Improvement of Inventory and Leaching Rate Measurements of C-14 in Hull Waste, and Separation of Organic Compounds for C
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Improvement of Inventory and Leaching Rate Measurements of C-14 in Hull Waste, and Separation of Organic Compounds for Chemical Species Identification Ryota Takahashi1, Michitaka Sasoh1, Yu Yamashita1, Hiromi Tanabe2, and Tomofumi Sakuragi2 1 Toshiba Corporation, 8, Shisugita-Cho, Isogo-Ku, Yokohama 235-8523, Japan 2 Radioactive Waste Management Funding and Research Center, Pacific Marks Tsukishima, 115-7 Tsukishima, Chuo-ku, Tokyo, 104-0052, Japan ABSTRACT In order to analyze the C-14 inventory and leaching rate for safety evaluation of transuranic waste disposal, it is necessary to establish an analytical method that can measure C-14 with sufficient precision [1]. Oxidative decomposition of organic compounds containing C-14 is carried out to absorb carbon dioxide (CO2) in an alkaline solution, which is mixed with a liquid scintillation cocktail, and the amount C-14 is quantified by measuring a beta ray spectrum with a liquid scintillation counter. It has been difficult to completely decompose carbon compounds in a sample, even to CO2, by using conventional oxidizing agents. In the work described here, we improved the method of oxidative decomposition used to completely decompose carbon compounds using peroxydisulfuric acid (K2S2O8). When C-14 in the form of CO2 was absorbed in a sodium hydroxide (NaOH) aqueous solution, only 80% of the actually used quantity was detected. Total organic carbon measurements showed that the entire quantity of CO2 was absorbed by NaOH. When NaOH aqueous solution was used, it was found that only the analytical value was 80%. The entire quantity of the actually used carbon could be measured by absorbing the CO2 in Carbo-Sorb®. An anion form and a neutral molecule exist in the organic compound released from activated metals. In order to identify organic compounds efficiently, fractionation into an anion and a neutral molecule and separation by high performance liquid chromatography (HPLC) are necessary. Here, we propose the combined use of an ion exchange resin and HPLC as an improved technique for identification of the chemical species. INTRODUCTION In order to evaluate the actual sources of C-14 in activated cladding metals, it is essential to measure the amount of C-14 released from radioactive cladding and to identify its chemical form. Transuranic (TRU) waste includes a large amount of C-14, which is one of the dominant radioactive nuclides. C-14 in metals such as Zircaloy, stainless steel, and Inconel is assumed to be released at a rate related to the individual corrosion rates of each metal. We consider four main issues associated with C-14 analysis: (1) Evaluating the oxidizing agents used in the wet oxidation method. (2) Improving the catalysts used in the oxidation furnace. (3) Examining the influence of the composition of the uptake liquid on liquid scintillation counter (LSC) measurements. (4) Improving chemical species identification. The C-14 inventory, leaching rate, and chemical form have been investigated in several studies to clarify the behavior of C-14 released from
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