TIFONE: a design-oriented code for the inter-wrapper flow and heat transfer in liquid metal-cooled reactors

The core of Lead-cooled Fast Reactors (LFRs) exploiting the closed sub-assembly (SA) option must be designed avoiding cold by-passes and preventing excessive thermal gradients among opposite faces of the assembly ducts. This requires a suitable coolant flow outside the assemblies themselves, in the so-called inter- wrapper (IW) region, compatibly with the extent of the IW gap, which is in turn determined by the core thermo- mechanical design. Moreover, for wrapped assemblies, the opportunity to perform gagging provides the designer with an extra degree of freedom, possibly allowing to reduce temperature inhomogeneities at the assemblies’ outlet. Therefore, the designer needs to be aware of the IW coolant axial and radial temperature profiles throughout the whole core (i.e. including all core SAs), as well as of the axial and perimetrical temperature profiles of the wrapper of each SA. Notably, the possibly different values of each side of the wrapper itself should be assessed, since they could induce SA bowing. To address these needs, a Design-Oriented Code (DOC), TIFONE, was developed and verified in compliance with ENEA software quality assurance requirements. TIFONE adopts the sub-channel method, leading to a sufficient level of spatial resolution while retaining the key features of a DOC, namely equilibrium, a low computational time and a clear application domain. The paper describes the code structure, governing equations and solution method. It also reports the results of a preliminary validation campaign performed against experimental data from the KALLA inter-wrapper flow and heat transfer experiment, confirming the code capability to reproduce the measured data in its anticipated validity domain.