The number of neutrons produced in one generation divided by the number in the generation before, accounting for leakage and all absorptions. A value of exactly 1 means critical, below 1 subcritical and above 1 supercritical. Criticality safety calculations for fuel storage and transport must show k-effective stays below an administrative margin such as 0.95 under normal and credible abnormal conditions, including uncertainties.
Rack analysis gives k-effective of 0.93 with the pool fully unborated, so we've still got margin to 0.95.
Also heard as
- keff
- k-eff
- effective multiplication factor
Related terms
Criticality
The state in which a chain reaction sustains itself at a steady rate, with each fission causing on average exactly one more.
Reactivity
A measure of how far a reactor is from criticality, positive when power will rise and negative when it will fall.
Criticality safety
The discipline of preventing an accidental chain reaction wherever fissile material is handled outside a reactor.
Poison
Any material that absorbs neutrons strongly, whether added deliberately for control or produced by fission.