On determination of βsub(eff) by the pulse neutron method

The method of determining effective share of delayed neutrons βsub(eff) by measuring prompt neutron decrement α is considered. The method is based on determination of prompt neutron criticality by extrapolating the reactivity dependence of α measured for subcritical states of a reactor to α=0. The effects of nonlinearity of the α dependence on the reactivity on the accuracy of βsub(eff) determination have been studied. An analytical expression to make corrections in the linear extrapolation is obtained. The sign and value of the correction are determined by neutron generation time variations, βsub(eff) and by the extrapolation range. Provided are examples of calculating the correction for different means of reactivity insertion in several reactor types. The application of linear extrapolation is shown to cause rather large errors in βsub(eff) determination -up to tens of per cent