Asked by  | 21st Mar, 2009, 11:05: AM

Expert Answer:

In a nuclear reactor, the neutron population at any instant is a function of the rate of neutron production (due to fission processes) and the rate of neutron losses (via non-fission absorption mechanisms and leakage from the system). When a reactor’s neutron population remains steady from one generation to the next, the fission chain reaction is self-sustaining and the reactor’s condition is referred to as "CRITICAL". When the reactor’s neutron production exceeds losses, characterized by increasing power level, it’s called "SUPERcritical", and; when losses dominate it’s "SUBcritical" & exhibits decreasing power.

The "six-factor formula" is the neutron life-cycle balance equation, which includes six separate factors, the product of which is equal to the ratio of the number of neutrons in any generation to that of the previous one; this parameter is called the effective multiplication factor (k), a.k.a. Keff. k = LfρLthfηЄ, where Lf = "fast non-leakage factor"; ρ = "resonance escape probability"; Lth = "thermal non-leakage factor"; f = "thermal fuel utilization factor"; η = "reproduction factor"; Є = "fast-fission factor".

k = (Neutrons produced in one generation)/(Neutrons produced in the previous generation) When the reactor is critical, k = 1. When the reactor is subcritical, k < 1. When the reactor is supercritical, k > 1.

Answered by  | 28th Mar, 2009, 06:27: PM

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