ABSTRACT Neutron flux per pulse reached world record at neutron source in Japan Proton Accelerator Research Complex (J-PARC). In the J-PARC, mercury target system is used as a spallation neutron source. A target vessel has a multi-walled protection system that comprises a mercury vessel enclosed with a double-walled water shroud. This is to prevent the leakage of the mercury outside the target vessel. The multi-walled structure needed to be complicated with a lot of welding lines. However, during the operation, we faced an unscheduled shutdown due to water leakage to the intermediate layer between the mercury vessel and water shroud. An investigation on the cause of the leakage was carried out. It is deduced that the leakage path was formed due to the crack propagation from welding defects that are caused by the complicated multi-walled structure. The crack propagation is attributed to the repeated stress by pressure waves generated in the mercury target. Based on the investigation results, the design was improved to remove the welding line on the complicated structure and to realize the stable operation with 1 MW proton beam, which is the final design value of the neutron source in J-PARC.

中文翻译：

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焊接缺陷导致的漏水和改进以达到 J-PARC 汞目标中的 1-MW 光束运行

摘要 日本质子加速器研究中心（J-PARC）的中子源每脉冲中子通量达到世界纪录。在 J-PARC 中，汞靶系统用作散裂中子源。目标容器具有多壁保护系统，该系统包括用双壁水罩封闭的水银容器。这是为了防止汞泄漏到目标容器外。多壁结构需要复杂的焊接线。然而，在操作过程中，由于水泄漏到汞容器和水罩之间的中间层，我们面临计划外停机。对泄漏原因进行了调查。推断泄漏路径是由复杂的多壁结构引起的焊接缺陷引起的裂纹扩展形成的。裂纹扩展归因于汞靶中产生的压力波的重复应力。根据调查结果，对设计进行了改进，去除了复杂结构上的焊缝，实现了1 MW质子束稳定运行，这是J-PARC中子源的最终设计值。