Rift initiation and propagation exert a primary control on Antarctic ice-shelf stability, yet fracture criteria applicable to viscous, nonlinear ice remain poorly constrained. Classical Linear Elastic Fracture Mechanics (LEFM) metrics such as the J-integral are rigorously defined for elastic materials [1], whereas ice shelves deform predominantly by creep over timescales relevant to rift evolution. In this context, the C* integral—an extension of the J-integral for steady-state creeping solids—offers a promising framework for quantifying fracture driving forces in ice [2]. Here we investigate the feasibility, numerical robustness, and interpretability of the C* integral in ice-shelf rift settings using idealized and realistic numerical models. We compute C* along contours surrounding rift tips within shallow-shelf (SSA) and higher-order viscous flow formulations, and perform systematic tests to evaluate sensitivity to contour size, mesh resolution, rift geometry, and domain configuration. These experiments are designed to establish practical guidelines for computing C* in large-scale ice-flow models and to identify regimes in which the integral is well behaved. Building on this numerical foundation, we outline a framework for integrating C* calculations with the newly developed Antarctic Rift Catalog (ARC), which provides continent-scale observations of rift geometry and propagation behavior [3]. Our approach is intended to enable future evaluation of whether variations in C* correspond to observed differences in rift activity, including active propagation, arrest, and stabilization. This work establishes a computational pathway for applying energy-based fracture mechanics to viscous ice and motivates the use of C* as a candidate metric for linking ice-shelf stress states to rift evolution in prognostic stability models. REFERENCES [1] Landes, J.D. and Begley, J.A., 1976. A fracture mechanics approach to creep crack growth. Astm Stp, 590, pp.128-148. [2] Rice, J.R., 1968. A path independent integral and the approximate analysis of strain concentration by notches and cracks. Journal of Applied Mechanics. [3] Walker, C.C., Lipovsky, B.P., Needell, C., Roberts, C. and Fricker, H.A., 2025. Pan-Antarctic observations of ice shelf rift propagation and their topographic signatures: Implications for calving rate and ice shelf stability. AGU25.