We have investigated the status of the nuclear debris in the Unit-2 Nuclear Reactor of the Fukushima Daiichi Nuclear Power plant by the method called Cosmic Muon Radiography. In this measurement, the muon detector was placed outside of the reactor building as was the case of the measurement for the Unit-1 Reactor. Compared to the previous measurements, the detector was down-sized, which made us possible to locate it closer to the reactor and to investigate especially the lower part of the fuel loading zone. We identified the inner structures of the reactor such as the containment vessel, pressure vessel and other objects through the thick concrete wall of the reactor building. Furthermore, the observation showed existence of heavy material at the bottom of the pressure vessel, which can be interpreted as the debris of melted nuclear fuel dropped from the loading zone.

中文翻译：

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宇宙μ子射线照相法对福岛第一核电站2号机组状态的调查

我们通过称为宇宙μ子射线照相术的方法调查了福岛第一核电站2号机组核反应堆中核碎片的状况。在这次测量中，μ 子探测器被放置在反应堆建筑物的外面，就像对 1 号机组反应堆的测量一样。与之前的测量相比，探测器的尺寸缩小了，这使我们能够将其放置在更靠近反应堆的位置，并特别是研究燃料装载区的下部。我们通过反应堆建筑物的厚混凝土墙识别出反应堆的内部结构，如安全壳、压力容器和其他物体。此外，观察显示压力容器底部存在重物，