Liquid neutron absorber alternatives for the MPTRR

The Multi-Purpose Type Research Reactor (MPTRR) control and first shutdown systems consist of six control plates of a Ag-In-Cd alloy. The second shutdown system is given by a liquid neutron absorber, a solution of boric acid, filling the inside of the chimney separating the core from the reflectors. The chimney is composed of four sides (four independent systems), each of them formed by two Zircaloy walls of 0.6 cm, and the empty central space inside (1.8 cm) filled with pure nitrogen during normal operation. The licensing criterion for the second shutdown system (the chimney, for brevity) requires a reactivity worth of ∼5000 pcm. The purpose of the work is the analysis of alternative liquid absorbers and the maximum reactivity worth reachable by the second shut-down system