Masaharu Sakagami

Radiolytic Environments in Boiling Water Reactor Cores

Radiolytic, environments in the BWR primary system were evaluated by using a theoretical model. Reactor core was divided into two regions, boiling and by-pass (non-boiling) channels. The major findings are summarized as follows: (1) Under normal operation without hydrogen addition, dissolved hydrogen and oxygen concentrations had their maximum values at the height where boiling started. Their concentrations in the boiling channel were lower than those in the by-pass channel because of hydrogen and oxygen release from liquid phase to gas phase. (2) The most efficient oxygen suppression by hydrogen addition was expected in the non-boiling regions of the reactor core where injected hydrogen was confined in the liquid phase. (3) When the bulk decomposition of water in the reactor core is represented by the coefficient decreased as hydrogen injection rate increased, but B hardly changed at a low hydrogen addition rate.

In‐Line Monitor for Electrical Conductivity of High‐Temperature, Aqueous Environments

This paper reports the development of an in-line monitor to determine electrical conductivity of aqueous solutions at elevated temperatures up to 300{degrees}C. By analyzing the frequency dependence of the impedance between three plating electrodes, the water resistivity was estimated separately from the impedance due to the surface reactions, which was the error source in electrical conductivity measurements at high temperature. By using the monitor, the effects of aqueous impurities, H{sub 2}SO{sub 4}, NaOH, and Na{sub 2}SO{sub 4} on the electrical conductivity were elucidated up to 300{degrees}C. Based on the measured conductivities, the first dissociation constant of H{sub 2}SO{sub 4} in high-temperature water was determined.

Bias Annealing of Radiation and Bias Induced Positive Charges in N- and P-Type MOS Capacitors

The radiation-induced positive charges trapped in an n-type MDS capacitor were observed to decrease with the number of C-V measurements. The positive gate bias applied on the capacitor was found to cause the decrease in the trapped charges. Its proposed mechanism was a recombination of the trapped positive charges with electrons injected from the Si substrate into the SiO2 layer due to the bias.

Structural Material Anomaly Detection System Using Water Chemistry Data, (II)

A calculation model was developed to predict the dose rate, caused by 58CO which is formed by the activation of 58Ni, around the recirculation pipes m boiling water reactors (BWRs). The model is characterized by considering direct deposition of Ni ion on the nuclear fuel cladding surface and the geometrical contact probability for the ferrite formation reaction between deposited Ni(Co) and Fe2O3 on fuel cladding surface. This model showed the important role of the amount of Fe crud on the surface to reduce 58CO ion concentration in the reactor water. And the necessary Fe concentration in the feedwater for reducing the dose rate in the primary system was estimated as a function of the operating time. This model also enables the quantitative predictions of the effect of prefilming treatment of the feedwater heater tubes or another methods to reduce dose rate in an Fe crud suppressed BWR.

Total-dose hardness assurance-testing for CMOS devices in space environment

A practical method for total-dose hardness assurance testing for CMOS devices in a space environment is presented to predict the radiation-induced threshold voltage shift and leakage current. Simple radiation response models for the threshold voltage shift and leakage current are given. The model parameters can be determined by laboratory irradiation testing with Co-60 gamma-rays at a high dose rate. Using this method, the threshold voltage shift and leakage current of MOSFETs can be predicted at low dose rate and at any temperature from room temperature to 80 degrees C.<<ETX>>

A Correction Method for Fluorescence Reduction Using Time-Resolved Fluorometry and Spectrophotometry

A method to correct fluorescence reduction due to foreign materials and temperature using time-resolved fluorometry and spectrophotometry has been developed. The factors taken into consideration were dynamic quenching and inner filter effects on the excitation beam and the fluorescence, and the fluorescence intensity with respect to these factors was theoretically analyzed. A theoretical approach for correcting the fluorescence intensity was obtained, with the use of the fluorescence lifetime, the absorbance at the excitation wavelength, and the absorbance at the fluorescence wavelength. Since these parameters are observable, a novel method can be applied to samples in cases where foreign materials and temperature are unknown. The proposed correction method is also suitable for noncontact and remote measurements. From experiments using a UO22+ ion, the proposed method was verified.

Conceptual design of a highburnup fuel rod for boiling water reactors using lowdensity UO/sub 2/ pellets of an annular type

Low density UO/sub 2/ fuel pellets of an annular type are used to solve two problems related to high-discharge burnup: the enhancement of the pellet/cladding mechanical interaction, which increases cladding permanent strain, and the increase in average neutron energy due to high enrichment, which changes the core neutronic characteristics. As an example, the design concept is applied to boiling water reactor fuel rods having 57 effective fullpower months (EFPMs). The fuel pellet density and the center hole diameter are determined to be 90% TD and 3.0 mm, respectively. The cladding permanent strain of the proposed fuel rod at EFPMs of 57 can be kept lower than the current fuel rod at 36 EFPMs. The EFPMs of 36 and 57 correspond respectively to the average discharge burnups of about 30 and 50 GWd/ tonne U. With an enrichment of 4.5 wt%, the former rods provide the same neutronic characteristics as that of current rods with 2.8 wt% enrichment. Furthermore, power generation cost in the newly designed core is reduced by about 10% from present cost levels.