Composition fluctuations arising from thermal effects are known to influence the spinodal decomposition in concentrated alloys. However, at very low temperatures these effects slow down because of the very small diffusion rates. This paper examines the possibility of having such fluctuations induced by radiation via the fluctuations in the supersaturated defect concentration. Various mechanisms are discussed. In particular, it is shown that the interstitial exchange with lattice atoms combined with diffusion leads to fluctuations that grow linearly with time. An estimate of this effect indicates that it has a significant contribution to the decomposition of an alloy. A detailed mathematical analysis of the phenomena is presented and application to some alloys that show spinodal like decomposition during irradiation is discussed.