Neptunium Holdup

Calculations of the reactivity gains In a reactor due to plutonium buildup assume Instantaneous formation of plutonium. The fact that plutonlum-239 formation Is delayed throuc the beta-decay of 2.33 day neptunium-239 makes It necessary to correct the calculated reactivity gains. This Is most conveniently done by assigning a reactivity loss for the neptunium holdup effect. The equilibrium neptunium holdup defect Is. 41 k. 

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