Control Rod Depletion in Sodium-Cooled Fast Reactor: Models and Impact on Reactivity Control

The current design studies on sodium-cooled fast reactors (SFRs) are breaking with the past since they are guided by a new set of design criteria arising from the objectives of Generation IV reactors. The new safety requirements lead to designing reactors with breakeven breeding cores because in terms of reactivity control, they minimize the need to limit the consequences of an inadvertent control rod withdrawal event. Furthermore, as the reactivity control needs are low, a breakeven core enables the use of absorbing materials with reduced efficiency (natural boron, hafnium, etc.), which may be less costly than enriched boron. However, control rods designed with low absorbing materials may present the disadvantage of a nonnegligible loss of efficiency due to their consumption under irradiation. This paper presents a methodology to accurately calculate and to analyze the impact of this consumption on reactivity control.