Page 197 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

168 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

boiling is reached only in a very severe condition in which the integrity of the struc-
tural material is compromised. For these liquid metals, the “vapor state” is then con-
sidered only if noncondensable gases are present.
In the present work, the use of the van der Waals equation of state for the vapor
phase of the considered metals is proposed. The equation of state (EOS) is

RT a
p ¼
v v b v 2
v
where

2
27R T 2 c RT c
a ¼ , b ¼ , v v,c ¼ 3b
64p c 8p c
This EOS can be solved iteratively to obtain the specific volume.
The thermal expansion coefficient is given by

1 ∂v v v v b
β T, pð Þ ¼ ¼
v 2
v v ∂T
p 2a v v b
v v T
R v v
while the isothermal coefficient of compressibility follows from the following
equation:

1 ∂v v 1
κ v T, pð Þ ¼ ¼ " #
v v ∂p T 2a RT
v v 3 2
v
v ð v v bÞ
Starting from the previous thermodynamic properties, the isobaric specific heat, the
specific internal energy, and the specific entropy can be found for the vapor phase as a
function of both temperature and pressure (Kolev, 2011).

4.4 RELAP5/Mod3.3 modified code and application

4.4.1 RELAP5/Mod3.3 modified code

The University of Pisa (UniPi), from the early 2000s, was involved in the implemen-
tation of a dedicated version of the RELAP5 code, capable to simulate liquid-metal-
cooled systems. More specifically, UniPi, in collaboration with ANSALDO and
ENEA, performed several simulations on the accelerator-driven system (ADS) cooled
by heavy liquid metal using the RELAP5/Mod3.2β code. The code was modified to
simulate the thermal hydraulics of lead- and LBE-cooled systems. Both the self-
standing version of the code and a version coupled with PARCS multigroup reactor
kinetics code were employed (Oriolo et al., 2000; Ambrosini et al., 2000).