After Fukushima accident, more and more attention has been paid on severe accident analysis. As an important severe accident mitigation strategy applied to advanced light water reactor for in-vessel retention (IVR), an important method is external reactor vessel cooling (ERVC). Extensive work has been done on the effectiveness of IVR-ERVC, however simplified assumptions have been applied for lower head in most of these work. Seldom study has been done for the fundamental research work related to IVR-ERVC. This paper will introduce the model development study for the IVR-ERVC process at Shanghai Jiao Tong University. The main points of the paper can be summarized as followed: (1) Based on two-dimensional spherical coordinate, a two-dimensional approach with the aim to investigate transient heat transfer behaviour in the lower head has been developed; (2) A theoretical critical heat flux (CHF) model has been developed based on Weisman-Pei's bubble crowding model to study the CHF phenomenon on the special condition during the implement of IVR-ERVC; (3) In- and ex-vessel coupled analysis has been performed with a modified heat transfer method considering the heat transfer inside and outside reactor pressure vessel (RPV), and also in the vessel wall. The present work shows that the new developed models can be used to assess the external reactor vessel cooling phenomenon and the effectiveness of IVR-ERVC, which is significant and necessary for the design of large scale advance passive nuclear power plants in the future. (C) 2018 Elsevier Ltd. All rights reserved.