Preparation and characterization of 10 B boric acid with high purity for nuclear industry

Boric acid (“Boric acid that appears in the following text refers to ¹⁰B boric acid.”) is widely used in nuclear power plant as coolant (moderator) for reactor to control nuclear reaction rate (Zhang et al. 2014, 2015). The important role of boric acid in nuclear power plant is to control nuclear fission rate and to influence the power generation of nuclear power plant (Odar 2007). Generally speaking, the rate of nuclear fission is controlled by neutron flux, which is released by that process, and boron is an atom that absorbs neutrons with perfect effect. ¹⁰B (one of B isotope) has very strong absorption ability, whose neutron absorption cross section of thermal neutron is five times more than boron with natural abundance, 20 times than graphite, and 500 times than traditional protective material of concrete. For that reason, the rate of nuclear fission can be controlled by injecting boric acid into a nuclear power furnace with ¹⁰B. Boric acid is prepared in a system consisting of boron and water supply, and enters into chemical volume control system by boron adding loop. The chemical volume control system controls the reactivity of the reactor by controlling boric acid concentration of the loop, and then further controls the power and safety of the reactor (Wootten et al. 1985; Mark 1989; Song and Lee 2003; Staudt et al. 2002).

The main advantages of boric acid solution for controlling water pressure reactor are (Pastina et al. 1999; Hohne et al. 2008): (1) boric acid features the property of dissolving in water. Since this property make boric acid’s effect on the reaction is uniform, and neutron absorption effect is well exerted without additional configuration space, a lot of control rods can be saved. Therefore, core arrangement and pressure vessel structure of the reactor on the top of the heap can be simplified. (2) Boric acid is chemically stable, and cannot react with the material of the loop easily, and its inertia is enhanced with the increase of temperature. Boric acid is neither being deposited itself, nor will be formed on the surface of the compound formed by the chemical composition of the reactor. (3) Boric acid can inhibit corrosion of reactor materials. Significant advantages have been shown by comparing enriched ¹⁰B acid with boric acid with natural abundance, since the increase of ¹⁰B concentration in reactor’s coolant system and the decrease of whole amount of boric acid can increase the safety and controllability of the reactor and improved, water chemical environment of coolant, and so on. For all the above reasons, the cost is effectively reduced.

Traditional preparation method of boric acid (Zheng 2000; Zhu et al. 2005; Li and Li 2008) is mostly to get the product with natural abundance and not high purity, whose impurities cannot meet the standard of high purity (Wang et al. 2014; Xue et al. 2015; Duan et al. 2012; Li et al. 2011). ¹⁰BF₃–methanol complex, prepared by separation device of laboratory boron isotope, was chosen as raw material for preparing boric acid, and calcium chloride and distilled water play the same role. In the reaction process, Fe²⁺ was oxidized to form precipitation due to the addition of H₂O₂, and the product of boric acid was purified. Finally, the content of impurity ion was detected by ICP to confirm that final product of boric acid meets the requirement of the national standard of high purity.