Toru Kawasaki

Radiolytic decomposition of organic C-14 released from TRU waste

It has been found that metallic TRU waste releases considerable portions of C-14 in the form of organic molecules such as lower molecular weight organic acids, alcohols and aldehydes. Due to the low sorption ability of organic C-14, it is important to clarify the long-term behavior of organic forms under waste disposal conditions. From investigations on radiolytic decomposition of organic carbon molecules into inorganic carbonic acid, it is expected that radiation from TRU waste will decompose organic C-14 into inorganic carbonic acid that has higher adsorption ability into the engineering barriers. Hence we have studied the decomposition behavior of organic C-14 by gamma irradiation experiments under simulated disposal conditions. The results showed that organic C-14 reacted with OH radicals formed by radiolysis of water, to produce inorganic carbonic acid. We introduced the concept of “decomposition efficiency” which expresses the percentage of OH radicals consumed for the decomposition reaction of organic molecules in order to analyze the experimental results. We estimated the effect of radiolytic decomposition on the concentration of organic C-14 in the simulated conditions of the TRU disposal system using the decomposition efficiency, and found that the concentration of organic C-14 in the waste package will be lowered when the decomposition of organic C-14 by radiolysis was taken into account, in comparison with the concentration of organic C-14 without radiolysis. Our prediction suggested that some amount of organic C-14 can be expected to be transformed into the inorganic form in the waste package in an actual system.Copyright

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.

Investigations and Countermeasures for Deactivation of Hydrogen Recombination Catalyst at Hamaoka Units 4 and 5

The hydrogen concentration in the outlets of off-gas recombiners increased at Hamaoka Units 4 and 5, and their reactors could not continue the startup operations. Therefore, we investigated why the recombination reactions were deactivated and we selected appropriate countermeasures for both plants. Two types of deactivation mechanisms were found from our investigations. The first cause was the decrease in the active surface area of alumina as support material due to dehydrative condensation. The other cause was the catalyst being poisoned by organic silicon compounds. Organic silicon was introduced from the organosilicon sealant used at the junctions of low-pressure turbines. We also found that a boehmite rich catalyst was deactivated more easily by organic silicon than gamma alumina because boehmite had numerous hydroxyl groups. Finally, we estimated that the deactivation of hydrogen recombination catalysts was caused by two combined factors; these were the characteristics of boehmite as the ingredient of catalysts support and the organic silicon poisoning the catalyst surface. As countermeasures, the boehmite was changed into more stable gamma alumina by adding heat treatment in a hydrogen atmosphere at 500°C for 1 h, and the source of organic silicon, organosilicon sealant, was removed. The improved catalysts were applied at Hamaoka Units 4 and 5. Moreover, the linseed oil that used to be used at the plants was applied again as sealant in the low-pressure turbine casing instead of organosilicon sealant. As a result of the application of these countermeasures, the reactors could be started without increasing the hydrogen concentration at these plants.

Investigations and Countermeasures for Deactivation of the Hydrogen Recombination Catalyst at Hamaoka Unit 4 and 5

At Hamaoka Unit 4 and 5, the hydrogen concentration in the outlet of off-gas recombiner had increased, and the reactors could not continue start-up operation. Therefore, we investigated the causes of the deactivating the recombination reaction and selected appropriate countermeasures to the plants. From our investigation, two types of deactivation mechanism are found. One of the causes was decreasing the active surface area of alumina as support material by the dehydrative condensation. The other cause was poisoning of the catalyst by organic silicon compound. The organic silicon was introduced from organosilicon sealant used at the junctions of the low-pressure turbine. We also found that the boehmite rich catalyst was deactivated more easily by the organic silicon than gamma alumina because boehmite had a lot of hydroxyl groups. Finally, we estimated that the deactivation of the hydrogen recombination catalysts was caused by combined two factors, which are characteristics of boehmite catalyst support and the poisoning by the organic silicon on the catalyst surface. As the countermeasures, the boehmite was changed into more stable gamma alumina by adding the heat treatment in hydrogen atmosphere at 500°C for 1 hour, and the source of organic silicon, organosilicon sealant, was removed. At Hamaoka Unit 4 and 5 improved catalysts were applied. Moreover, linseed oil that used to be used at the plants was applied again as sealant of the low-pressure turbine casing instead of the organosilicon sealant. As a result of application of these countermeasures, the reactors could be started without increase of the hydrogen concentration at these plants.Copyright