Boron-10 effect on the reactivity of the IPR-R1 Triga research reactor

Abstract

The isotope boron-10 (B-10) has a high thermal neutron absorption cross-section and is used to poison the chain reaction in some light-water reactors (chemical shim). The purpose of this work was to show the effectiveness of boron as a neutron absorber in controlling the reactivity of nuclear reactors cooled by light water. In this way, samples were placed in sealed containers with various concentrations of boric acid in the IPR-R1 Triga nuclear research reactor core. Thus, the reactivity variation of this reactor was determined. The sample characterization was performed before and after the experiments by the measurement of pH and electrical conductivity. The IPR-R1 reactor is located at the Nuclear Technology Development Center (CDTN) in Belo Horizonte, Brazil. Variations of reactivities were evaluated using the static reactivity null method and the dynamic method. The results obtained made it possible to simulate B-10 consumption during the operation of a reactor and its effect on reactivity with increasing boric acid concentrations. The pH values showed small increases after irradiation and their conductivities showed minor changes. As a result of this experiment, a correlation was drawn between various boric acid concentrations and reactor reactivity.