Comparing the Neutronic Behavior of LR-0 reactor During the First 20 Shakes ‎from Startup When Controlled by Boron vs. Silver Control Rods

Buildup of neutron flux in moderator and neutron absorption in control rods of ‎LR-0 reactor, which is a mockup of the Russian PWR WWER-400 were ‎investigated over the first 200 nano seconds from reactor startup when ‎controlled by Boron only, Silver only, and mixed Boron & Silver control rods. ‎Calculations were carried out using MCNP5 code. Three models of LR-0 reactor ‎were studied. One model was controlled by Boron control rods only, another ‎model were controlled by Silver control rods only, and a third model was ‎controlled by equal numbers of identical Boron and Silver control rods. In each ‎model, the buildup of neutron flux in moderator, and the neutron absorption in ‎control rods were tallied. Profile of change of neutron absorption in control rods ‎with time was significantly different in the three models. However, neutron flux ‎buildup in moderator was almost unaffected by the type of control rods. Also, ‎energy spectrum of the absorbed neutrons in all models was almost the same, ‎signifying that spectrum of absorbed neutrons in control rods is not dependent ‎on the type of control rod material. ‎