Yuanzineng kexue jishu (Aug 2023)
Study on Deterministic Calculation Method for Electron Transport Process
Abstract
Electron transport process is a crucial factor in the formulation of the electronic current in nuclear detectors. Accurate calculation of electron transport process is the essential function for advanced nuclear detector design and analysis software. While powerful Monte Carlo codes, such as MCNP and Geant4, can accurately simulate electron transport in various situations, the calculation efficiency of those stochastic simulation methods is relatively low mainly due to the short mean free path and highly forward-peaked nature of the electron transport process. Thus, in this study, the electron transport process was described by using the differential-integral equation in the form of the multigroup Boltzmann transport equation. To obtain the multigroup electron-atomic cross-section, a new module was developed in the nuclear data processing code NECP-Atlas to process the atomic electron crosssection data (EEDL) in EPICS2017. The module considered four important interactions, including ionization, excitation, bremsstrahlung and elastic scattering. Among those, excitation and bremsstrahlung could only change the energy of the free electrons without changing their direction of motion, while elastic scattering could only change the direction of motion without losing energy. Each ionization reaction produced two electrons, including the scattered electron and the recoil electron. During this process, the Auger electrons which may be emitted was neglected due to its low production. Once those multigroup electron-atomic cross-section library applicable to the traditional Boltzmann equation was created, a solver that can solve the Boltzmann transport equation can be employed to carry out the electron transport calculation. Accordingly, a deterministic electron transport calculation program was designed, implemented and constructed using the neutron transport calculation kernel from Bamboo-Lattice which is a lattice calculation code utilized for the pressurized water reactor (PWR) core. In this solver, the method of characteristic (MOC) was employed to solve the Boltzmann transport equation in complex geometry. To validate the accuracy of the deterministic code, various test cases were employed, including both homogeneous and heterogeneous problems, single element and multiple elements problems. The results obtained from the deterministic code were compared with those from the stochastic method. Encouraging conclusions have been demonstrated, as the computational results of the deterministic code are consistent with the ones from the stochastic program, while the deterministic calculation efficiency is 82-571 times higher. The positive results encourage further work. In the following study, the deterministic electron transport computing software will be used to calculate the response current of the self-powered neutron detector (SPND) in the PWR core, replacing the existing stochastic program.
