No progress yet on the NTR calculations, can dive into the SciLab calculations soon. The main problem with the fuel flow is the effectivity at which heat from the reactor can be transfered into the propellant and the required length of the reactor core. The reactor geometry might become very ineffective in terms of neutron flux and thus reactivity. If not used as NTR, the smallest flown space reactor had 30 kW thermal power, about half of your NTR.