The influence of the mesh and of the fuel cladding in the heat transfer in a simulated spent fuel pool

FERNANDO PEREIRA; CORZO, SANTIAGO; FABIANO CARDOSO; JÉSSICA ACHILLES; RAMAJO DAMIAN; CLAUBIA PEREIRA; DARIO GODINO; ANTONELLA COSTA

Santos

Congreso; International Nuclear Atlantic Conference 2019; 2019

Brazilian Nuclear Energy Association

This work presents studies of a simulated Spent Fuel Pool (SFP) storing Spent Fuels (SF) of the types UO2, (Th,TRU)O2 and MOX presumably discharged from Pressurized Water Reactor (PWR). Different types of meshes were performed, including different algorithms and element sizes. The studies were performed in the absence of an external cooling system of the pool, and the goal was to determine the impact of different types of meshes and the presence/absence of the fuel cladding in the water boiling time (Tb) of the pool. The SFs are volumetric heat sources which intensities are the decay heat values at time t=0 year after reactor discharge. The simulations were implemented in CFX Ansys Workbench. This platform contains a robust package of algorithms and tools for meshing of geometries. This package was used in the present modeling. The SFP was modeled based on the real geometrical dimensions of the pool of ANGRA II, in Brazil. Both classes of simulations were implemented. In the first class, the amount of water was scaled to correspond to that of nine elements of SF into the pool, being three elements of either (Th,TRU)O2 or MOX, and six of UO2. Viewing from the top, the elements of SF are arranged as a square lattice, whose elements of a single diagonal are either (Th,TRU)O2 or MOX. This arrangement is the minor structure of repetition of the pool. In the second class of simulations, the minor structure of repetition contains four elements of SF. One of the four is either (Th,TRU)O2 or MOX, and the remaining are UO2. Since UO2 is the standard fuel, for both classes of simulations was performed one case with all the nine and other case with all the four elements of SF being UO2. The results concerning different types of meshes show how Tb varies as a function of the refining of the mesh, and the cost in terms of computational time. The results also show how the fuel cladding impacts Tb. As expected, as higher is the thermal conductivity and lower is the specific heat of the cladding, less important is its presence to the heat transfer.