The point kinetic component of neutron noise in an MSR

•Analysis of the point kinetic equations for an MSR.•Proof of the inapplicability of the traditional procedure.•Method for the analytical determination of the point kinetic component of the noise in an MSR.

The point kinetic approximation, and the calculation of the point kinetic component of the neutron noise in Molten Salt Reactors (MSR) is revisited. First, the derivation of the point kinetic equations in an MSR, found in the literature, is discussed. It is shown that to make the equations solvable, some simplifications need to be made whose validity is not justified. Then the point kinetic component of the noise is derived from the full space-frequency dependent solution in an analytical form by a projection to the static adjoint. The solution of the simplified point kinetic equations and the linearly exact point kinetic component obtained by the projection technique are compared quantitatively and it is shown that the solution of the simplified point kinetic equations cannot reconstruct some important features of the true solution.