Development and preliminary validation of TIFONE, a design-oriented code for the inter-wrapper flow and heat transfer in liquid-metal-cooled reactors

Among the goals of the core design for Lead-cooled Fast Reactors (LFRs) exploiting the closed Sub-Assembly (SA) option, cold by-passes should be minimised and excessive thermal gradients among opposite faces of the assembly ducts prevented. To this aim, given an Inter-Wrapper (IW) gap determined by the core thermomechanical design, a suitable coolant flow outside the assemblies themselves must be guaranteed. Moreover, the designer has the opportunity to introduce flow restrictions to tune the intra-wrapper flow fraction at the SA level, possibly allowing to reduce temperature differences at the outlet of the assemblies. Therefore, the designer needs to be aware of the axial and radial temperature profiles of the IW coolant 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 temperature 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 current best practices in terms of software quality assurance. 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 preliminary validation of TIFONE against data from inter-wrapper flow and heat transfer experiments performed in the frame of the SESAME project at the THESYS loop within the KALLA laboratory, confirming the code capability to reproduce the measured data in its anticipated validity domain.