Study on optimisation of target head design for the TEF-T LBE spallation target

Wan, T.; Obayashi, Hironari  ; Sasa, Toshinobu   

JAEA has proposed an Accelerator Driven System (ADS) for nuclear transmutation. To realize the future ADS, the ADS Target Test Facility (TEF-T) will be constructed under the framework of J-PARC. In TEF-T, pulsed proton beams will bombard a Lead-bismuth eutectic (LBE) spallation target to produce neutrons. To design the target, the verification of target structural integrity is the primary task. For this purpose, firstly, cavitation damage caused by the negative pressure in LBE is an essential issue needs to be considered. In the present study, the possibility of cavitation damage occurrence caused by pressure waves and turbulent LBE flow was investigated for the TEF-T LBE target through the numerical simulations. Results show that the maximum expansion ratio of cavitation bubble is only 1.2 due to the pressure waves, so that severe cavitation damage will not occur due to the pressure waves; the maximum negative pressure due to the turbulent LBE flow is only -4.5 kPa on a steady-state flow condition, which is too small to drive the growth of bubbles, so neither cavitation damage will occur due to the turbulent LBE flow. Secondly, the LBE flow behavior needs to be investigated because it determines the temperature distribution on the LBE target vessel, which affects the integrity of the target vessel. The CFD analyses have been carried out to study LBE flow pattern. However, some stagnant regions exist in the LBE for the original target design. To solve this problem, the target head was modified to reduce the stagnant region effectively and efficiently. The CFD analyses results showed that the stagnant region has been effectively reduced due to the modification of target head. As a result, thermal-hydraulic and structural analyses results showed that the maximum temperature on the LBE vessel is decreased by 35 degree centigrade, and the maximum thermal stress on the BW has been decreased by approximately 31 MPa. The safety margin of target has been improved.