Shingo Tashiro

Segregation of the elements of the platinum group in a simulated high-level waste glass

Segregation of the elements of the platinum group occurred during vitrification of the borosilicate glass containing 20 wt% simulated high-level waste oxides. The segregated materials were composed of two crystalline phases: one was the solid solution of ruthenium and rhodium dioxides and the other was that of palladium and rhodium metals also with tellurium. The segregated materials were not distributed homogeneously throughout the glass: (i) on the surface of the glass, there occurred palladium, rhodium and tellurium alloy alone; and (ii) at the inner part of the glass, the agglomerates of the two phases were concentrated in one part and dispersed in the other.

Volatilization of cesium from nuclear waste glass in a canister

Volatilization of /sup 134/Cs from simulated high-level waste glass in a canister during several reheatings up to a maximum of 1000/sup 0/C was examined. The results showed that the temperature dependence of the amount of /sup 134/Cs suspended in the air inside the canister could be divided into two categories. As the temperature was increased above 500/sup 0/C, the amount of /sup 134/Cs suspended in the air inside the canister also increased. On the other hand, for temperatures <500/sup 0/C, the amount of /sup 134/Cs suspended in the air inside the canister had an almost constant value after several reheatings up to a maximum of 1000/sup 0/C. In this case, the air contamination by cesium-bearing material inside the canister is considered to be significant even at waste storage temperatures <500/sup 0/C.

Study on the permeability of engineered barriers for the enhancement of a radioactive waste repository system

To develop engineered barriers and construction methods for an enhanced radioactive waste repository, an advanced application of cement/concrete and bentonite was studied. On the basis of the tests on fundamental properties of the materials, model structures were prepared by actual construction methods, and then the permeability was evaluated For cement/concrete, two model silos were constructed by different methods and then the reduction in permeability was evaluated. One was constructed by an ordinary method and then grouted with cement milk containing fine cement and silica fume. The whole permeability of the silo after grouting decreased to one-sixteenth of the value before grouting. The other was constructed by a crack-controlling method. This method could make the whole permeability of the silo as low as one-tenth of that of the cracked silo. For bentonite, a compaction method and a spraying method were examined with a mixture of sodium-type bentonite and sand. To demonstrate these methods, model structure were constructed using full-scale machines. Then the relationship between the dry. density and the permeability was examined. For a 20 to 30% bentonite mixture, the permeability was almost equally low for both methods, while the density was lower for the spraying method than for the compaction method. In contrast, for a 10% bentonite content, low permeability could only be obtained with the high-density structure. The permeability of both the concrete structures and the bentonite-sand structures was significantly low as engineered barriers, showing some differences with the structures and their construction methods. Referring to the test results, an engineerd red barrier system proving low permeability was suggested by, a combination of the structures and the construction methods.

Well-type NaI(Tl) spectrometry for quantitative analysis of 244Cm leached from curium-doped synroc

Abstract The count rates in the 42.8-keV peak of 244Cm are integrated from 32.0 to 52.5 keV, and the net area under this peak is computed. The 244Cm activity is obtained by multiplying this area with the calibration factor, which is measured as a function of the volume of the curium solution. In the static leach test at 90°C, the normalized curium-leach rate does not vary significantly with time, and averages 1.1 × 10−3 g m−3 day−1 with an estimated total uncertainty of 75%.

Continouos-flow leach tests of simulated high-level waste glass in synthetic basalt groundwater

Abstract Continuous-flow leach tests have been carried out on simulated high-level waste glass in synthetic Grande Ronde basalt groundwater at 90 °C for up to 180 d. Preliminary results obtained without irradiation are described here as reference data for later comparison with those from future experiments with irradiation. The time-dependence of the concentrations of silicon is traced, and the maximum concentration at the plateau is estimated. It is concluded from the results that, above a linear flow rate of 0.1 cm/d, the normalized leach rates of silicon tend to level off at about 6 μg · cm −2 · d −1 which is the maximum value under the present flow conditions.

Skin Contamination by Radioisotopes, (V) Pig Skin Contamination by 239Pu

This paper deals with the contaminabilily and the permeability of Pu with varying soiling lime and acidity of the soiling solution applied to pig skin. It was found that the contaminability of Pu was affected by the formation of colloidal substances in soiling solution, as in the case of Pm, Sb, Po and U, described previously. It was also found that 0.05% of the Pu penetrated through the pig skin with pH 1 soiling solution after 60 min.

Adsorption on various leach container materials of plutonium and curium leached from nuclear waste glasses

Abstract The adsorption tendency of leached-out 238Pu and 244 Cm on the wall of leach containers, during the leaching of waste glasses, was studied. The test pieces of quartz glass, PFA Teflon, gold and stainless steel, which are candidates for a leach container, were immersed in deionized water with the waste glass containing 238Pu or 244 Cm in a Pyrex glass container at 100°C, and then they were decontaminated with dilute nitric acid. The quartz glass was found to have the smallest contamination of 238Pu and 244CM. The adsorption amounts of 244Cm on the PFA Teflon and quartz glass were approximately the same, and for 238Pu the Teflon showed about twice the amount of adsorption as that measured on the quartz glass. The gold and stainless steel showed 30–40 times the adsorption amount of 238Pu as that on the quartz glass. Adsorption and desorption of curium and plutonium were discussed in relation with difference of materials, time dependence and acidity of leachate. Curium, which has been previously leached out from waste glasses, showed a relatively simple adsorption and desorption behavior. In the case of plutonium, the colloidal species would take a large part in the adsorption and desorption processes. The relationship between the ratio of the colloidal to the ionic species of plutonium and the adsorption-desorption behavior was discussed. The observation of alpha autoradiographs elucidated that the ionic adsorption was desorbed more easily than the colloidal one.

Contaminative Behavior of Radioactive Materials on Protein Film Surface

The mechanism of skin contamination with radioactive materials was studied using protein film to simulate the human skin. The protein films were contaminated with 35S(H2SO4), 204Tl (TlNO3) and 147Pm(PmCl3), and many factors such as soiling time, radioactive concentration, specific activity and acidity of the soiling solutions, and the concentration of coexisting electrolytes were changed to examine their effect. It is concluded that the protein film is a useful material for studying the mechanism of skin contamination with radioactive materials. The contaminative behavior of the different radioisotopes on the film surface was found to reflect their respective properties, and varied accordingly.

Contaminative Behavior of Plutonium Chloride on Protein Film

This paper deals with the contaminative behavior of plutonium chloride on a protein film, which was studied in order to contribute to the knowledge of actual skin contamination. The experiments were carried out by changing such factors as soiling time, radioactive concentration, the concentration of coexisting electrolyte, acidity of the soiling solution and washing time. It was found that the contamination of plutonium varied with soiling time and with the acidity of the soiling solution. Maximum contamination was observed at pH 0.9. The mechanism of contamination is discussed, and it is concluded that contamination would appear be promoted by the formation of aggregated plutonium produced by the interaction with the surface of the protein film.