Due　to　the　remarkable　influence　of　aggregate　characteristics　on　the　mechanical　behaviors　of　concrete　materials,　and　in　particular　the　microcracking　development,　complex　aggregates　shapes　instead　of　widely　used　spherical　-shape　need　to　be　considered　in　advanced　numerical　approaches.　Apart　from　that,　in　numerical　simulations,　an　extra　consideration　of　the　influences　of　concrete＇s　heterogeneity　on　its　softening　behaviors　is　strongly　recommended　by　the　scientific　community.　In　this　context,　the　softening　behaviors　of　concrete　materials　undergoing　heterogeneous　expansion　in　the　aggregates　due　to　fast　neutron　radiation　were　investigated　in　the　present　paper,　and　the　influences　of　both　aggregate　shape　and　the　heterogeneity　of　aggregate　expansion　were　considered.　According　to　the　real　shapes　of　aggregates,　polygon-shaped　aggregates　with　random　orientation　were　placed　into　a　3D　numerical　concrete　specimen,　and　a　two-stage　finite　element　(FE)　approach　allowing　a　coupled　thermal-mechanical　analysis　was　proposed.　In　the　first　stage,　the　temperature　field　evolves　in　time　and　the　3D　concrete　specimen　was　estimated.　In　the　second　stage,　the　temperature-and　neutron　fluence-dependent　heterogeneous　expansion　in　the　aggregates　was　calculated　and　introduced　into　the　3D　mesoscopic　model,　and　the　development　of　microcracks　in　the　concrete,　the　resulting　mechanical　responses,　the　loss　in　mechanical　properties　of　the　radiation-induced　concrete　was　evaluated.　Surmounting　the　limitations　due　to　the　spherical-shape　of　aggregate　and　the　homogeneous　assumption　of　the　aggregate　expansion　in　the　concrete,　the　present　paper　developed　a　new　methodology　in　which　the　combined　effects　of　aggregate＇s　shape　and　the　heterogeneous　distribution　of　aggregate　expansion　on　the　mechanical　properties　of　radiation-induced　concrete　were　considered,　permitting　evaluating　the　changes　in　the　dimensional　and　mechanical　properties　of　radiation　-induced　concrete.　The　proposed　model　provides　a　reference　to　assess　the　long-term　durability　and　the　structural　integrity　of　nuclear　power　plants.