Hot duct break transient with two- and three-loop ALLEGRO models

Abstract

ALLEGRO is a concept of a small nuclear reactor with the primary aim to demonstrate the viability of the Generation IV (GFR) Gas cooled Fast Reactor technology and to ensure the experimental and qualification background for its new refractory fuel. In the GFR development the so-called bypass transients represent a pivotal role during safety analysis. Since the hot duct is located inside the cold duct there is no loss of coolant during the transient, nevertheless a huge core bypass may develop, which threatens the cladding integrity. The current ALLEGRO design consists of two primary cooling loops but a three-loop version is also investigated. In this paper the hot duct break transient is studied with a two- and three-loop ALLEGRO model by using the French CATHARE thermal hydraulics code. The preliminary analysis showed that the three-loop model has a better cooling performance.