Abstract
This paper describes the calculation method of debris bed cooling model for a Sodium-Cooled Fast Reactor (SFR). The existing method requires much calculation time in transient by a high calculated load due to small mesh and time step in boiling region. Thus, we study the method for calculated load reduction. The consideration of the cooling model equation suggests that the boiling region be steady behavior in transient. In addition, the behavior is also confirmed in the transient calculation for the typical SFR debris bed conditions. On the basis of the results above, we propose the new calculation method which is calculated in two steps by dividing the cooling model into two. In the first step, the transient calculation is performed with the cooling model in which the equivalent thermal conductivity of boiling region is changed to the simplified large value. By the simplification, we can use large mesh size and time step in boiling region, which reduces the calculated load. On the other hand, as a result of the simplification, the temperature and saturation distributions in the boiling region are not properly calculated in transient calculation. Thus, in second step, we calculate them with the steady calculation. The validation of this model is confirmed for the typical SFR debris bed conditions. The calculation speed of the proposed method is significantly faster than the existing method.
