Research on the spatial distribution of n-γ field outside of the spent fuel cask based on Monte Carlo method

For systematically understanding the spatial distribution of the n-γ field and its dosage level outside of the spent fuel cask, we calculated the initial energy spectrum of both neutron and γ particles first. Then, in the Geant4 framework, we set up the sampling method of n-γ particles and built the physical model of the cask within fully loaded spent fuel modules to simulate the radiation field. Based on the simulation result, we plotted the spectrum of both neutron and γ particles and concluded the characteristics of the spectrum before and after penetrating the cask wall. At the end, we made a comparison of the simulation result with the field measurement data collected from the Daya Bay nuclear power plant (China) to test the validity of our model. The relative error of our simulation result with the field measurement data is 23.8%–33.7%. It is proven that our method can be a useful way to calculate the n-γ mixture field when multiple groups of spent fuel modules need to be transported in the future.