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Yamane Y.,Nuclear Safety Research Center | Amano Y.,Nuclear Safety Research Center | Tashiro S.,Nuclear Safety Research Center | Abe H.,Nuclear Safety Research Center | And 3 more authors.
Journal of Nuclear Science and Technology | Year: 2015

The release behavior of radioactive materials from high active liquid waste (HALW) has been experimentally investigated under boiling accident conditions. In the experiments using HALW obtained through laboratory-scale reprocessing, the release ratio was measured for fission product (FP) nuclides such as Ru, Tc-99, Cs, Sr, Nd, Y, Mo, Rh and actinides such as Cm-242 and Am-241. As a result, the release ratio was 0.20 for Ru and was around 1×10−4 for the FP and actinide nuclides. Ru was released into the gas phase in the form of both mist and gas. For its released amount, weak dependency was found to its initial concentration in the test solution. The release ratio decreased with the increase in the initial concentration. For other FP nuclides and actinides as non-volatile, released into the gas phase in the form of mist, the released amount increased with the increase in the initial concentration. The release ratio of Ru and NOx concentration increased with the increase in the temperature of the test solutions. They were released together almost at the same temperature between 200 and 300 °C. Size distribution of particles like mist was measured. The data show that there was a difference between distributions at the temperatures below 150 °C and over 200 °C. © 2015 Atomic Energy Society of Japan. All rights reserved.


A simple equation for the first peak power in a criticality accident due to instantaneous reactivity insertion into nuclear fuel solution system has been developed to improve the accuracy in the estimation of the first peak power keeping the easiness of calculation.The equation is based on the assumption that temperature feedback reactivity is a second-order function of an increase in fuel temperature. Peak power estimated using the equation was in a range between about a half and twice of experimental value. Its applicability to a wide range of initial reactivity and accuracy of estimation have been confirmed in the comparison to one-point kinetics numerical calculation.The expression suggests the first peak power increases with the square of small initial reactivity and three-halves power of large initial reactivity. © 2015 Atomic Energy Society of Japan. All rights reserved.


Ishikawa J.,Nuclear Safety Research Center | Kido K.,Nuclear Safety Research Center | Yoshida K.,Nuclear Safety Research Center
Transactions of the Atomic Energy Society of Japan | Year: 2013

The development of an accident consequence analysis method has been carried out at Japan Atomic Energy Agency for the development of a probabilistic safety assessment method for nuclear fuel facilities. A computer tool has been developed to simulate the boiling event of reprocessed liquid waste, which is postulated to occur due to the loss of the cooling function at a fuel reprocessing plant. The thermodynamic properties of a nitric acid solution containing radioactive waste in boiling and condensing states are necessary to quantitatively assess the amount of radioactive materials transferring to the gas phase. The developed tool simulates the boiling and condensation processes of liquid waste based on ebullioscopy. A simulation study demonstrated that the behaviors of liquid waste temperature and nitric acid concentration were in good agreement with the experimental results. © 2013 Atomic Energy Society of Japan, All Rights Reserved.


Yoshida K.,Nuclear Safety Research Center | Tashiro S.,Nuclear Safety Research Center | Amano Y.,Nuclear Safety Research Center | Yamane Y.,Nuclear Safety Research Center | And 2 more authors.
Transactions of the Atomic Energy Society of Japan | Year: 2014

An accident of evaporation to dryness by boiling of high-level liquid waste (HLLW) is postulated as one of the severe accidents to occur as a result of the loss of cooling function at a fuel reprocessing plant. In this case, a large amount of ruthenium (Ru) is volatilized and transferred to the vapor phase in the tank, and could be released to the environment. Therefore, the quantitative estimation of the amount of released Ru is one of the key issues in the assessment of the accident consequence. To resolve this issue, an empirical correlation for the rate of Ru transfer to the vapor phase with the temperature, nitric acid mole fraction and activity of HLLW has been developed using the data obtained from the accelerated experiments using simulated HLLW. A simulation study with the developed correlation demonstrated that the estimated amount of Ru transferred to the vapor phase was in good agreement with that obtained from the long-term experiment using actual HLLW.


Yoshida K.,Nuclear Safety Research Center | Ishikawa J.,Nuclear Safety Research Center | Abe H.,Nuclear Safety Research Center
Transactions of the Atomic Energy Society of Japan | Year: 2015

An accident of evaporation to dryness caused by boiling of high-level liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, some amount of fission products (FPs) will be transferred to the vapor phase in the tank, and could be released to the environment. Therefore, the quantitative estimation of the transport and release behavior of FPs is one of the key issues in the assessment of the accident consequence. To resolve this issue, a systematic analysis method with computer codes has been developed on the basis of the phenomenological behavior in the accident of evaporation to dryness caused by boiling of HLLW. A simulation study demonstrated that the behavior of liquid waste temperature and the entrainment of mists were in good agreement with the experimental results during the early boiling stage, and that some issues to be resolved were pointed out for the estimation of the amount of transferred Ru to the vapor phase at the late boiling stage. © 2015 Atomic Energy Society of Japan, All Rights Reserved.

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