India has developed its own indigenous Pressurized Heavy Water Reactor (PHWR) design that consists of 220 MWe, 540 MWe and 700 MWe units. India is currently operating 16 units of 220 MWe and two units of 540 MWe. Construction of two 700 MWe units is underway. The Indian PHWR was developed from the experience in the operation of earlier units and from indigenous R&D efforts. The important features introduced in these units include two diverse and fast-acting shutdown systems, double containment of the reactor building, water-filled calandria vault, integral calandria end shield assembly, and calandria tube filled and purged with carbon dioxide to monitor pressure tube leak by monitoring the dew point of carbon dioxide. These units also include a valve-less primary heat transport system and a simplified control room concept, as well as advanced control and instrumentation systems that incorporate computer-based systems to match with the advancement in technology.