Shutdown system for a nuclear steam supply system

Abstract

A nuclear steam supply system having a shutdown system for removing residual decay heat generated by a nuclear fuel core. The steam supply system may utilize gravity-driven primary coolant circulation through hydraulically interconnected reactor and steam generating vessels forming the steam supply system. The shutdown system may comprise primary and secondary coolant systems. The primary coolant cooling system may include a jet pump comprising an injection nozzle disposed inside the steam generating vessel. A portion of the circulating primary coolant is extracted, pressurized and returned to the steam generating vessel to induce coolant circulation under reactor shutdown conditions. The extracted primary coolant may further be cooled before return to the steam generating vessel in some operating modes. The secondary coolant cooling system includes a pumped and cooled flow circuit operating to circulate and cool the secondary coolant, which in turn extracts heat from and cools the primary coolant.

What is claimed is: 
     
         1 . A nuclear steam supply system with startup primary coolant heating system, the nuclear steam supply system comprising:
 a reactor vessel having an internal cavity;   a reactor core comprising nuclear fuel disposed within the internal cavity and operable to heat a primary coolant;   a steam generating vessel fluidly coupled to the reactor vessel;   a riser pipe positioned within the steam generating vessel and fluidly coupled to the reactor vessel;   a primary coolant loop formed within the reactor vessel and the steam generating vessel, the primary coolant loop being configured for circulating primary coolant through the reactor vessel and steam generating vessel; and   a primary coolant heating system comprising:
 an intake conduit having an inlet fluidly coupled to the primary coolant loop; 
 a pump fluidly coupled to the intake conduit, the pump configured and operable to extract and pressurize primary coolant from the primary coolant loop and discharge the pressurized primary coolant through an injection conduit; 
 the injection conduit having an outlet positioned inside the riser pipe to inject the pressurized primary coolant into the riser pipe from the pump; and 
 a heat exchanger configured and operable to heat the pressurized primary coolant.; 
 an injection nozzle fluidly coupled to the outlet of injection conduit for injecting the heated pressurized primary coolant into the riser pipe. 
   
     
     
         2 . The nuclear steam supply system according to  claim 2 , wherein the injection nozzle is a Venturi nozzle which discharges the heated pressurized primary coolant vertically upwards into the riser pipe to induce flow of the primary coolant through the primary coolant loop. 
     
     
         3 . The nuclear steam supply system according to  claim 1 , wherein the inlet of the intake conduit is located at a bottom of the reactor vessel. 
     
     
         4 . The nuclear steam supply system according  claim 1 , wherein the inlet of the intake conduit is located at a bottom of the steam generating vessel. 
     
     
         5 . The nuclear steam supply system according to  claim 1 , wherein the inlet of the intake conduit is located at a bottom of the riser pipe. 
     
     
         6 . The nuclear steam supply system according to  claim 1 , wherein the steam generating vessel comprises a steam generating section and a superheater section disposed above the steam generating section in vertically stacked relationship, the superheater section being operable to heat a secondary coolant to superheated steam conditions. 
     
     
         7 . The nuclear steam supply system according to  claim 6 , further comprising:
 the steam generating section and the superheater section including a pair of vertically spaced apart tubesheets and a tube bundle comprising a plurality of vertically-oriented tubes extending between the tubesheets; and   wherein the injection nozzle is positioned so as to inject the pressurized primary coolant into the riser pipe of the steam generating section at or near an elevation of a bottom one of the tubesheets.   
     
     
         8 . The nuclear steam supply system according to  claim 1 , wherein the injection conduit is a pipe having a diameter of approximately six inches and wherein the injection nozzle has a diameter of approximately three inches. 
     
     
         9 . The nuclear steam supply system according to  claim 1 , wherein injecting the pressurized primary coolant into the riser pipe through the injection nozzle creates a low pressure Venturi effect that causes the primary coolant to flow through the primary coolant loop. 
     
     
         10 . The nuclear steam supply system according to  claim 1 , further comprising:
 the steam generating vessel including a plurality of stacked heat exchangers fluidly connected in a vertically stacked relationship;   the stacked heat exchangers each including a pair of vertically spaced apart tubesheets and a tube bundle comprising a plurality of vertically oriented tubes extending between the tubesheets;   wherein upon injecting the pressurized primary coolant into the riser pipe, the primary coolant flows vertically upwards through the riser pipe to a top of the steam generating vessel, vertically downwards from the top of the steam generating vessel through the tubes of the stacked heat exchangers, vertically downwards through a downcomer in the reactor vessel to the bottom of the reactor vessel, vertically upwards within a riser column in the reactor vessel, and from the riser column in the reactor vessel back into the riser pipe in the steam generating vessel; and   wherein a secondary coolant flows upwards between the tubes on a shell side of each of the stacked heat exchangers.   
     
     
         11 . The nuclear steam supply system according to  claim 1 , wherein the reactor vessel, the steam generating vessel, and the primary coolant heating system are positioned within a containment vessel. 
     
     
         12 . The nuclear steam supply system according to  claim 1 , wherein at least a portion of the primary coolant heating system is positioned external to the reactor vessel and the steam generating vessel. 
     
     
         13 . The nuclear steam supply system according to  claim 1 , wherein the primary coolant heating system is a one-way fluid flow circuit in which the primary coolant flows from the primary coolant loop through the intake conduit, through the pump, into the injection conduit, through the heat exchanger, further through the injection conduit, and into the riser pipe of the steam generating vessel via the injection nozzle. 
     
     
         14 . The nuclear steam supply system according to  claim 1 , wherein the primary coolant heating system further comprises a valve that is fluidly coupled to the reactor vessel by a piping nozzle at one end and at another end to an inner pipe fluidly coupled to the valve and arranged inside an outer pipe that concentrically surrounds the inner pipe, the inner and outer pipes collectively forming the intake conduit. 
     
     
         15 . The nuclear steam supply system according to  claim 1 , wherein the primary coolant heating system extracts a portion of the total volume of the primary coolant from the primary coolant loop, the remainder of the primary coolant remaining in the primary coolant loop. 
     
     
         16 . The nuclear steam supply system according to  claim 13 , further comprising a pressure vessel enclosing the valve, a valve stem of the valve protruding from the pressure vessel, and wherein a connection between the inner pipe and the valve and a connection between the valve and the integral piping nozzle of the reactor vessel are located within the pressure vessel. 
     
     
         17 . The nuclear steam supply system according to  claim 1 , wherein the pressurized primary coolant from the injection nozzle mixes with the primary coolant drawn into the riser pipe from the reactor vessel by a Venturi flow effect to form a mixed primary coolant flow through the riser pipe. 
     
     
         18 . The nuclear steam supply system according  claim 1 , wherein the primary coolant is cooled in the heat exchanger by water from a component heating system. 
     
     
         19 . The nuclear steam supply system according to  claim 1 , wherein the heat exchanger is a shell and tube type. 
     
     
         20 . A nuclear steam supply system with startup heating system, the nuclear steam supply system comprising:
 a reactor vessel having an internal cavity;   a reactor core comprising nuclear fuel disposed within the internal cavity and operable to heat a primary coolant;   a steam generating vessel fluidly coupled to the reactor vessel and containing a secondary coolant for producing steam to operate a steam turbine, the steam generating vessel including a superheater section and a steam generating section;   a riser pipe positioned inside the steam generating vessel and fluidly coupled to the reactor vessel;   a primary coolant flow loop formed within the reactor vessel and the steam generating vessel, the primary coolant flow loop being configured and operable for circulating primary coolant through the reactor vessel and steam generating vessel;   a primary coolant startup heating system comprising:
 a first pump having an inlet fluidly coupled to the primary coolant flow loop, the first pump configured and operable to extract and pressurize a portion of the primary coolant from the primary coolant loop; 
 a Venturi injection nozzle having an inlet fluidly coupled to a discharge of the first pump and an outlet positioned inside the riser pipe in the steam generating vessel, the injection nozzle receiving and injecting the pressurized portion of the primary coolant into the riser pipe from the pump; and 
 a heating element operable to heat the extracted primary coolant prior to injecting the pressurized portion of the primary coolant into the riser pipe. 
   
     
     
         21 . The nuclear steam supply system according to  claim 20 , wherein the heating element is a shell and tube heat exchanger configured to receive auxiliary steam from a steam source other than the steam generator which flows through a shell side, the primary coolant flows through a tube side of the heat exchanger and is heated by the steam. 
     
     
         22 . The nuclear steam supply system according to  claim 20 , wherein the steam generating vessel and reactor vessel are vertically elongated, the superheater section and steam generating section of steam generating vessel being disposed in vertically stacked relationship and the superheater section being positioned above the steam generating section. 
     
     
         23 . The nuclear steam supply system according to  claim 20 , wherein the portion of the primary coolant extracted by the pump is less than 50% of the total volume of primary coolant contained in the primary coolant flow loop. 
     
     
         24 . A nuclear steam supply system with startup system, the nuclear steam supply system comprising:
 a reactor vessel having an internal cavity;   a vertically elongated reactor core comprising nuclear fuel disposed within the internal cavity and operable to heat a primary coolant;   a vertically elongated steam generating vessel fluidly coupled to the reactor vessel and containing a secondary coolant for producing steam to operate a steam turbine, the steam generating vessel including a superheater section and a steam generating section;   a vertically elongated riser pipe positioned inside the steam generating vessel and fluidly coupled to the reactor vessel;   a primary coolant flow loop formed within the reactor vessel and the steam generating vessel, the primary coolant flow loop being configured and operable for circulating primary coolant through the reactor vessel and steam generating vessel;   a secondary coolant flow loop formed outside of the reactor vessel and steam generating vessel, the secondary coolant flow loop being configured and operable for circulating secondary coolant through the steam generating vessel; and   a Venturi jet pump disposed inside the riser pipe of the steam generating vessel, the jet pump including an injection nozzle fluidly coupled to the primary coolant flow loop by a pump fluidly coupled to the primary coolant flow loop which extracts and pressurizes a portion of the primary coolant from the primary coolant flow loop and discharges the pressurized portion of the primary coolant to the injection nozzle;   wherein the jet pump receives and injects a portion of the primary coolant into the riser pipe which draws and mixes primary coolant from the reactor vessel with the injected portion of the primary coolant in the jet pump to circulate the primary coolant through the primary coolant flow loop.   
     
     
         25 . The nuclear steam supply system according to  claim 24 , further comprising a first heat exchanger disposed upstream of the jet pump, the heat exchanger configured and operable to heat the portion of the primary coolant received by the jet pump before injection into the riser pipe. 
     
     
         26 . The nuclear steam supply system according to  claim 24 , wherein the injection nozzle discharges primary coolant in an upwards directions inside the riser pipe.