Reactor supplementary reactivity control

Reactivity Control. The movable boron-carbide control rods are sufficient to provide reactivity control from the cold shutdown condition to the full-load condition. Supplementary reactivity control in the form of solid burnable poison is used only to provide reactivity compensation for fuel burnup or depletion effects. The movable control rod system is capable of bringing the reactor to the subcritieal when the reactor is an ambient temperature (cold), zero power, zero xenon, and with the strongest control rod fully withdrawn from the core. In order to provide greater assurance that this condition can be met in the operating reactor, the core is designed to obtain a reactivity of less than 0.99, or a 1% margin on the stuck rod condition. See Fig. 7. 

Answer It can be re-otorted almost too easily. Additional control is necessary to keep the reactor subcrltlcal during the outage and provide supplementary reactivity control so that the safety rods may be wlthdrawTi and the pile re-startod. 

The cold or hot reactivity of the water-cooled loading Is not to exceed the coinblned negative reactivity worth associated with the Horizontal Control Rod System the xenon present In the reactor Inserted supplementary control devices and the poison pieces or poison columns under Irradiation. That Is the reactivity In excess of that coiqpensated by Inserted supplementary and permanent poisons Is not to exceed the strength of the Horizontal Control Rods, 1 5 per cent k/k In the... 

Supplementary control In the operating reactor shall be limited In use to compensate for not more than i4>.0 per cent excess reactivity. Supple-... 

Answer After about two days the reactivity gain will exceed the capacity of the horizontal rod system in the older piles, and the reactor must be kept subcrltlcal with the vertical safety rods and/or supplementary control or temporary poison. 

Reactivity Transient - The variation of available excess reactivity with time. Since the iiactor is normally operated with a nearly constant power level (tha.t is, Kex equal to 1.000) the reactivity transient is the variation with time of the amount of control red, plus any supplementary control in the reactor. 

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