Neutron fluctuations: the importance of being delayed

TL;DR

This paper demonstrates that delayed neutrons, despite their small proportion, significantly influence neutron fluctuations and spatial clustering in nuclear reactors, highlighting their critical role in reactor stability.

Contribution

It reveals the crucial impact of delayed neutrons on neutron fluctuation dynamics and spatial clustering, emphasizing their importance in reactor operation models.

Findings

Delayed neutrons effectively quench spatial clustering.

Neutron fluctuations are significantly affected by delayed neutron contributions.

Delayed neutrons play a key role in reactor stability.

Abstract

The neutron population in a nuclear reactor is subject to fluctuations in time and in space due to the competition of diffusion by scattering, births by fission events, and deaths by absorptions. As such, fission chains provide a prototype model for the study of spatial clustering phenomena. In order for the reactor to be operated in stationary conditions at the critical point, the population of prompt neutrons instantaneously emitted at fission must be in equilibrium with the much smaller population of delayed neutrons, emitted after a Poissonian time by nuclear decay of the fissioned nuclei. In this work, we will show that the delayed neutrons, although representing a tiny fraction of the total number of neutrons in the reactor, have actually a key impact on the fluctuations, and their contribution is very effective in quenching the spatial clustering.