Solid rocket motor (SRM) design requires thorough understanding of the slag accumulation process in order to: predict thrust continuity, optimize propellant conversion efficiency, predict coning effects from sloshing, and assess potential orbital debris (slag) hazard. Current state-of-the-art models for SRM environment do not have the capability to simulate the accumulation and dynamics of slag in SRMs as they rely on a Lagrangian particle approach that is only capable of predicting the location of accumulation. In this STTR effort, CFDRC will team up with Mississippi State University and Tetra Research to develop models for quantifying the effects of slag accumulation and dynamics on SRM performance. To enhance current slag modeling capabilities, an Eulerian-Lagrangian approach to accurately model a slag-phase is proposed, in which Lagrangian particles can be converted to an Eulerian description and vice-versa. The Phase I project aims at developing the basic numerical model for the transport and accumulation of a slag-phase in Loci/CHEM. The multiphase framework, comprising of gas-phase, a dense slag-phase, and Lagrangian particles representing aluminum and alumina, will be developed and demonstrated in the Phase I effort with a TRL starting at 2 and ending at 3. In Phase II, the models will be extended and validated to provide an accurate numerical approach for slag dynamics that incorporates many of the physical phenomena present during SRM operation, including the transfer from Eulerian to Lagrangian description of slag at burnout, increasing the technology readiness level by the end of a Phase II project from 3 to 5.