Remark on the neutron noise by propagating perturbations in a MSR

Paper in proceeding, 2014

The neutron noise induced by propagating perturbations in a bare 1-D Molten Salt Reactor (MSR) model is calculated and analyzed using one-group diffusion theory. The neutron noise for different noise sources of which two have not been accounted for, corresponding to the fluctuations of the fission and absorption cross sections as well as to the fuel velocity is calculated and the results are qualitatively compared. Unlike in previous work, the solution is obtained through the matrix Green's function of the flux and precursor equations being kept separate. It is shown that in the case when the noise is represented by the fluctuations of the fission cross-section, the noise source attains a complex structure which is different from that in traditional reactors. On the other hand, in the cases investigated, despite all qualitative differences in the noise calculation procedure as well as in the structure of the noise source, it turns out that the noise induced by the absorption and the fission cross sections follow a similar behaviour. In addition, it is observed that the inclusion of the fluctuations in the fuel velocity examined in this paper slightly suppresses the total neutron noise for low frequency region i.e. below ∼ 2 Hz but on the other hand it enhances the latter one by one of order of magnitude for high frequencies i.e. above ∼ 2 Hz compared to the effect of other noise sources. The results contribute to the understanding and interpretation of the neutron noise in MSRs.