An examination of the structural integrity and defects of a fabricated mercury target vessel for Japan Proton Accelerator Research Complex (J-PARC) spallation neutron source is presented. Ultrasonic testing (UT) and radiographic testing (RT) were employed as nondestructive inspection methods. The mercury target vessel is composed of SUS316L stainless steel and was designed with multi-walled structures consisting of double-guard vessels with thin walls of 3-mm thickness and assembled by tungsten inert gas welding. The mercury target vessel has complex characteristic, and the weld defect for the thin walls is often very difficult to detect using conventional UT techniques. To overcome this barrier, we employed two new UT techniques, namely 1) immersion ultrasonic with a 50-MHz ultrasonic probe and 2) phased arrays ultrasonic with the full matrix capture (FMC) and the total focusing method (TFM). The examination revealed the formation of small defects and cracks wherein the wall thickness was less than 6 mm. Therefore, new UT techniques are useful for evaluating the structural integrity and defects of the new fabricated mercury vessels.

The design and the fabrication process of the mercury target vessel was also evaluated and improved in this study. The use of wire electric discharge machining (EDM) in the fabrication process is desirable to reduce the amount of welding and subsequent welding deformation. The roughness and chemical compositions of the processed surface layer by wire EDM were also examined. The oxide layer was perfectly removed by two-step chemical polishing, and the chemical composition of the layer was analyzed using energy dispersive X-ray spectrometry. In addition, the surface roughness was reduced after polishing to enhance fatigue life and minimize internal defects caused by welding.

介绍了对日本质子加速器研究中心（J-PARC）散裂中子源制造的汞靶船的结构完整性和缺陷的检查。超声波测试（UT）和射线照相测试（RT）被用作无损检查方法。汞靶容器由SUS316L不锈钢组成，并设计成多壁结构，该结构由厚度为3毫米的薄壁双层保护容器组成，并通过钨极惰性气体保护焊组装。汞靶容器具有复杂的特性，薄壁的焊接缺陷通常很难使用常规UT技术检测到。为了克服这一障碍，我们采用了两种新的UT技术，即1）使用50-MHz超声探头的浸入超声，和2）具有全矩阵捕获（FMC）和总聚焦方法（TFM）的相控阵超声。检查发现形成了小的缺陷和裂纹，其中壁厚小于6mm。因此，新的UT技术可用于评估新制造的汞容器的结构完整性和缺陷。

在这项研究中，还对汞靶容器的设计和制造过程进行了评估和改进。为了减少焊接量和随后的焊接变形，在制造过程中使用电火花线切割加工（EDM）是理想的。还检查了通过电火花线切割加工的表面层的粗糙度和化学成分。通过两步化学抛光完美地去除了氧化物层，并使用能量色散X射线光谱分析了该层的化学成分。另外，抛光后降低了表面粗糙度，以延长疲劳寿命并使焊接引起的内部缺陷最小化。