在棒的四周围着中子减速剂。

The rod is surrounded with a neutron-slower .

石墨是很好的减速剂，减慢中子并且让它们的反应保持在一个适当的温度范围内。

Graphite is a great moderator, slowing down the neutrons and keeping their reaction in the proper temperature range.

燃料棒放置在反应堆中心，核反应就在这里发生。速度和反应是由控制棒和减速剂来控制的。

The speed and reactions are controlled by control rods and a moderator.