Thought Of The Day 2.0

Reactivity Coefficients


The amount of reactivity (r) in a reactor core determines what the neutron population, and consequently the reactor power, are doing at any given time. The reactivity can be affected by many factors for example, fuel depletion, temperature, pressure, or poisons. To quantify the effect that a variation in parameter which is, increase in temperature, control rod insertion, increase in neutron poison will have on the reactivity of the core. Reactivity coefficients are the amount that the reactivity will change for a given change in the parameter. For instance, increases in moderator temperature will cause a decrease in the reactivity of the core. The amount of reactivity change per degree change in the moderator temperature is the moderator temperature coefficient. Reactivity coefficients are generally symbolized by (ax) where x represents some variable reactor parameter that affects reactivity.

Example 1

Example 1 shows the effect of a relatively large initial reactivity, ignoring several important limiting effects, leading to a rapid rise to a "blowup." The unacceptable behavior which would result from a continuation of this exponential response is modified in real reactors by two important effects.

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