There already exist better solutions for the primary circuit than using steam, e.g. using supercritical carbon dioxide in a closed cycle. This allows the operation of the reactor at higher temperatures, while also increasing the efficiency of the heat transfer in the heat exchangers, which increases the overall energy efficiency. Moreover, this also greatly reduces the size of all components (which however must operate at much higher pressures than with steam, because that is the reason for the great reduction in size).

Making very big heatsinks to radiate all the heat from a nuclear reactor will not be a problem on Mars or Moon, as long as the metal, e.g. aluminum, is extracted locally. One will have no neighbors and no need to buy real estate, so any amount of land area can be used without restrictions.