[en] A pressuriser for a water cooled reactor is described. It comprises a pressure vessel divided into a water space and a gas space by a movable diaphragm sealingly secured to the pressure vessel. The pressuriser may be arranged as an integral unit in a reactor pressure vessel. In this case, the pressure vessel is divided into an upper chamber and a lower chamber by a casing. The reactor core and primary coolant circuit are arranged in the lower chamber and the pressuriser is arranged in the upper chamber. The diaphragm may be loaded by springs and dampers to prevent its oscillation or it may be an elastic membrane. Alternatively, the pressuriser may be a unit separate from the reactor pressure vessel. (author)

[en] One or more pipes interconnect a steam space of a pressuriser with an upper portion of the primary coolant circuit and one or more surge ports interconnect a water space of the pressuriser with a water-filled portion of the primary coolant circuit. The surge ports have low flow resistance for water from the water space to the primary coolant circuit and high flow resistance in the opposite direction. The reactor may be a pressurised water reactor or an indirect cycle boiling water reactor and may be integral or dispersed. The pressuriser may be integral with the reactor, where a shroud divides the pressuriser from the primary coolant circuit, or may be in a separate pressuriser pressure vessel. The arrangement controls the pressure in the primary circuit in the indirect cycle BWR, allows excess vapour to escape from the primary circuit under normal and fault conditions to prevent steam blanketing of the core and allows the pressuriser to act as a core flood tank for emergency cooling. (author)

[en] A water cooled nuclear reactor is described which comprises a reactor core, a primary water coolant circuit and a pressuriser arranged as an integral unit in a pressure vessel. The pressure vessel is divided into an upper and a lower chamber by a casing. The reactor core and primary water coolant circuit are arranged in the lower chamber and the pressuriser is arranged in the upper chamber. A plurality of spray pipes interconnect a steam space of the pressuriser with the downcomer of the primary water coolant circuit below a heat exchanger. A plurality of surge ports interconnect a water space of the pressuriser with the primary water coolant circuit. The surge ports have hydraulic diodes so that there is a low flow resistance for water from the water space of the pressuriser to the primary water coolant circuit and high flow resistance in the opposite direction. The spray pipes provide a desuperheating spray of cooled water into the pressuriser during positive volume surges of the primary water coolant. The pressuriser arrangement may also be applied to integral water cooled reactors with separate pressurisers and to dispersed pressurised water reactors. The surge ports also allow water to flow by gravity to the core in an emergency. (author)