Simulation study on recoil implantation in 316 stainless steel for the Spallation Neutron Source.

摘要

The Spallation Neutron Source (SNS) was proposed to produce high-flux neutrons for neutron scattering research. Liquid mercury was selected as the target material, which is to be contained in a 316 stainless steel vessel. Conventional studies focus on the radiation damage due to the direct effect of the incident proton beam and the resulting spallation neutrons at the container vessel. In the present work, the possible effects of the recoiling atoms that are implanted into the stainless steel vessel adjacent to surrounding mercury were studied.; LAHET (Los Alamos High Energy Transport Code) was used to simulate the transport of protons and HTAPE was used to obtain the recoil energy spectrum. Programs were developed by the author to retrieve recoil information (atomic number, energy, position, and direction of motion) from the LAHET output HISTP file and to generate the input file for another code: TRIM (Transport of Ions in Matter). TRIM was then used to simulate the transport of the recoils through the mercury layer adjacent to the stainless steel wall and into the wall itself.; Calculations of implanted recoil concentration and the consequent displacement concentration as a function of penetration distance into the stainless steel wall were performed based on the TRIM output. The calculated recoil and displacement concentrations in the near-surface region of the wall appear to be quite significant, but decrease rapidly with the penetration depth and become negligibly small at about 0.5 micrometers. The recoil concentration and displacement concentration rates at the surface of the 316SS vessel are estimated to be about 0.0015 per year and 17 dpa per year, respectively. The latter can be compared to 36 dpa produced by protons and neutrons at the same location.; The question arises whether it is possible to test the results of calculations of recoil-atom concentration and displacement concentration versus depth with results of experiments. It is not possible at present to irradiate 316SS in the SNS since the facility has not yet been constructed. However, calculations are provided in this study that would enable the same or similar mercury concentration profile to be simulated by Hg-ion bombardment of 316SS. Similarly, the simulation of the displacement concentration profile is described in terms of Fe-ion bombardment of 316SS.; Similar calculations on the possible effects of tungsten implantation into Inconel 718 for the Accelerator Production of Tritium (APT) target were performed and are appended.