Large Heavy-Water Power Reactor with Prestressed-Concrete Pressure Vessel

The construction of large heavy-water pressure-vessel reactors depends on the possibility of building large pressure vessels. Large core dimensions, which characterize natural uranium reactors, necessitate technical solutions that do not impose any practical limit on the power output of the reactor. The concept developed by Siemens is a heavy-water moderated and cooled reactor designed to use a prestressed-concrete vessel suitable for very high coolant pressures. A further advantage is that the upper vessel cover can be removed, which previously seemed inconceivable with prestressed-concrete vessels. This new design of pressure vessel makes it possible to arrange inside the reactor vessel all the main primary circuit components, such as the steam generator and coolant pumps. The reactor is moderated and cooled with heavy water. The main coolant is circulated by impeller pumps. An average quality of approximately 10% is achieved in the water at the cooling channel outlet. A portion of the coolant is subcooled approximately 100°C and fed as moderator to the moderator tank. The primary heavy-water cooling circuit is at an operating pressure of 100 kg/cm2 abs. In the secondary light-water circuit live steam of ∼274°C at 60 kg/cm2 abs. is attained. The core consists of 336 cooling channels. Each channel accommodates one fuel bundle consisting of 36 uranium dioxide fuel rods. The shroud tubes are not insulated from the moderator. The reactor is designed for natural uranium. An average burnup of 8500 MWd/t U is achieved. On-load refuelling is carried out by means of an internal loading machine inside the pressure vessel. The steam generator is arranged at the periphery of the reactor core and consists of groups of many small units. Each group comprises a condenser, a subcooler and a moderator cooler section. The high-speed axial-flow pumps are placed in the bottom concrete plug. There are 36 control rods driven by an external mechanism mounted on the pressure vessel. The reference design presented in this paper refers to a plant size of 600 MW(e). It is believed that this reactor concept is fully competitive and that it compares favourably with any other developed to date. (author)