The Multi-Physics Approach Applied to the Modelling and Analysis of the Generation IV Lead Fast Reactor

In this book, the Multi-Physics Modelling (MPM) approach is briefly presented, and is applied to study the nuclear reactor core behavior. On the basis of R&D activities carried out at the Politecnico di Milano, this approach represents an integrative analysis implement in the design development of innovative nuclear reactors and reveals a useful tool when dealing with reactor dynamics, safety and control. The MPM fundamental feature is represented by the capability to simultaneously solve the coupled equations, which govern the different physical phenomena occurring in a nuclear reactor, in the same simulation environment. This prevents the implementation of additional code pieces for coupling neutron kinetics and thermal-hydraulics codes. Moreover, the Coupled Code Techniques (CCT) can require significant modifications of the considered codes. On the contrary, the adoption of a MPM tool allows the analyst to minimize the programming burden and to focus on the physical aspects of the problem. An important advantage given by the employment of such MPM approach is the possibility to perform more accurate thermal-hydraulic simulation by using computational fluid dynamics schemes comprising the description of turbulent flows, which occur in the majority of nuclear reactor cores. The approach discussed in this book is applied to the modelling and analysis of the Generation IV Lead-cooled Fast Reactor (LFR), with reference to the ELSY (European Lead System) reactor design, chosen as case study in order to demonstrate the MPM adequacy to simulate the core behavior and to perform preliminary safety analyses. For this system, two accident scenarios are considered, namely the unprotected loss of flow (ULOF) and the unprotected transient overpower (UTOP). Both transients are simulated showing that the multi-physics modelling gives additional information when compared to simplified thermal-hydraulic description. In this book, the MPM theoretical basis is first summarized, and compared with the classical CCT approach. Then, some relevant issues related to the LFR technology are discussed and a brief description of ELSY layout is given. Finally, the multi-physics modelling adopted to analyze the steady-state and transient behavior of the ELSY reactor is discussed.