ModeratorMaterialien

ModeratorMaterialien, often translated as moderator materials, are substances used in nuclear reactors to slow down fast neutrons. This process is crucial for sustaining a nuclear chain reaction, as most nuclear fuels, like uranium-235, are more likely to undergo fission when struck by slow, or thermal, neutrons. The act of slowing down neutrons is called moderation.

Common moderator materials include water (both light water and heavy water), graphite, and beryllium. Light water, composed of ordinary hydrogen and oxygen, is the most widely used moderator in the world, found in Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs). Heavy water, which contains deuterium instead of hydrogen, is also an effective moderator and is used in CANDU reactors. Graphite has been employed in early reactor designs and in some advanced gas-cooled reactors. Beryllium, while an excellent moderator, is less common due to its toxicity and cost.

The choice of moderator material depends on various factors, including reactor design, cost, availability, and safety considerations. A good moderator should efficiently slow down neutrons without absorbing too many of them, as neutron absorption can reduce the number of neutrons available to sustain the chain reaction. The moderating ratio, which is a measure of a material's effectiveness in slowing down neutrons relative to its absorption cross-section, is a key property considered in selecting moderator materials.