Hideo Yusa

Deposition of Iron Oxide on Heated Surfaces in Boiling Water

AbstractThe deposition of suspended iron oxide in boiling water at atmospheric pressure on a heated Zircaloy surface has been studied. The effects of various factors, including heat flux of the heated surface, concentration of iron oxide, and flow rate of boiling water, on the deposition rate during the initial period have been investigated.A model based on the microlayer evaporation and drying out phenomena that occur in the nucleate boiling bubble is proposed for an interpretation of the deposition rate. Close agreement is obtained between calculations using that model and the experimental results.

Decomposition of ion exchange resins by pyrolysis

Pyrolysis of spent ion exchange resins is one of the most effective methods for reducing radioactive waste volume and for making the final waste form more stable. Fundamental experiments were perfo...

A Calculation Model for Predicting Concentrations of Radioactive Corrosion Products in the Primary Coolant of Boiling Water Reactors

A calculation model was developed to predict the shutdown dose rate around the recirculation pipes and their components in boiling water reactors (BWRs) by simulating the corrosion product transport in primary cooling water. The model is characterized by separating cobalt species in the water into soluble and insoluble materials and then calculating each concentration using the following considerations: (1) Insoluble cobalt (designated as crud cobalt is deposited directly on the fuel surface, while soluble cobalt (designated as ionic cobalt) is adsorbed on iron oxide deposits on the fuel surface. (2) Cobalt-60 activated on the fuel surface is dissolved in the water in an ionic form, and some is released with iron oxide as crud. The model can follow the reduction of /sup 60/Co in the primary cooling water caused by the control of the iron feed rate into the reactor, which decreases the iron oxide deposits on the fuel surface and then reduces the cobalt adsorption rate. The calculated results agree satisfactorily with the measurements in several BWR plants.

Removal of radioactive cobalt ion in high temperature water using titanium oxide

Abstract The adsorption of Co 2+ on titanium oxide (TiO 2 ) has been experimentally evaluated as a function of temperatures in the range 20–280°C. The selectivity experiments showed that corrosion products such as Co 2+ , Ni 2+ and Mn 2+ in reactor water are preferentially adsorbed at high temperatures. The data suggest that there are two reaction mechanisms, i.e. an ion exchange reaction at low temperatures, and chemical adsorption with the formation of insoluble cobalt meta-titanate (CoTiO 3 ) on the TiO 2 surface at high temperatures.

Iron Oxide Deposition on Heated Surfaces in Pressurized Boiling Water

The deposition of suspended iron oxide in water at a 10-atm pressure during nucleate boilings on a Zircaloy heated surface has been studied. The effects of pressure on the deposition rate during the initial period have been investigated. The previously proposed iron oxide deposition model, based on the microlayer evaporation and dryout phenomena that occur in the nucleate boiling bubble at atmospheric pressure, is extended to high-pressure nucleate boiling conditions. The model is shown to be applicable for high-pressure studies.

An Empirical Formula Predicting Shutdown Dose Rate of the Recirculation Pipes in Boiling Water Reactors

An empirical formula is proposed to estimate the shutdown dose rates around the primary cooling system of boiling water reactors. The formula is characterized by defining the average activation time of /sup 60/Co, which is proportional to the iron feed rate into the reactor. The constants of the formula are determined by quantitatively evaluating the static balances of corrosion products in the primary coolant on the basis of measured results from the Shimane Nuclear Power Station of Chugoku Electric Power Company. The effects of four radiation reduction procedures on the shutdown dose rate are evaluated using the proposed formula. It is demonstrated that the oxygen injection method is the most effective procedure to reduce the dose rate (to approx. 1/4). Further reduction (to approx. 1/50) can be achieved by a combination of the four procedures.

Removal of radioactive methyl iodide by silver impregnated alumina and zeolite

Abstract The removal efficiency of methyl iodide for silver impregnated alumina and zeolite has been experimentally evaluated as functions of the relative humidity in the atmosphere and the amount of impregnated silver. At high relative humidities silver alumina performs with a larger removal efficiency using a smaller amount of impregnated silver than does silver zeolite. This difference is explained by effective reacting surface. The pore size dependency is correlated with the pore diffusion rate as the determining adsorption mechanism.

Effect of Metallic Impurities on Oxidation Reaction of Ion Exchange Resin, (I)

Dry oxidation of spent ion exchange resin is one of the most effective methods to reduce radioactive waste volume and also to make the final waste form more stable. Thermo-gravimetric measurements were performed using cation exchange resins with or without Fe in either an ionized or unionized form to clarify the effect of metallic impurities on the resin oxidation. The presence of an ionized Fe resulted in a considerable increase in the reaction rate constant, indicating that the Fe functioned as a catalyst. On the other hand, the unionized Fe showed no catalytic activity. Measurement of EPMA revealed that the ionized Fe was distributed uniformly throughout the resin particles, while the unionized one was distributed only on the surface of the resin particle. Catalytic activity increased with ionized Fe concentration up to 0.5 mmol-Fe/g-dry resin, above which the activity tended to decrease. The X-ray diffraction study attributed this to Fe coagulation in the resin particle. Kinetic models for solid-gas r...

Application of the Warm Water Injection Method to Improve the Efficiency of In-Core Wet Sipping for Leaker Detection

To improve the efficiency of in-core wet sipping leaker detection, a warm water injection method was developed. The method was characterized by pouring warm water into the channel box through the sipper cap and replacing all the water originally present with the poured water. Basic experiments were performed to determine the efficiency of the method. Mockup experiments were undertaken to confirm this and to ascertain the effects of operational conditions on the efficiency. These were done by the sipping procedures by means of a facility that included a full-scale 8 x 8 simulated fuel assembly. It was demonstrated that (a) the efficiency of detection for bottom leaks increased about a hundred times over the commonly used method, and (b) the increase in efficiency came from flattening the temperature distribution along the axial direction and exciting the natural convection flow in the whole assembly to promote the fission product transfer. Optimal operational conditions for the method were also proposed.

Development of a laundry waste treatment system

Abstract Fundamental and pilot plant experiments developed a laundry waste treatment system for nuclear power plants, consisting of a reverse osmosis unit for removal of radioactive materials and pre-concentration, and an evaporator for the final concentration. A sponge ball cleaning method was employed for the reverse osmosis unit and a heat-resistant antifoam reagent for the evaporator. The pilot plant test, using simulated wastes, showed a decontamination factor of above 10 3 and a volume reduction ratio of 10 −3 .