ICONE23-2180 EXPERIMENT ON RELEASE INHIBITION OF RUTHENIUM IN DRY OUT SITUATION OF HIGH LEVEL LIQUID WASTE

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In Japan, new regulatory requirements for nuclear fuel facilities came into force in December 2013. Cooling system malfunction is one important scenario to be taken into account for safety management of the nuclear facilities. Some radioactive material in high level liquid waste (HLLW) tank can potentially be released when the HLLW is heated, evaporated, and dried out due to the decay heat during cooling system malfunction. However, little study on transport behavior of these materials has been carried out. This experiment was planned to measure the fraction of radioactive material released, especially Ru, from the heated genuine HLLW. It has been considered that Ru could oxidize and volatile in a hot and concentrated nitric acid solution, therefore, we also planned to confirm a inhibition effect on the Ru release fraction of adding sucrose which is expected to decompose nitric acid. The genuine HLLW, called high radioactive concentration (HAC) here, was prepared by concentrating and denitrating high radioactive raffinate (HAR), which had been obtained after dissolution of a spent fuel irradiated up to 60 GWd/tU in a conventional power plant and removal of U and Pu from the other fission products and minor actinides. The Ru release fraction was found to be 0.4 % and 4 %, in experiments heating up to 393 K and 673 K, respectively. Inhibition effect of sucrose on Ru release was studied at the several molar ratios of sucrose/nitric acid (HNO_3). The addition of sucrose reduces the Ru release fraction, especially to 0.2 % and 0.03 % at molar ratios of 1/24 and 1/12. Therefore, the addition of sucrose to HLLW is an effective method to mitigate an environmental impact owing to Ru in case of an accidental loss of the cooling function equipped the HLLW storage tanks.

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