Patent Number: 050154362
Section: claims

1. A water-cooled direct cycle nuclear power plant comprising a nuclear reactor, a turbine, a condenser, a condensed-water purifying means and a feed water heater successively arranged as main constitution, further comprising: means for measuring iron concentration in cooling water, and  means for injecting iron into cooling water for controlling iron amount at an optimum level during operation of the nuclear power plant, said iron-injecting means having a processing unit which calculates a necessary amount of iron concentration based on the data obtained by said iron concentration measuring means in order to supply iron amount into said cooling water for making an iron accumulation rate on fuel rod be not less than 0.5 mg/m.sup.2 /hr, but not more than 2.0 mg/m.sup.2 /hr, during operation of the nuclear power plant and a control unit for controlling the iron amount in the cooling water. 2. A water-cooled direct cycle nuclear power plant claimed in claim 1, wherein said iron amount in the cooling water is controlled to make an iron accumulation rate be in a range of 1-2 mg/m.sup.2 /hr. 3. A water-cooled direct cycle nuclear power plant claimed in claim 2, wherein said means for injecting iron into cooling water is located downstream of the condensed-water purifying means. 4. A water-cooled direct cycle nuclear power plant claimed in claim 1, wherein said iron concentration in cooling water is measured at a point downstream of the condensed water-purifying means and upstream of the feed water heater, or at a point between the nuclear reactor pressure vessel and the feed water heater, or at both of said points. 5. A water-cooled direct cycle nuclear power plant claimed in claim 1, wherein the means for injection into the cooling water includes, an ionic iron-generating means for supplying at least one of iron components in the outlet of an means, having chemical states of iron ion, iron hydroxide, and iron oxide; and a pump for injecting the water containing said iron component, the pump acting to inject the water containing said iron component into cooling water of the nuclear power plant during operation of the plant. 6. A water-cooled direct cycle nuclear power plant claimed in claim 1, wherein the means for injection into the cooling water includes, a tank for storing water containing at least one of iron components having chemical states of iron ion, iron hydroxide, and iron oxide; and a pump for injecting the water containing said iron component, the pump acting to inject said water containing at least one of iron components into cooling water of the nuclear power plant during operation of the plant. 7. A method of operating a water-cooled direct cycle nuclear power plant including a nuclear reactor, a turbine, a condenser, a purifying means and a feed water heater successively arranged as main constitution, comprising the steps of: measuring iron concentration in cooling water; calculating iron amount to be added on the basis of said measured iron concentration for supplying an iron amount so as to make the iron accumulation rate on fuel rod to be not less than 0.5 mg/m.sup.2 /hr, but not more than 2.0 mg/m.sup.2 /hr; and injecting a suitable additional iron amount into the cooling water, said injecting being performed during operation of the plant. 8. A method of operating a water-cooled direct cycle nuclear power plant having a nuclear reactor, a turbine, a condenser, a purifying means and a feed water heater successively arranged as main constitution, comprising the steps of: measuring iron concentration in cooling water; calculating iron accumulation rate on fuel rod; measuring nickel concentration; calculating ration of iron concentration to nickel concentration in cooling water on the basis of said measured nickel concentration and said measured iron concentration; and injecting a suitable additional iron amount into the cooling water so as to make said concentration ratio to be greater than 2 when the measured concentration ratio is not more than 2 even in a case where the calculated iron accumulation rate is not less than 0.5 mg/m.sup.2 /hr, said injecting being performed during operation of the plant. 9. A water-cooled direct cycle nuclear power plant claimed in claim 1, wherein said means for injecting iron into cooling water injects the iron both during an initial operation period of the plant and thereafter. 10. A water-cooled direct cycle nuclear power plant claimed in claim 5, wherein the pump acts to inject the water containing said iron component both during an initial operation period of the plant and thereafter. 11. A water-cooled direct cycle nuclear power plant claimed in claim 6, wherein the pump acts to inject said water containing at least one of iron components both during an initial operation period of the plant and thereafter. 12. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 7, wherein said injecting is performed both during an initial operating period of the plant and thereafter. 13. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 8, wherein said injecting is performed both during an initial operating period of the plant and thereafter. 14. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 8, wherein said injecting is performed so as to make said concentration ratio greater than 2 and at most 10. 15. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 8, including the further step of calculating an iron amount to be added on the basis of said measured iron concentration, for supplying an iron amount so as to make the iron accumulation rate on the fuel rod to be not less than 0.5 mg/m.sup.2 /hr but not more than 2.0 mg/m.sup.2 /hr; and, in the injecting step, injecting a suitable additional iron amount into the cooling water even if said concentration ration is grater than 2, so as to achieve said concentration ratio to be greater than 2, and said iron accumulation rate to be not less than 0.5 mg/m.sup.2 /hr, but not more than 2.0 mg/m.sup.2 /hr, during operation of the plant. 16. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 7, wherein after 5000 hours of operation an iron amount to make the iron accumulation rate on the fuel rod not less than 0.5 mg/m.sup.2 /hr but not more than 1.0 mg/m.sup.2 /hr is calculated, and a suitable additional iron amount, based upon the calculated iron amount to make the iron accumulation rate not less than 0.5 mg/m.sup.2 /hr but not more than 1.0 mg/m.sup.2 /hr, is injected into the cooling water. 17. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 7, wherein the injecting is performed so as to make the iron concentration of the cooling water relatively large during an initial period of operation of the plant and relatively small thereafter. 18. A method of operating a water-cooled direct cycle nuclear power plant claimed in claim 8, wherein a suitable additional iron amount is injected into the cooling water so as to make said concentration ratio be greater than 2 but not more than 5.