In a hole in the center of this system is placed a subcritical sphere of fissionable material . 在这个系统的中心圆洞中放置一枚次临界的球形可裂变物质。
2.
The reaction is slowed by a combination of depletion of the fissionable material and expansion of the core . 由于裂变物质的耗尽以及由于核心的膨胀，才使反应减慢下来。
3.
Operations with fissionable materials outside reactors , nuclear criticality safety in 外部反应堆可裂变材料的核临界安全性操作
4.
The fissionable material defined by the preceding paragraph should be reported to the atomic energy council once every half - year 前项可分裂物质，应每半年向原子能委员会申报一次。
