Tritium Cleanup System Research Articles

Bend points of hydrogen partial pressure curves obtained by tritium removal simulation tests

A tritium cleanup system has been developed for exhaust gases containing tritium in various chemical forms. This system is distinguished from conventional procedures in that tritium is removed as tritiated hydrogen molecules. Basically, the system consists of five main components, including a hydrogen separator and a decomposition-processing vessel. A previous study assumed that the gas for processing consisted of hydrogen, methane, and helium, with some proportion of tritiated hydrogen and methane. The performance of this tritium cleanup system was examined using a computer-based simulation. To monitor the removal of tritium from the exhaust gas, the partial pressures of the respective components were examined during processing. The curve for the partial pressure of hydrogen contains two clear bends. In the present study, the correspondence between these bend points and their time width and simulation condition was examined in relation to the hydrogen partial pressure curves obtained under 28 conditions, differing in component proportion and process gas volume. It was found that two bend points moved, depending on the process gas condition, and three patterns appeared for the hydrogen partial pressure curves. A mechanism was proposed for explaining the movement of the bend points and the three patterns.

A Simple Flow Analysis of Diffuser-Getter-Diffuser Systems

Tritium clean-up systems typically deploy gas processing technologies between stages of palladium-silver (Pd/Ag) diffusers/permeators. The number of diffusers positioned before and after a gas clean-up process to obtain optimal system performance will vary with feed gas inert composition. A simple method to analyze optimal diffuser configuration is presented. The method assumes equilibrium across the Pd/Ag tubes and system flows are limited by diffuser vacuum pump speeds preceding or following the clean-up process. A plot of system feed as a function of inert feed gas composition for various diffuser configuration allows selection of a diffuser configuration for maximum throughput based on feed gas composition.

STAR Facility Tritium Accountancy

The Safety and Tritium Applied Research (STAR) facility has been established to provide a laboratory infrastructure for the fusion community to study tritium science associated with the development of safe fusion energy and other technologies. STAR is a radiological facility with an administrative total tritium inventory limit of 1.5g (14,429 Ci)[1]. Research studies with moderate tritium quantities and various radionuclides are performed in STAR. Successful operation of the STAR facility requires the ability to receive, inventory, store, dispense tritium to experiments, and to dispose of tritiated waste while accurately monitoring the tritium inventory in the facility.This paper describes tritium accountancy in the STAR facility. A primary accountancy instrument is the tritium Storage and Assay System (SAS): a system designed to receive, assay, store, and dispense tritium to experiments. Presented are the methods used to calibrate and operate the SAS. Accountancy processes utilizing the Tritium Cleanup System (TCS), and the Stack Tritium Monitoring System (STMS) are also discussed. Also presented are the equations used to quantify the amount of tritium being received into the facility, transferred to experiments, and removed from the facility. Finally, the STAR tritium accountability database is discussed.

The Safety and Tritium Applied Research (STAR) Facility: Status-2004

The Safety and Tritium Applied Research (STAR) Facility, a US DOE National User Facility at the Idaho National Engineering and Environmental Laboratory (INEEL), comprises capabilities and infrastructure to support both tritium and non-tritium research activities important to the development of safe and environmentally friendly fusion energy. Research thrusts include (1) interactions of tritium and deuterium with plasma-facing-component (PFC) materials, (2) fusion safety issues [PFC material chemical reactivity and dust/debris generation, activation product mobilization, tritium behavior in fusion systems], and (3) molten salts and fusion liquids for tritium breeder and coolant applications. This paper updates the status of STAR and the capabilities for ongoing research activities, with an emphasis on the development, testing and integration of the infrastructure to support tritium research activities. Key elements of this infrastructure include a tritium storage and assay system, a tritium cleanup system to process glovebox and experiment tritiated effluent gases, and facility tritium monitoring systems.

Theoretical expressions for removing tritium from exhaust gas

A tritium cleanup system for application to exhaust gases discharged from a large helical device has been developed. It is constructed of five main components and is able to remove tritium in the chemical form of hydrogen molecules. In a previous study, a decomposition-processing vessel was developed, which is one of the five main components, and the system's performance installed in this vessel was tested based on computer simulations. In the simulations, the process gas was assumed to be made up of hydrogen, methane and helium, where part of the hydrogen and methane had been tritiated, and helium had been added to maintain a proper flow rate in the cleanup system. Several assumptions about the gas component fraction and tritium ratio in the gas to be processed were made. Two fundamental equations were used to express the removal of tritium in both chemical forms of hydrogen molecules and methane in the simulations. However, detailed descriptions of the assumptions and equations were not given. In the present paper, both the assumptions and equations are theoretically explained.

Behavior of tritium in the TSTA test cell combined with operation of the Experimental Tritium Cleanup (ETC) system

Tritium and deuterium are expected to be the fuel for the first fusion power reactors. Being radioactive, tritium is a health, safety and environment concern. Room air tritium clean systems can be used to handle tritium that has been lost to the room from primary or secondary containment. Such a system called the Experimental Tritium Cleanup (ETC) systems is installed at the Tritium Systems Test Assembly (TSTA) at Los Alamos National Laboratory. The ETC consists of (1) two compressors which draw air from the room, (2) a catalyst bed for conversion of tritium to tritiated water, and (3) molecular sieve beds for collection of the water. The exhaust from this system can be returned to the room or vented to the stack. As part of the US–Japan fusion collaboration, on two separate occasions, tritium was released into the 3000 m 3 TSTA test cell, and the ETC was used to handle these releases. Each release consisted of about one Curie of tritium. Tritium concentrations in the room were monitored at numerous locations. Also recorded were the HT and HTO concentrations at the inlet and outlet of the catalyst bed. Tritium surface concentrations in the test cell were measured before and at a series of times after the releases. Surfaces included normal test cell equipment as well as idealized test specimens. The results showed that the tritium became well-mixed in the test cell after about 45 min. When the ETC was turned on, the tritium in the TSTA test cell decreased exponentially as was expected. The test cell air tritium concentration was reduced to below one DAC (derived air concentration) in about 260 min. For the catalyst bed, at startup when the bed was at ambient temperature, there was little conversion of tritium to HTO. However, once the bed warmed to about 420 K, all of the tritium that entered the bed was converted to HTO. Immediately after the experiment, surfaces in the room initially showed moderately elevated tritium concentrations. However, with normal ventilation, these concentrations soon returned to routine levels. The data collected and reported here should be useful for planning for the operation of existing and future tritium facilities.

Computer simulation of the processing of tritium in exhaust gas from the LHD

A new type of tritium cleanup system that differs from conventional systems in its application of a decomposition-processing vessel has been investigated by means of computer simulation. In the decomposition-processing vessel, tritiated compounds are decomposed so that it is possible to extract the tritium in the form of hydrogen molecules while other elements such as carbon are fixed within the vessel. In our computer simulation of the removal of tritium, a single run of processing was assumed to handle 1 N m 3 of a gaseous mixture that contained 1 GBq tritium and was 90% hydrogen, 5% methane and 5% helium. As a result, three pressure curves, one for hydrogen, a ‘both-sum’ (hydrogen+methane) curve and a ‘total-sum’ (hydrogen+methane+helium) curve, showed strong and marked changes in trend at almost the same elapsed time. This time corresponded to the completion of a single cycle of processing. The changes in trend suggest that the three curves had been dominated in the first cycle by the hydrogen initially contained in the exhaust gas and that, after one cycle, they had come to be dominated by the remaining methane and by the hydrogen generated by methane decomposition. It took about 8.7 h for the concentration of tritium in the gas being processed to fall below the relevant limit.

Nitriding reactions with a Zr–Mn–Fe metal getter

The metal getter Zr–Mn–Fe (SAES ST909) is an important component of a metal hydride-based tritium clean-up system at Los Alamos National Laboratory (LANL). The system is normally used to clean a glovebox with a helium/nitrogen atmosphere. During start-up operations, it was found that the Zr–Mn–Fe alloy exhibited an anomaly during activation, namely an exotherm upon initial exposure to nitrogen. The purpose of this work is to better understand this nitriding reaction. Nitrogen absorption studies, temperature profile experiments, and powder X-ray diffraction (XRD) were used to study the nitriding reaction. An exothermic reaction between nitrogen and ST909 was observed at ∼450°C only when the getter was heated for the first time. ST909 that had been previously heated without nitrogen did not produce an exotherm when heated a second time with nitrogen. Based on the XRD evidence, it was speculated that nitrogen reacts exothermically with the zirconium in the ST909 material. After heating above ∼660°C, the aluminum binder in the ST909 melts and may alloy with the zirconium. The resulting alloy appears to be less reactive with nitrogen and does not produce an exotherm.

Development of tritium cleanup system for LHD

Energy is vital for humans and we have been consuming a large amount of fossil fuel especially from the beginning of the industrial revolution. Nowadays its huge consumption has however come to threaten our life and we have to prepare nonfossil fuels, for instance solar energy, biomass energy, nuclear energy and so on. Fusion energy is an unlimited resource and one of the strongest candidates of the future energy source. At the National Institute for Fusion Science (referred to as ‘NIFS’ hereafter), we have constructed a new fusion experimental device called large helical device (referred to as ‘LHD’ hereafter) in 1998. The device will generate a small amount of tritium, as a fusion product. In order to remove it from the exhaust gas, we have designed a tritium cleanup system based on a new concept. This system is mainly composed of a palladium permeater, a decomposer and hydrogen absorbing alloys. It may perfectly recover the tritium from exhaust gas without oxidizing it. This system is applicable for the future needs at fusion power plants. In order to remove tritium discharged from fusion experimental facilities, it is usual to employ a system by which tritiated constituents, in various chemical forms, are entirely converted to a form of water vapor by catalytic oxidation. The water vapor containing tritiated form is then absorbed by molecular sieve (referred to as ‘wet system’ hereafter). However, in the case of LHD, it is not rational to deliberately convert the discharged tritium into the water vapor, because the tritium discharged from LHD is almost in a form of hydrogen molecules. Moreover, the tritium in the form of water vapor affects the human body 18 000 times stronger than that of hydrogen molecules. In accordance with these view points, we have developed another type of tritium cleanup system based on a new concept, in which hydrogen molecules including tritiated ones (HT, DT and T 2) found in the exhaust gas of LHD are directly fixed to hydrogen absorbing alloys. Other impurities such as methane and water vapor, parts of which are tritiated, will be decomposed into each elemental form by the decomposition process and hydrogen molecules, including tritiated constituents from the decomposition (referred to as ‘dry system’ hereafter).

Development of a Tritium Cleanup System for a Large Helical Device Using Nonvolatile Getter Materials

A tritium cleanup system has been conceptually developed for the large helical device (LHD) at the National Institute for Fusion Science. The system is a processing device employed to remove tritium from exhaust gas. In the exhaust gas discharged from the LHD in normal operation, the major part of tritium constituents should be in a form of hydrogen molecules because the fuel used in plasma experiments with the LHD is hydrogen molecules. From this viewpoint, we have designed a tritium cleanup system, which is characterized by tritium being removed and stored in a form of hydrogen molecules with less impurities, like oxygen and carbon, and its decomposition and the separation processes are introduced to convert various tritiated compounds into a form of hydrogen molecules of high purity. Besides these, there is another aspect in that getter materials are applied in both decomposition of tritiated compounds and storage of hydrogen molecules containing tritium.The system design is composed of three essential component parts: a hydrogen separator, a hydrogen absorbing vessel, and a decomposition process vessel. The hydrogen separator and the decomposition process vessel make a process loop repeat to remove hydrogen into a form of hydrogen molecules with less impurities. It is important that “less impurities” means having a less bad influence on hydrogen-absorbing materials used in the storage vessel.We think that the hydrogen separator will be manufactured by employing a palladium hydrogen purifier system, which is available in the marketplace, and the hydrogen storage vessel will also be manufactured by using hydrogen-absorbing alloys like titanium. Thus, the serious problem imposed on us is how to realize the decomposition process vessel. To develop the decomposition process vessel, we thought nonvolatile getter materials were promising and carried out performance tests of methane decomposition by the nonvolatile getter materials, where methane was used because it is hardly decomposed and there is little data for a flowing-gas system.The tritium cleanup system that was designed is presented. Also, a methane decomposition curve with ZrNi alloys used as one of the typical nonvolatile getter materials is shown, and the probability of the realization of the decomposition process vessel is examined.

Uranium Getters for Tritium Cleanup at the Tritium Laboratory Karlsruhe (TLK)

This paper reports on in a three-stage tritium cleanup system in which the gaseous impurities O{sub 2}, N{sub 2}, Co{sub 2}, Co, Ch{sub 4}, NH{sub 3} and H{sub 2}O are removed from a contaminated hydrogen stream. Cleanup is performed with uranium getters which operate at temperatures between 500{degrees}C and 900{degrees}C. In long term experiments carried out in the VERDI test facility a capacity factor of approximately 60% has been achieved so far. The impurities have been retained so far. The impurities have been retained down to values between {lt} 1 ppmv and 10 ppmv. The cleanup system for the Tritium Laboratory Karlsruhe is presently under construction.

Design and Operational Experience with a Portable Tritium Cleanup System

We built a portable tritium cleanup system to scavenge tritium from contaminated gases in any tritium-containing system in the LLNL Tritium Facility. The cleanup system uses standard catalytic oxidation of tritium to water followed by water removal with a molecular sieve dryer. The cleanup unit, complete with instrumentation, is contained in a portable cart that is rolled into place and connected to the apparatus to be cleaned. The cleanup systems is effective, low-tech, simple, and reliable. The nominal flow rate of the system is 30 liters/minute, and the decontamination factor is > 1000. In this paper we will show design information on our portable cleanup system, and will discuss our operational experience with it over the past several years.

Comparison of Precious Metal Catalysts with Hydrophilic Porous Substrate for Tritium Cleanup System

Abstract Existence of the structure water in the hydrophilic porous substrate can give various effects on tritium behavior in a tritium recovery system consisted of precious metal catalyst bed and adsorption bed because the catalytic isotope exchange reaction or the isotope exchange reaction proceeds besides oxidation reaction or adsorption reaction. Properties of Pt catalysts loaded on various hydrophilic porous substrate are compared in this study. It is known from experiment that Pt-Alumina catalyst has the largest exchange capacity and that Pt-MS 5A catalyst has the largest total capacity because it has the effective adsorption capacity. For silica gel substrate, certain transport reaction of tritium in the substrate whose rate is rather slower than the rate of isotope exchange reaction is observed and it gives peculiar undesirable quality for silica gel to use in a tritium recovery system.

Conceptual design of a closed vacuum pumping system using turbomolecular pump for fusion reactor

Abstract As a vacuum pumping system for a D—T fusion reactor, a closed type of pumping system which does not exhaust DT fuel gas and removes only impurity gas including helium ash is proposed. The closed system is defined as a closed vacuum circuit in which only DT fuel gas can be circulated and refueled to the reactor. The basic components in the system consist of turbomolecular pumps, dry vacuum pumps, cryocondensation pumps and gas reservoirs. Helium ash removal is affected by use of getter materials for DT gas. Other impurity gas is pumped with 50 K cryocondensation pumps, and at the regeneration phase the pumped gas is dealt with by a tritium clean-up system. The detailed design of the system is described and the possibility of the system for practical use is discussed.

Comparison of precious metal catalysts with hydrophilic porous substrate for tritium cleanup system.

Abstract Existence of the structure water in the hydrophilic porous substrate can give various effects on tritium behavior in a tritium recovery system consisted of precious metal catalyst bed and adsorption bed because the catalytic isotope exchange reaction or the isotope exchange reaction proceeds besides oxidation reaction or adsorption reaction. Properties of Pt catalysts loaded on various hydrophilic porous substrate are compared in this study. It is known from experiment that Pt-Alumina catalyst has the largest exchange capacity and that Pt-MS 5A catalyst has the largest total capacity because it has the effective adsorption capacity. For silica gel substrate, certain transport reaction of tritium in the substrate whose rate is rather slower than the rate of isotope exchange reaction is observed and it gives peculiar undesirable quality for silica gel to use in a tritium recovery system.

TFTR Tritium Program

The Tokamak Fusion Test Reactor (TFTR) at Princeton began operation in December 1982. Since then it has operated successfully with protium and deuterium achieving energy confinement time at peak electron density of 10/sup 19/ m/sup -3/s, with ion temperatures of 20 keV. This paper describes the systems and preparations required for D-T operation, i.e. introducing and operating the tokamak with tritium in order to achieve the scientific break even point of Q=1. These systems include the tritium storage and delivery system, the tritium injection systems, the tritium clean-up systems, and the plasma exhaust and collection systems. It is expected that TFTR will have these systems fully operational, with trained personnel.

Catalyst Study for the Decontamination of Glove-Box Atmospheres Containing Tritium at MPC Levels

The BEATRICE loop was designed for studying the conversion of tritium at very low activity levels using catalytic oxidation followed by water trapping. The purpose is to study kinetic parameters required for the design of the NET tritium cleanup system with the two main objectives to operate without isotopic swamping and to determine the ability of efficient conversion at room temperature. From experiments carried out between 20 and 250/sup 0/C it is concluded that two palladium/alumina and platinum/alumina catalysts are very efficient in removing tritium from contaminated gas mixtures down to a few MPC levels without isotopic swamping and even at room temperature. However at room temperature, in relation to tritium species trapped on the catalyst surface a progressive deactivation with time occurs. This phenomenon may be a concern for process efficiency and tritium inventory and regeneration conditions have to be determined in order to demonstrate industrial feasibility of operating at room temperature.

Conceptual Design of A Self-Cooled FLiBe Blanket

There are a number of attractive features for Flibe, such as: (1) low-pressure operation, (2) relatively inert to air and water, (3) low activation, (4) high-temperature stability, and (5) low electrical conductivity. If these features can be incorporated into a self-cooled blanket, a simple, high-performance, and reliable blanket may be possible. Detailed analysis has uncovered some attractive features and some potential problems. A highly compact and efficient primary loop can be developed with a conversion efficiency of 46%. The blanket is designed to be inherently safe for at least a 4.7 MW/m/sup 2/ neutron wall loading. Since no reflector is needed, the mass utilization is very high. A similar blanket for MINIMARS has a mass utilization figure of 138 kW(e)/tonne, the highest among the four blanket candidates. In addition, a very simple blanket can be designed. There is, however, concern about the lithium doping idea for tritium control. The issues cannot be resolved until experimental verification is available. However, if a vanadium alloy is used for the structural material, a large fraction of tritium will permeate back through the first wall to the plasma. Permeation through the first wall will result in a tritium partial pressure of < 10/sup -4/more » Torr. If this is the case, the primary blanket tritium recovery system can be combined with the plasma exhaust system. A highly efficient tritium cleanup system will still be required to reduce the tritium permeation problem. A countercurrent extraction system can be used for tritium cleanup.« less

Recovery of tritium in inert gas by precious metal catalyst supported by hydrophilic substrate.

In this study, it is proposed to use exchange reaction between hydrogen isotopes in gas phase and those in hydrophilic substrate of the precious metal catalyst for the purpose of recovering tritium as molecular form from the inert gas such as the atomosphere in the secondary containment, where no oxygen is expected. The values of the equilibrium constant and reaction rate constant for this reaction are obtained for tritium-protium system and deuterium-protium system experimentally. It is also certified that the tritium concentration at the outlet of Pt-alumina catalyst bed is evaluated in good agreement with experimental values. Behaviors of the tritium cleanup system for the secondary containment applying this reaction are compared for various operational conditions, and it is concluded that isotope exchange reaction using hydrophilic catalyst bed is applicable for the secondary contaiment. The bed of the precious metal catalyst can also be active as oxidation catalyst even when air in the tertiary conta...

Operation of the Room Air Tritium Removal System at the Tritium Systems Test Assembly

AbstractFusion reactor facilities will be required to minimize releases of hazardous materials to the environment during both normal operations and accident situations. The Tritium Systems Test Assembly (TSTA) at the Los Alamos National Laboratory has a tritium removal system, capable of processing room air to collect tritium accidentally released into the tritium handling areas of the facility. This system, the Emergency Tritium Cleanup (ETC) system, will both minimize accidental releases to the environment from TSTA and demonstrate the feasibility and operations of a large room air detritiation system. The system is also designed to study tritium releases under controlled conditions. Based on the initial nontritium tests described in this paper, we have determined that the ETC has a single-pass efficiency for tritium collection of greater than 99.9%.