Nuclear fission reactors require the presence of a neutron moderator in order to sustain a chain reaction, as it slows down neutrons sufficiently in order for them to be absorbed by fuel (e.g. U-235) nuclei. While moderation is a consequence of interactions or ''collisions'' between neutrons and nucleons and is a process which occurs at the length scale of atomic nuclei, atoms are in most cases parts of larger molecules, which might in general have an anisotropic structure. Therefore, one would expect that when examining the problem of neutron transport on the molecular length scale, neutron transport and moderation are influenced by the molecular structure, since there exists an ''average/overall'' molecular scattering cross section. Furthermore, if all of the moderator molecules in some volume of space are aligned in a certain direction, one would expect the anisotropy to be also exhibited at macroscopic length scales.
Therefore, I'm interested by the following:
- Does molecular strucure and its anistropy directly influence nuclear moderation (is this statement true)?
- If the moderator is anisotropic on a macroscopic length scale, does this influence reactor operation (assuming a reactor architecture similar to usual BWR or PWR reactors)?
- Would there exist any benefits to the performance of a nuclear reactor if macroscopic moderation properties (cross section) can somehow by manipulated or tuned during operation?
I have previously come across the following articles: ''The Effect of Anisotropic Scattering Upon the Elastic Moderation of Fast Neutrons'' (https://www.tandfonline.com/doi/abs/10.13182/NSE71-A19668) and ''The Effect of Linearly Anisotropic Neutron Scattering on Disatvantage Factor Calculations'' (https://www.researchgate.net/profile/C_Siewert/publication/242048056_EFFECT_OF_LINEARLY_ANISOTROPIC_NEUTRON_SCATTERING_ON_DISADVANTAGE_FACTOR_CALCULATIONS/links/554350cd0cf24107d3949fc8.pdf), which discuss anisotropic scattering, but as far as I gathered it concerns anisotropy on the length scales of atomic nuclei, so I'm not entirely sure of the articles' relevance.