# Nuclear Fission Lab

Fission: One Nucleus:

Select the “Fission: One Nucleus” tab at the top left.  Experiment with shooting the neutron gun and watching what happens.  Then answer the questions below.

1)    What happens when the U-235 nucleus is “hit” with a neutron?  There are two steps here- describe them both in as much detail as you can.

Once the neutron is shot, then the U-235 turns into U-236, starts shaking and splits into two parts which are the daughter nuclei and loses 3 neutrons.

Chain Reaction:

Select the “Chain Reaction” tab at the top.  Experiment with changing the settings and shooting the neutron gun and watch what happens.  Then answer the questions below.

2)    Set the initial number of U-235 nuclei to 100.  What happens when you fire the neutron gun?

When I fire the gun, the neutron is let out, hitting a U-235 which splits then the daughter nuclei of that hits another U-235 splitting that into 2 daughter nuclei and so on.

3)    Explain what makes this a “chain reaction”.

This is a chain reaction because the reaction of one U-235 nuclei getting hit effects another and that one effects another and so on.

4)    Set the initial number of U-238 nuclei to 100.  Explain what happens when you fire the gun and if this is a chain reaction or not.

This is not a chain reaction because once one U-238 is hit, that reaction doesn’t effect any other nuclei.

5)    Set the initial numbers of U-235 nuclei and U-238 nuclei to the numbers in the table below.  Record your results.

U-235   U-238      % of 235U fissioned after 1 firing   # firings required to                                                                                             fission all 235U

100          0             98%                                                       2

70           30            98%                                                       3

50           50            1%                                                         12

30           70            36%                                                       13

0             100           0%                                                        N/A

6)    What happens to the reaction as the proportion of U-238 nuclei increases?

After the proportion of U-238 nuclei increases, then it decreases the chances of the U-235 nuclei to get hit. It also makes it harder to hit them because the U-238 nuclei get in the way and stop the neutrons from passing.

7)    If you were trying to design the most efficient fission reactor possible, what ratio of U-235 to U-238 would you want?  Explain why. What if you were trying to design a nuclear weapon?

If I was trying to design a fission reactor, I would want about 70 U-235 and 30 U-238 because I wouldn’t be able to control the reactor if the whole reaction happened at once. If I was making a bomb, I would make it to be that there are no U-238 nuclei because I would want it to be all U-235 because the U-238 would get in the way of the reaction.

Nuclear Reactor:

Select the “Nuclear Reactor” tab at the top.  Experiment with changing the settings and firing the neutrons and watch what happens.  Then answer the questions below.

8)    The bar graphs on the right of the display show the “Power Output” and the “Energy Produced”.  What is the difference between these two quantities?

The power output is the amount of energy that is used and the energy produced is the product of how much power is put out.

9)    Watch very closely to the fission reactions as they happen.  Specifically watch what happens to the loose neutrons after the reaction.

a)  What happens if the neutrons hit another nucleus?

When the neutrons hit another nucleus, then there’s a chain reaction.

b)  What happens if the neutrons hit a control rod?

If it hits a control rod, then they just bounce off.

10)    Compare the chain reaction that occurs when the control rods are inserted further into the reactor versus when they are pulled all/mostly out of the reactor.

11)    If the purpose of a nuclear reactor in a power plant is to produce energy, why are there control rods?

There are control rods there so it doesn’t react all at once. When there are control rods there, then it makes it easier to control.