where [bar.[rho]] is the mean density, [??] is the velocity vector, [bar.p] is the mean pressure, [??] is the gravitational vector, k is the turbulent kinetic energy, [??] is the specific enthalpy, [[??].sub.s] is the scalar solid temperature, [mu] is the dynamic viscosity of the fluid, [lambda] is the thermal conductivity of the fluid, [[bar.C].sub.p] is the mean specific heat of constant pressure of the solid material, [[lambda].sub.s] is the thermal conductivity of the solid material, and [Q.sub.H] and [Q.sub.s] are the volumetric heating source of the fluid and solid material, respectively.

Appropriate thermophysical properties such as dynamic viscosity, thermal conductivity, and mean specific heat of constant pressure of deuterium and helium were considered [17-20].