221. A heterogeneous reactor is the one, in which the moderator and the

coolant are different materials.
coolant are present in different phases (e.g., heavy water and graphite).
fuel are present in different phases (e.g. uranium and heavy water).
none of these.
✅ The correct answer is option C.

226. Nuclear fuel generally used in reactors is uranium oxide instead of uranium, because the former has higher

melting point, hence can be subjected to higher temperature.
density ; hence core volume for a given power output would be smaller.
resistance to effects of irradiation.
all (a), (b) and (c).
✅ The correct answer is option D.