The　nuclear-data　uncertainties　impact　the　best-estimate　predictions　of　the　nuclear　reactor　system.　In　this　paper,　total　uncertainty　analyses　have　been　performed　for　the　TMI-1　assembly　at　both　hot　zero-power　and　hot　full-power　conditions　to　evaluate　the　impacts　of　nuclear-data　uncertainties　on　the　predictions　of　lattice　calculations,　based　on　the　statistical　sampling　method.　With　an　improved　multigroup　cross-section　perturbation　model,　the　contributions　of　various　basic　cross　sections　to　the　uncertainties　of　k(infinity)　and　two-group　macroscopic　cross　sections　are　obtained.　For　the　total　uncertainty　analyses,　a　172-group　cross-section　covariance　library　produced　from　ENDF/B-VII.1　is　used　to　generate　the　samples　for　the　multigroup　microscopic　cross-section　library,　and　DRAGON　5.0　is　applied　to　perform　lattice　calculations　for　each　sample.　The　numerical　results　show　that　the　relative　uncertainty　of　k(infinity)　can　reach　about　4.7　parts　per　thousand　using　the　v(p)　covariance　matrix　of　U-235-v　and　7.1　parts　per　thousand　using　the　v(t)　covariance　matrix　of　U-235-v.　The　relative　uncertainties　of　two-group　macroscopic　cross　sections　vary　from　about　2.9　parts　per　thousand　(for　the　total　cross　section　of　the　thermal　group)　to　about　11.9　parts　per　thousand　(for　the　scattering　cross　section　from　the　fast　group　to　the　thermal　group).　Moreover,　through　detailed　analysis　toward　uncertainty　origins,　it　has　been　observed　that　U-235,　U-238,　O-16,　and　H-1　are　the　four　most　significant　contributors,　and　the　uncertainties　of　U-235-(nu,　sigma(f),　sigma(gamma)),　U-238-(sigma(gamma),　sigma((n,　inel)),　sigma((n,　elas)),　nu),　O-16-(sigma((n,　elas))),　and　H-1-(sigma((n,　elas)),　sigma(gamma))　are　the　most　significant　cross-section　contributors.