6. Multiphysics

6.1 Need for coupling

In pressurized water reactors, the neutron balance depends on fuel temperature and coolant density, which means that the Boltzmann and Navier-Stokes equations, as well as those governing fuel behavior, have to be solved by coupling.

Neutronics studies, coupled with other disciplines, are mainly used for the design and safety of nuclear systems. The demonstration of safety requires the determination of margins with respect to the consequences induced by the most severe accident sequences. To achieve this, neutronic, thermal and thermal-hydraulic simulations are needed to simulate various normal and accidental operating transients. In principle, the analysis should be carried out simultaneously for all three disciplines:

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