The bronze process is a mature technology for the production of Nb3Sn superconducting wires exploiting reaction diffusion behaviour in the Cu-Nb-Sn system. However, the superconducting properties depend strongly on the applied heat treatment, and optimisation of the heat treatment is still largely by trial and improvement. Modelling of the reaction-diffusion behaviour would allow improved heat treatments to be designed; combination of this with a nondestructive in situ characterisation technique would also permit improved superconducting wires to be produced. A finite difference reaction diffusion model has been designed to permit rapid calculation of the bronze matrix composition and Nb3Sn layer thickness profiles across the wire cross-section as a function of time for any applied heat treatment. The model has also been designed to calculate the electrical resistivity of the wire, which has previously been demonstrated as a suitable in situ characterisation technique. This model has been applied to isothermal and more complex heat treatments and compared with experimental results. Good qualitative agreement has been found, and plans for further improvement of the model are described in detail.