the supercritical pressure
conditions. When such reactor concepts are studied, it is
necessary that also the
simulation codes used for design and
safety-demonstrations of such reactors are able to
simulate water flows above the critical pressure. In
APROS process simulation software,
the two-phase flow can be simulated with a variable level
of sophistication: with a
homogeneous model, with a 5-equation drift-flux model and
with a 6-equation two-fluid
model. At supercritical pressures the distinction between
the liquid and gas phases
disappears: boiling and condensation are not observed,
but instead the properties of the
fluid vary smoothly from those of a liquid-like fluid to
those of a gas-like fluid, and
from the macroscopic point of view the
supercritical-pressure fluid can always be
considered a single-phase fluid. Because of this, the
homogeneous model would be ideal
for the thermal hydraulic simulation at and above the
critical pressure. However, in the
nuclear power plant applications the homogeneous model is
seldom sufficient for the
calculation of two-phase flow below the critical
pressure, and thus the six-equation
model has to be used in the general case. When the
six-equation model is applied to
supercritical-pressure calculation, the problems how the
model behaves near and above
the critical pressure, and how the phase transition
through the supercritical-pressure
region is handled, are inevitably encountered. Above the
critical pressure the heat of
evaporation disappears and the whole concept of phase
change is no longer meaningful.
In the present paper the use of the six-equation
thermal-hydraulic model for
supercritical-pressure calculation is described. The
changes made in the constitutive
equations are discussed. The applicability of the numeric
model is demonstrated by
simulating two basic test cases.

Original language | English |
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Publication status | Published - 2008 |

MoE publication type | Not Eligible |

Event | NUTHOS-7: The 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and SafetySeoul, Korea, October 5-9, 2008 - Seoul, Korea, Democratic People's Republic of Duration: 5 Oct 2008 → 9 Oct 2008 |

### Conference

Conference | NUTHOS-7: The 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and SafetySeoul, Korea, October 5-9, 2008 |
---|---|

Abbreviated title | NUTHOS-7 |

Country | Korea, Democratic People's Republic of |

City | Seoul |

Period | 5/10/08 → 9/10/08 |

### Keywords

- Thermal Hydraulics
- Supercritical Pressures
- System-Code Development

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## Cite this

Hänninen, M., & Kurki, J. (2008).

*Simulation of flows at supercritical pressures with a two-fluid code*. Paper presented at NUTHOS-7: The 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and SafetySeoul, Korea, October 5-9, 2008, Seoul, Korea, Democratic People's Republic of. http://www.vtt.fi/inf/julkaisut/muut/2008/NUTHOS-7_final.pdf