Arbitrarily large neutron amplification in subcritical nuclear reactors

TL;DR

This paper proposes methods to achieve arbitrarily large neutron amplification in subcritical reactors with keff less than 1, enabling high power output from faint neutron sources through a multi-layer system verified by simulations.

Contribution

It introduces novel strategies to exploit the independence of output power from keff and source intensity in subcritical reactors, enabling large neutron amplification.

Findings

Demonstrated arbitrarily large neutron amplification with keff=0.97

Verified amplification strategies using Monte-Carlo simulations

Showed potential for low-source-power reactor operation

Abstract

In a subcritical reactor, each neutron produces only keff < 1 neutron per generation (asymptotically and on average), and thus the neutron population decreases exponentially in the absence of external source. The chain reaction is thus easy to stop, making such reactors inherently stable. Interestingly, and contrary to common wisdom, there is no relation between keff, the external source intensity, and the output power of the reactor. In this paper, I present various possible strategies to exploit this fact, and apply them to the design of a rudimentary multi-layer system that allows to reach an arbitrarily large number of fissions per source neutron, while keeping keff < 1 fixed (I used keff=0.97). The behavior of the amplifier is verified with simple Monte-Carlo transport simulations. The proposal admittedly brings complications and subtleties that need to be studied further, but, if developed, could allow to drive subcritical reactors with faint neutron sources, e.g. radioisotope based.