Study of boron diffusion models and dilution accidents in nuclear reactor: A comprehensive review

Abstract Due to the large neutron absorption cross section, the boron is widely used in the reactivity control of nuclear reactors. According to the experience of reactor operation, the non-uniform distribution of boron concentration in the reactor would lead to reactivity accidents or the difficulty of accurate adjustment of the reactor core power, threating the safety operation of reactors. More attention has been paid to the boron dilution accidents in nuclear reactor and a large amounts of experimental and theoretical studies have been carried out during the past decades. Several integral experiment facilities were set up to study the time and concentration of unborated water entering the pressure vessel and the mixing characteristics of borated water in the downcomer and lower plenum under the boron dilution accidents. The model for calculating boron transport are studied and the appropriate numerical algorithm schemes were implemented in the best-estimate code, subchannel code and CFD software, respectively. Higher order schemes were used to solve the boron conservation equations to reduce the numerical errors. The effect of power feedback under boron dilution accident is also studied by neutronic-thermohydraulic couple studies. In this paper, the current research status of boron dilution accident in nuclear reactor is summarized and the challenges are identified. This paper would contribute to a better understanding of the boron dilution scenario and provide future work guidance for researchers.