Speaker
Description
In the Material and Life Science Experimental Facility (MLF) at J-PARC, six T0 choppers are operated on JAEA instruments. These choppers have been in operation for over ten years since their installation, and to enhance functionality, we have developed a second-generation T0 chopper. Since the first-generation, Inconel X750—a nickel-based alloy—has been used for the hammer material. However, due to decreasing demand and rising costs, the price of Inconel X750 has increased significantly, making its continued use economically unfeasible for future T0 chopper. Therefore, we have initiated a project to replace the hammer material with an alternative alloy. Our initial research, which focused on mechanical properties, identified several alloys containing nickel and iron as potential alloys. Furthermore, each alloy was evaluated by simulation regarding specific neutron experiment requirements.
The simulations were carried out using PHITS (Particle and Heavy Ion Transport code System). We modeled the T0 chopper structure in PHITS, ensuring that important components, such as the hammer size and beam window thickness, accurately reflect the actual T0 chopper geometry. For incident pulsed neutron beams, we utilized publicly available simulation data from a moderator under 1 MW operation, which is provided on the MLF website.
For the T0 burst shielding analysis, the model, which incorporates a hammer made of each candidate materials, was irradiated with the T0 burst. We then calculated the resulting neutron flux at a point located 10 meters downstream of the chopper. The shielding performance of each material was evaluated by comparing its measured flux with the flux measured for Inconel X750.
Activation of hammer was also simulated. Since the hammer is irradiated with high-energy and high-intensity neutron beams, radioactive nuclides are produced within it. Of particular concern are long-lived radionuclides, such as Co-60, which accumulate over time and present heavy radiation exposure hazard during chopper maintenance. In this simulation, we calculated the dose rates and radionuclide production over an estimated five-year operational period to assess the activation effects of each candidate material.
This poster will present our comprehensive simulation results aimed at selecting the optimal replacement material for the T0 chopper’s hammer.
Key Words
chopper, PHITS