The concept of design envelope energy system optimization was developed and used to investigate the feasibility of small modular reactor (SMR) deployment at a remote off-grid mine in northern Canada. A set of design envelope demands was produced based on engineering estimates to represent the anticipated actual nominal and peak demands of the mine, with a focus on preserving characteristic variability on a per-utility basis. The formulation of design envelope optimization was successful in optimizing a mine’s energy supply system given a design envelope of nominal and peak energy demands to ensure the peak demand could always be satisfied, as demonstrated through optimization of a wind-diesel hybrid system. A SMR was integrated into the optimal mine site energy supply (OMSES) optimization model. However, the SMR was not an economic solution for the mine given the economic circumstances of the project. The high specific capital cost of the SMR was not competitive against an incumbent wind-diesel hybrid system. Therefore, additional opportunities to integrate a SMR more deeply into a mine’s operation were conceptualized and proposed for future work.