Development of Bamboo-Transient2.0 for three-dimensional PWR-core pin-by-pin Transient analysis

In order to ensure the safety of the core, three-dimensional whole-core transient analysis would be carried out to obtain the pin-power distribution required by safety analysis. For this purpose, this paper presents the development of Bamboo-Transient2.0, a three-dimensional pin-by-pin transient analysis program. It adopts a fullyimplicit backward finite difference method for time variable discretization, a method of exponential function expansion nodal (EFEN) SP3 for spatial and angle domain neutronic calculation, and a multi-channel model for the thermal-hydraulic feedback calculation. In addition, Picard iteration is used to couple the neutronics and the thermal-hydraulics, which is intended to guarantee the convergence of coupling iteration at each time step. Moreover, the program can perform parallel computing based on Message Passing Interface (MPI) for the wholecore pin-by-pin transient analysis. Besides, a series of acceleration techniques have been applied to further reduce the computational time. The methodology and code implementation have been verified via a series of numerical tests. As demonstrated by the numerical results, the code developed in this paper shows good agreement with the reference. Furthermore, the acceleration method used in this paper enables a 141.5 times speedup in SP3 neutron kinetics calculation, while the parallel efficiency maintains above 80 %. BambooTransient2.0 can yield great results, whose pin-wise distributions of state parameters are reliable and thus can satisfactorily meet the requirements and purpose of safety analysis.