It is necessary to consider how a glove box's confinement function will be lost when evaluating the amount of radioactive material leaking from a nuclear facility during a fire. In this study, we ...build a model that consistently explains the weight loss of glove box materials because of heat input from a flame and accompanying generation of the pyrolysis gas. The weight loss suggests thinning of the glove box housing, and the generation of pyrolysis gas suggests the possibility of fire spreading. The target was polymethyl methacrylate (PMMA), used as the glove box panel. Thermal gravimetric tests on PMMA determined the parameters to be substituted in the Arrhenius equation for predicting the weight loss in pyrolysis. The pyrolysis process of PMMA was divided into 3 stages with activation energies of 62 kJ/mol, 250 kJ/mol, and 265 kJ/mol. Furthermore, quantifying the gas composition revealed that the composition of the pyrolysis gas released from PMMA can be approximated as 100% methyl methacrylate. This result suggests that the released amount of methyl methacrylate can be estimated by the Arrhenius equation. To investigate the validity of such estimation, a sealed vessel test was performed. In this test, we observed increase of the number of gas molecules during the pyrolysis as internal pressure change of the vessel. The number of gas molecules was similar to that estimated from the Arrhenius equation, and indicated the validity of our method. Moreover, we also performed the same tests on bisphenol-A-polycarbonate (PC) for comparison. In case of PC, the number of gas molecules obtained in the vessel test was higher than the estimated value.
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.
For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, this study investigated the fundamental properties of ...herschelite adsorbent and evaluated its adsorption vessel for hydrogen production and corrosion. The hydrogen produced by the herschelite sample is oxidized by radicals as it diffuses to the water surface and thus depends on the sample's water level and dissolved species. The hydrogen production rate of herschelite submerged in seawater or pure water may be evaluated by accounting for the water depth. From the obtained fundamental properties, the hydrogen concentration of a reference vessel (decay heat = 504 W) with or without residual pure water was evaluated by thermal-hydraulic analysis. The maximum hydrogen concentration was below the lower explosive limit (4%). The steady-state corrosion potential of a stainless steel 316L increased with the absorbed dose rate, but the increase was repressed in the presence of herschelite. The temperature and absorbed dose at the bottom of the 504 W vessel were determined as 60 °C and 750 Gy/h, respectively. Under these conditions, localized corrosion of a herschelite-contacted 316L vessel would not immediately occur at Cl
−
concentrations of 20,000 ppm.
Volatile iodine production due to radiation chemical effects is known to be an important uncertainty source in the evaluation of the source term for severe accidents of light water reactors (LWRs). ...The gaseous release fractions of molecular iodine and organic iodine from gamma-irradiated 10
−4
mol/L cesium iodide aqueous solution were measuredwith the dose rate ∼ 7 kGy/h at room temperature. The solution was buffered with 0.1 mol/L boric acid and sodium hydroxide (pH ∼7) and contained up to 10
−3
mol/L methyl isobutyl ketone (MIBK) as an organic additive. The concentrations of MIBK in the solution and oxygen in the sweep gas were changed as experimental parameters. The total iodine release fraction of the original aqueous inventory and the fraction released as organic iodine were 2-47 and 0.02-1.5%, respectively, at the end of 2 h of irradiation. They were dependent on both the aqueous MIBK concentration and oxygen concentration in the sweep gas. Under a constant cover gas condition, the total iodine release showed a decreasing trend and theorganic iodine release showed an increasing trend when the MIBK concentration increased. This behavior can be explained by the branching of the reaction path of radiolytic degradation of ketones depending on the availability of dissolved oxygen, and competition between iodine and organic compounds on the consumption of radicals produced by water radiolysis.
To contribute to the confinement safety evaluation of radioactive materials in a glove box (GB) fire accident, combustion tests with polymethyl methacrylate (PMMA) and polycarbonate (PC) as typical ...panel materials for the GB have been conducted with a relatively large-scale apparatus. As important data for evaluating confinement safety, the release ratio and the particle size distribution of soot generated from burned materials as source term data for analyzing the migration behavior of soot particles were obtained. Furthermore, the effect of soot loading on the rise of the different pressure (ΔP) of the high efficiency particulate air (HEPA) filter ΔP was also investigated. The results showed that the release ratio of the soot generated from the burned PC was about seven times as large as PMMA and the relatively large particles of the soot from PC were also larger than PMMA. In addition, by considering the effect of the loading volume of the soot particles in the relatively low loading region of the soot, it was found that the behavior of the rise of ΔP accompanied with soot loading could be represented uniformly regardless of the kinds of combustion materials.
Recent Japanese nuclear regulations have focused on the hazards of in-cell solvent fires at reprocessing facilities. In this work, a mixture of tributyl phosphate and dodecane-based solvents was ...burned to generate an aerosol composed of soot and unburned solvent that was then loaded onto a high-efficiency particulate air filter simulating the ventilation system of reprocessing facilities. A radical increase of differential pressure occurred in the filters during these tests after the dodecane burned out from the solvent in a phenomenon we named as rapid clogging, likely caused by the burnout of dodecane. This relationship provides valuable insight into the establishment of new regulations for reprocessing facilities. Moreover, an analysis of the aerosol revealed an increase in unburned solvent content and aerosol particle size generated during the rapid clogging. As such, the rapid clogging may be caused by the unburned solvent release or interactions between the soot and unburned solvent vapor. Overall, this work indicates that clogging of ventilation filters during solvent fires may occur more rapidly than previously estimated.
A clogging behavior of a high-efficiency particulate air (HEPA) filter has been investigated for solvent fire accidents to provide valuable data for establishing a risk assessment method for ...reprocessing facilities in Japan. In this study, the burning rates of 30% tri-butyl phosphate (TBP)/dodecane and dodecane solvents and the differential pressure ΔP change of a high airflow-type HEPA filter applied in ventilation systems of reprocessing facilities in Japan were measured in the solvent burning. It was confirmed that the dodecane in the 30% TBP/dodecane mixed solvent burned mainly at the early stage of the burning of the mixed solvent and that the TBP burned mainly at the late stage of the burning of the mixed solvent. In addition, the burning rate of dodecane in the early stage and the rate of the TBP in the late stage were estimated, respectively. As a result, the former rate was almost the same as the burning rate of burning only the dodecane without TBP. Furthermore, the rapid increase of the ΔP of the HEPA filter was observed at the late stage of burning the mixed solvent. The increase of the release ratio of the airborne particles of unburned solvent (i.e., TBP and/or degradation products of TBP) and inorganic phosphorus (i.e., P
2
O
5
) was considered to contribute to the rapid increase. The empirical formulas for representing the relationship between the mass of the loading airborne particles onto the HEPA filter and the ΔP of the HEPA filter, except for the region of the rapid increase of the ΔP, under the mixed-solvent burning could be induced.
The release characteristics of Ru from highly active liquid waste (HALW) have been investigated under the condition of accidental evaporation to dryness by boiling of HALW. Using a laboratory-scale ...apparatus, the simulated HALW (s-HALW) was heated with an external heater to dryness to observe the release characteristics of Ru and gaseous nitrogen oxides. As a result, Ru was significantly released between 120 and 300℃ of the s-HALW. The cumulative release ratio of Ru was 0.088. It was also found that the partially released amount of Ru against the temperature of the s-HALW had two peaks at about 140℃ and about 240℃. Referring to the results of the release rate of gaseous nitrogen oxides and the volume of condensate, which was a collection of the mixed vapors of steam and nitric acid released from the s-HALW, we discussed the causes of Ru release around these peaks.
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