I'm a Nuclear Reactor Controller!

A simple, Monte Carlo style nuclear fission simulation.

Created by Dylan McCall (dylanmccall@gmail.com)

Finally, YOU can control a nuclear reactor!

With this power, you can finally learn how they harness nuclear fission without that terrifying risk of blowing up the neighbourhood.

This is a very simple simulation, designed to highlight the fundamentals. I hope it can be a helpful toy for someone just beginning to learn about nuclear fission.

This is open source software. Source code is provided under the Mozilla Public License.



Zip archive of executable and source files: NuclearReactorSim.zip

Installer: NuclearReactorSim.exe

Play on Pjio.com


First, follow the on screen instructions to open a scene of your choosing. They are all slightly different, so be sure to read their descriptions as well!

You should now see an image in the main window containing various coloured rectangles. This is a visualization of the reactor core you are controlling.

It is possible to manipulate the scene using the buttons on the side bar:

Add Neutron Source

Pressing this button will add an object which continually emits fast neutrons. Press it again to remove the object.
The fast neutrons will need to be slowed down before they will be useable for fission; this is performed by a Moderator, which in this case is regular water.
Note: Once a reaction is stable, the neutron source can be removed; fast neutrons are produced by each fission reaction with the fuel, which causes the reaction to sustain itself. Often, the neutron source only has to stay on in time for one or two fissions to occur.

Control Rods

So far, our reaction has not been very successful; fast neutrons are emitted by the neutron source and slowed down into slow (or "thermal") neutrons, but then they mostly disappear.
This is because the control rods are still lowered.
Control rods are used to control a reaction by absorbing slow neutrons before they make contact with the fuel rods.
Raise the control rods using the arrow buttons on the side bar or by typing a percentage into the text box in the "Control Rods" section. Now, more slow neutrons are making contact with fuel rods and performing fission.
At this point, you have probably accomplished a chain reaction. Try removing the neutron source and the reaction should continue on its own.

Simulation Speed

You can adjust the simulation speed using this slider in order to view details in slow motion, or to view the reaction at a higher speed.


SCRAM is an acronym for "Safety Control Rod Axe Man". In the first nuclear reactor experiments, control rods were suspended by ropes and in the event of an emergency these ropes would be cut, causing the control rods to fall back into place.
Obviously we have come a long way since then, but the expression is still used today.
Pressing the button will lower the control rods to their lowest position, which helps to slow down, and eventually stop, the reaction.
It is important to use control rods in order to limit the reaction, as producing too much energy can lead to a meltdown. If they are too hot, components of the reactor will melt. Naturally, such damage leads to all sorts of issues, all of which are very bad.

Remove Moderator

Press this button to drain the moderator fluid. You will notice that fast neutrons are no longer transformed into slow neutrons, causing the reaction to very quickly come to a halt.