Question

1.Which statement is true about nuclear fission or bombs?
A moderator slows down neutrons to make fission less likely.
The nuclear bomb dropped on Hiroshima in WWII was called Fat Man.  
A moderator slows down neutrons to make fission more likely.
The nuclear bomb in WWII that used ²³⁵U and a gun-type design was called Fat Man.
The maximum amount of fissile material that will sustain a chain reaction is called the critical mass.

Tries 0/2

The correct ranking of countries from highest to lowest for either their total nuclear power generation or for their percentage of electrical power from nuclear is:
Total nuclear power generation: France, U.S., China, South Korea
Percentage of electrical power from nuclear : South Korea, U.S., France, China
Total nuclear power generation: France, South Korea, U.S., China
Percentage of electrical power from nuclear : U.S., South Korea, France, China
Total nuclear power generation: U.S., France, China, South Korea

Which statement is true about a nuclear reactor?
Adding the moderator to the reactor slows down fission.
A sudden loss of primary coolant water in a pressurized water reactor slows down fission.  
Removing the control rods from the reactor slows down fission.
Removing the moderator from the reactor speeds up fission.
A sudden loss of primary coolant water in a pressurized water reactor speeds up fission.

Answer 1

1) The answer will be a moderator slows down neutrons to make fission more likely (Third option).

Explanation: The nuclear bomb that dropped on Hiroshima in WWII was called "Little Boy". So, we can ignore second option. The nuclear bomb in WWII that used 235U & a gun-type design was called "Little Boy". So, we can ignore fourth option. The minimum amount of fissile material that will sustain a nuclear chain reaction is called the critical mass. So, we can ignore last option. During nuclear fission, fuel atoms spilt its nucleus by absorbing neutron. To make this process continuous, fuel atoms must absorb neutron continuously. Now, there is a greater chance to absorb neutron(s) by fuel atoms if neutrons are going slow. Moderator slows the neutron speed. Thus, moderator helps to attain continuous nuclear fission process. So, correct answer will be third option.

2) The answer will be total nuclear power generation: U.S., France, China, South Korea (last option).

Explanation: US is the top producer in the world in terms of total nuclear power generation & France is ranked top in the world in terms of percentage of electrical power from nuclear source. Further, top six country in the world in terms of net nuclear power capacity are US, France, China, Japan, Russia & S. Korea. Among the given options only last option is correctly matched.

3) The answer will be a sudden loss of primary coolant water in a pressurized water reactor slows down fission (Second option).

Explanation: Adding the moderator to the reactor & removing the control rods from the reactor speeds up fission. So, we can ignore first & third options. Removing the moderator from the reactor slows down fission. So, we can ignore fourth option. Also, sudden loss of primary coolant water in a pressurized water reactor slows down fission. So, we can ignore last option. Thus, correct answer will be second option.