Neutronics in Molten Salt Reactors

Licentiate thesis, 2010

This thesis contains two studies of the MSR properties. The first uses one-group theory and data that correspond to a traditional uranium fuelled light water reactor to investigate the basis physical differences that might arise due solely to the movement of the fuel. The second employs two-group theory and data corresponding to a thorium-fuelled thermal reactor to investigate the properties of a more realistic possible realisation of an MSR system, as well as data corresponding to more traditional systems for contrast. For both systems, the Green's functions and the dynamic adjoint functions are investigated in the general case of arbitrary fuel recirculation velocity and in the limiting case of infinite fuel velocity which permits closed form solutions both in the static and dynamic case. It is found that the amplitude of the induced noise is generally higher and the domain of the point kinetic behaviour valid up to higher frequencies than in a corresponding traditional system. This is due to the differing behaviour of the delayed neutron precursors as compared to the traditional case. The MSR equations are not self-adjoint and the adjoint equations and adjoint functions have to be constructed, which is also done here. Finally the space-dependent neutron noise, induced by propagating perturbations of the absorption cross section is calculated. A number of interesting properties that are relevant to full size MSRs are found and interpreted. The results are consistent with those in traditional systems but the domains of various behaviour regimes (point kinetic, space dependent etc.) are shifted to higher frequencies or system sizes.