UPSC Prelims Practice Questions — The Nazi nuke: Werner Heisenberg was more off target than he believed

Q1. With reference to the neutron multiplication factor (k) of a fission reactor, consider the following statements: Which of the statements given above is/are correct?

1. When the multiplication factor equals one, the reactor's power output stays steady.
2. A power reactor in normal steady operation is kept supercritical so that its output remains constant.
3. When each generation produces fewer fission neutrons than the one before, the chain reaction gradually dies away.

• A. 1 and 3 only
• B. 1 only
• C. 1, 2 and 3
• D. 2 and 3 only

Q2. A fission reactor is operating at a steady power level. Its operators then insert the cadmium control rods further into the core. Which one of the following is the most likely immediate consequence?

• A. More neutrons are absorbed, so k rises above one and power output climbs
• B. Neutron absorption stays unchanged, so k remains at one and power output holds
• C. More neutrons are absorbed, so k falls below one and power output declines
• D. More neutrons are slowed down, so k rises above one and power output climbs

Q3. Consider the following statements: Which of the following is correct in respect of the above statements?

1. Pressurised Heavy Water Reactors in the first stage of India's nuclear power programme run on natural uranium rather than enriched uranium.
2. In a Pressurised Heavy Water Reactor, heavy water is the fuel, and its deuterium nuclei undergo fission to release energy.

• A. Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
• B. Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
• C. Statement-I is correct, but Statement-II is incorrect
• D. Statement-I is incorrect, but Statement-II is correct