Study of Chemical Decontamination Process for CRUD Removal

As nuclear power plants are getting older, gradual accumulation of CRUD in nuclear power plant is in progress, so decontamination process has been concerned. Chalk River Unidentified Deposit (CRUD) is a technical term in nuclear engineering which is an accumulated material on external fuel rod cladding surfaces in nuclear power plants. It is a corrosion product which is composed of either dissolved ions or solid particles such as Ni, Fe and Co. Corrosion product can be activated through nuclear reactions to form radio-nuclides such as Cobalt-60 (60Co). It can affect to human health and environment, so decontamination process is essential for reducing occupational exposures, limiting potential releases and uptakes of radioactive materials. Therefore, the main goal of this study is study of synthesis of simulated CRUD and chemical dissolution characteristics of CRUD. For synthesis of simulated CRUD, nickel ferrite which is main phase composition of outer layer of CRUD and cobalt ferrite was composed as powder foam, and corrosion product of CRUD was generated on surface of metallic coupon which is compose of SUS 304 (Ni: 8~11%, Cr: 18~20%). According to XRD, XRF, and SEM-EDS, synthesis of cobalt ferrite process, and it worked. After simulated CRUD was synthesized, dissolution test using the simulated CRUD with different chemical reagents (Oxalic acid, Malonic acid, Citric acid, and Nitric acid) to find the good condition (pH and Temperature) for effective cobalt release. In dissolution test of cobalt ferrite and nickel ferrite, oxalic acid shows the most effective chemical reagent. Generally the lower pH, the dissolution amount of cobalt, nickel and iron is much higher. And also, temperature goes higher, the dissolution amount of cobalt, nickel and iron is much higher. In addition, electro kinetic process was applied to investigate the cobalt, nickel and iron removal mechanism from contaminated wastewater which result from the decontamination process. Under the condition of pH 1.8, there are no precipitation phenomena in cobalt ferrite and nickel ferrite. On the other hand, under the condition of cobalt ferrite and nickel ferrite in pH 3.5, cobalt ferrite with oxalic acid and nickel ferrite in malonic acid, citric acid and nitric acid show the precipitation phenomena respectively.