In this study, we develop an algorithm to implement the physics of a mooring tether connected to a submerged wave energy converter (WEC). The algorithm, built as a java subroutine, is implemented and tested on a high-fidelity computational fluid dynamic (CFD) code STAR-CCM+. A fluid-structure interaction (FSI) model for a fully submerged buoy absorber WEC connected to a single mooring tether, with an internal fault in the power take-off (PTO) system, is simulated. The PTO fault, i.e. a seized PTO drive shaft or generator short circuit in electrical systems, is being modelled and simulated using the high-performance computing (HPC) clusters at Sandia National Laboratories and University of California Berkeley. The algorithm and simulation results are verified and partially compared to the mid-fidelity open source code, WEC-Sim. The results include dynamic responses of the WEC body, tether tension, and PTO stroke. Based on the simulation results, the significance of a PTO failure event on the WEC integrity is discussed.