In this chapter, the Multi-Physics Modelling (MPM) approach to the study of nuclear reactor dynamics is discussed. Based on the several activities (of development and validation) carried out at the Politecnico di Milano, MPM reveals a useful tool when dealing with reactor safety and control, and can be considered as an integrative analysis implement in the design process of reactor layout. 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 safety analyst from implementing 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 chapter is applied to different case studies in order to demonstrate the MPM adequacy to perform preliminary safety analysis. In particular, two innovative Generation IV systems are taken into account, namely the Molten Salt Reactor (MSR) and the Lead-cooled Fast Reactor (LFR). The MPM approach is particularly well suited to the MSR, which features a liquid fuel that also serves as coolant. For this system, two of the main accident transients to be considered in the safety analysis are 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. As for the LFR, the ULOF transient represents a minor accident because of the weaker coupling between thermal-hydraulic conditions and neutronics, whereas the insertion of prompt reactivity must be considered as a main accident scenario in the safety analysis. In this chapter, the MPM theoretical basis is first summarized, and compared with the classical CCT approach. Then, a brief system description along with general remarks about the safety features is separately given for each studied reactor, showing the adopted multi-physics models and presenting the performed transient analyses.

The Multi-Physics Modelling Approach Oriented to Safety Analysis of Innovative Nuclear Reactors

CAMMI, ANTONIO;LUZZI, LELIO;
2011

Abstract

In this chapter, the Multi-Physics Modelling (MPM) approach to the study of nuclear reactor dynamics is discussed. Based on the several activities (of development and validation) carried out at the Politecnico di Milano, MPM reveals a useful tool when dealing with reactor safety and control, and can be considered as an integrative analysis implement in the design process of reactor layout. 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 safety analyst from implementing 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 chapter is applied to different case studies in order to demonstrate the MPM adequacy to perform preliminary safety analysis. In particular, two innovative Generation IV systems are taken into account, namely the Molten Salt Reactor (MSR) and the Lead-cooled Fast Reactor (LFR). The MPM approach is particularly well suited to the MSR, which features a liquid fuel that also serves as coolant. For this system, two of the main accident transients to be considered in the safety analysis are 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. As for the LFR, the ULOF transient represents a minor accident because of the weaker coupling between thermal-hydraulic conditions and neutronics, whereas the insertion of prompt reactivity must be considered as a main accident scenario in the safety analysis. In this chapter, the MPM theoretical basis is first summarized, and compared with the classical CCT approach. Then, a brief system description along with general remarks about the safety features is separately given for each studied reactor, showing the adopted multi-physics models and presenting the performed transient analyses.
Advances in Energy Research. Volume 5
9781617618970
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11311/608454
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