Abstract: [Background] When the reactor core temperature changes, the reaction cross sections at different temperatures need to be generated with on-the-fly methods. Among the existing on-the-fly cross-section generation methods, the curve fitting method is becoming a common tool used in MCNP6, but the efficiency of this method is quite low.[Purpose] This study aims to accurately simulate the interaction between neutrons and various materials at different temperatures in the reactor by developing an on-the-fly generation method of nuclear cross sections.[Methods] In order to overcome the low efficiency of Doppler broadening in the parameter fitting method of MCNP6, double exponential method and Gauss-Hermite method are combined to replace the original analytical integral method to increase the width of the cross section generate efficiency.[Results] The typical nuclides test results showed that the curve fitting calculation efficiency of the numerical integration method is more than 10 times higher than the original one. Doppler reactivity coefficient benchmark example shows that the curve fitting of the numerical integration method is relative to the accuracy of the original method within 1.54%.[Conclusion] This method can be used for multi-physics coupling calculation of reactors.

Key words: Neutron cross section, Numerical integration, On-the-fly, Doppler broadening