A 1D model of a Reactor Vessel Auxiliary Cooling System (RVACS) has been developed, and implemented, in the Julia Programming Language. The governing differential equations are presented and explained. The model is benchmarked with the fast reactor dynamics and safety analysis code SAS4A/SASSYS-1, and it is shown that the developed RVACS model agrees well with results calculated by SAS4A. We conclude that both the SAS4A model and our model benefit from a higher axial node count as it leads to convergence between the two models. Suggestions for future development include porting the RVACS model to FORTRAN and adopting it in the BELLA code to enable an expeditious and safety informed design of metal cooled reactors.