excess reactivity

excess reactivity

[′ek‚ses ‚rē·ak′tiv·əd·ē]
(nucleonics)
The amount of surplus reactivity over that needed to achieve criticality; it is built into a reactor (by using extra fuel) in order to compensate for fuel burnup and the accumulation of fission-product poisons during operation.
References in periodicals archive ?
The batch refueling design necessitates a large excess reactivity at beginning of cycle; therefore two reactivity control systems were designed for the Canadian SCWR.
For the initial core almost without burnup, if only the fresh fuel spheres with 8.5% enrichment are loaded, the excess reactivity will be too big to control.

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