Yukie Ishizawa

Development of a method to lower recontamination after chemical decontamination by depositing Pt nano particles: (I) Consideration of the suppression mechanism using a quantum dynamics calculation

The Pt coating (Pt-C) process has been developed to lower the recontamination by radioactive elements after chemical decontamination of piping surfaces. In this process, a layer of fine Pt nano particles is formed in an aqueous solution on the base metal of the piping following the chemical decontamination. In this study, we confirmed that the suppression effect by the Pt-C toward 60Co deposition on type 316 stainless steel using a 60Co deposition test under hydrogen water chemistry. Furthermore, we investigated the suppression mechanism of deposition of radioactive elements by a quantum molecular simulation. The deposition amounts of 60Co which were incorporated in oxides after 1000 h with and without the Pt-C process were about 90 and 10.2 Bq/cm2, respectively. The amount of 60Co deposition with Pt-C is about 10% that of non-coated specimens. The 60Co incorporation for the Pt-C specimen was suppressed by decreasing the formation of oxides. We considered this phenomenon using a quantum dynamics calculation and concluded that the Fe–O bonds in oxides were weakened by the effect of Pt and hydrogen radicals which were produced in the reaction between H2 and Pt, and then oxides were dissolved into the water.

Development of a method to lower recontamination after chemical decontamination by depositing Pt nano particles: (II) consideration of the Pt effect on oxide composition

ABSTRACT The Pt coating (Pt-C) process has been developed to lower the recontamination by 60Co which was incorporated in oxides on piping surface after chemical decontamination. In order to determine the suppression mechanism of 60Co deposition by Pt-C, it is important to investigate the formation of oxide film 60Co deposition behavior on oxide with Pt-C specimens. In this paper, we observed the composition change of oxide after a 60Co deposition test under the hydrogen water chemistry condition, and considered the 60Co deposition behavior on oxide for Pt-C specimens. The Ni and Co metal concentrations in oxide were dramatically changed by Pt-C process. The Ni metal concentrations in oxide for specimens with and without the Pt-C process were 11.2% and 18.0%, respectively. On the other hand, the Co metal concentrations in oxide for specimens with and without the Pt-C process were 1.2% and 0.2%, respectively. This composition change of the oxides indicated that 60Co incorporation for the Pt-C specimens was suppressed by replacing 60Co with Ni. We concluded that the Ni2+ ions were incorporated into the 8a site of the oxide spinel structure instead of Co2+ ions due to the effect of the conversion deposition energy.