[en] Dilation is defined as the uniform radial growth of the assembly duct component, and the distortion of the assembly duct by internal coolant pressure is also included in this paper. Maximum dilation especially occurs at the mid-core plane of the assembly duct. If the consequence of duct dilation is greater than the gap between neighboring assembly ducts, the contacts between assembly ducts will occur, and would push assembly ducts outward radially. The objective of this paper is to update the dilation model for assembly duct in the NUBOW2D-KMOD code. The experimental equation for the stainless steel was included in the dilation model of NUBOW2D-KMOD code. But because the material of assembly duct for KALIMER is HT9, it is not proper to use the old dilation model. This paper upgrade the dilation model into analytical model, so it is possible to apply the dilation model to KALIMER. The analytical results of this model are compared with those of FIAT and CRAMP