Application and Validation of Particle Transport Code PHITS in Design of J-PARC 1 MW Spallation Neutron Source

Abstract

Spallation Neutron Source (JSNS) is one of the major experimental facilities in the Japan Proton Accelerator Research Complex (J-PARC). JSNS operates with 3 GeV and 1 MW pulsed proton beams, and has the highest-class neutron intensity in the world. In the design stage, aiming for the best neutronic performance, the PHITS code was fully applied in the JSNS neutronics design, and calculations for several thousand cases were performed using complicated models. Not only optimization of neutronic performance, but also shielding calculation, nuclear heat estimation for the engineering design, residual radioactivity estimation for the cask design, and radiation damage estimation for the life and maintenance design were also done with the PHITS code. JSNS is one of the first facilities in the world to fully adapt such a simulation code to the neutronics design. In these calculations, note the change in particle energy from GeV to meV (12 decades), and that neutron fluxes are reduced by 10 decades or more. To confirm their reliability, these calculations were validated by measurement data for neutron spectral intensities, pulse shape, nuclear heat generation, and radioactivity. The results showed that the calculated values were in good agreement with the measured values. We confirmed that the PHITS code was reliable for such design calculations. At the same time, this indicates that the PHITS code is a powerful tool for neutronic design in other radiation source facilities and accelerator facilities.