Environment & Energy
In reply to the discussion: I have a question about nuclear weapons. Anyone here know much about them? [View all]
PamW
(1,825 posts)NO - the borated steel is actually MORE EFFECTIVE that control rods.
A single fuel assembly can't sustain a chain reaction by itself. You can only get a chain reaction if more than one fuel assembly "share" or pass neutrons among themselves. If you can totally block the neutron exchange between assemblies, then you can defeat crititcality.
Imagine we have some dark cloth and our object is to block light from traversing through the fuel assembly. What is the best way to make use of that black cloth.
Suppose we took our black cloth and rolled it into several tubes and put those tubes in amongst the fuel rods. Well that would block light, but only light whose path took it through the black cloth tubes.
Suppose we took our black cloth and made drapes that we put on the north, south, east, and west sides of the fuel assembly. Any light that is attempting to cross the fuel assembly in the horizontal plane has to encounter our black cloth drapes and will be absorbed.
A "curtain" on the surface is MUCH, MUCH more effective than rods. In fact, in the reactor you actually want to minimize the effect of a given rod so that if that rod were ejected the reactivity swing would be manageable. The reactor relies on having a great number of rods for control. Additionally PWRs put boric acid in the coolant water.
A solid curtain like the racks that EVERY SINGLE spent fuel pool has is MUCH, MUCH more effective than rods as the above analogy shows.
PamW
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