Patent Number: 050892185
Section: summary

The present invention relates to water cooled nuclear reactors, and pressurizers therefor, and is particularly of benefit for small, low pressure, low temperature water cooled nuclear reactors. The pressurizer of a pressurized water nuclear reactor (PWR) of the prior art is essentially a volume of saturated water and vapour in thermodynamic equilibrium in a vessel which communicates with the primary circuit via a surge line. The present invention seeks to provide a pressurized water cooled nuclear reactor, and a pressurized therefor, in which normal or abnormal changes in water volume or water space can be accommodated by mechanical means not requiring support systems such as electrical immersion heaters and their power supplies as required by prior art saturated water pressurizers. Accordingly the present invention provides a water cooled nuclear reactor comprising a reactor core, a primary water coolant circuit arranged to cool the reactor core, a pressurizer, the reactor core, and at least a portion of the primary coolant circuit being located in a pressure vessel, the pressurizer having a movable diaphragm sealingly secured to a pressurizer pressure vessel to divide the pressuriser pressure vessel into a first water space and a second fluid space, the second fluid space being arranged to contain a gas, at least one surge port means which communicates between the pressurizer and the primary coolant circuit to connect the first space of the pressurizer with the primary coolant circuit, the diaphragm being movable so as to allow changes in the volume or pressure of the water in the first space of the pressurizer and the primary coolant circuit. The reactor core, the primary water coolant circuit and the pressurizer may be arranged as an integral unit enclosed by an integral pressure vessel, at least one casing being located in the integral pressure vessel to substantially divide the integral pressure vessel into a first chamber and a second chamber, the pressurizer being located in the first chamber, the reactor core and the primary water coolant circuit being located in the second chamber. The casing may divide the pressure vessel into a first vertically upper chamber and a second vertically lower chamber. The casing may comprise an annular member which extends downwards from the peripheral region thereof, the annular member being sealingly secured to the pressure vessel to form an annular lower portion of the first water space. The casing may comprise an annular member which is sealingly secured to and extends downwards from the pressure vessel, the annular member having the at least one surge port means at its lower end. The diaphragm may be sealingly secured to the pressure vessel by bellow means. The diaphragm may be sealingly secured to the casing by bellow means. The diaphragm may be spring loaded. The bellow means may comprise a spring. The diaphragm may have damper means. The bellow means may be arranged to expand with an increase in the volume or pressure of the water. The bellow means may be arranged to contract with an increase in the volume or pressure of the water. The reactor may be arranged in the lower region of the second chamber, the primary coolant circuit comprising a riser passage to convey relatively hot water and steam to a heat exchanger, and a downcomer passage to convey relatively cool water from the heat exchanger to the reactor core. The riser passage may be defined by a hollow cylindrical member, the downcomer passage being defined between the hollow cylindrical member and the pressure vessel. The heat exchanger may be positioned in an upper region of the downcomer passage. The reactor core may be positioned in the lower region of the second chamber, the primary coolant circuit comprising a riser passage defined by a hollow cylindrical member to convey relatively hot water and steam to a heat exchanger or boiler, and a downcomer passage defined between the hollow cylindrical member and the pressure vessel to convey relatively cool water from the heat exchanger, or boiler, to the reactor core. The casing may be positioned coaxially with the hollow cylindrical member, the casing extending downwards from the pressure vessel into the hollow cylindrical member. The pressure vessel may have a vent to interconnect the second fluid space with atmosphere. The vent may have a relief valve. The diaphragm may be an elastic membrane. A pressurizer for a water cooled nuclear reactor may comprise a pressure vessel, a movable diaphragm sealingly secured to the pressure vessel to divide the pressure vessel into a first space and a second space, the first space being arranged to interconnect with the water cooled nuclear reactor for the supply of water therebetween, the second space being arranged to contain a gas, the diaphragm being movable so as to allow changes in the volume or pressure of the water in the first space of the pressurizer and the water cooled nuclear reactor. The diaphragm may be sealingly secured to the pressure vessel by bellow means. The diaphragm may be spring loaded. The bellow means may comprise a spring. The diaphragm may have damper means. The bellow means may be arranged to expand with an increase in the volume or pressure of the water. The bellow means may be arranged to contract with an increase in the volume or pressure of the water. The pressure vessel may have a vent to interconnect the second space with atmosphere. The vent may have a relief valve. The diaphragm may be an elastic membrane.