Assessment of the ³He pressure inside the CABRI transient rods - Development of a surrogate model based on measurements and complementary CFD calculations

DEN CAD/DER/SRES CEA Cadarache, Bt 721. 13108 St Paul Lez Durance, France .
DEN CAD/DER/SESI CEA Cadarache, Bt 1222. 13108 St Paul Lez Durance, France .
Blaise, DEN CAD/DER/SPEX CEA Cadarache, Bt 238. 13108 St Paul Lez Durance, France .
IRSN/PSN-RES/SEREX Cadarache, BP3 13115 Saint-Paul-Lez-Durance Cedex, France.

email: olivier.clamens@cea.fr

Published online: 10 January 2018

Abstract

CABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute (IRSN) and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under RIA conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber (³He) situated in transient rods inside the reactor core. The shapes of power transients depend on the total amount of reactivity injected and on the injection speed. The injected reactivity can be calculated by conversion of the ³He gas density into units of reactivity. So, it is of upmost importance to properly master gas density evolution in transient rods during a power transient. The ³He depressurization was studied by CFD calculations and completed with measurements using pressure transducers. The CFD calculations show that the density evolution is slower than the pressure drop. Surrogate models were built based on CFD calculations and validated against preliminary tests in the CABRI transient system. 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. This phenomenon can be studied by a multiphysics approach based on reaction rate calculation thanks to Monte Carlo code and study the resulting heating effect with the validated CFD simulation.