In this study, depletion validation is conducted and then propagated into criticality safety analysis (CSA) to identify significant uncertainty components. First, the Polaris code (SCALE) is validated to characterize the spent nuclear fuel (SNF), focusing on uranium and plutonium isotopes typically used in the actinide-only burnup credit CSA. The validation data consists of 146 PWR PIE samples from the SFCOMPO database. The bias and its uncertainty are characterized, along with uncertainties from nuclear data and the fuel assembly design and irradiation. It is shown that the bias is a few percent on average. However, its uncertainty could be significant. Second, a CSA is conducted using the MCNP code on a PWR SNF disposal canister. The CSA includes the bias, its uncertainty, and other uncertainties relevant to both the depletion and the criticality. The criticality validation uses the Whisper code and selected ICSBEP criticality benchmarks. It is shown that depletion bias-uncertainty, followed by criticality bias and its uncertainty, are significant components driving criticality safety margins. The study highlights the relevance of consistently evaluating the PIE depletion benchmarks and the need for higher similarity benchmarks in SNF depletion and criticality applications.