Analysis of the drop dynamics of control rod assembly in a LBE-cooled research reactor

Abstract

The lead-based fast reactor is very attractive as one of the Generation-IV nuclear energy systems due to high-power density, heavy liquid metal coolants with a high boiling point as well as harmless interaction with air or water. Nuclear heat is generated from very high neutron flux that is regulated and controlled by the drop of the Control Rods (CRs) for safe operation. The resisting effect of the Lead Bismuth Eutectic (LBE) due to high density on the driving force of the CR Assembly (CRA) during the fall is crucial, which some delays may lead to unavoidable accidents. The mathematical approach has been applied to investigate the CRA dynamics of lead-based research reactor. The non-linear differential equations governing the motion of the CRA as well as the LBE flow have been ascertained to capture the pertinent parameters. Using the Fourth-Order Runge-Kutta iteration method, a computer program was developed with MATLAB and it can be used to calculate the drop time of the CRA and other important parameters described and presented in the study. Compared with the results of the experiment in the available literature, the program developed was proved to be applicable and reliable. The results showed that among the LBE flow characteristics, the density is the most influential parameter on the drop time and tends to have a positive relationship with the drop time. The total CRA mass contributes to the driving force of the CRA to reduce drop time when increased. Finally, the result of the theoretical model will serve as a basis to analyse the auxiliary mechanism and thus, help make informed choice on LBE flow parameters during modification to improve safety.