Session: 02-10: Physics and Transport Theory - II

Paper Number: 130801

130801 - Thermal Cut-Off Energy for Accurate Analysis of Prismatic High-Temperature Gas-Cooled Reactor 

Abstract: 

The thermal cut-off energy for accurate neutron transport calculations of the prismatic high-temperature gas-cooled reactor was investigated. For accurate neutron transport calculations, the thermal motion of target nuclei and the effects of bonds within molecules and lattices need to be considered in the neutron scattering cross-sections. In general, the thermal cut-off energy, which is the maximum neutron incident energy for considering thermal treatment, is specified in the reactor analysis. The thermal cut-off energy has been typically set below 10 eV for the analysis of High-Temperature Test Reactor (HTTR), a prismatic high-temperature gas-cooled reactor. However, the appropriate thermal cut-off energy for the reactor analysis has not been thoroughly studied. Thus, the study aimed to discuss the appropriate thermal cut-off energy for high-precision analysis of the HTTR considering the wide range of fuel and graphite temperature.

 

The Monte Carlo code MVP3.0 was used for the evaluation of the impact of changing the thermal cut-off in the analysis of a single fuel element system of the HTTR. The effects were evaluated by changing a parameter ETH, corresponding to the thermal cut-off energy, for various fuel and graphite temperatures. These evaluations were performed for both the Beginning Of Life (BOL) and End Of Life (EOL). In these calculations, the fuel and graphite temperatures were set at 300K at first, and the appropriate thermal cut-off energy was investigated by either increasing the fuel temperature or the graphite temperature independently. When increasing the fuel temperature, all temperatures within the fuel compact (including the fuel kernel, coating, and matrix materials) were changed. In the case of increasing the moderator temperature, the carbon outside the fuel compact (including BP pellets) was changed. The graphite sleeve's temperature was fixed at 1200K, and the helium temperature was fixed at 1000K in these calculations.

 

As a result of these calculations, to keep the difference in multiplication factor within about 100 pcm from the reference solution obtained by setting ETH = 40 eV, a thermal cut-off energy of at least 20 eV is necessary for fuel temperatures around or above 800K, and at least 10 eV for graphite temperatures over 800K. No significant difference is shown in the required thermal cut-off energy between the BOL and EOL. Furthermore, calculations were performed with the thermal cut-off energy increased up to 100 eV, setting the fuel temperature at 1900K and the moderator temperature at 300K. The results confirmed that by setting the thermal cut-off energy to 30 eV, the difference in the multiplication factor from the reference solution obtained by ETH = 100 eV can be reduced to approximately 50 pcm or less.

Presenting Author: Satoshi Takeda Osaka University

Presenting Author Biography: Satoshi Takeda, Ph.D.
Assistant professor at Osaka University

Authors:

Satoshi Takeda Osaka University
Takanori Kitada Osaka University
Akio Yamamoto Nagoya University
Kazuya Yamaji Mitsubishi Heavy Industries, Ltd.
Hiroki Koike Mitsubishi Heavy Industries, Ltd.
Koji Asano Mitsubishi Heavy Industries, Ltd.