Preliminary analysis of an integral Small Modular Reactor operating in a submerged containment

This work addresses the conceptual design of a submerged nuclear power plant, where a horizontal cylindrical hull, placed on the floor of a sea or an artificial lake, hosts an integral pressurized Small Modular Reactor (SMR). A scaled version of the International Reactor Innovative and Secure (IRIS) that matches the requirements of the submerged containment is here proposed, providing a preliminary sizing of the primary components. Based on the presence of a large water reservoir (sea or lake) acting as a permanent heat sink, a basic fully passive safety strategy has been developed and its principles have been investigated, by means of the numerical simulation of a Station Black-Out (SBO) scenario. The outcomes show that natural circulation flows in the primary circuit and in the Emergency Heat Removal System (EHRS) can provide a very effective heat transfer capability from the fuel rods to the external water. The submerged reactor design owns very interesting safety features, which inherently prevent from the Fukushima-like scenarios, i.e. Loss Of Offsite Power (LOOP) and a Loss of Ultimate Heat Sink(LUHS), thus representing a noticeable improvement for a next generation nuclear reactor. However, some critical issues for the deployment of such a concept are also identified and briefly discussed.