Reactivity oscillations and stability with delayed neutrons

The generalization in reactor kinetics problems that the addition of delayed neutron effects leads to greater stability in the system is challenged. An example is the problem of the oscillation of reactivity, say a control rod, in a reactor described by a lumped neutron model without feedback. Two exact solutions of this problem by previous authors have shown that at zero mean reactivity there is a steady upward drift of the mean neutron level. These solutions are laborious to develop, however, and a more easily handled approximate method which shows the same effect has been given by a third author. It involves a prompt jump approximation with oscillating reactivity and a single precursor group. The present paper contributes a simplification of the integration needed to obtain the result. (UK)