Heavy water as fission moderator and coolant

[xeryuswil]

Describe the feature you'd like

Have the option to increase reactivity in the fission reactor by using heavy water as a coolant instead of normal water. Heavy water acts as a better moderator than normal light water meaning neutrons are slowed even more increasing reactivity.

Leave the option to use normal water as a coolant.

Describe alternatives you've considered

No response

Additional context

"A reduced-moderation lattice and heavy-water coolant are used to yield an epithermal-to-fast neutron spectrum, which is beneficial for attaining a large conversion ratio and reducing the burnup reactivity swing throughout the core lifetime."

https://www.sciencedirect.com/science/article/abs/pii/S0306454920306423 https://www.sciencedirect.com/science/article/abs/pii/S0306454906000478 https://arxiv.org/abs/physics/0206076 https://www.sciencedirect.com/science/article/abs/pii/S0969804315000676 https://onlinelibrary.wiley.com/doi/abs/10.1002/er.4827 https://www.osti.gov/etdeweb/biblio/22270260

[xeryuswil]

Heavy water also naturally does not absorb as many neutrons as light water which further increases reactivity.