A　subchannel　code　(ATHAS)　is　developed　for　preliminary　analyses　of　flow　and　enthalpy　distributions　and　cladding　temperatures　at　supercritical　water　conditions.　The　code　is　applicable　for　transient　and　steady　state　calculations.　A　number　of　heat-transfer　correlations,　frictional　resistance　correlations,　and　mixing　models　have　been　implemented　into　the　code　as　options　for　sensitivity　analyses.　In　addition,　a　3D　heat　conduction　model　has　been　introduced　to　establish　the　cladding　temperature.　The　results　show　that　(1)　a　CANFLEX　[Inch,　W.W.T.,　Thompson,　P.D.,　Suk,　H.C.,　2000.　Introduction　of　the　new　fuel　bundle　CANFLEX　into　an　existing　CANDU　reactor.　In:　Proceedings　of　the　12th　Pacific　Basin　Nuclear　Conference,　October　29-November　2,　Seoul,　Korea.]　bundle　is　appropriate　for　use　in　the　CANDU　supercritical　water-cooled　reactor　(SCWR)　based　on　heat　transfer　analysis,　(2)　the　selection　of　heat　transfer,　friction,　and　mixing　correlations　has　a　significant　impact　on　the　prediction　of　the　maximum　cladding-surface　temperature,　and　(3)　the　inclusion　of　the　3D　heat　conduction　in　the　calculation　has　provided　a　more　realistic　prediction　of　the　maximum　cladding-surface　temperature　than　assuming　a　uniform　cladding　temperature　due　to　the　heterogeneous　characteristic　of　rods.　(C)　2009　Elsevier　B.V.　All　rights　reserved.