In a hole in the center of this system is placed a subcritical sphere of fissionablematerial.
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 fissionablematerial 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
The ingenuity of our scientists will provide special safe conditions under which such a bank of fissionablematerial can be made essentially immune to surprise seizure.