Patent Number: 
Section: claims

1. A method of chemical decontamination for a carbon steel member of a nuclear power plant, comprising steps of:bringing a reduction decontaminating solution including a malonic acid and an oxalic acid within a range from 50 to 400 ppm into contact with a surface of a carbon steel member of a nuclear power plant; andexecuting reduction decontamination for the surface of the carbon steel member by the reduction decontaminating solution. 2. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 1, comprising step of:removing cations eluted from the carbon steel member into the reduction decontaminating solution by the reduction decontamination, from the reduction decontaminating solution. 3. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 1, comprising step of:injecting oxygen gas into the reduction decontaminating solution including the malonic acid and the oxalic acid within the range from 50 to 400 ppm,wherein the reduction decontamination for the surface of the carbon steel member is performed by using the reduction decontaminating solution including the malonic acid and the oxalic acid within the range from 50 to 400 ppm with the injected oxygen gas. 4. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 3, wherein the oxygen gas is micro bubbles generated by a micro-bubble generation apparatus. 5. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 1, wherein a malonic acid concentration of the reduction decontaminating solution is within a range from 2100 to 19000 ppm. 6. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 5, wherein the malonic acid concentration is within a range from 2100 to 7800 ppm. 7. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 1, comprising steps of:putting the carbon steel member detached from the nuclear power plant in a decontamination vessel; andsupplying the reduction decontaminating solution into the decontamination vessel,wherein the reduction decontamination for the surface of the carbon steel member is performed by bringing the reduction decontaminating solution into contact with the carbon steel member in the decontamination vessel. 8. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 7, wherein a concentration of the malonic acid of the reduction decontaminating solution is within a range from 12300 to 19000 ppm. 9. A method of chemical decontamination for a carbon steel member of a nuclear power plant, comprising steps of:connecting a second pipe to a first pipe, which is made of carbon steel, of the nuclear power plant; andsupplying a reduction decontaminating solution including a malonic acid and an oxalic acid within a range from 50 to 400 ppm to the first pipe through the second pipe,wherein reduction decontamination for an inner surface of the first pipe is performed by bringing the reduction decontaminating solution into contact with the inner surface. 10. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 9, comprising step of:removing cations eluted from the first pipe into the reduction decontaminating solution by the reduction decontamination, from the reduction decontaminating solution. 11. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 9, comprising steps of:forming a closed loop including a first pipe, a second pipe, and a third pipe by connecting one end portion the second pipe to the first pipe and by connecting another end portion of the second pipe to the third pipe made of stainless steel and connected to the first pipe;supplying an oxidation decontaminating solution injected from an oxidation decontaminating solution injection apparatus connected to the second pipe into the third pipe through the second pipe;performing oxidation decontamination for an inner surface of the third pipe by the oxidation decontaminating solution; andperforming the reduction decontamination for the inner surface of the third pipe by the reduction decontaminating solution supplied to the third pipe through the second pipe as well as performing reduction decontamination for an inner surface of the first pipe. 12. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 11, wherein the reduction decontaminating solution is generated by the malonic acid injected from a malonic acid injection apparatus connected to the second pipe into the second pipe and the oxalic acid injected from an oxalic acid injection apparatus connected to the second pipe into the second pipe. 13. A method of chemical decontamination for a carbon steel member of a nuclear power plant, comprising steps of:injecting oxygen gas into a reduction decontaminating solution including a malonic acid and an oxalic acid;bringing the reduction decontaminating solution including the malonic acid and the oxalic acid with the injected oxygen gas into contact with a surface of the carbon steel member of the nuclear power plant; andperforming reduction decontamination for the surface of the carbon steel member by the reduction decontaminating solution brought into contact with the surface of the carbon steel member. 14. The method of chemical decontamination for a carbon steel member of a nuclear power plant according to claim 13, comprising steps of:putting the carbon steel member detached from the nuclear power plant in a decontamination vessel;supplying the reduction decontaminating solution including the malonic acid and the oxalic acid into the decontamination vessel; andinjecting the oxygen gas into the reduction decontaminating solution in the decontamination vessel,wherein the reduction decontamination for the surface of the carbon steel member is performed in the decontamination vessel by bringing the reduction decontaminating solution including the malonic acid and the oxalic acid with the injected oxygen gas into contact with the carbon steel member.