Integrated modular water reactor (IMR) design

Integrated modular water reactor (IMR) has been developed as one of the advanced small-scale light water reactors, with a thermal output of 1000 MW. The IMR adopts natural circulation and self-pressurization in the primary cooling system, and a reactor vessel built-in steam generators. The core design has been performed using the current light water reactor technology. Thermal-hydraulic sensitivity analyses have been done from the viewpoint of the departure from nucleate boiling (DNB) limitation. The IMR core, with 97 21×21-type fuel assemblies and natural circulation in the primary coolant system, shows a good nuclear and thermal-hydraulic behavior and good allowable margins for the DNB phenomenon. The reactivity change with burnup is about 1%Δk by using burnable absorbers, and only 12 rod-cluster-controls are used through the operating cycle. The 20 m-height reactor vessel encloses steam generators in vapor and liquid portions. Plant dynamic analyses have been also performed in order to evaluate the IMR behavior from the viewpoints of plant operation and control. This study shows that the IMR will operate with enough margins for the core safety and will be stably controlled for load demand changes expected during normal operations.