4 (20 points) (a) What's the difference between a "thermal reactor" and a "fast reactor"? ( 5 points) (b) What is the primary reason for neutrons to slow down in a reactor? (5 points) (c) What are "BWR" and "PWR"? What's their difference? (5 points) (d) Name one so-called advanced reactor. Briefly explain how it works. (5 points) 4 (20 points) (a) What's the difference between a "thermal reactor" and a "fast reactor"? ( 5 points) (b) What is the primary reason for neutrons to slow down in a reactor? (5 points) (c) What are "BWR" and "PWR"? What's their difference? (5 points) (d) Name one so-called advanced reactor. Briefly explain how it works. (5 points)