This study has researched an estimation method for the amounts of residual sodium film and sodium lumps on dummy fuel pins in the Japanese prototype fast breeder reactor Monju by fundamental experiments and demonstration experiments. The residual sodium amounts on the pin surface were measured using three types of test specimens: (a) single pin, (b) 7-pin assembly, and (c) 169-pin assembly. The single pin and 7-pin assembly experiments revealed that the withdrawal speed of the pins and improvement of the sodium wetting drastically increased the residual sodium amounts. Furthermore, the 169-pin assembly experiments measured the practical amounts of the residual sodium in the Monju dummy fuel assembly and demonstrated sodium draining behavior through small gaps between the pins. The estimation method includes four models such as a viscosity flow model, Landau-Levich-Derjaguin (LLD) model, an empirical equation related to the Bretherton model, and a capillary force model in a tube. These calculation results were comparable to the residual sodium amounts obtained by the experiments. In the tests of improving sodium wetting, the amounts of residual sodium on the test specimen were close to 1.4 times larger than those of the thin sodium film estimated by the LLD model. The increased amount of residual sodium by improving the sodium wetting was explained by the ratio of the adhesion energy (?(SO)-?(SL)).

Herein, the wall shear stress in a double contraction nozzle has been evaluated experimentally to produce a liquid lithium (Li) target as a beam target for intense fusion neutron sources such as the International Fusion Materials Irradiation Facility (IFMIF), the Advanced Fusion Neutron Source (A-FNS), and the DEMO Oriented Neutron Source (DONES). The boundary layer thickness and wall shear stress are essential physical parameters to understand erosion–corrosion by the high-speed liquid Li flow in the nozzle, which is the key component in producing a stable Li target. Therefore, these parameters were experimentally evaluated using an acrylic mock-up of the target assembly. The velocity distribution in the nozzle was measured by a laser-doppler velocimeter and the momentum thickness along the nozzle wall was calculated using an empirical prediction method. The resulting momentum thickness was used to estimate the variation of the wall shear stress along the nozzle wall. Consequently, the wall shear stress was at the maximum in the second convergent section in front of the nozzle exit.

We developed a diagnostics tool for a liquid lithium (Li) target intended for use in intense fusion neutron sources such as the International Fusion Materials Irradiation Facility (IFMIF). The current design of IFMIF requires that the thickness of the liquid-Li target be maintained to within +/- 1 mm while operating under normal conditions. This paper deals with two topics: a conceptual design of the Li target diagnostics and verification tests of a candidate diagnostics (long-distance LP system). The overall concept of the Li target diagnostics is described first, and then the system configuration of the long-distance LP method, which is to be installed 7 m in front the Li target to measure the Li target thickness accurately, is shown. In addition, we present the results of verification tests aiming to examine the applicability of the long-distance LP system. The precision error resulting from long-distance measurement was estimated using a stationary specular-reflection object and a water-model simulating the Li target. As a result, we verified that the LP system has a precision of 16-40 mu m even at a sampling rate of 500 kHz measurement from a distance of 10 m.

A liquid Li free-surface stream flowing at 15 m/s under a high vacuum of 10 −3 Pa is to serve as a beam target (Li target) for an intense neutron source such as the planned International Fusion Materials Irradiation Facility (IFMIF). This study examines cavitation-like acoustic noise occurring upstream of the Li target. This noise is detected using an acoustic emission sensor that is installed at a Li target assembly in which the Li target was produced. A time-frequency analysis by continuous wavelet transform (CWT) was performed to characterize the acoustic noise, which determined the cause of the acoustic signal was cavitation. And the occurrence of cavitation was discussed by using Bernoulli’s equation and compared with the experimental observations. As a consequence, we revealed a criterion of inception of cavitation and a proper startup pressure of the Li target, which will be a design basis for the future IFMIF Li target facility.

A liquid Li jet flowing at 15 m/s under a high vacuum of 10−3 Pa is intended to serve as a beam target (Li target) in the planned International Fusion Materials Irradiation Facility (IFMIF). The engineering validation and engineering design activities (EVEDA) for the IFMIF are being implemented under the broader approach (BA) agreement. As a major activity of the Li target facility, the EVEDA Li test loop (ELTL) was constructed by the Japan Atomic Energy Agency. A stable Li target under the IFMIF conditions (Li temperature: 523.15 K, velocity: 15 m/s, and vacuum pressure: 10−3 Pa) was demonstrated using ELTL. This study focuses on a cavitationlike acoustic noise detected in a downstream conduit where the Li target flowed under vacuum conditions. This noise was investigated using acoustic-emission (AE) sensors installed at eight locations via acoustic wave guides. The sound intensity of the acoustic noise was examined against the cavitation number of the Li target. In addition, two types of frequency analysis, namely, fast Fourier transform (FFT) and continuous wavelet transform (CWT), were performed to characterize the acoustic noise. Owing to the acoustic noise's intermittency, high frequency, and the dependence on cavitation number, we conclude that this acoustic noise is generated when cavitation bubbles collapse and/or the structural material of the pipe is cracked because of the collapse of cavitation bubbles (cavitation pitting). The location of the cavitation was fundamental for presuming the mechanism. In this study, the propagation of acoustic waves among AE sensors placed at three locations was used to localize the cavitation and a method to determine the location of cavitation was formulated. As a result, we found that cavitation occurred only in a narrow area where the Li target impinged on the downstream conduit; therefore, we concluded that this cavitation was induced by the impingement. The design of the downstream conduit of the IFMIF Li target facility should be tackled in future based on information obtained in this study.

To show the Hertz-Knudsen equation is applicable to the prediction of the evaporation rates of Li and volatile impurities from the Li target surface at the International Fusion Materials Irradiation Facility (IFMIF), we analytically and experimentally studied these rates for a high-speed Li jet via engineering-scale tests performed under IFMIF conditions (vacuum pressure: 10(-3) Pa, Li temperature: 250 degrees C, jet speed: 7-15 m/s). The rates of evaporation and deposition were analytically predicted using the Hertz-Knudsen equation and the cosine law with known Li impurity concentrations (36 wppm for Na and 10 wppm or less for K). As pointed out in earlier works, Na and K are volatile impurities in Li. The evaporation rates of Na and K from liquid Li at a temperature of 250 degrees C are non-negligible, even if their concentrations in Li are as small as tens of wppm. To measure the deposition rate of evaporants from the Li jet, we used a quartz crystal microbalance and a neutralization titration method. The measured deposition rate was highly consistent with the deposition rate estimated analytically for weak evaporation. Also, the measured deposition rate was independent of the flow speed in the range of 7-15 m/s. We concluded that combining the Hertz-Knudsen equation and the cosine law is a reliable method for predicting the evaporation and deposition rates of Li and volatile impurities from a Li jet surface at the IFMIF.

This paper reports on validation results for the stability of a liquid lithium (Li) target intended for use as an intense fusion neutron source such as for the International Fusion Materials Irradiation Facility (IFMIF), an advanced fusion neutron source (A-FNS), and a demonstration fusion power plant (DEMO)-oriented neutron source (DONES). The variation in the thickness of a Li target must be suppressed to within +/- 1 mm inside a deuteron beam footprint to both maintain the integrity of the Li target and guarantee the desired level of neutron flux. We achieved a stable Li target with an average thickness variation of just 0.17 mm inside the beam footprint under standard IFMIF operating conditions (target speed: 15 m s(-1); vacuum pressure: 10(-3) Pa; and Li temperature: 250 degrees C). Moreover, the mean and maximum wave amplitudes at the beam center under such conditions were found to be 0.26 mm and 1.46 mm, respectively; these are small enough to satisfy operational requirements. Finally, it was determined that the stability of the Li target remained unchanged despite using it for an extended period of 1561 h. This finding is regarded as a significant step toward the realization of the IFMIF and the potential use of relevant neutron sources such as A-FNS and DONES.

The International Fusion Materials Irradiation Facility (IFMIF), presently in the Engineering Validation and Engineering Design Activities (EVEDA) phase was started from 2007 under the frame of the Broader Approach (BA) agreement. In the activities, a prototype Li loop with the world's highest flow rate of 3000 L/min was constructed in 2010, and it succeeded in generating a 100 mm wide and 25 mm thick with a free-surface lithium flow along a concave back plate steadily at a high-speed of 15 m/s at 250 °C for 1300 h. In the demonstration operation it was needed to develop the Li flowing measurement system with precious resolution less than 0.1 mm, and a new wave height measuring method which is laser-probe method was developed for measurements of the 3D geometry of the liquid Li target surface. Using the device, the stability of the variation in the Li flowing thickness which is required in the IFMIF specification was ± 1 mm or less as the liquid Li target, and the result was satisfied with it and the feasibility of the long-term stable liquid Li flow was also verified. The results of the other engineering validation tests such as lithium purification tests of lithium target facility have also been evaluated and summarized.

The lithium target facility of IFMIF (International Fusion Materials Irradiation Facility) consists of target assembly, lithium main loop, lithium purification loops, the diagnostic systems, and remote handling system. Major impurities in the lithium loop are proton, deuterium, tritium, 7-Be, activated corrosion products and the other species (C, N, O). It is very important to remove nitrogen content in lithium loop during operation, in order to avoid the corrosion/erosion of the nozzle of lithium target for the stable lithium flow on the target assembly. Nitrogen in the lithium can be removed by N hot trap using Fe-5% Ti alloy at temperatures from 400 to 600 degrees C. In this study, the specification and the detailed design were evaluated, and the component of N hot trap system was fabricated. (C) 2016 The Japan Society of Plasma Science and Nuclear Fusion Research

The International Fusion Materials Irradiation Facility (IFMIF) is an accelerator-based D+-Li neutron source in which two 40-MeV-D+ beams with a total current of 250 mA are injected into a liquid Li stream flowing at 15 m/s (Li target). The EVEDA Li test loop (ELTL), which simulates the hydraulic conditions of the Li target and a part of the purification system envisaged in IFMIF, is a main activity in the Li target facility of the IFMIF/EVEDA project and has been implemented under the Broader Approach (BA) agreement since 2007. The key issues to be validated in ELTL were as follows: (1) validation of the Li target, Li target diagnostics, and cold trap (CT), and (2) validation of long-term operation. This study describes the stability of the Li target in an integrated long-term operation run of the entire system as a demonstration of the IFMIF Li target facility. The Li target was continuously operated with the CT for 571 h, and its stability was evaluated periodically using a high-precision Li target diagnostic. Therefore, the Li target essentially satisfied the stability requirement of <+/- 1 mm throughout the continuous operation. (C) 2015 Elsevier B.V. All rights reserved.

In the framework of the Engineering Validation and Engineering Design Activities (EVEDA) project of the International Fusion Materials Irradiation Facility (IFMIF), we measured surface velocity fields of a lithium (Li) target at the EVEDA Li test loop under specifically-designated IFMIF conditions (target speeds of 10, 15, and 20 m/s, vacuum pressure of 10(-3) Pa, and Li temperature of 250 degrees C). In the current design of the IFMIF, the free surface of the Li target is under a most severe heat load condition with respect to Li boiling. The objective of this study is to measure the actual free-surface velocity under these IFMIF conditions to evaluate the heat removal performance of the Li target. The measured results (using the surface-wave tracking method that our team developed) showed two-dimensional time-averaged velocity distributions around the IFMIF beam footprint being virtually uniform, and close to the cross-sectional average velocity. The uniformity of the velocity distributions was less than 1 m/s. The comparison between the measured and analyzed surface velocity at the beam center showed that the analysis accurately predicts the measurement results within a margin of 3%. Finally, it was confirmed that the Li target delivers adequate heat removal performance in the IFMIF as designed. (C) 2015 Elsevier B.V. All rights reserved.

Three different partners, ENEA, JAEA ed University of Tokyo, have been involved during 2014-2015 in the Round Robin experimentation for the assessment of the soundness of the analitycal procedure for the determination of the Nitrogen impurities contained inside a solid Lithium sample. Two different kinds of Lithium samples, differing by about an order of magnitude in Nitrogen concentration (similar to 230 wppm; similar to 20-30 wppm), have been selected for this cross analysis. The agreement of the achieved results appears very good for what concerns the most concentrated Lithium and indicates each partner's procedure is appropriate and intrinsecally able to lead to meaningful values, characterized by a relative uncertainty of just few %. The smaller agreement in the case of the less concentrated Lithium anyway points out that particular attention must be paid to reduce as much as possible any source of external contamination and highlights the importance of the proper blank subtraction. (C) 2016 EURATOM-ENEA. Published by Elsevier B.V. All rights reserved.

In this study, the free-surface characteristics of a liquid Li wall jet for the Li target of the International Fusion Materials Irradiation Facility (IFMIF) are comprehensively reviewed. In developing the IFMIF Li target, a scientific understanding of the free-surface wave characteristics and the development of diagnostic tools to measure these characteristics were critical issues. The same issues must be faced in other liquid metal applications in fusion engineering, such as liquid first walls or liquid diverters. Thus far, diagnostic tools and methods to measure all of the characteristics of waves (i. e., wavelength, wave period, wave speed (free-surface speed), wave height (amplitude)), and average jet thickness have been developed, and the probability distributions applicable to these wave parameters, as well as their statistical characteristic values, have been determined, validating the stability of the IFMIF Li target. Our findings, both the wave characteristics and the diagnostic tools, can be applied to not only the IFMIF Li target but also innovative liquid metal diverters or first walls in fusion engineering. (C) 2016 The Japan Society of Plasma Science and Nuclear Fusion Research

In order to exchange the components which received irradiation damage during the operation at the International Fusion Materials Irradiation Facility, the adhered lithium, which is partially converted to lithium compounds such as lithium oxide and lithium hydroxide, should be removed from the components. In this study, the dissolution experiments of lithium compounds (lithium nitride, lithium hydroxide, and lithium oxide) were performed in a candidate solvent, allowing the clarification of time and temperature dependence. Based on the results, a cleaning procedure for adhered lithium on the inner surface of the components was proposed.

A high-speed (nominal: 15 m/s, range: 10-16 m/s) liquid lithium wall jet is planned to serve as the target for two 40 MeV and 125 mA deuteron beams in the International Fusion Materials Irradiation Facility (IFMIF). The design requirement of target thickness stability is 25 +/- 1 mm under a vacuum of 10(-3) Pa. This paper presents the results of the target thickness measurement conducted in the EVEDA Li Test Loop under a wide range of conditions including the IFMIF condition (target speed of 10, 15, and 20 m/s; vacuum pressure of 10(-3) Pa; and Li temperature of 250 degrees C). For measurement, we use a laser probe method that we developed in advance; this method generates statistical measurements method using a laser distance meter. The measurement results obtained under the IFMIF nominal condition (15 m/s, 10(-3) Pa, 250 degrees C) at the IFMIF beam center are as follows: average target thickness = 26.08 +/- 0.09 mm (2 sigma), mean wave amplitude = 0.26 +/- 0.01 mm (2 sigma), and maximum wave amplitude = 1.46 +/- 0.25 mm (2 sigma.). Of the total wave components, 99.7% are within the design requirement. The analytically predicted target thickness is in excellent agreement with the experimental data, resulting in successful characterization of the Li target thickness. (C) 2015 Elsevier B.V. All rights reserved.

A liquid-Li free-surface stream flowing at 15 m/s under a high vacuum of 10^<-3> Pa serves as a beam target (Li target) for the planned International Fusion Materials Irradiation Facility (IFMIF). The Engineering Validation and Engineering Design Activities (EVEDA) for the IFMIF are implemented under the Broader Approach Agreement. As a major activity of the Li target facility, the EVEDA Li test loop (ELTL) was constructed by the Japan Atomic Energy Agency. The stable Li target under the IFMIF conditions (Li temperature: 250 °C, velocity: 15 m/s, vacuum pressure: 10^<-3> Pa) has been demonstrated so far by using the ELTL. This study focuses on a cavitation-like acoustic noise that was detected in a downstream conduit where the Li target flowed under vacuum conditions. This noise was investigated using acoustic-emission sensors installed at eight locations via acoustic wave guides. The sound intensity of the acoustic noise was examined against the cavitation number of the Li target. In addition, two types of frequency analysis by the fast Fourier transform (FFT) and the continuous wavelet transform (CWT) were performed to characterize the acoustic noise. The results are as follows: 1) the acoustic noise was intermittent and consisted of multiple acoustic emissions whose time-width and frequency were 0.2 ms and less than 350 kHz respectively, and 2) the development of the acoustic noise was distinguished by four stages with regards to the change of sound intensity by using the cavitation number. From these results, we concluded that acoustic noise was generated from cavitation occurring in the downstream conduit.

A liquid-Li free-surface stream flowing at 15 m/s under a high vacuum of 10(-3) Pa is to serve as a beam target for the planned International Fusion Materials Irradiation Facility (IFMIF). The Engineering Validation and Engineering Design Activities (EVEDA) for the IFMIF is implemented under the Broader Approach. As a major activity for the Li target, the EVEDA Li test loop (ELTL) was constructed by the Japan Atomic Energy Agency. The present study demonstrates a stable Li target that satisfies the IFMIF design conditions (250 degrees C, 15 m/s, 10(-3) Pa) and presents the procedure for operating the Li target which consists of seven stages. We used a laser-based method to verify that the Li target is adequately stable. In addition, we examine cavitation occurring during startup of the Li target, and consequently, determine the appropriate startup pressure. (C) 2015 Elsevier B.V. All rights reserved.

When replacing lithium target components in the International Fusion Materials Irradiation Facility, the lithium adhering on the surface of components will chemically react with the surrounding atmosphere. In this study, we investigate the chemical reaction of pure lithium in room temperature air, oxygen, nitrogen, and argon of various humidities. In air, oxygen, and argon, the weight gain increases with time and humidity, and no significant difference is observed in these gases. In nitrogen, except for the test with 75% relative humidity (RH), the weight gain accelerates with time, and the weight gain rate decreases with increasing RH. We attribute the weight gain increase observed in low humidity to the acceleration due to lithium nitride formation. Upon increasing the moisture content of the gas, the main lithium reaction becomes lithium hydroxide formation.

A technique was needed for measuring the thickness of the liquid lithium target of the International Fusion Materials Irradiation Facility (IFMIF1). Thus, the applicability of a laser-based distance meter was evaluated within the framework of Engineering Validation and Engineering Design Activities (EVEDA) of IFMIF. This device is usually used against diffuse objects. However, in the present case, it is used against specular, finely deformed liquid metal surfaces. Both the measurement resolution and precision are required to be 0.1 mm or less to measure the thickness variation of +/- 1 mm. To ensure sufficient power of the reflected laser from the liquid metal surface, the laser spot diameter was set to 0.1 mm, considering previous experimental data regarding the dominant wavelength of surface waves. An experiment was conducted at the Osaka University Li loop in the velocity range 10-15 m/s and Li temperature of 300 degrees C under an argon atmosphere of 0.12 MPa. The experimental results showed that the laser-based distance meter can be used to measure the Li-jet thickness at a jet velocity of up to 15 m/s and with superior precision at 16 mu m, which is a much more precise value than required. (C) 2014 Elsevier B.V. All rights reserved.

Engineering Validation and Engineering Design Activities (EVEDA) for the International Fusion Materials Irradiation Facility (IFMIF) have been carried out under the "Broader Approach" (BA) agreement. As a major activity for the Li target facility, the EVEDA Li test loop (ELTL) was constructed at the Japan Atomic Energy Agency's Oarai site to validate the hydraulic conditions of the IFMIF Li target. This paper presents the first operational results of the Li target in the ELTL. A series of tests were performed to check the operational performance of the Li target. The conclusions are as follows: (1) the start-up procedure of the Li target was examined and consequently achieved the Li target and (2) the Li target whose velocity was 20 m/s under pressurized and vacuum conditions was observed by image devices and confirmed to be stable. (C) 2014 Elsevier B.V. All rights reserved.