Past exam of the MPhil in nuclear energy course of the University of Cambridge / 2019 / Module NE1 / 3 / b

At a steady state, all three accumulation terms vanish. The fuel balance gives $Q_{FM}=P$, the moderator balance then gives $Q_{MC}=P$, and the coolant balance equates that input to its advective output. ThereforeEach successive region adds the temperature drop needed to carry the same thermal power through its thermal resistance. Summing the original balances cancels both internal transfers, providing the independent total energy balance $P=W_C{c}_C(T_o-T_i)$.