Remark on the neutron noise induced by propagating perturbations in an MSR

•Neutron noise due to propagating perturbations in 1D model of a MSR is studied.•The investigation is performed using 1 and 2 energy group diffusion theory.•The effect of the perturbation on several cross-sections and fuel velocity is accounted for.•New features concerning the Green’s matrix, noise structure and induced noise are discussed.•The difference with similar investigation in LWRs is also pointed out.

The neutron noise induced by propagating perturbations in a simple model of a Molten Salt Reactor (MSR) is calculated and analyzed using one/two-group diffusion theory. The novelty, as compared to previous works, is that the noise source includes also the fluctuations of the fission cross sections and the fluid velocity, in addition to the previous case when only the fluctuations of the absorption cross section were accounted for. Another novelty is that the solution is obtained through the matrix Green’s function of the flux and precursor equations, these two being kept separate. Inclusion of each of these two new noise sources leads to a structure of the noise source, and hence also that of the neutron noise, which is conceptually different from the case when only the fluctuations of the absorption cross sections are treated, with some surprising features. The use of the matrix Green’s function is advantageous to understand the new features, and it helps to point out some new aspects of the neutron noise even in traditional systems, which have not been noticed before. The results contribute to the understanding and interpretation of the neutron noise in MSRs.