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Developing a better ceramic breeder (Li-containing oxide) is a key challenge for realizing fuel-self-sufficient fusion reactors. Ceramic breeder pebbles of hyper-stoichiometric lithium metatitanate...

Adaptation of the phosphate conversion technique was undertaken and evaluated for application to the recycle process of the spent electrolyte generated from metal electrorefining process. In order to confirm the conversion behaviors of fission product (FP) chlorides to the phosphates, conversion experiments were carried out for some alkali metal, alkaline earth metals and rare-earth elements and their results were compared with that of thermodynamic calculations of previous study [I. Amamoto, H. Kofuji, M. Myochin et al., in: Proceedings of Global 2007, Boisi, Idaho, USA, 2007]. Among these elements, rare-earth chlorides were converted into phosphates and Cs was not, according to the prediction by the calculation. As for alkaline earth metals, their equilibrium constants were nearly 1 based on the results of the calculations, the conversion reactions were difficult to occur. In addition, it was clarified that phosphates were thermally unstable, easily to decompose at higher temperature, through the measurements of their heat flow and vapor pressure.

A phosphate conversion process has been developed to reduce the high-level radioactive waste (HLW) generated in metal-electrorefining. In this study, the results of thermodynamic phosphate conversion reaction calculations are examined experimentally. Rare Earth Element (REE) chlorides were discovered to be easily converted into phosphates. Furthermore, regarding the use of an additive in the phosphate conversion reaction, the high temperature behavior of lithium phosphate was evaluated in elucidating its thermodynamic properties.

Lithium titanate (Li 2 TiO 3 ) is one of the most promising candidates among the proposed solid breeder materials in fusion reactors because of its chemical satiability. Addition of H 2 to inert sweep gas has been proposed for enhancing the release of bred tritium from breeder material. However, the mass of Li 2 TiO 3 has been found to decrease with time in the hydrogen atmosphere. In order to control the mass change at the time of high-temperature use, development of Li 2 TiO 3 which has excess Li 2 O is needed. Li 2 TiO 3 (L100) and Li 2.1 TiO 3.05 (L105) were prepared by solid-state reaction at 1273 K of Li 2 CO 3 and TiO 2 powders. In thermogravimetry, the masses of samples L100 and L105 were found to decrease with time in a hydrogen atmosphere, then to increase after a change of the atmosphere from hydrogen to oxygen. Sample L105 has fewer oxygen defects than L100. An atmosphere-controlled high-temperature mass spectrometer has provided the vapor pressure data for L100 and L105, under the conditions of D 2 atmospheres. Sample L105 has a higher partial pressure of total Li-containing species than L100 above 1093 K.

The 129I AMS system at MALT (Micro Analysis Laboratory, Tandem accelerator, The University of Tokyo) was reconfigured to use a gas ionization detector and achieved a background 129I/127I

Li2TiO3 is one of the most promising candidates among proposed solid breeder materials in fusion reactors because of its chemical satiability. Addition of H2 or H2O to inert sweep gas has been proposed for enhancing the release of bred tritium from breeder material in fusion reactors. However, its vaporization characteristic has not been well established. Application of an atmosphere-controlled high-temperature mass spectrometer has provided the vapor pressure data of Li-compounds evolved from Li2TiO3, under individual conditions of vacuum, D2, D2O and O2 atmospheres. The observed characteristics of vapor species evolved from Li2TiO3 under these conditions are presented here. The sum of the partial pressures of Li-containing species was figured out. The highest pressure was obtained in D2 followed by D2O and then, in vacuum, with the lowest being in O2. Furthermore, the temperature dependence of Li vapor pressure indicated that Li-containing species appeared above 1273 K in vacuum and O2 atmosphere, and above 973 K in D2 or D2O atmospheres. After the vapor pressure measurement in D2 atmosphere, the color of the sample changed from white to dark blue. This change of color with the oxygen content decreased, suggested change from Ti4+ to Ti3+ in reduction atmosphere.

The high-temperature gaseous molecules YbH, YbO and YbOH have been identified and their thermochemistry investigated by the Knudsen effusion mass spectrometry technique coupled with a controlled pressure gas inlet system.Solid ytterbium monosilicide and disilicide samples were made to react in the Knudsen cell with H 2 (g) and H 2 (g)/O 2 (g); in these conditions, several gaseous species (Yb, YbO, YbH, YbOH, SiO, SiO 2 , H 2 O) were formed under equilibrium conditions. The temperature dependences of the partial pressures of the observed gaseous molecules were analyzed to derive the Yb-X bond energies (X=H, O, OH). Selected values are D o 0 (Yb-H)= 179.4 ′ 2.0 kJ mol - 1 , D o 0 (Yb-O) = 384 ′ 10 mol - 1 and D o 0 (Yb-OH)=322+12kJmol - 1 , and Δ a t H o 0 (YbOH)=746′12kJmol - 1 . Density functional theory (DFT) calculations were also performed. Experimental and computational results are discussed and compared to previous data when available. The SiO/SiO 2 high-temperature gaseous equilibrium was also observed.

The atmosphere controlled high temperature mass spectrometer has provided the vapor pressure data for a promising tritium breeding material, Li2TiO3, under condition of low-pressure hydrogen atmosphere. The observed vaporization behavior of Li2TiO3 under hydrogen addition is presented here. It was pointed out that hydrogen addition may cause formation of non-stoichiometric composition phase. For elucidating its possible non-stoichiometric character, the composition of Li2TiO3 has been investigated mainly by means of thermogravimetry. The results revealed that Li2TiO3 has doubly non-stoichiometric composition, Li2-xTiO3-y

Vaporization behaviors of Cs 2 U 4 O 12 were studied by using the Knudsen effusion mass spectrometric method at temperatures from 1273 to 1573 K. To clarify vaporization properties of Cs 2 U 4 O 12 in case of severe accident conditions of light water reactors, partial pressure measurements were made in D 2 O/D 2 mixtures. The D 2 O/D 2 environments were established in the Knudsen cell by introducing D 2 (g) or D 2 (g) + O 2 (g) gas into the cell through a fine platinum tube attached to the bottom of the cell. Cesium vapor Cs(g) was found as the dominant vapor species over the compound either in vacuum or in the simulated atmospheres. In this study, the average temperature applied was 1423 K, the pressure of Cs(g) over the specimen in vacuum was 1.97 Pa while the oxygen potential measured was −148.2 kJ/mol. The pressure of Cs(g) increased moderately to 2.26 Pa after the introduction of the D 2 (g), and it decreased slightly to 1.56 Pa with the admission of D 2 (g)+O 2 (g).

For analysis of fission products release and transportation in severe accidents of nuclear reactors, vaporization behaviors of BaUO3, SrUO3, Cs2UO4, and Cs2U4O12 were investigated by using a Knudsen effusion high temperature mass spectrometer. To simulate water vapor and hydrogen environments in severe accident conditions of nuclear reactors, the environmental conditions inside the Knudsen cell were controlled by introducing proper amounts of gases, such as D2(g), D2O(g), O2(g), or their mixtures from outside reservoirs. To maintain dynamic equilibrium being established inside the Knudsen cell, however, the amount of input gas can not be too large. So the experimental result from the mass spectrometry can only apply for a small range of environmental conditions compared to those in a real severe accident of nuclear reactors. A calculation was made by using computer code Chemsage for other possible environmental conditions, such as wet condition with high H2O(g)/H2(g) ratio, reducing condition with low H2O(g)/H2(g) ratio, high temperatures up to 2500 K and high pressures up to 1 MPa. Both the experimental results and the calculation showed that environmental conditions have a great influence on vaporization properties of these compounds.

A new mixed gas inlet system for a Knudsen cell was developed for the introduction of a H2-O2 mixture and other mixed gases into a Knudsen cell of a high temperature mass spectrometer from outside reservoirs. Pressure of the gases as introduced into the Knudsen cell is controlled by the gas flow rates through low conductance capillary tubes connected to the outside reservoirs. The experimentally obtained gas flow rates agreed fairly well with the calculated ones for room temperature. However, the measured temperature dependence of the gas pressure in the Knudsen cell showed a negative departure from that of the theoretical values, which became especially large above about 1400 K. It was confirmed that, compared to the case of using the conventional direct H2O introduction method, water vapor can be supplied much promptly into a Knudsen cell in mass spectrometer from the outside by introducing H2 and O2 gases separately through the mixed gas inlet system developed in this study.

The atmosphere controlled high temperature mass spectrometer has provided vapor pressure data for lithium-based oxide ceramics under condition of low pressure hydrogen introduction. The measured vaporization behaviors under hydrogen addition of Li4SiO4, LiAlO2, Li2TiO3, and Li2ZrO3 are summarized. From the experimental data, sum of the partial pressures of lithium containing species was estimated for each oxide. It was pointed out that hydrogen addition seemed to cause the formation of a nonstoichiometric layer at the surfaces of Li4SiO4 and Li2ZrO3. Work function measurement was employed as a new method for investigation of such oxygen deficient layers. The results of the work function measurements showed the formation of an oxygen deficient surface layer for Li4SiO4 and for Li2ZrO3, whereas such was not the case for Li2TiO3.

With regard to the behavior of high radioactivity fission products in the case of accidents, the thermochemical behavior of Cs 2 UO 4 at high temperature is not completely known. A study of the vaporization of Cs 2 UO 4 was carried out from 873 to 1373 K using the Knudsen effusion mass spectrometric method. To simulate some LWR accident atmospheres, a D 2 /D 2 O environment was established by introducing D 2 (g) and/or D 2 O(g) gas into the Knudsen cell, separately or as a mixed gas. Thus, the influence of the input of D 2 /D 2 O on the vaporization of Cs 2 UO 4 was investigated quantitatively.

The vapor pressures in the Li 2 TiO 3 D 2 D 2 O system were measured by means of atmosphere controllable high temperature Knudsen effusion mass spectrometry. The effect of D 2 and D 2 O on vaporization behavior was investigated. The enthalpies of the reactions, Li 2 TiO 3 ⇌ 2Li+1/2O 2 +TiO 2 and Li 2 TiO 3 + D 2 O ⇌ 2LiOD + TiO 2 were calculated to be 1000.9 ± 32.4 and 449.6 ± 53.5 kJ/mol, respectively. From the results of this study, the maximum allowable temperature with respect to Li transport through the sweep gas in fusion reactor blanket was estimated.

Effects of various environments on vaporization characteristics of BaUO3 and SrUO3 have been studied by means of the Knudsen effusion mass spectrometry. Three kinds of Knudsen cells were employed for simulating different accident atmospheres over temperature ranges from 1470 to 1920 K. The vapor pressures obtained in a platinum Knudsen cell were used as the standard values, with which those obtained in other conditions were compared. A graphite Knudsen cell was utilized to simulate the graphite environment of high temperature gas-cooled reactors (HTGR). On the other hand, a specially designed Knudsen cell with a gas inlet system attached to its bottom was employed in order to introduce reactive gases such as D2(g) or D2O(g) from the outside of the mass spectrometer into the cell. In this way, the effects of hydrogen or water vapor on the vaporization of fission products barium and strontium were examined.

The vaporization properties of SrUO 3 have been studied for the first time by means of Knudsen effusion mass spectrometry over a temperature range of 1534 to 1917 K. The sample used was a mixture of SrUO 3 and 23 wt% UO 2 . The main vapor species over the mixture were Sr(g), UO 2 (g) and SrO(g) in decreasing order of their partial pressures. The standard enthalpy of formation of SrUO 3 was evaluated by using the second law and the third law treatments, in which estimated values of H °( T ) − H °(298.15) and gef( T ) were employed on account of absence of published data. The standard enthalpies of the formation of SrMO 3 with pseudo-cubic perovskite structure, where M stands for metallic cations with the valence of four, were also discussed based on the relationship between the ionic radii of M 4+ of the compounds and their enthalpy values.

An ‘atmosphere controllable high temperature mass spectrometer’ was developed in order to investigate the effect of D 2 and/or D 2 O on vaporization behavior of ceramic breeder blanket materials. The measurements were made on Li 4 SiO 4 , LiAlO 2 and Li 2 TiO 3 . The enhancement of Li vaporization and the formation of LiOD caused by D 2 and D 2 O introduction, respectively, were confirmed quantitatively. From the resulting thermodynamic data, an discussion on Li loss from the breeder ceramic materials was made. The maximum allowable temperature with respect to lithium transport through the sweep gas in fusion reactor blanket was estimated.

The equilibrium vapor pressures in the D2D2OLiAlO2 system were measured by means of an atmosphere-controllable high temperature mass spectrometer in the temperature range 1573–1773 K. Based on the reaction, 5LiAlO2(s) + 2D2O(g) = 4LiOD(g) + LiAl5O8(s), the heat of formation of LiAl5O8 was evaluated to be −4553.9 kJ/mol, which is in good agreement with the data in previous studies based on the reaction, 5LiAlO2(s) = 4Li(g) + O2(g) + LiAl5O8(s). The results of this study enabled estimation of the maximum allowable temperature with respect to lithium transport by the sweep gas in fusion reactor blanket.

An investigation of the vaporization of BaUO3 has been carried out for the first time by means of Knudsen effusion mass spectrometry in the temperature range of 1770–1920 K. The main vapor species over BaUO3 were BaO(g), Ba(g) and UO2(g) in decreasing order of their pressures. The standard enthalpy of formation of BaUO3 was evaluated by the second law and the third law treatments, in which the estimatedH0(T) − H0(298.15) andgef(T) values were employed on account of the absence of published data. Considering the compounds ofBaMO3 with the same perovskite structure whereM stands for metallic cations with the valence of four, a comparison of their standard enthalpies of formation was made in relation to the ionic radius ofM4+.

Gas/solid equilibria in the system Li 4 SiO 4 D 2 D 2 O were studied by means of Knudsen effusion mass spectrometry. A Knudsen effusion mass spectrometer was modified to enable studies of reactions of hydrogen and/or water vapor with ceramic breeder materials. A gas inlet system was constructed to allow the introduction of gases into a platinum Knudsen cell, from which the equilibrated gaseous reaction products effuse. From the experimental results, it has been deduced that the equilibrium constants of vaporization reactions differ correspondingly to the nonstoichiometry of lithium orthosilicate.

The vaporization behavior of cesium molybdate (Cs2MoO4) has been studied by using the Knudsen effusion mass spectrometry. A combination of a molybdenum outer cell and an alumina inner Knudsen cell was utilized in the Nuclide 12–90 HT high temperature mass spectrometer. The obtained vapor pressure P(Pa) of Cs2MoO4(g) is as follows: logP = −1.21 × 104 / T + 9.80 for temperatures higher than the melting point of Cs2MoO4, 1229.5 K, and, logP = −1.36 × 104T + 11.02 for temperatures lower than 1229.5 K, where T is in K.

A thermodynamic study of the vaporization of U-0.3 at%Fe alloy was performed by using the Knudsen-effusion mass spectrometric method in the temperature range of 1,780~2,180 K. Vapor pressures of U and Fe were determined as a function of temperature and the activity coefficients were derived which were compared with the activity coefficients calculated from phase diagrams. Both experimental and calculated values of Fe activity coefficient were considerably small and agreed well with each other, suggesting the estimation method of this study to be appropriate.

In order to evaluate the applicability of Li2SnO3 as a tritium breeding blanket material of a fusion reactor, a thermodynamic study of the vaporization of solid Li2SnO3 was performed by Knudsen effusion mass spectrometry. Partial vapor pressures of Li(g), O2(g), LiO(g), Li2O(g) and SnO(g) were determined over Li2SnO3. The measured partial pressure of Li(g) over Li2SnO3 is relatively high and ranks between those of Li2SiO3 and Li2TiO3. The Gibbs energy of formation of Li2SnO3 was obtained in the temperature range of 1455 to 1590 K. Computer calculations by use of the SOLGASMIX code proved that Li2SnO3 can show excellent performance as a breeder material with regard to tritium recovery and compatibility with stainless steel.