Assessment of the 3He pressure inside the CABRI transient rods - Development of a surrogate model based on measurements and complementary CFD calculations
Résumé
CABRI is an experimental pulse reactor, funded bythe French Nuclear Safety and Radioprotection Institute (IRSN)and operated by CEA at the Cadarache research center. It isdesigned to study fuel behavior under RIA conditions. In orderto produce the power transients, reactivity is injected by depressurizationof a neutron absorber (3He) situated in transient rodsinside the reactor core. The shapes of power transients dependon the total amount of reactivity injected and on the injectionspeed. The injected reactivity can be calculated by conversion ofthe 3He gas density into units of reactivity. So, it is of upmostimportance to properly master gas density evolution in transientrods during a power transient. The 3He depressurization wasstudied by CFD calculations and completed with measurements using pressure transducers. The CFD calculations show that the density evolution is slower than the pressure drop. Studies also show that it is harder to predict the depressurization during the power transients because of neutron/3He capture reactions that induce a gas heating. Surrogate models were built based onCFD calculations and validated against preliminary tests in the CABRI transient system. Two methods were identified to evaluate the gas density evolution CFD calculations and reverse pointkinetics. The first one consists in adding a heat source in transient rods based on the experimental power conversion. The secondone consists in using the measured power by boron ionization chambers to evaluate the net reactivity by a reverse point kinetics (PK) method and to subtract the reactivity feedbacks calculated with the DULCINEE multi-physics code.