Thermal-hydraulic design requirements for moderators are to prevent boiling of hydrogen and to suppress hot spots decreasing neutronic performance.
As a result of a conceptual design study, impinging jet is used to remove high heat deposited on the bottom wall of moderator vessel near target. It is necessary to reduce re-circulation and stagnant flows which cause hot spots in the hydrogen flow so as to suppress the temperature rise of hydrogen in the moderator vessel within 3K. Thermal-hydraulic analyses, as well as experiments have been carried out to prove the feasibility of this
The analyses show that the local temperature rise in the re-circulation and stagnant flow regions could be suppressed within 3K. The hydrogen temperature increases up to 26K adjacent to the vessel surface due to nuclear heating of the vessel. This hot layer, however, would not change the neutronic performance because its thickness is very thin of less than 0.3mm.