Modeling nuclear reactors is complex, requiring multiphysics solutions between neutronics, thermal hydraulics, and fuel behavior. Monte Carlo methods are becoming more desirable and feasible with advances in parallel computing technology, yet they are still impractical for full-core simulations. However, aspects of the simulation where a higher level of modeling fidelity is required could be performed with Monte Carlo codes, and then these solutions could be coupled to deterministic codes.Serpent 2, a three-dimensional continuous-energy Monte Carlo reactor physics burnup calculation code, has been tested and produces accurate cross sections for the Advanced Test Reactor (ATR) and the Transient Reactor Test Facility (TREAT), both at INL, and is desirable for use in future TREAT simulations. MAMMOTH is being developed at INL to produce a full-core solution: neutronics, thermal hydraulics, and fuel behavior. Preferably, a coupled solution will be obtained which contains Serpent 2 neutronics coupled with MAMMOTH thermal hydraulics and fuel performance.