Sodium would be at unrealistically high pressures to keep it liquid. Due to being above its critical temperature, sodium would also lose its thermal conductivity, which is the reason for its use.
IIRC, Liquid Lithium would be an ideal coolant for non-liquid pellet (probably Civillian) designs; critical point ~3200k, even lighter and thermally superior to sodium.
For minmaxed (military) ships, we'd use TaHfC kernels with liquified uranium (or plutonium, or whatever is optimal when we take melting points out of the consideration) metal cores and operate at 4200k core temp - a nice 200k away from meltdown! Then we can jack up the output to 3300-3500 and save radiator area. If we want a low pressure reactor (TaHfC has average structural properties) we'd probably use liquid Niobium or something as the coolant.
Pretty heavy, but the 'giant cylinder of reactor coolant' design in CoADE is a little unrealistic!
Less than half fission neutrons are fast. However, since I don't have anything more concrete than "less than half", I'll have to be conservative and consider that the neutron flux is twice the fast neutron flux:
3.47E+14 n/(m2·s) · 2 = 6.93E+14 n/(m2·s)
This value is log10(1.00E+16/6.93E+14) = 1.159 orders of magnitude inferior to the minimum allowed by the game limits. A neutron flux so low seems to be in accordance with the links I posted two posts above.
Assuming that 3.50E+23 n/m2 is the maximum fast neutron fluence before the reactor reaches EOL, the years a reactor can operate at full power given a certain neutron flux is calculated as fast neutron fluence over fast neutron flux:
Conversely, the neutron flux of a reactor that has to operate for a certain amount of years is twice the fast neutron flux, which in turn is calculated as fast neutron fluence over time (this formula can also be extrapolated from the one above):