Reactivity experiments with different boric acid concentrations in the IPEN/MB-01 reactor

According to general design criteria GDC26 (NUREG0800)[1], the reactor design requires two independent shutdown of different design principles must be provided. One of the systems must be capable to holding the reactor core subcritical under cold conditions. The LABGENE reactor was designed in accordance with GDC26, one of the systems uses control rods banks, based on a positive means for inserting the rods and is capable of reliably controlling reactivity changes to assure that under conditions of normal operation, and with an appropriate margin for malfunctions such as stuck rods. The second system is chemical shim based on soluble boron in form of boric acid (H3BO3), the soluble boron solution is inject directly in the primary circuit. The objective of this work is to present a series of critical experiments conducted in the IPEN/MB-01 critical facility as part of V&V process of LABGENE reactor core design methodologies. The experiment was designed to address the boric acid reactivity considering five different concentrations in the reactor moderator at room temperature. All experiments were evaluated and modeled properly with the SCALE system and MCNP Monte Carlo code.