Consider the modified rocket equation that takes into account the parasitic weight of the nuclear reactor and its associated shielding.
Where,
ML = Payload mass
M0 = Initial mass
∆v = total change in spacecraft velocity for a given engine firing (burn)
ue = propellant exhaust velocity
tb = duration of a given burn
α = specific power (Mass of reactor and supporting equipment divided by available reactor power, P) typically in kg/kW or its equivalent
η = thrust chamber efficiency:
Determine the relative impact of the specific power and the efficiency on the delivered payload mass. (This is likely most easily done by differentiation and/or plotting the equation as a function of one or the other. In plotting, be sure to use reasonable values for both α and η)
Discuss ways in which α and η are coupled and also how one might be optimized without degrading the other.