Comparison of passivation behavior of SS316L with that of SS304 in tritiated water solution

The effects of tritium on the passivation behavior and passive layer formed in tritiated water circum- stance for SS316L were investigated by means of an anodic polarization measurement technique and X- ray photoelectron spectroscopy, respectively. The results were compared with those for SS304, since it was predicted from a model of the tritium effects on corrosion suggested in the previous studies that SS316 would be less affective to tritiated water circumstance than SS304. As the results, the passiva- tion inhibitory effect of tritium could not be observed for SS316L, while it was observed for SS304 and the other researched materials so far, as predicted. However, the thickness of the passive layer and the boundary between the passive layer and bulk of SS316L were found affected by tritium; thickened and gradated, respectively. From these results, it was concluded that SS316L would be more sustainable in tri- tiated water circumstance than SS304, although the corrosion of SS316L would be more or less enhanced in tritiated water circumstance

Development of a real-time process gas analysis system using a semiconductor laser

In the fuel cycle of ITER and future fusion reactors, which consists of processes which are fueling, burning (by fusion reaction), vacuum pumping, purification (with recovery from tritiated impurities), isotope separation and storage, tritium accountancy control will be required from the viewpoint of operation and safety. Under ITER-EDA, as one of activities to establish the technological basis for tritium tracking and process system control, a remote and multi-location analysis system of hydrogen isotopes and tritiated molecular impurities in process gases by application of laser Raman spectroscopy was developed and validated at Tritium Process Laboratory (TPL) of JAEA [1]. Then, we had validated followability to process gas composition change and a detection limit of T2 gas of less than 1 kPa with an optimized system. More than 20 years after that development, great progress of laser and detection systems (especially, semiconductor lasers and Peltier-cooled CCD detectors, which have become very conventional and of high performance) has been achieved, which will enable us to make the system much simpler and conventional. A prototype system has been made at TPL, which consists of a semiconductor laser (488 nm, 200 mW, size: 31 mm×32.5 mm×63.5 mm), spectroscope (FL: 460 mm, 1200/mm grating) with a Peltier-cooled CCD detector, and an optical system. Results of some preliminary tests being conducted to confirm sensitivity (detection limits), stability, accuracy with static and dynamic test systems are presented.3rd Asia Pacific Symposium on Tritium Science (APSOT-3

Basic concept of JA DEMO fuel cycle

In the JA DEMO, the deuterium-tritium (DT) fuel will be supplied by a combination of gas puff, pellet injection and neutral beam injection. Since the combustion rate of fuel in the JA DEMO is approximately 1.7%, it is necessary to establish the closed deuterium-tritium fuel cycle in the facility for fuel recycling. The fuel cycle for DEMO inevitably differs from that for ITER. Compared to the ITER fuel cycle, which requires high flexibility for fuel supply based on the requirements of plasma experiments, the flexibility required for the fuel cycle decreases in the DEMO reactor. The flow in the fuel cycle becomes steadier. Therefore, the fuel cycle of the DEMO shifts to the continuous processing system. In addition, considering the tritium breeding in the blanket, the fuel cycle must be established so that tritium in the DEMO facility can be balanced. The process components of the fuel cycle that process a large amount of tritium-containing gas are provided with multiple barriers that confine tritium, and the detritiation system processes the confined tritium. The confinement of tritium in the DEMO facility according to nuclear safety regulations is an important safety issue. As a result, the fuel cycle becomes a complex chemical plant. Assuming safety requirements, it is necessary to consider the reduction of the tritium inventory as much as possible at the design stage of the DEMO fuel cycle. The tritium inventory in the fuel cycle is closely related to the requirements to pellet manufacturing and hydrogen isotope separation, and the reduction of the requirements to the hydrogen isotope separation is the major issue in the fuel cycle. For this purpose, it is necessary to minimize the D/T separation based on the concept of direct fuel cycle with the D/T mixture. For the possible shortage in the preparation of the initial loading tritium for the DEMO reactor, it is necessary to design the fuel cycle through dynamic numerical simulation so that the fuel cycle can be started with the minimum initial loading tritium. In the system design of the fuel cycle, it is necessary to support various operation modes from the startup of DT operation to steady operation. The requirements to design the JA DEMO fuel cycle are being investigated in the JA DEMO design activity

Importance of Simultaneous Combustion of Tritium and Hydrocarbons by Detritiation System in a Fire Event at Nuclear Fusion Facility

A detritiation system (DS) is required to remove tritium from the atmosphere of a nuclear contain-ment in any extraordinary situations. Realization of a DS that does not require heating of a catalyst reactor for tritium oxidation and frequent switching operation of adsorption columns for tritiated vapor collection will greatly contribute to the improvement of fusion safety. Concerning the catalyst reactor, it has been demonstrated that tritium can be oxidized at room temperature without any heating by the developed hydrophobic catalyst. To achieve a high tritium conversion efficiency for detritiation, it has already been revealed that suppression of production of tritiated hydrocarbons by hydrogenation reactions as side reactions of tritium oxidation in a catalyst reactor is the key issue to be solved. We have to pay special attention to ethylene among hydrocarbons because ethylene is easily tritiated by reaction of hydrogenation. In this study, complete combustion of ethylene at room temperature in the catalyst reactor is proposed as a measure to suppress the formation of tritiated hydrocarbons. Catalytic combustion characteristics of hydrocarbons were obtained, and the change in the ignition temperature by a change in each design parameter of the catalyst was demonstrated. Concerning noble metal species, platinum is superior to palladium due to less susceptibility to water vapor. The smaller the particle size of noble metal is, the higher the activity is, but because it is more susceptible to water vapor, the particle size of noble metal can be optimized. It was suggested that there is an optimum value for the pore size of the catalytic support

Development of a compact real-time process gas analysis system for tritium accountancy for a DEMO fusion reactor by an application of laser Raman spectroscopy

In the fuel cycle of ITER and the future DEMO fusion reactors, which has many processes of tritium provision/consumption/recovery/loss, such as, fueling, DT burning, vacuum pumping, purification, isotope separation and storage, detritiation, etc., tritium accountancy control will be required in its operation and safety management. In contrast to ITER, which will have frequent intervals between operations, a DEMO fusion reactor generating electricity must be operated continuously for long periods. This requires a dynamic tritium accountancy control, especially at the mass balance area boundary of the Tokamak including the vacuum vessel. To make a dynamic tritium accountancy system for a DEMO fusion reactor, based on our past work carried out during the ITER EDA, we are developing a new compact hydrogen isotope gas analysis system by the application of laser Raman spectroscopy advanced by technological progress in laser and detection systems. A prototype system has been made at TPL using a semiconductor laser with a Peltier-cooled CCD detector, with a simple optical system. Results of some preliminary tests being conducted to confirm sensitivity and accuracy under static and dynamic conditions are presented

Technical background on design of DS recombiner for fusion facility

Detritiation system of a nuclear fusion facility should maintain its detritiation performance even in an event of accident of the facility such as fire. The major technical background on design of recombiner for tritium oxi-dation are detailed kinetics data including the impact of possible gaseous impurities on kinetics, characteristics on pressure drop, impact of heat of reaction and effect of flow rate on kinetics. The volume of catalyst is evaluated by the overall reaction rate constant, required conversion efficiency and gas flow rate for processing. Our demonstration showed that the overall reaction rate constant has the effect of hydrogen concentration. Among possible impurity gases, water vapor, ammonia and halogenated acids affect tritium oxidation. Experimental demonstration revealed that the scale of recombiner have little effect on the overall reaction rate constant. The height of the catalyst layer is determined first from the allowable pressure drop considering the upstream line of the recombiner not to be pressurized. Then, the inner diameter of the recombiner is determined from the volume of catalyst. The concept of adiabatic recombiner with a vacuum jacket can be applied to avoid tritium permeation. The rate of tritiated methane produced by side reactions on the catalyst between methane and tritium was negligibly small