Payamara - Islamic Azad University, Shahre-Rey Branch, Iran TShahed University

In the calculations and the considerations of the conclusions made from the Reactors orBasic Reactors we may talk of compression which indicates the condition and also somecoefficients which likely or not are needed, likethfwhich is the ratio of the flux of the fastneutrons to the flux of the Thermal neutrons and is in some special conditions greater that1, andthrfr which is the ratio of the effect of returning the fast neutrons to the Thermalneutrons and is smaller than zero and comes back in the reactor core with a minuscoefficient in the positive direction. This means that the moderator slows down the fastneutrons within the reactor core. These ratios have been calculated.