Chapter 31, Problem 11Q

To determine

A reactor that uses highly enriched Uranium can use ordinary water (instead of heavy water)as a moderator and still have a self-sustaining chain reaction. Explain.

Answer to Problem 11Q

Solution:

Yes, a reactor that uses highly enriched Uranium can use ordinary water (instead of heavy water)as a moderator and still have a self-sustaining chain reaction. This is because the highly enriched Uranium has a large number of neutrons as compared to ordinary Uranium. Even though the ordinary water absorbs more neutrons as compared to the heavy water but the chain reaction is still self-sustaining because of the large number of neutrons in the highly enriched Uranium.

Explanation of Solution

Heavy water is used as a moderator in nuclear reactors.Heavy water captures fewer neutrons as compared to the ordinary water and is thus more effective in controlling the chain reaction if the fuel is not too enriched. Highly enriched Uranium has a large number of neutrons as compared to ordinary Uranium. Even though the ordinary water absorbs more neutrons as compared to the heavy water but the chain reaction is still self-sustaining because of the large number of neutrons in the highly enriched Uranium. Thus, a reactor that uses highly enriched Uranium can use ordinary water (instead of heavy water)as a moderator and still have a self-sustaining chain reaction.