1. Fertile meaning the none fissionable uranium 235. 丰富的意思是裂变的铀。
2. The isotope of uranium with mass number235, fissionable with slow neutrons. 锕铀铀的同位素，原子质量数为235，与慢。
3. 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。
4. 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。
5. There also need to be enough fissionable atoms about for the neutrons to bumpinto—in other words, a critical mass. 同时还需要足够多的、可裂变的原子核用于中子进行撞击，换句话说，需要一个临界质量。
