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The Facility
Cooling
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Moderator
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Fuel
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Shielding
Control
<p>When the NRU reactor is operating, uranium atoms in the fuel are splitting apart. Each fission creates heat and two or three neutrons. These neutrons are slowed down as they pass through the heavy water in the core. A slow moving neutron can join another uranium atom causing it to split apart, and the process continues. To control the reaction, or stop it completely, rods of material that absorb neutrons are used. These can be raised and lowered into the core. If more neutrons are absorbed by the control rods, less are available for the fission reaction.</p> <p>Instruments measure the power of NRU. If the operator wants to raise the power, a control system raises the rods of neutron-absorbing material out of the core, less neutrons are absorbed, more are available for fission, so the power goes up. If the operator wants to lower the power, the control system lowers the rods of neutron-absorbing material into the core, less neutrons are available for fission, so the power goes down.</p> <p>To turn off the reactor completely, absorbers are lowered all the way into the core. Very few neutrons are left in the core and so the fission reaction stops.</p>
