RRB RPF RPSF SI and CONS Model Papers 10 with solutions

(3) Nuclear reactors function by delaying (moderating) the fastest neutrons or increasing the proportion of fissile atoms.
To slow these neutrons, called slow neutrons, a moderator such as graphite is needed. Commonly-used moderators include regular (light) water (in 74.8% of the world’s reactors), solid graphite (20% of reactors) and heavy water (5% of reactors.