Phenomenology involved in self-pressurized, natural circulation, low thermo-dynamic quality, nuclear reactors: The thermal–hydraulics of the CAREM-25 reactor

Abstract The interwoven phenomena involved in a prototypical self-pressurized natural circulation, low thermo-dynamical quality nuclear reactor such as CAREM-25 are analytically presented. These phenomena present many differences with traditional light water nuclear power plants. The dependence between mass flow and core inlet enthalpy on generated power is found. The need of tuning the mass flow rate in accordance to the design value is found to be important in order to keep the thermal margin and the heat transfer coefficients in the steam generators. The influence of condensation in structures or walls in the upper dome on the two-phase boundary is also studied. The dynamic consequences of all these results are therefore discussed. A numerical code is then used to verify the aforementioned findings and to test the validity of the modeling approximations. From the results it is clear that the way the phenomena interact causes the resulting dynamics in CAREM-25 to be substantially different from that existing in reactors such as PWRs, BWRs and also natural circulation BWRs. It is thus clear that the combination of different effects makes CAREM-25 behavior impossible to be extrapolated from existing knowledge and accumulated experience.