Patent Number: 047132094
Section: claims

1. A drain recovery system for the condensate feedwater system of a nuclear power plant, said condensate feedwater system including condensate pumps for boosting the condensate from a condenser, and feedwater heaters for heating the condensate from said condensate pumps, said drain recovery system comprising: drain pumping-up recovery means including a drain tank for storing a feedwater heater drain, and drain pump means connected to said drain tank for pumping up the drain therein to injet the drain into said condensate feedwater system at a predetermined portion thereof; and  drain level control means including conduit means connected between a portion of said drain pumping-up recovery means upstream of said drain pump means and a portion of said condensate feedwater system upstream of said condensate pumps for causing the drain in said drain tank to be returned to said portion upstream of said condensate pumps by a pressure differential therebetween so as to maintain a drain level in said drain tank at a predetermined position when the plant operates at a low load level or said drain pump means malfunctions. 2. A drain recovery system according to claim 1, wherein said drain level control means further include means for detecting a load level of the plant, and control valve means connected to said conduit means and responsive to an output signal from said load level detecting means to control the communication through said conduit means so as to maintain the drain level in said drain tank at the predetermined position. 3. A drain recovery system according to claim 2, wherein said drain level control means further includes means further includes means for detecting a trip of the drain pump means, and wherein said control valve means is also responsive to the output signal from said trip detecting means to control the communication through the conduit means so as to maintain the drain level in said drain tank at the predetermined position. 4. A drain recovery system according to claim 1, wherein said drain pumping-up recovery means further includes means for detecting a drain level in said drain tank, and a first control valve connected to the downstream side of said drain pump means, and wherein said drain level control means further includes means for detecting a load level of said plant, means for detecting a trip of said drain pump means, a second control valve connected to said conduit means, and change-over means connected to said drain level detecting means, said load level detecting means and said trip detecting means to transfer the output signal from said drain level detecting means to said first control valve to thereby allow said drain pumping-up recovery means to control the drain level in said drain tank, when no output signal is received from any one of said load level detecting means and said trip detecting means, and transfer the output signal from said drain level detecting means to said second control valve to thereby allow said conduit means to control the drain level in said drain tank therethrough, when an output signal is received from at least one of said load level detecting means and said trip detecting means. 5. A drain recovery system according to claim 1, wherein said drain level control means includes an overflow pipe connected to one end of said conduit means and disposed in said drain tank. 6. A drain recovery system according to claim 5, wherein said drain level control means further includes loop seal means connected in said conduit means for maintaining the pressure differential between said drain tank and the portion of said condensate feedwater system upstream of said condensate pumps. 7. A drain recovery system according to claim 1, wherein said portion of said condensate feedwater system upstream of said condensate pumps to which said conduit means is connected comprises said condenser. 8. A drain recovery system according to claim 1, wherein said condensate pumps include low-pressure condensate pumps and high-pressure condensate pumps, and said feedwater heaters include a low-pressure feedwater heater and a high-pressure feedwater heater positioned downstream of said high- and low-pressure condensate pumps, and wherein said drain tank is connected to said high- and low-pressure feedwater heaters so as to store the drains from both the feedwater heaters. 9. A drain recovery system according to claim 8, wherein said drain pumping-up recovery means further includes drain purifier means connected between said drain pump means 13 and said predetermined portion of said condensate feedwater system. 10. A drain recovery system according to claim 8, wherein said predetermined portion of said condensate feedwater system comprises a portion positioned on the inlet side of said high-pressure condensate pumps.