Speaker
Description
A preliminary benchmark study has been conducted to investigate the large-angle neutron scattering cross section of liquid nitrogen (LN₂). This work is motivated by the crucial role of nitrogen as a constituent nuclide in several materials used for the blanket and shielding systems of fusion reactors. Despite its importance, existing nuclear data for nitrogen remain insufficiently accurate, particularly in the high-energy neutron range. Hence, an experimental benchmark is essential to validate and improve these data.
The benchmark experiment was performed at the OKTAVIAN facility, Osaka University, Japan, employing the two-shadow-bar technique previously established by the author’s group [1]. Four irradiation configurations were conducted, corresponding to two shadow-bar sizes (S1 and S2) with and without the target, denoted as S1t, S1nt, S2t, and S2nt. Unlike previous studies using solid targets, the present work utilized a liquid nitrogen target enclosed by Styrofoam to sustain the cryogenic condition during irradiation.
Monte Carlo simulations using MCNP5 [2] was carried out among major evaluated nuclear data libraries: JENDL-4.0 [3], JEFF-3.3 [4], and ENDF/B-VIII.0 [5]. The results indicated considerable discrepancies between experimental and calculated values. This large statistical error mainly attributed to target instability caused by LN₂ evaporation during irradiation. So that, several technical improvements are being developed, including optimization of container design, enhancement of thermal insulation, and selection of highly effective activation foils.
References
[1] Hayashi, N., Ohnishi, S., Fujiwara, Y., et al., Optimization of Experimental System Design for Benchmarking of Large-angle Scattering Reaction Cross Section at 14 MeV Using Two Shadow Bars, Plasma Fusion Res., vol.13, 2018, 2405002.
[2] X-5 Monte Carlo Team, “MCNP—A General Monte Carlo N-Particle Transport Code, Version 5”, Los Alamos National Laboratory, Report LA-UR-03-1987, 2003.
[3] Shibata K, Iwamoto O, Nakagawa T, et al., JENDL-4.0: A new library for nuclear science and engineering, J Nucl Sci Technol, vol.48, 2011, pp. 1-30.
[4] NEA, JEFF-3.3, https://www.oecdnea.org/dbdata/jeff/jeff33/index.html (accessed 2024-08-15)
[5] Brown, D.A., Chadwick, M.B., Capote, R., et al., ENDF/B-VIII.0: The 8th Major Release of the Nuclear Reaction Data Library with CIELOproject Cross Sections, New Standards and Thermal Scattering Data, Nucl. Data Sheets, vol.148, 2018, pp.1-142.
