Thermal and mechanical characteristics of the moderator cell in a cold neutron source

The moderator cell is the key structural component of a cold neutron source (CNS), which is installed close to the core of the research reactor to increase the cold neutron flux. It is subjected to great heat load by radiation and the neutron moderators inside it are generally inflammable matters such as hydrogen and deuterium. Therefore, its thermal and mechanical characteristics are closely related to the reactor safety. In this study, thermal and stress analyses are performed for the structural integrity evaluation of the moderator cell of China Advanced Research Reactor (CARR) CNS. The thermal performances in two operating modes, normal mode and stand-by mode, are calculated by the computational fluid dynamics code, FLUENT. The maximum temperatures of liquid hydrogen and walls in normal mode are 21.9 K and 23.0 K, respectively. The maximum wall temperature in stand-by mode is below 393 K. These results satisfy the user’s requirement. The static and thermal stresses are analyzed using the finite element analysis program, ANSYS. The stresses are far below the allowable values of the ASME code. The results of the analyses show that the helium direct cooling plays an important role in the cooling for the moderator cell with a helium cooling jacket and the stresses of the moderator cell are significantly affected by the wall thickness. It is expected that the results presented in this paper will be useful in the design and safety evaluation of the moderator cell in CNS.

► We analyze thermal and mechanical characteristics of the moderator cell in CARR CNS. ► More than 70% of nuclear heat is taken away by the helium direct cooling. ► The moderator cell can be adequately cooled in normal and stand-by modes. ► The static and thermal stresses are far below allowable values of the ASME code. ► The stresses of the moderator cell are significantly affected by the wall thickness.