Page 209 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

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and simulated water inlet and outlet temperatures in the secondary side of the HX.
Experimental water inlet temperature has been reproduced as a boundary condition
in RELAP5 during HX activation—from t¼1.86h to t¼7.6h—thus, only the outlet
temperature was calculated by RELAP5. The results shown in Fig. 4.13 present a good
agreement between the experimental water outlet temperature and the RELAP5
predictions.

4.5 Other STH codes used in the SESAME project

4.5.1 CATHARE code
Code for Analysis of Thermal Hydraulics during an Accident of Reactor and safety
Evaluation (CATHARE) is a thermal-hydraulic system code mainly employed for
safety analysis of light-water reactors and for the evaluation of the management
actions performed during accidental scenarios. The code is also used for the definition
of operational procedures and for licensing support to nuclear power plants. The code
was actively developed since 1979, and it is the result of a collaboration among the

Commissariat a ` l’Energie Atomique (CEA), Institut de Radioprotection et de Su ˆret e

Nucl eaire (IRSN), Electricit e de France (EDF), and AREVA NP.
Similarly to RELAP5, the CATHARE code treats the thermal hydraulics of fluids
mainly in one-dimensional motion flow with a two-phase model (liquid and gas).
CATHARE solves the balance equations for mass, momentum, and energy for each
phase in the six main variables: liquid and gas specific enthalpy, liquid and gas phase
velocity, pressure and void fraction with further optional equations to treat the trans-
port of noncondensable gases (up to 4), and radiochemical species (up to 12). More-
over, the code is provided with closure relations to consider the conservation of mass,
momentum, and heat exchanged between the two phases and between each phase and
the walls.
The space is discretized with a finite-volume scheme in the balance equations of
mass and energy and with a finite-difference scheme for what regards the momentum
equations. The time discretization uses an implicit numerical scheme for 0-D and 1-D
modules and a semi-implicit scheme in the case of 3-D elements including interphase
exchange, pressure, and convective terms. The system resolution is based on an iter-
ative method of Raphson-Newton. Thanks to its robustness and reliability, the code
allows to obtain a good compromise between precision and calculation time efficiency
giving also many advantages in the extension to other applications in light-water reac-
tor systems. As a matter of fact, the numerical solver is generic, and the existing tools
for pre- and postprocessing can be used for all applications. Basic modeling features,
like circuits with heat exchangers, various hydraulic elements, valves, and walls,
already existing are well consolidated and can be used for generic purpose. This is
the reason why the new capabilities will be integrated as independent options in a
unique standard version of the code respecting the same stringent procedures for qual-
ity assurance.