A Mathematical Model Design for Pu Content Analyzed by ²⁴⁴Cm in Spent Fuel of Fast Reactors

Pyroprocessing is employed in the reprocessing of integral fast reactors (IFRs). According to China's domestic regulations of nuclear material control, analysis of the content of uranium (U) and plutonium (Pu) should be carried out during the interval from unloading spent fuel to its transition into pyroprocessing. Nondestructive analysis (NDA) is a common technique to analyze the content of U/Pu in spent fuel. However, due to the high radio activity of spent fuel from fast reactors, the complexity of the signal characteristics, and the weak signal from Pu, it isn't easy to apply conventional NDA techniques directly. The article studies the reaction principle between ²⁴⁴Cm and Pu, which provides a theoretical basis for new NDA methods to indirectly measure the content of U/Pu through ²⁴⁴Cm. A model based on the one-speed neutron-diffusion equation, which selects burnup (BU), cooling time (CT), initial enrichment of uranium (IE), and the mass of ²⁴⁴Cm to characterize the physical properties of the spent fuel, is established and validated in the article. On this basis, the liquid metal fast breeder reactors are simulated to obtain the information of plutonium and curium of 336 groups under different BU/CT/IE, and the nonlinear multivariate regression model of Pu content concerning the BU/CT/IE and ²⁴⁴Cm content is obtained by using the nonlinear multiple regression analysis, and R² is greater than 0.99.