Technique for Radioactivity Measurement in Drum Package Waste by Using Scattered Gamma-Rays

An evaluation method for the radionuclide content in low level drum package waste by using scattered γ-rays has been investigated. Gamma-rays are counted by a detector after passing through a collimator having appropriate vertical and horizontal openings both for the segmented scan and for the average geometrical efficiency being almost independent of the source position. The attenuation of unscattered γ-rays is estimated from the intensity ratio of scattered rays to unscattered ones of the nuclide emitting the highest γ-ray energy in the drum. Satisfactory results were obtained in numerical simulations and basic experiments carried out using test equipment with a pure Ge detector and a rectangular collimator, and sample 200l drums, containing sealed ⁶⁰Co and ¹³⁷Cs sources, and having a uniform density of 2.2 g/cm³. The error of the evaluated content, which depended slightly on the activity distribution, was a maximum of about ±30%.     

Evaluation of Migration of Cesium-137 Adsorbed on Fine Soil Particles through Natural Aerated Soil Layer

In order to evaluate migration of ¹³⁷Cs adsorbed on fine soil particles in natural aerated soil layers, filtration constants of fine soil particles between soil and pore water were determined by the inverse analysis of the results of a large scale indoor migration test (STEM) using the soil layer samples collected from the natural aerated soil layers of Tokai and Rokkasho-mura without any disturbance. The amounts of ¹³,Cs which migrated through the soil layer samples with the movement of fine soil particles were also determined by the inverse analysis. The filtration constant for a loamy soil layer was larger than that for a sandy soil layer and the dependence of the filtration constant on mean diameter was the same as that obtained in small scale column experiments. On the other hand, the amount of ¹³⁷Cs which migrated through the soil layer sample with the movement of fine soil particles was 0.15~6.5% of introduced ¹³⁷Cs and dependent on size distribution and solidification degree of the soil layer sample. Therefore, it seems that the amount of ¹³⁷Cs which migrates to a long distance with the movement of fine soil particles is small in the case of a fine and solidified soil layer. A trial evaluation of the migration of ¹³⁷Cs adsorbed on fine soil particles using the result of the analysis showed that the concentration decreasing effect of Rokkasho's soil layer including the loamy soil layer was larger than that of Tokai's sandy soil layer.     

Diffusion Behavior of Cesium,Strontium and Cobalt in Pellet Waste Package

A leaching model for a radioactive pellet package for nuclear power plant wastes was studied. Calculated results obtained in term of the model were compared with experimental ones, where volumetric averages of diffusion coefficients in the Na₂SO₄ pellet and in the cement-glass were used to solve the diffusion equation in the pellet package. Since Na₂SO₄ pellets dissolved quickly, the pellet part were simulated by saturated Na₂SO₄ solution. The leaching ratios were meaured with different volume ratios of cement-glass in the package to discuss the validity of the model. The cement glass diffusion coefficient and distribution factor, which were required to solve the equation, were also measured. The calculated results agreed with the experimental ones within a 20% error.     

Three Year Experimental Study of Leaching Phenomena from Low Level Radioactive Cement-Based Waste Forms

Abstract

This study was carried out in order to demonstrate the safety of homogeneous cementbased waste forms (hereinafter called cement forms) for BWR's low level radioactive wastes as engineered barriers. Eighteen full scale simulated cement forms were manufactured with the addition of ¹³⁷Cs, ⁶⁶Co and ⁹⁰Sr.

Leaching tests on these forms were carried out for approximately three years. In order to study the relationship of leachability to environments at disposal sites, this Three Year Leaching Test was conducted for three kinds of environmental conditions, sea water, land water and soil. After the tests, all of these forms were cut to measure the distribution of the radionuclide's density within them. In case of the soil tests, the distribution of radionuclide in the soil was also measured.

The radionuclide leachability results reveal that ⁶⁰Co was almost completely retained in the cement forms and that ¹³⁷Cs leached from cement forms was mostly adsorbed by the soil. On the other hand, ⁹⁰Sr was not trapped in the forms and leaked through the soil around them in retard. This study also showed that simulated cement forms buried in the soil were more physically and chemically stable, and had longer term stable radionuclide containment capability than those which were submerged in sea or land water.     

Elution Behavior of Cesium from Ferrierite Column by Using Inorganic Salt and Acid Solutions

The distribution coefficient (K_d) of Cs on ferrierite decreased with increasing concentration of the coexisting inorganic cations in the order of Na⁺>H⁺>K⁺>NH₄ ⁺. A linear relationship with a slope of about —1 was obtained between log K _d and log[M⁺] above 0.1M (=mol/dm³). The retention volume (V _R ) of Cs in chromatography also decreased in a similar manner to K _d , depending on the kind of inorganic cations. The V _R value can be predicted from the K _d value based on the linear relation. The column efficiency was improved with fine particles of ferrierite, yielding the elution percentage above 95%.     

Recovery of Heat-Generating Nuclides in Eluted Solutions

To study about microstructure and chemical composition of oxide films formed on surface of stainless steel is most important for understanding of stress corrosion cracking (SCC) and irradiation assisted stress corrosion cracking (IASCC). In this work, a new sample preparation method for microstructure observation of oxide films was developed. To prevent to break oxide films during fabrication, surface of specimens were protected with plating. Focused ion beam (FIB) processing was conducted to prepare thin foil samples of cross section of oxide films. After sample preparation, microstructure of cross section of oxide films was observed by transmission electron microscope (FE-TEM), and microscopic chemical composition was analyzed by energy dispersed X-ray spectrometer (EDS). From the results, effects of silicon (Si) doping for oxide film formation in two oxidation conditions are discussed.     

Separation of Heat-Generating Nuclides from High-Level Liquid Wastes through Zeolite Columns

Heat-generating nuclides Cs and Sr were separated from simulated high-level liquid wastes (HLLW) by successive adsorption on columns of ferrierites (F) and zeolite A. Adsorbed Cs and Sr were efficiently eluted with NH₄NO₃ and EDTA solutions, respectively, yielding the recovery over 96%. A simulated waste solution containing 29 components was denitrated with a formic acid up to pH 7.92. The amounts of nuclides adsorbed from this denitrated solution were experimentally estimated to be 0.33 mmol Cs/g·F and 0.19 mmol Sr/g·A, respectively.     

Formation of Analcime Film under Hydrothermal Conditions

Polycrystalline analcime film was prepared from hydrogels under hydrothermal conditions. The analcime film of about 200 pm thickness built up on a porous alumina support at temperatures above 160°C, and the size and crystallinity of analcime increased with temperature. The thickness of analcime film increased with incubation time, and the growth rate at 180°C was faster than that at 160°C. The analcime film obtained was thermally stable at temperatures up to 700°C, and no structural changes were observed after treatment in nitric acid solutions below 0.01M. Analcime had an ion-sieve ability to large sized Cs⁺ ion, and Ag⁺ and Rb⁺ ions of small sizes were incorporated in analcime.     

Experimental and Analytical Study on the Behavior of Cesium Iodide Aerosol/Vapor Deposition onto Inner Surface of Pipe Wall under Severe Accident Conditions

The WAVE experiments have been performed at JAERI to investigate the CsI deposition onto the inner surface of pipe wall under typical severe accident conditions. It was shown that relatively large amount of CsI was deposited at the upstream floor of the pipe and that larger amount of CsI was deposited on the ceiling than the floor at the downstream. Analyses of the experiments have also been conducted with the three-dimensional thermohydraulic code, SPRAC, and the radionuclide transport analysis code, ART. The experimental results were well reproduced with ART by using peripherally subdivided pipe cross section and associated representative thermohydraulic information from SPRAC prediction. It was clarified through the present experiment and analyses that major deposition mechanisms for the chemical form of CsI are thermophoresis and condensation. Accordingly, the coupling of the FP behavior and the detailed thermohydraulic analyses was found to be essential in order to accurately predict the CsI deposition in the pipe, to which little attention has been paid in the previous studies.     

Analysis of Adsorption Behavior of Cesium onto Quartz Using Electrical Double Layer Model

The adsorption behavior of Cs onto quartz was investigated with the use of a high performance liquid chromatograph. The surface-based distribution coefficient (K_a) of Cs onto quartz was determined in the solution of which pH ranged from 6 to 11 and ionic strength from 10^?3 M to 10^?1 M. The K_a values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully analyzed by an electrical double layer model and the optimum parameter values of the double layer electrostatics and adsorption reactions were obtained. The adsorption mechanisms of alkali metal ions was discussed on the basis of the present analysis.