Toshiaki Matsuo

Activated carbon filter treatment of laundry waste water in nuclear power plants and filter recovery by heating in vacuum

Laundry waste water including such organic compounds as surfactants is generated from washing workers’ clothes in nuclear power plants. An activated carbon filter (ACF) to remove them for water purification and vacuum heating (VH) treatment for the spent ACF recovery were studied. For the purification test, 2×10−2 m3 of simulated waste water (SWW) were circulated in an experimental apparatus at 1.5×10−3 m3/min, passing through the ACF (0.205×1.2 m) roll continuously, until total organic carbon (TOC) concentration was lowered from 100 ppm to 10 ppm. To measure TOC, 1×10−5 m3 of SWW were sampled every 10 min. After that, the ACF roll was removed and treated by VH at 800°C for 2 h. Then, the second allotment of SWW was introduced. The purification test was started again to check the VH effect. The dependence of ACF adsorption rate and amount adsorbed, on the recovery number was checked. It took about 5 h to lower TOC. This adsorption performance was recovered by VH treatment. The dependence of ACF adsorption rate on the recovery number peaked at 10 times, and then dropped gradually. In contrast, the adsorption amount of organic compounds was simply lowered. This was attributed to the effect of macropore length reduction being transiently larger than the influence of the specific surface area lowering.

LiNO3 Addition to Prevent Hydrogen Gas Generation from Cement-Solidified Aluminum Wastes

LiNO3 addition to the cement solidified miscellaneous wastes has been proposed for preventing hydrogen ges generation caused by the corrosion of aluminum materials contained in the wastes. To determine an additive among alkaline metal ions, galvanic current was measured in 0.1 M alkaline metal hydroxide solution between aluminum and platinum electrodes. The volume of hydrogen gas generated from an aluminum specimen was measured in a KOH solution with LiNO3, LiCl, LiBr, Li2CO3 or Li2SO4 to decide the best additive. Applicability of the chosen additive to cement was confirmed by hydrogen gas generation measurement from an aluminum specimen in cement paste. The prevention mechanism was analyzed by X-ray diffraction, SEM and SIMS. The current measured in LiOH solution decreased with time, then reached 0 μA/mm2, while the current was detected in other alkaline metal hydroxide solutions. The least volume of hydrogen gas generation was measured in a KOH solution with LiNO3. The volume of generated hydrogen gas i...

Compatibility of the ultraviolet light-ozone system for laundry waste water treatment in nuclear power plants

As an alternative treatment system for laundry waste water in nuclear power plants, a system was chosen in which such organic compounds as surfactant would be oxidized by ultraviolet (UV) light and ozone. The system compatibility, UV light source, and dissolved ozone concentration were examined through experiments. First, ozone gas was absorbed in the waste water. After the dissolved ozone concentration equilibrated at the desired value, the waste water was irradiated by a mercury lamp. Then, the time dependence of the concentrations of the organic compounds, the dissolved ozone, and the hydrogen peroxide were measured to estimate the treatment rate of the system. The mercury lamp with a 10{sup 5}-Pa vapor pressure achieved large UV radiation and a treatment rate increase, leading to a compatible system without secondary waste generation. The effect of the dissolved ozone concentration on the treatment rate was saturated when concentration was >3.3 {times} 10{sup {minus}4} mol/10{sup {minus}3} m{sup 3} at the time UV radiation was started. Numerical results indicated the saturation was due to hydrogen peroxide generation, which prevents hydroxyl radical generation.

Treatment rate improvement of the ozone oxidation method for Laundry Waste Water

Radioactive laundry waste water generated in nuclear power plants includes organic compounds to be removed, for which ozone oxidation treatment is a possibility. To verify the applicability, its total organic carbon concentration (TOC) lowering rate improvement was examined in 0.5x10-3 m3 batch and 3x10-2 m3 pilot equipment experiments. In the batch experiments, ozone at a concentration of 200g/Nm3 was dispersed into 0.5x10-3 m3 of Simulated Laundry Waste Water (SLWW) with TOC of 11 mM. Total organic carbon concentration was measured every hour to see the effects of the temperature, and the initial concentrations of both H2O2 and NaOH which were added to urge OH radical generation from ozone. In the pilot equipment experiments, 1x10-2 to 3x10-2 m3 of the SLWW were circulated using an ejector to disperse the ozone. The influences of the flow rate and the SLWW volume on lowering TOC were examined, because they were related to the ejector dispersion performance and the appropriate ozone addition per SLWW volume. Appropriate initial H2O2 and NaOH concentrations in the batch experiments were 14.7mM and ImM, respectively. Lowering of TOC became faster at higher temperatures, because ozone self-decomposition and OH radical diffusion to the organic compound molecules were promoted. Lowering of TOC also became faster at higher flow rates, while the influence of the volume became saturated.

Influence of Finite Absorption of Radionuclides on Radionuclide Migration in an Engineered Barrier System

Abstract This study, which develops a safety assessment code for radioactive waste disposal, consists of two-dimensional analyses of underground water infiltrated flow and near-field radionuclide migration, one-dimensional analyses of far-field migration, and the dose equivalent. The study takes into account the influence of a finite absorption amount of radionuclides in an engineered barrier system (EBS). The safety assessment code is applied to 14C migration calculations. The near-field cylindrical model consists of an equally mixed region of wasteforms and backfill, bentonite, and rock. Carbon-14 coexists with 3.1 × 106 times as much 12C in the wasteforms. The distribution coefficient, maximum absorption amount, and solubility of CO32- against the equally mixed region are assumed to be 2.0 m3/kg, 3.06 mol/kg, and 544 mol/m3, respectively. Then, the release rate from the wasteforms (10-4 to 10-6/yr) and underground water detachment period from the wasteforms are examined to lower the dose equivalent by the intake of well water. The 14C concentration on the EBS boundary is 20 times as large in the case of EBS finite absorption as in the case of infinite absorption. So, the EBS finite absorption leads to absorption saturation and accelerated release of the radionuclides. The influence of the absorption saturation could not be prevented by lowering the release rate. A 3 × 104/yr detachment lowered the dose equivalent to 1/40 of the original case.