Optimization of mercury flow with microbubbles in the target-vessel design by means of machine learning

Kogawa, Hiroyuki; Futakawa, Masatoshi; Haga, Katsuhiro; Tsuzuki, Takayuki*; Murai, Tetsuro*

JAEA-Technology 2022-023, 128 Pages, 2022/11

JAEA-Technology-2022-023.pdf:9.0MB

In a mercury target of the J-PARC (Japan Proton Accelerator Research Complex), pulsed proton beams repeatedly bombard the flowing mercury which is confined in a stainless-steel vessel (target vessel). Cavitation damage caused by the propagation of the pressure waves is a factor of the life of the target vessel. As a measure to reduce damages, we developed a bubbler to inject the gas microbubbles into the flowing mercury, which can reduce the pressure waves. To operate the mercury target vessel stably with the 1 MW high-intensity proton beams, further reduction of the damage is required. The bubbler setting position should be closer to the beam window to increase the bubble population, which could enhance the reduction effect on the pressure waves and damage. However, the space at the beam window of the target vessel is restricted. The bubbler design and setting position as well as the vane design for the mercury flowing pattern are optimized by means of a machine learning technique to get more suitable bubble distribution, increasing in bubble population and optimizing bubble size nearby the beam window of the target vessel. The results of CFD analyses performed with 1000 cases were used for machine learning. Since the flow rate of mercury affects the temperature of the target vessel, this was used for the constraint condition. As a result, we found a design of mercury target vessel that can increase the bubble population by ca. 20% higher than the current design.

Mechanism of the flashing phenomena induced by microwave heating

Fujita, Shunya*; Abe, Yutaka*; Kaneko, Akiko*; Yuasa, Tomohisa*; Segawa, Tomoomi; Yamada, Yoshikazu

no journal, , 

A mixed solution of uranyl nitrate and plutonium nitrate is converted to MOX raw powder by the microwave heating de-nitration method in nuclear fuel reprocessing. Since the microwave heating causes a boiling phenomenon, it is necessary to sufficiently confirm operating conditions to prevent flushing and overflow phenomena of solution. In this study, visualization observation of the microbubble generation and growth behavior near the liquid surface, measuring of bubble diameters, calculating the frequency of nucleation and estimating the quantity of heat of required for generation and growth of microbubbles were performed for the purpose of clarifying the generation mechanism of the flushing phenomena caused by microwave heating. As a result of comparative study with the amount of heat of released by flushing, it was confirmed that the quantities of the heat of released by flushing and the heat of required for generation and growth of microbubbles agree on the order.