This is an active nuclear reactor, and down there are uranium fuel rods undergoing fission reactions.

这是一个活跃的核反应堆，下面是正在进行裂变反应的铀燃料棒。

Uranium fuel rods contain tiny pellets of specially prepared uranium encased in a sheath of zirconium alloy.

铀燃料棒含有若干微型特制铀芯块，这些芯块被包裹在锆合金护套里。