A reactor and a reactor system for carrying out high temperature and high pressure reactions is disclosed herein. The reactor has an isolatable inner vessel for allowing for heat energy efficient cooling and heating of the reactor. The reactor comprises an outer reactor adapted for withstanding a reaction pressure and a reaction temperature, the outer reactor having a sealable reactor lid; an inner vessel within the outer reactor for containing a reaction solution and at least one reaction vessel, the inner vessel being open to the outer reactor such that the reaction pressure of the inner vessel and the outer reactor are substantially equalized and vapor in the inner vessel passes to the outer vessel, the inner vessel having a splatter shield for substantially preventing spillage of the reaction solution from the inner vessel into the outer reactor; a vapor injector in communication with the inner vessel for injecting vapor into the inner vessel for heating the reaction solution; an outlet in the outer vessel for exhausting vapor from the outer reactor and the inner vessel; and an outer reactor outlet for draining a liquid contained between the outer reactor and the inner vessel.