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The tritium laboratory karlsruhe: R&D work and laboratory layout
Fusion Engineering and Design 12 (1990) 331-341 North-Holland
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THE TRITIUM LABORATORY KARLSRUHE: R&D WORK AND LABORATORY LAYOUT
H.J. A C H E , M. G L U G L A , E. H U T T E R , G. J O U R D A N , R.-D. P E N Z H O R N K. S C H U B E R T , H. S E B E N I N G a n d J.E. V E T T E R
*, D. R O H R I G ,
Nuclear Research Center Karlsruhe, Postfach 3640, 7500 Karlsruhe, Fed. Rep. Germany
Submitted 31 August 1989; accepted 10 November 1989 Handling Editor: R.W. Conn
The Tritium Laboratory Karlsruhe (TLK) provides the technical means for R&D work on the fuel cycle and components of the next fusion device within the framework of the European Fusion Technology Programme. Other areas of tritium research such as blanket interfaces, fueling devices, plasma facing components, etc. are within the wider scope of the future activities. This paper summarizes current tritium research activities at the Nuclear Research Center Karlsruhe; these investigations constitute the basis for the first large scale experiments at the TLK. The infrastructure of the TLK is treated in detail, in particular information is given on tritium processing systems such as storage, transfer, chemical purification, and isotope separation. Important tritium safety aspects and the control system are described. The present status of the laboratory and the time schedule for licensing and commissioning is also addressed.
1. Introduction
Fuel cycle technology is one of the key issues for NET and ITER. The N E T / I T E R fuel cycle differs substantially from current developments at JET in that a life-time total of about 30 kg of tritium will be burned. In addition, stringent requirements on the allowable releases from maintenance as well as from operational and accidental conditions over an extended period of time must be met together with a minimization of tritium waste. The N E T / I T E R fuel cycle technology should serve to demonstrate in practice during an early stage the feasibility of safe operation and low environmental impact of future generation reactor systems. This cannot solely be achieved by improving methods and single components, but it is also necessary to demonstrate the reliable dosed loop operation of large facilities. Furthermore, the operation of these facilities will serve to train the personnel required for the much more complex fusion machines of the future. After the Fusion Technology Project was launched in KfK and established within the European Fusion Technology Program it was decided to implement a * To whom correspondence should be adressed.
Tritium Laboratory in Karlsruhe (TLK) and to expand the already existing tritium activities in order to provide technical means for experiments with realistic quantities of tritium, typical of future fusion devices. Work in TLK will concentrate on the development of advanced processes for plasma-exhaust fuel clean-up of the N E T / I T E R basic machine. Another area of great interest concerns cryogenic pumping which, as a prestep to plasma exhaust purification, is subject to very difficult-to-define operation conditions on the input side and has to couple to the clean-up system on the output side. As study work on blanket design progresses - two concepts are presently being followed in KfK - many new technical questions will emerge. Future discussions will indicate to what extent tritium tests will be required to qualify process components and to demonstrate integrated systems. Further tritium technology related tasks defined within the European program are pursued at other European tritium laboratories. The development of the NET design and the publication of new results from the accompanying R & D work will have an impact on the TLK test program and on the infrastructure. It will be necessary to increase the TLK infrastructure (storage capacity, control proce-
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dures and diagnostics) in line with the growth in dimension and complexity of the tested N E T / I T E R prototype components.
2.
Research
program
2.1. Purpose
The Tritium Laboratory Karlsruhe is mainly devoted to R & D work with tritium on a technical scale within the needs of N E T / I T E R . Experiments carried out at other laboratories of KfK with model gaseous mixtures and tracer amounts of tritium provide the basis for the processes and technologies to be verified and tested in the TLK. The principal activities at TLK are: development of advanced fuel clean-up technology, - process development for the recovery of tritium from lithium materials to be used in KfK's helium cooled ceramic and self-cooled liquid blankets * testing of prototype components such as vacuum and transfer pumps, valves, cryotraps, fueling devices, etc., work on the development of process analytics, - studies on the radiochemistry of fusion fuel cycle impurities, and investigations on environmental problems such as the behaviour of tritium in the system plant/soil. It is also expected that the operation of the TLK with its partly novel components and processes of the infrastructure will yield valuable know-how on tritium handling. This is specially true in the fields of hydrogen isotope purification and separation. Z2. Role in the fusion program
The development of large peripheral components will be required for the detailed engineering of NET. The performance of these components will be examined using relevant amounts of tritium in single or integral tests. While it is generally agreed that the clean-up of plasma exhaust gas is not a critical feasibility issue, there still is a need for a fully demonstrated concept,
* Investigations on the off-line recovery of tritium from breeder ceramics will not be carried out in the TLK, because irradiated materials are handled more readily in the Hot Cells of KfK.
not only on a technical scale but also with NET relevant quantities of tritium. The goal of attaining fuel self-sufficiency in a fusion reactor requires the demonstration that the selected option is highly reliable and achievable with very low tritium inventories and low losses for all subsystems. Complementary to experiments with engineering scaling the key components of the systems under investigation should be tested in long-term runs for mechanical stability and endurance towards the exposure to relevant amounts of tritium. Highly efficient and powerful pumping systems are required for the attainment of a vacuum in the plasma chamber of a fusion reactor. Cryopumping is an adequate method, which can also cope with the problems of radiation and magnetic fields. For the pumping of helium together with hydrogen isotopes and impurities cryocompound systems are under development that need to be tested in a tritium environment. For handling, transfer, and storage of large quantities of tritium appropriate getter materials must be identified. Extensive tests under a variety of conditions are required to evaluate these getters. Experiments with tritium (aging studies) will provide information concerning long-term detrimental effects on the material properties of the getters and on the release characteristics of decay helium. Control and surveillance of tritium processing systems require suitable in- and off-line analytics. Efforts will therefore be devoted to the development of selective and sensitive tritium compatible analytical instruments that are characterized by low or no sample consumption. A better understanding of the role of secondary radiochemical reactions occuring between gaseous tritium and impurities is needed. To fill this gap systematic theoretical and laboratory work with tritium is required to identify radiochemical reactions that can occur in the various tritium processing units. 2.3. Technologies investigated
The fusion related tritium technology activities at KfK are integrated into the European Fusion Technology Program. Research activities are under way on the following specific technologies: - development of a catalytic process for the plasma exhaust purification - optimization of cryogenic vacuum pumping of helium - absorption of hydrogen isotopes on metal beds other than uranium - development of fusion reactor vacuum components in cooperation with industry
H.J. Ache et al. / The Tritium Laboratory Karlsruhe absorption of impurities relevant to the fusion fuel cycle on hot metal beds - cold trapping and recovery of bred tritium from a N a K intermediate loop - cryosorption on molecular sieves or alternative adsorbents tritium extraction by permeation with solid getters from eutectic liquid Pb-17Li. Furthermore, technology oriented work in the fields of development of tritium purification with getters for the use in TLK, development of analytical instrumentation for the determination of tritium containing species, and - study work in the fields of (i) development of helium cryopumping materials and design concepts of cryocompound pumps for NET, (ii) development of a plasma exhaust purification system for NET based on catalytic reactions, and (iii) development of technology for the recovery of tritium from a helium cooled solid ceramic blanket is in progress.
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2.4. Status of work and major results 2.4.1. Fuel clean-up process for N E T A process concept based on extensive experimental work in KfK has been proposed for the reprocessing of the primary vacuum exhaust gas of the NET fusion reactor during burn and dwell as well as for the recovery of tritium from the waste gases produced during bakeout, glow discharge cleaning or carbonization. This concept involves recycling of tritium entirely as DT, the least objectionable chemical form with respect to radiological hazards. In a first step most of the free hydrogen isotopes are recovered and purified by a main pall a d i u m / silver permeator. Tritium/deuterium chemically bonded in species such as hydrocarbons, ammonia, and water are liberated by selective catalytic reactions and recovered with a second PdAg permeator. Experimentally, it was shown that at temperatures above 300°C the rate of hydrogen permeation through commercial palladium/silver permeators of high permeation areas, e.g. 0.12 m 2 is not influenced by the presence of any of the impurities relevant to the fusion fuel cycle, even if present at high partial pressures. For the conversion of water into hydrogen the water gas shift reaction is employed using a zinc stabilized copper chromite catalyst. This reaction, which takes place in high yield at temperatures below 200"C, requires only a small amount of catalyst and an excess of carbon monoxide not larger than C O / H 2 0 = 1.5.
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Methane, higher hydrocarbons, and ammonia are decomposed into their elements on a nickel catalyst at temperatures below 500°C. A complete kinetic study of the corresponding reactions has been carried out, also employing relevant gaseous mixtures, in closed loop operation and in once through flow systems. The mechanism of the decomposition has been confirmed with polytritiated methane and polytritiated ammonia. Carbon produced from the cracking of hydrocarbons can be volatilized by reaction with carbon dioxide. This reaction increases the life-time of the catalyst. The tritium inventory of the catalyst was found to be comparatively low. Only a few kilograms of catalyst per year of operation to process the exhaust gases of a large fusion machine are sufficient. Detailed engineering planning of a fuel clean-up facility for NET is nearly completed. Based on this planning, a facility will be constructed to demonstrate the catalytic concept on an engineering scale in the TLK, employing appropriate amounts of tritium. The construction of a facility to carry out long-term tests in the TLK on the performance of commercial permeators exposed to high levels of tritium is well in progress. 2.4.2. Optimization of the cryogenic vacuum pumping of helium Extensive screening tests have been conducted with cryosorption panels consisting of a surface of active sorbent material bonded to a heat conductive substrate. Candidate materials were selected on the basis of their helium pumping speed, stability upon thermal cycling, and sorption capacity. Promising samples are examined in poisoning tests with deuterium to simulate tritium exchange with adsorbed impurities and its effect on helium pumping over a period of several regeneration cycles (see fig. 1). Aging experiments and long-term endurance tests will be necessary in the TLK because of the concern of tritium induced deterioration of the sorption properties in technical cryocompound pumps. 2. 4.3. Absorption of hydrogen isotopes on metal beds other than uranium The objective of this research program is the development of getter materials with low dissociation pressure at room temperature, comparatively low tritium release temperatures, chemical inertness towards air and other impurities, high storage capacity, etc. Another goal of technical importance is the development of tritium getter vessels suitable for storage, transport, and pumping of tritium gas. A comprehensive study of the properties of zirconium/cobalt alloy in view of its use as storage
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H.J. Ache et al. / The Tritium Laboratot~ Karlsruhe
Fig. I. Cryosorption experiment HELENE.
material for tritium has been completed. Kinetic studies with hydrogen isotopes indicate that the reaction is as fast as the one with uranium powder. The effect of preexposure of ZrCo powder to increasing amounts of the contaminants 02, N 2, CH4, CO, and C O 2 o n the pressure/concentration isotherms of Z r C o / H 2 or D 2 was systematically investigated up to the temperatures required for the recovery of the gas, i.e. < 400°C. Of these impurities only oxygen shows fast reaction at temperatures above 280°C. Thus the pyrophoricity of ZrCo is subtantially lower than that of other getters, e.g. uranium, used for tritium storage. An investigation with tritium indicates that the amount of hydrogen trapped in the ZrCo getter can be reduced to less than 10 -4 tool T / m o l ZrCo by evacuating the sample at 450°C. To round off the picture, aging studies of ZrCo tritide at various temperatures are required and accurate p - c isotherms with tritium need to be measured. Two experimental devices are presently being assembled in separate glove boxes. In addition, three getter beds of a type presently under construction for use in a large
Fig. 2. The PEGASUS facility for getter experiments.
H.J. Ache et al. / The Tritium Laboratory Karlsruhe fusion device containing either uranium or zirconium/ cobalt alloy will be compared using all hydrogen isotopes from a technical point of view. 2.4.4. Industrial development of fusion reactor vacuum components This task is concerned with the development of NET size vacuum pumps. Relevant prototype testing will be carried out at KfK in the near future. The necessity of exposing full scale components and systems to tritium as well as the extent of testing is still under discussion. In any event, the TLK provides the capacity for real size tests. 2.4.5. Absorption of impurities relevant to the fusion fuel cycle on hot getter beds An experimental facility (PEGASUS) for the investigation of the reaction of hot metal getters with impurities in helium or in hydrogen isotopes in once through or closed loop operation has been constructed and is now in operation (see fig. 2). Several getter beds of technical size containing different getter materials are under investigation. The PEGASUS facility is presently being completed for tests with up to 100 Ci of tritium. 2.4.6. CoM trapping and recovery of bred tritium from a NaK loop This program is based on some interesting features of a self-cooling liquid Pb-17Li eutectic breeder blanket. Due to the very low solubility of hydrogen in this eutectic it seems possible to extract tritium by permeation into an intermediate NaK cooling cycle. This cycle is provided with a cold trap to precipitate and retain the tritide. For the determination of the kinetics of hydrogen uptake and release a NaK test loop operated with deuterium is used. Verification tests of the two step process with tritium will be necessary in the future. 2.4.7. Cryosorption on molecular sieves or alternative sorbents First efforts within this activity concentrated on a basic study of the trapping of tritium in molecular sieves treated isothermally or isochorically to temperatures up to 450°C. The adsorption of gases from gaseous mixtures, such as the plasma exhaust gas or the hefium solid blanket coolant and sparge gas, on molecular sieves and charcoal is investigated with tritium in a closed loop employing a cryostat that can be operated at temperatures between - 2 2 0 and 450°C. The objective of these studies is to evaluate the cosorption of tritium with tritiated or non-tritiated impurities, to determine the permanent
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trapping of tritium in zeolites, to study exchange reactions, and to evaluate the detrimental effects of radiation. Prototype adsorption traps are under development. 2.4.8. Development of process analytics At present several techniques, e.g. gas chromatography, infrared spectroscopy, mass spectrometry, and cyclotron resonance mass spectrometry (omegatron) are under development for use in process control, research, and tritium accountancy. Commercial gas chromatographs are being adapted to the requirements of tritium measurements, i.e. minimization of waste, high leak tightness, and versatility. Small samples in the injection loop are pressurized up to carrier gas pressure using a capillary with a length of 15 m. Waste losses are kept to a minimum by this procedure. Fourier transform infrared spectroscopy is employed for the simultaneous in-line qualitative and quantitative determination of impurities typical to the fusion fuel cycle. Using a high resolution infrared spectrometer a large number of hydrocarbons with various hydrogen isotope compositions were determined quantitatively. Infrared spectrometers provided with cells having sapphire windows, which can selectively analyze one or more species are tested for use in process control. Commercial mass spectrometers are modified for in-line analysis in process systems. The omegatron is a particularly useful instrument for the analysis of gaseous species of low mass. The instrument now in operation at KfK has a resolution of 2000/M, where M is the mass number; it has been used for the analysis of hydrogen isotope mixtures. An investigation with tritiated species is in progress. 2.5. Future plans A process for the extraction of tritium from a helium purged solid blanket with a daily tritium production of about 100 g needs to be developed. While present efforts concentrate on conceptual study work, there is a need for the development of tritium proven technology in the future.
3. TLK facilities and equipment 3.1. General description, design guidelines and main features The TLK has been planned as a central facility in KfK to implement the research program described in
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H.J. Ache et al. / The Tritium Laboratoo, Karlsruhe
section 2. Centralization was chosen because of safety, licensing, and cost criteria. The T L K is integrated into the KfK safety organization, in particular radiation protection, medical service and fire brigade. The laboratory has a well equipped infrastructure with conventional, tritium processing and safety systems to support the R & D work. 3.1.1. Buildings The laboratory is being installed in an existing building having a large area for the accommodation of the equipment needed in the experiments and for the infrastructure (see table 1). Fig. 3 shows the main laboratory building with its hip roof and stack as well as the control and office buildings. The three buildings are interconnected. The 50 m high stack, an emergency power supply and major services from the Karlsruhe Nuclear Research Center were already available. Dimensions of the laboratory and layout of the various ground floor rooms are illustrated in fig. 4. 3.1.2. Tritium processing systems The tritium systems of the infrastructure are located in separate rooms of the laboratory building (for a
Table 1 TLK: area distribution (m 2) Ground jloor Experiments of these in the control area Infrastructure operation of these in the control area corridors, lockers, other rooms, staircases
total area
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detailed description of the systems refer to 3.2). The distances for transfers from and to the experimental facilities are kept short to facilitate a reliable tritium supply and recovery, as well as to minimize the risk of incidents and tritium losses. Tritium transfers between the experiments and the infrastructure will occur either
Fig. 3. Office, control room and laboratory buildings of the TLK.
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The water, gas, and energy supplies are located in the basement and to some extent outside the building. The main power supply is backed up by diesel and battery power supplies to enable continuous power delivery to the experiments and the infrastructure, particularly to their safety related systems and sensitive components. The supply lines are routed as mains along the external wall. The power supply terminals are arranged at regular distances to which the experiments and the infrastructure systems can be connected. A similar layout was selected for the primary water coolant supply. Cooling of the secondary system is achieved with two open cooling towers. Forced air draft was chosen to achieve a high air throughput within the building. With an air conditioning system the relative humidity is kept between 38 and 55% in all rooms of the building throughout the year.
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Fig. 4. Layout of the TLK ground floor (experimental zones section lined).
by direct connections or with a mobile transfer system via a central transfer station, which also serves for sample analysis and accountability (see fig. 5). Uranium beds are used for the storage of tritium. The infrastructure systems have been designed to enable tritium recycling. A purification system based on hot metal getters together with a gas chromatographic isotope separation system will be installed. All solid, liquid, and gaseous wastes are conditioned within the Tritium Laboratory before they are sent to the Central Disposal Department of KfK. The conditioning proce-
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A central process control and instrumentation system with a stored program combined with a hard wired safety circuit has been chosen for monitoring and safe operation of the laboratory. The control console will be installed in a separate room outside the controlled area. To allow for automation of the processes the control has been designed for single shift operation of the whole
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facility. Unless imposed by a process, all operations are conducted at a pressure below 900 mbar. All primary systems are installed in secondary containments (mostly glove boxes) with either an air or an inert gas atmosphere. The secondary containments are maintained at a pressure below that of the TLK hall. Secondary containments are provided with individual detritiation units. In addition, for safety reasons, the exhaust from the individual detritiation units is passed through a central gas detritiation system before it is discharged into the stack (see fig. 6). Detailed descriptions of the major safety installations and of their operation are given in sections 3.3 and 3 4. 3.1.5. Licensing
A governmental license in accordance with art. 3 of the Radiation Protection Regulations as part of the German Atomic Law will be needed for the handling of tritium in the Tritium Laboratory. The licensing procedure was started in February 1988 with a license application to the Ministry of Environmental Affairs of the Federal State of BadenWiirttemberg, which was accompanied by a preliminary
Safety Analysis Report. Further documentation on the systems layout and safety related issues has been or will be submitted to the authority. The response from the authorities safety advisory experts on the safety design features of some of the tritium handling systems of the TLK has been positive. 3.1.6. Costs and time schedule
The total cost of the Tritium Laboratory is estimated at DM 38 million. Detailed planning of the laboratory and of its infrastructure systems started in 1986 in cooperation with a general engineer. The construction work on the laboratory building was commenced during the same year and is now finished. The interior of the building and the installation of the components for the service systems are also completed (status mid-1989). Meanwhile the detailed engineering planning of most of the tritium process systems has been completed and orders are placed with industry. The projected date for the start of cold commissioning is mid-1991. Hot commissioning of the Tritium Laboratory is envisaged to start six months later.
H.J. Ache et al. / The Tritium Laboratory Karlsruhe 3.2. Tritium processing systems The tritium processing systems have to comply with the following design guidelines: - operation pressure in primary systems < 900 mbar, tritium process gases are pumped by the receiving systems, - standard components, i.e. pumps, valves, sensors, etc., - only oil-free pumps, - double valve closing at tube terminals in glove boxes, i.e. sampling positions, - tritium transfer tubing outside glove boxes is double walled, - each system can be individually evacuated. -
3.2.1. Tritium storage During the initial phase the TLK will operate with 10 g of tritium. This quantity of tritium will be immobilized in four uranium getter beds. Each getter bed contains 200 g uranium to store a max. of 9.3 × 1014 Bq, which corresponds to 40% of the loading capacity. The getter beds are connected to a manifold coupled to an expansion vessel. Five of 10 open positions of the manifold are presently occupied by uranium getter beds. The others are available for tritium storage upgrade employing the same or more advanced getter beds containing uranium or other getter materials. The up-graded version of the tritium storage system is designed for 200 g tritium. Double walled containers are used for tritium storage. The electrically heated inner vessel is designed to withstand a pressure of 30 bar, which is more than the pressure attained if the uranium is loaded up to 40% of its capacity and the closed vessel is heated up to 550°C. A pump transfers tritium gases from the transfer station into empty uranium storage beds held at room temperature. Hydrogen isotopes are released from the uranium bed at a temperature at which the pressure remains below 900 mbar. The transfer pump of the transfer system is used for pumping the gas. Within the storage system tritium gas can be pumped from one storage bed to another, for instance for the removal of decay helium. 3.2.2. Transfer system Hydrogen isotopes or hydrogen isotope/helium mixtures that do not contain other impurities are transfered through the tritium transfer system (see fig. 5). This system is also designed to accept newly supplied tritium, to deliver tritium to and receive tritium from the experimentalists, and to deliver and receive tritium from
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the storage system, the purification system and the isotope separation system. In experiments requiring large quantities of tritium the gas can be supplied and recovered via direct piping. Accountancy of the received and delivered tritium is also carried out in this system. The tritium transfer system has three vessels having a volume of 1, 16, and 100 ! respectively, which are used for the accountancy of different amounts of tritium. A pump combination (Metal Bellows pump and NORMETEX spiral pump) permits an evacuation down to 10-2 mbar. The tritium transfer system has a reception and a delivery station with appropriate connections to the uranium tritide beds and to the vessels employed for the tritium transport from and to the experiments. A mobile transfer system consisting of a vessel and a pump is used to transport gas from completed experiments to the purification system. 3.2.3. Purification system Purification of hydrogen isotopes from impurities such as N2, 02 CO, CO2, CQ4 , NQ3 , Q20 (Q = H, D, T) etc. is carried out with three hot uranium getter beds. The first bed, which is operated at approx. 500°C, retains oxygen from O 2 and Q20, yielding uranium oxide and free hydrogen isotopes. In the second bed, held at about 700°C, predominantly the N containing species react to form nitrides. The last bed is maintained at 900°C to crack hydrocarbons with a satisfactory kinetics and getter carbon atoms from these and other impurities. The construction of the hot metal getter beds is similar to that of the storage beds, with the exception that the inner vessels of the two beds operated at temperatures above 500°C are made of aluminum oxide ceramic. Ceramics are chosen for minimization of permeation losses and material compatibility reasons. Four vessels are used to store the purified and contaminated gas fractions. 3.2.4. Isotope separation system The purified gaseous mixture of hydrogen isotopes and helium is separated into its components via a gas chromatographic isotope separation technique. The separation is carried out with a liquid nitrogen cooled molecular sieve colunm. Concentration profiles are followed catharometrically or by proportional counting. The signals from the measurement devices activate valves of the getter beds used for interim storage of the various hydrogen isotope fractions. Further components of the isotope separation system are a pump, a 100 l reception vessel, and a circulation pump for the carrier gas. An additional getter bed at the system outlet is
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H.J. Ache et el. / The Tritium Laboratory Karlsruhe
employed for the removal of hydrogen isotope traces from the carrier gas to enable recycling of pure carrier gas without disturbing the gas chromatographic separation. The isotope separation system is designed for a throughput of 1 m o l / d equimolar hydrogen isotope mixture.
3.2.5. Analytic system The analytic system of the TLK is connected on-line to the transfer system for accountancy purposes and to the tritium purification system for purity control of the gases in the reception vessels and those containing purified gases. The analytical system is installed between these two systems. In exceptional cases, the analytic system is available for samples from other systems or from the experiments. Because impurity concentrations cover a wide range (from the % region down to ppm levels) and, in addition, hydrogen isotope mixtures need to be analyzed a total of three gas chromatographs installed in a glove box is required. 3.3. Safety
A multibarrier concept consisting of a primary tritium carrying system with double walled heated components completely enclosed by a secondary containment (glove box) is used throughout the TLK. The primary systems are essentially constructed of standard UHV metallic components.
3.3.1. Secondary containments and tritium retention systems Secondary containments consist of glove boxes connected to a central underpressurization system (fig. 7). Each glove box is provided with an individual tritium pretreated exhaost gas from primary system
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retention system (fig. 8) and a tritium monitoring system. Glove boxes consist of one or more standardized modules with the dimensions 1.5 × 1 × 2 or 1 × 1 x 2 m3. The leak rate of the glove boxes is specified to < 0.1 vol %/h at a constant underpressure in the range 4-7 mbar. In case of glove rupture a forced flow of 50 m3/h into the glove box is maintained. The tritium retention systems are based on conventional technology comprising a catalyst bed for the oxidation of hydrogen and hydrocarbons (Pd or C u e ) and a molecular sieve adsorber. During normal operation the activity of the glove box atmosphere is specified to < 4 × 106 Bq/m3: it is controlled with two tritium monitors. The central tritium retention system treats all gases from primary systems and from secondary containments prior to their discharge into the stack (fig. 6). It consists of a main tritium retention system (fig. 7) and a pretreatment system for exhaust gases from the primary systems. The main tritium retention system processes in a loop all discharges from the secondary containments, the pretreated primary exhausts, and from other gases, which may be contaminated. The loop provides the underpressure for all glove boxes in the entire laboratory. The gas is circulated in the loop at constant flow and underpressure. Steady state conditions are achieved by discharge of clean gas into the stack. The main tritium retention system also processes the gas circulating in the loop. The main tritium retention system and the individual retention systems work on the same principle. All exhaust gases from primary systems are collected in buffer tanks of a pretreatment system. This collected gas is cycled in a separate closed tritium retention
H.J. Ache et al. / The Tritium Laboratory Karlsruhe
system until it can be discharged into the main tritium retention system. Safety relevant components of the central tritium retention systems, e.g. buffer tanks, pressure regulation valves, and compressors are redundant. 3.3.2. Tritium monitoring Laboratory atmosphere: Monitoring of the laboratory atmosphere is carried out with tritium collector monitors (adsorption principle), capable of distinguishing between HT and HTO, and with ionization chambers with an alarm function. Laboratory exhaust air: The exhaust air of the laboratory is monitored with proportional counters and ionization chambers, which detect tritium unspecifically. In addition, collector monitors capable of distinguishing between HT and HTO surveil the exhaust. Cooling water and drain water: The activity of the cooling and drain water is controlled regularly by sampiing of the various loop systems. The detection limit for tritium is 2 × 102 Bq/l. If the concentration exceeds a limit the water from the loop is renewed. 3.4. Central control system
The central control system of TLK comprises a central process data processing system, and a protection system. The central process data processing system serves to control, operate, and monitor all tritium systems. The conventional systems in the laboratory are also operated, monitored, and partially controlled by this system. Sensors from the tritium process systems or the conventional systems deliver data to one of several process stations, which can carry out autonomously certain control and monitor operations. The various process stations are interconnected via a BUS. The BUS is also connected to the central control room thus enabling the control and monitoring of the complete facility. -
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All safety relevant limits and parameters of various TLK systems are, in addition, surveyed by a safety system. This system monitors these parameters and brings automatically those components or entire systems that show exceeded limit values into a safe condition. The safety system is subdivided into an excitation level, an interconnection level, an actuating level, an operator level, and an information and registration level. The excitation level transform signals from all safety relevant sensors to standardized analog signals. After passing a limit comparator, they are converted into binary output signals. The interconnection level connects the binary signals to predetermined signal chains, which activate the relevant procedures in the next level. The actuating level switches off the power supply of all safety relevant mechanical and electrical components and instruments in order to bring the system into a safe condition. The operator level allows manual intervention into the safety circuits. The operator can activate the safe condition of individual systems as well as of the entire laboratory from the main control room. Individual systems can also be switched off locally. The information and registration level displays events and system status on a display screen, by optical signals on an indicator board, and by acustical signals, as well as recording on a printer. 3.5. Operation
A trained staff is responsible for tritium supply, tritium purification, isotope separation, safety, and waste disposal, and also supports the installation and operation of experiments.
Acknowledgments
We gratefully acknowledge many valuable comments from S. Huber, H.R. Ihle, P. Schira and D. Stiinkel.
331
THE TRITIUM LABORATORY KARLSRUHE: R&D WORK AND LABORATORY LAYOUT
H.J. A C H E , M. G L U G L A , E. H U T T E R , G. J O U R D A N , R.-D. P E N Z H O R N K. S C H U B E R T , H. S E B E N I N G a n d J.E. V E T T E R
*, D. R O H R I G ,
Nuclear Research Center Karlsruhe, Postfach 3640, 7500 Karlsruhe, Fed. Rep. Germany
Submitted 31 August 1989; accepted 10 November 1989 Handling Editor: R.W. Conn
The Tritium Laboratory Karlsruhe (TLK) provides the technical means for R&D work on the fuel cycle and components of the next fusion device within the framework of the European Fusion Technology Programme. Other areas of tritium research such as blanket interfaces, fueling devices, plasma facing components, etc. are within the wider scope of the future activities. This paper summarizes current tritium research activities at the Nuclear Research Center Karlsruhe; these investigations constitute the basis for the first large scale experiments at the TLK. The infrastructure of the TLK is treated in detail, in particular information is given on tritium processing systems such as storage, transfer, chemical purification, and isotope separation. Important tritium safety aspects and the control system are described. The present status of the laboratory and the time schedule for licensing and commissioning is also addressed.
1. Introduction
Fuel cycle technology is one of the key issues for NET and ITER. The N E T / I T E R fuel cycle differs substantially from current developments at JET in that a life-time total of about 30 kg of tritium will be burned. In addition, stringent requirements on the allowable releases from maintenance as well as from operational and accidental conditions over an extended period of time must be met together with a minimization of tritium waste. The N E T / I T E R fuel cycle technology should serve to demonstrate in practice during an early stage the feasibility of safe operation and low environmental impact of future generation reactor systems. This cannot solely be achieved by improving methods and single components, but it is also necessary to demonstrate the reliable dosed loop operation of large facilities. Furthermore, the operation of these facilities will serve to train the personnel required for the much more complex fusion machines of the future. After the Fusion Technology Project was launched in KfK and established within the European Fusion Technology Program it was decided to implement a * To whom correspondence should be adressed.
Tritium Laboratory in Karlsruhe (TLK) and to expand the already existing tritium activities in order to provide technical means for experiments with realistic quantities of tritium, typical of future fusion devices. Work in TLK will concentrate on the development of advanced processes for plasma-exhaust fuel clean-up of the N E T / I T E R basic machine. Another area of great interest concerns cryogenic pumping which, as a prestep to plasma exhaust purification, is subject to very difficult-to-define operation conditions on the input side and has to couple to the clean-up system on the output side. As study work on blanket design progresses - two concepts are presently being followed in KfK - many new technical questions will emerge. Future discussions will indicate to what extent tritium tests will be required to qualify process components and to demonstrate integrated systems. Further tritium technology related tasks defined within the European program are pursued at other European tritium laboratories. The development of the NET design and the publication of new results from the accompanying R & D work will have an impact on the TLK test program and on the infrastructure. It will be necessary to increase the TLK infrastructure (storage capacity, control proce-
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H.J. Ache et a L / The Tritium L~lboratoO, Karlsruhe
dures and diagnostics) in line with the growth in dimension and complexity of the tested N E T / I T E R prototype components.
2.
Research
program
2.1. Purpose
The Tritium Laboratory Karlsruhe is mainly devoted to R & D work with tritium on a technical scale within the needs of N E T / I T E R . Experiments carried out at other laboratories of KfK with model gaseous mixtures and tracer amounts of tritium provide the basis for the processes and technologies to be verified and tested in the TLK. The principal activities at TLK are: development of advanced fuel clean-up technology, - process development for the recovery of tritium from lithium materials to be used in KfK's helium cooled ceramic and self-cooled liquid blankets * testing of prototype components such as vacuum and transfer pumps, valves, cryotraps, fueling devices, etc., work on the development of process analytics, - studies on the radiochemistry of fusion fuel cycle impurities, and investigations on environmental problems such as the behaviour of tritium in the system plant/soil. It is also expected that the operation of the TLK with its partly novel components and processes of the infrastructure will yield valuable know-how on tritium handling. This is specially true in the fields of hydrogen isotope purification and separation. Z2. Role in the fusion program
The development of large peripheral components will be required for the detailed engineering of NET. The performance of these components will be examined using relevant amounts of tritium in single or integral tests. While it is generally agreed that the clean-up of plasma exhaust gas is not a critical feasibility issue, there still is a need for a fully demonstrated concept,
* Investigations on the off-line recovery of tritium from breeder ceramics will not be carried out in the TLK, because irradiated materials are handled more readily in the Hot Cells of KfK.
not only on a technical scale but also with NET relevant quantities of tritium. The goal of attaining fuel self-sufficiency in a fusion reactor requires the demonstration that the selected option is highly reliable and achievable with very low tritium inventories and low losses for all subsystems. Complementary to experiments with engineering scaling the key components of the systems under investigation should be tested in long-term runs for mechanical stability and endurance towards the exposure to relevant amounts of tritium. Highly efficient and powerful pumping systems are required for the attainment of a vacuum in the plasma chamber of a fusion reactor. Cryopumping is an adequate method, which can also cope with the problems of radiation and magnetic fields. For the pumping of helium together with hydrogen isotopes and impurities cryocompound systems are under development that need to be tested in a tritium environment. For handling, transfer, and storage of large quantities of tritium appropriate getter materials must be identified. Extensive tests under a variety of conditions are required to evaluate these getters. Experiments with tritium (aging studies) will provide information concerning long-term detrimental effects on the material properties of the getters and on the release characteristics of decay helium. Control and surveillance of tritium processing systems require suitable in- and off-line analytics. Efforts will therefore be devoted to the development of selective and sensitive tritium compatible analytical instruments that are characterized by low or no sample consumption. A better understanding of the role of secondary radiochemical reactions occuring between gaseous tritium and impurities is needed. To fill this gap systematic theoretical and laboratory work with tritium is required to identify radiochemical reactions that can occur in the various tritium processing units. 2.3. Technologies investigated
The fusion related tritium technology activities at KfK are integrated into the European Fusion Technology Program. Research activities are under way on the following specific technologies: - development of a catalytic process for the plasma exhaust purification - optimization of cryogenic vacuum pumping of helium - absorption of hydrogen isotopes on metal beds other than uranium - development of fusion reactor vacuum components in cooperation with industry
H.J. Ache et al. / The Tritium Laboratory Karlsruhe absorption of impurities relevant to the fusion fuel cycle on hot metal beds - cold trapping and recovery of bred tritium from a N a K intermediate loop - cryosorption on molecular sieves or alternative adsorbents tritium extraction by permeation with solid getters from eutectic liquid Pb-17Li. Furthermore, technology oriented work in the fields of development of tritium purification with getters for the use in TLK, development of analytical instrumentation for the determination of tritium containing species, and - study work in the fields of (i) development of helium cryopumping materials and design concepts of cryocompound pumps for NET, (ii) development of a plasma exhaust purification system for NET based on catalytic reactions, and (iii) development of technology for the recovery of tritium from a helium cooled solid ceramic blanket is in progress.
-
-
-
-
2.4. Status of work and major results 2.4.1. Fuel clean-up process for N E T A process concept based on extensive experimental work in KfK has been proposed for the reprocessing of the primary vacuum exhaust gas of the NET fusion reactor during burn and dwell as well as for the recovery of tritium from the waste gases produced during bakeout, glow discharge cleaning or carbonization. This concept involves recycling of tritium entirely as DT, the least objectionable chemical form with respect to radiological hazards. In a first step most of the free hydrogen isotopes are recovered and purified by a main pall a d i u m / silver permeator. Tritium/deuterium chemically bonded in species such as hydrocarbons, ammonia, and water are liberated by selective catalytic reactions and recovered with a second PdAg permeator. Experimentally, it was shown that at temperatures above 300°C the rate of hydrogen permeation through commercial palladium/silver permeators of high permeation areas, e.g. 0.12 m 2 is not influenced by the presence of any of the impurities relevant to the fusion fuel cycle, even if present at high partial pressures. For the conversion of water into hydrogen the water gas shift reaction is employed using a zinc stabilized copper chromite catalyst. This reaction, which takes place in high yield at temperatures below 200"C, requires only a small amount of catalyst and an excess of carbon monoxide not larger than C O / H 2 0 = 1.5.
333
Methane, higher hydrocarbons, and ammonia are decomposed into their elements on a nickel catalyst at temperatures below 500°C. A complete kinetic study of the corresponding reactions has been carried out, also employing relevant gaseous mixtures, in closed loop operation and in once through flow systems. The mechanism of the decomposition has been confirmed with polytritiated methane and polytritiated ammonia. Carbon produced from the cracking of hydrocarbons can be volatilized by reaction with carbon dioxide. This reaction increases the life-time of the catalyst. The tritium inventory of the catalyst was found to be comparatively low. Only a few kilograms of catalyst per year of operation to process the exhaust gases of a large fusion machine are sufficient. Detailed engineering planning of a fuel clean-up facility for NET is nearly completed. Based on this planning, a facility will be constructed to demonstrate the catalytic concept on an engineering scale in the TLK, employing appropriate amounts of tritium. The construction of a facility to carry out long-term tests in the TLK on the performance of commercial permeators exposed to high levels of tritium is well in progress. 2.4.2. Optimization of the cryogenic vacuum pumping of helium Extensive screening tests have been conducted with cryosorption panels consisting of a surface of active sorbent material bonded to a heat conductive substrate. Candidate materials were selected on the basis of their helium pumping speed, stability upon thermal cycling, and sorption capacity. Promising samples are examined in poisoning tests with deuterium to simulate tritium exchange with adsorbed impurities and its effect on helium pumping over a period of several regeneration cycles (see fig. 1). Aging experiments and long-term endurance tests will be necessary in the TLK because of the concern of tritium induced deterioration of the sorption properties in technical cryocompound pumps. 2. 4.3. Absorption of hydrogen isotopes on metal beds other than uranium The objective of this research program is the development of getter materials with low dissociation pressure at room temperature, comparatively low tritium release temperatures, chemical inertness towards air and other impurities, high storage capacity, etc. Another goal of technical importance is the development of tritium getter vessels suitable for storage, transport, and pumping of tritium gas. A comprehensive study of the properties of zirconium/cobalt alloy in view of its use as storage
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H.J. Ache et al. / The Tritium Laboratot~ Karlsruhe
Fig. I. Cryosorption experiment HELENE.
material for tritium has been completed. Kinetic studies with hydrogen isotopes indicate that the reaction is as fast as the one with uranium powder. The effect of preexposure of ZrCo powder to increasing amounts of the contaminants 02, N 2, CH4, CO, and C O 2 o n the pressure/concentration isotherms of Z r C o / H 2 or D 2 was systematically investigated up to the temperatures required for the recovery of the gas, i.e. < 400°C. Of these impurities only oxygen shows fast reaction at temperatures above 280°C. Thus the pyrophoricity of ZrCo is subtantially lower than that of other getters, e.g. uranium, used for tritium storage. An investigation with tritium indicates that the amount of hydrogen trapped in the ZrCo getter can be reduced to less than 10 -4 tool T / m o l ZrCo by evacuating the sample at 450°C. To round off the picture, aging studies of ZrCo tritide at various temperatures are required and accurate p - c isotherms with tritium need to be measured. Two experimental devices are presently being assembled in separate glove boxes. In addition, three getter beds of a type presently under construction for use in a large
Fig. 2. The PEGASUS facility for getter experiments.
H.J. Ache et al. / The Tritium Laboratory Karlsruhe fusion device containing either uranium or zirconium/ cobalt alloy will be compared using all hydrogen isotopes from a technical point of view. 2.4.4. Industrial development of fusion reactor vacuum components This task is concerned with the development of NET size vacuum pumps. Relevant prototype testing will be carried out at KfK in the near future. The necessity of exposing full scale components and systems to tritium as well as the extent of testing is still under discussion. In any event, the TLK provides the capacity for real size tests. 2.4.5. Absorption of impurities relevant to the fusion fuel cycle on hot getter beds An experimental facility (PEGASUS) for the investigation of the reaction of hot metal getters with impurities in helium or in hydrogen isotopes in once through or closed loop operation has been constructed and is now in operation (see fig. 2). Several getter beds of technical size containing different getter materials are under investigation. The PEGASUS facility is presently being completed for tests with up to 100 Ci of tritium. 2.4.6. CoM trapping and recovery of bred tritium from a NaK loop This program is based on some interesting features of a self-cooling liquid Pb-17Li eutectic breeder blanket. Due to the very low solubility of hydrogen in this eutectic it seems possible to extract tritium by permeation into an intermediate NaK cooling cycle. This cycle is provided with a cold trap to precipitate and retain the tritide. For the determination of the kinetics of hydrogen uptake and release a NaK test loop operated with deuterium is used. Verification tests of the two step process with tritium will be necessary in the future. 2.4.7. Cryosorption on molecular sieves or alternative sorbents First efforts within this activity concentrated on a basic study of the trapping of tritium in molecular sieves treated isothermally or isochorically to temperatures up to 450°C. The adsorption of gases from gaseous mixtures, such as the plasma exhaust gas or the hefium solid blanket coolant and sparge gas, on molecular sieves and charcoal is investigated with tritium in a closed loop employing a cryostat that can be operated at temperatures between - 2 2 0 and 450°C. The objective of these studies is to evaluate the cosorption of tritium with tritiated or non-tritiated impurities, to determine the permanent
335
trapping of tritium in zeolites, to study exchange reactions, and to evaluate the detrimental effects of radiation. Prototype adsorption traps are under development. 2.4.8. Development of process analytics At present several techniques, e.g. gas chromatography, infrared spectroscopy, mass spectrometry, and cyclotron resonance mass spectrometry (omegatron) are under development for use in process control, research, and tritium accountancy. Commercial gas chromatographs are being adapted to the requirements of tritium measurements, i.e. minimization of waste, high leak tightness, and versatility. Small samples in the injection loop are pressurized up to carrier gas pressure using a capillary with a length of 15 m. Waste losses are kept to a minimum by this procedure. Fourier transform infrared spectroscopy is employed for the simultaneous in-line qualitative and quantitative determination of impurities typical to the fusion fuel cycle. Using a high resolution infrared spectrometer a large number of hydrocarbons with various hydrogen isotope compositions were determined quantitatively. Infrared spectrometers provided with cells having sapphire windows, which can selectively analyze one or more species are tested for use in process control. Commercial mass spectrometers are modified for in-line analysis in process systems. The omegatron is a particularly useful instrument for the analysis of gaseous species of low mass. The instrument now in operation at KfK has a resolution of 2000/M, where M is the mass number; it has been used for the analysis of hydrogen isotope mixtures. An investigation with tritiated species is in progress. 2.5. Future plans A process for the extraction of tritium from a helium purged solid blanket with a daily tritium production of about 100 g needs to be developed. While present efforts concentrate on conceptual study work, there is a need for the development of tritium proven technology in the future.
3. TLK facilities and equipment 3.1. General description, design guidelines and main features The TLK has been planned as a central facility in KfK to implement the research program described in
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H.J. Ache et al. / The Tritium Laboratoo, Karlsruhe
section 2. Centralization was chosen because of safety, licensing, and cost criteria. The T L K is integrated into the KfK safety organization, in particular radiation protection, medical service and fire brigade. The laboratory has a well equipped infrastructure with conventional, tritium processing and safety systems to support the R & D work. 3.1.1. Buildings The laboratory is being installed in an existing building having a large area for the accommodation of the equipment needed in the experiments and for the infrastructure (see table 1). Fig. 3 shows the main laboratory building with its hip roof and stack as well as the control and office buildings. The three buildings are interconnected. The 50 m high stack, an emergency power supply and major services from the Karlsruhe Nuclear Research Center were already available. Dimensions of the laboratory and layout of the various ground floor rooms are illustrated in fig. 4. 3.1.2. Tritium processing systems The tritium systems of the infrastructure are located in separate rooms of the laboratory building (for a
Table 1 TLK: area distribution (m 2) Ground jloor Experiments of these in the control area Infrastructure operation of these in the control area corridors, lockers, other rooms, staircases
total area
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Operation (conventional equipment, electricity distribution network, etc) Experiments Corridors, staircaises, other rooms
1,200 300 540
total area
2,040
detailed description of the systems refer to 3.2). The distances for transfers from and to the experimental facilities are kept short to facilitate a reliable tritium supply and recovery, as well as to minimize the risk of incidents and tritium losses. Tritium transfers between the experiments and the infrastructure will occur either
Fig. 3. Office, control room and laboratory buildings of the TLK.
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The water, gas, and energy supplies are located in the basement and to some extent outside the building. The main power supply is backed up by diesel and battery power supplies to enable continuous power delivery to the experiments and the infrastructure, particularly to their safety related systems and sensitive components. The supply lines are routed as mains along the external wall. The power supply terminals are arranged at regular distances to which the experiments and the infrastructure systems can be connected. A similar layout was selected for the primary water coolant supply. Cooling of the secondary system is achieved with two open cooling towers. Forced air draft was chosen to achieve a high air throughput within the building. With an air conditioning system the relative humidity is kept between 38 and 55% in all rooms of the building throughout the year.
E
Hot workshop T2-processingrooms Decontamination Wastestorage , Stack Coolingtowers
Fig. 4. Layout of the TLK ground floor (experimental zones section lined).
by direct connections or with a mobile transfer system via a central transfer station, which also serves for sample analysis and accountability (see fig. 5). Uranium beds are used for the storage of tritium. The infrastructure systems have been designed to enable tritium recycling. A purification system based on hot metal getters together with a gas chromatographic isotope separation system will be installed. All solid, liquid, and gaseous wastes are conditioned within the Tritium Laboratory before they are sent to the Central Disposal Department of KfK. The conditioning proce-
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A central process control and instrumentation system with a stored program combined with a hard wired safety circuit has been chosen for monitoring and safe operation of the laboratory. The control console will be installed in a separate room outside the controlled area. To allow for automation of the processes the control has been designed for single shift operation of the whole
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facility. Unless imposed by a process, all operations are conducted at a pressure below 900 mbar. All primary systems are installed in secondary containments (mostly glove boxes) with either an air or an inert gas atmosphere. The secondary containments are maintained at a pressure below that of the TLK hall. Secondary containments are provided with individual detritiation units. In addition, for safety reasons, the exhaust from the individual detritiation units is passed through a central gas detritiation system before it is discharged into the stack (see fig. 6). Detailed descriptions of the major safety installations and of their operation are given in sections 3.3 and 3 4. 3.1.5. Licensing
A governmental license in accordance with art. 3 of the Radiation Protection Regulations as part of the German Atomic Law will be needed for the handling of tritium in the Tritium Laboratory. The licensing procedure was started in February 1988 with a license application to the Ministry of Environmental Affairs of the Federal State of BadenWiirttemberg, which was accompanied by a preliminary
Safety Analysis Report. Further documentation on the systems layout and safety related issues has been or will be submitted to the authority. The response from the authorities safety advisory experts on the safety design features of some of the tritium handling systems of the TLK has been positive. 3.1.6. Costs and time schedule
The total cost of the Tritium Laboratory is estimated at DM 38 million. Detailed planning of the laboratory and of its infrastructure systems started in 1986 in cooperation with a general engineer. The construction work on the laboratory building was commenced during the same year and is now finished. The interior of the building and the installation of the components for the service systems are also completed (status mid-1989). Meanwhile the detailed engineering planning of most of the tritium process systems has been completed and orders are placed with industry. The projected date for the start of cold commissioning is mid-1991. Hot commissioning of the Tritium Laboratory is envisaged to start six months later.
H.J. Ache et al. / The Tritium Laboratory Karlsruhe 3.2. Tritium processing systems The tritium processing systems have to comply with the following design guidelines: - operation pressure in primary systems < 900 mbar, tritium process gases are pumped by the receiving systems, - standard components, i.e. pumps, valves, sensors, etc., - only oil-free pumps, - double valve closing at tube terminals in glove boxes, i.e. sampling positions, - tritium transfer tubing outside glove boxes is double walled, - each system can be individually evacuated. -
3.2.1. Tritium storage During the initial phase the TLK will operate with 10 g of tritium. This quantity of tritium will be immobilized in four uranium getter beds. Each getter bed contains 200 g uranium to store a max. of 9.3 × 1014 Bq, which corresponds to 40% of the loading capacity. The getter beds are connected to a manifold coupled to an expansion vessel. Five of 10 open positions of the manifold are presently occupied by uranium getter beds. The others are available for tritium storage upgrade employing the same or more advanced getter beds containing uranium or other getter materials. The up-graded version of the tritium storage system is designed for 200 g tritium. Double walled containers are used for tritium storage. The electrically heated inner vessel is designed to withstand a pressure of 30 bar, which is more than the pressure attained if the uranium is loaded up to 40% of its capacity and the closed vessel is heated up to 550°C. A pump transfers tritium gases from the transfer station into empty uranium storage beds held at room temperature. Hydrogen isotopes are released from the uranium bed at a temperature at which the pressure remains below 900 mbar. The transfer pump of the transfer system is used for pumping the gas. Within the storage system tritium gas can be pumped from one storage bed to another, for instance for the removal of decay helium. 3.2.2. Transfer system Hydrogen isotopes or hydrogen isotope/helium mixtures that do not contain other impurities are transfered through the tritium transfer system (see fig. 5). This system is also designed to accept newly supplied tritium, to deliver tritium to and receive tritium from the experimentalists, and to deliver and receive tritium from
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the storage system, the purification system and the isotope separation system. In experiments requiring large quantities of tritium the gas can be supplied and recovered via direct piping. Accountancy of the received and delivered tritium is also carried out in this system. The tritium transfer system has three vessels having a volume of 1, 16, and 100 ! respectively, which are used for the accountancy of different amounts of tritium. A pump combination (Metal Bellows pump and NORMETEX spiral pump) permits an evacuation down to 10-2 mbar. The tritium transfer system has a reception and a delivery station with appropriate connections to the uranium tritide beds and to the vessels employed for the tritium transport from and to the experiments. A mobile transfer system consisting of a vessel and a pump is used to transport gas from completed experiments to the purification system. 3.2.3. Purification system Purification of hydrogen isotopes from impurities such as N2, 02 CO, CO2, CQ4 , NQ3 , Q20 (Q = H, D, T) etc. is carried out with three hot uranium getter beds. The first bed, which is operated at approx. 500°C, retains oxygen from O 2 and Q20, yielding uranium oxide and free hydrogen isotopes. In the second bed, held at about 700°C, predominantly the N containing species react to form nitrides. The last bed is maintained at 900°C to crack hydrocarbons with a satisfactory kinetics and getter carbon atoms from these and other impurities. The construction of the hot metal getter beds is similar to that of the storage beds, with the exception that the inner vessels of the two beds operated at temperatures above 500°C are made of aluminum oxide ceramic. Ceramics are chosen for minimization of permeation losses and material compatibility reasons. Four vessels are used to store the purified and contaminated gas fractions. 3.2.4. Isotope separation system The purified gaseous mixture of hydrogen isotopes and helium is separated into its components via a gas chromatographic isotope separation technique. The separation is carried out with a liquid nitrogen cooled molecular sieve colunm. Concentration profiles are followed catharometrically or by proportional counting. The signals from the measurement devices activate valves of the getter beds used for interim storage of the various hydrogen isotope fractions. Further components of the isotope separation system are a pump, a 100 l reception vessel, and a circulation pump for the carrier gas. An additional getter bed at the system outlet is
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H.J. Ache et el. / The Tritium Laboratory Karlsruhe
employed for the removal of hydrogen isotope traces from the carrier gas to enable recycling of pure carrier gas without disturbing the gas chromatographic separation. The isotope separation system is designed for a throughput of 1 m o l / d equimolar hydrogen isotope mixture.
3.2.5. Analytic system The analytic system of the TLK is connected on-line to the transfer system for accountancy purposes and to the tritium purification system for purity control of the gases in the reception vessels and those containing purified gases. The analytical system is installed between these two systems. In exceptional cases, the analytic system is available for samples from other systems or from the experiments. Because impurity concentrations cover a wide range (from the % region down to ppm levels) and, in addition, hydrogen isotope mixtures need to be analyzed a total of three gas chromatographs installed in a glove box is required. 3.3. Safety
A multibarrier concept consisting of a primary tritium carrying system with double walled heated components completely enclosed by a secondary containment (glove box) is used throughout the TLK. The primary systems are essentially constructed of standard UHV metallic components.
3.3.1. Secondary containments and tritium retention systems Secondary containments consist of glove boxes connected to a central underpressurization system (fig. 7). Each glove box is provided with an individual tritium pretreated exhaost gas from primary system
,.s.e regulation
pressure regulation
= overpressore
protection
glove-box -41o -7 mbar ion
chambol"s Fig. 7. Flow sheet of the main tritium retention system.
I
cooling
loop loop
i
] (molecular * | sieve) / _
~--
-
I
~ catalytic , ~ oxydation ( Pd or Cu0)
) 15-60m3/h
J
h£ ...... J
T
from glove-box U[~ 10 gnove-box
]
~" >~cooler
4Ira
Fig. 8. Flow sheet of glove box retention system.
retention system (fig. 8) and a tritium monitoring system. Glove boxes consist of one or more standardized modules with the dimensions 1.5 × 1 × 2 or 1 × 1 x 2 m3. The leak rate of the glove boxes is specified to < 0.1 vol %/h at a constant underpressure in the range 4-7 mbar. In case of glove rupture a forced flow of 50 m3/h into the glove box is maintained. The tritium retention systems are based on conventional technology comprising a catalyst bed for the oxidation of hydrogen and hydrocarbons (Pd or C u e ) and a molecular sieve adsorber. During normal operation the activity of the glove box atmosphere is specified to < 4 × 106 Bq/m3: it is controlled with two tritium monitors. The central tritium retention system treats all gases from primary systems and from secondary containments prior to their discharge into the stack (fig. 6). It consists of a main tritium retention system (fig. 7) and a pretreatment system for exhaust gases from the primary systems. The main tritium retention system processes in a loop all discharges from the secondary containments, the pretreated primary exhausts, and from other gases, which may be contaminated. The loop provides the underpressure for all glove boxes in the entire laboratory. The gas is circulated in the loop at constant flow and underpressure. Steady state conditions are achieved by discharge of clean gas into the stack. The main tritium retention system also processes the gas circulating in the loop. The main tritium retention system and the individual retention systems work on the same principle. All exhaust gases from primary systems are collected in buffer tanks of a pretreatment system. This collected gas is cycled in a separate closed tritium retention
H.J. Ache et al. / The Tritium Laboratory Karlsruhe
system until it can be discharged into the main tritium retention system. Safety relevant components of the central tritium retention systems, e.g. buffer tanks, pressure regulation valves, and compressors are redundant. 3.3.2. Tritium monitoring Laboratory atmosphere: Monitoring of the laboratory atmosphere is carried out with tritium collector monitors (adsorption principle), capable of distinguishing between HT and HTO, and with ionization chambers with an alarm function. Laboratory exhaust air: The exhaust air of the laboratory is monitored with proportional counters and ionization chambers, which detect tritium unspecifically. In addition, collector monitors capable of distinguishing between HT and HTO surveil the exhaust. Cooling water and drain water: The activity of the cooling and drain water is controlled regularly by sampiing of the various loop systems. The detection limit for tritium is 2 × 102 Bq/l. If the concentration exceeds a limit the water from the loop is renewed. 3.4. Central control system
The central control system of TLK comprises a central process data processing system, and a protection system. The central process data processing system serves to control, operate, and monitor all tritium systems. The conventional systems in the laboratory are also operated, monitored, and partially controlled by this system. Sensors from the tritium process systems or the conventional systems deliver data to one of several process stations, which can carry out autonomously certain control and monitor operations. The various process stations are interconnected via a BUS. The BUS is also connected to the central control room thus enabling the control and monitoring of the complete facility. -
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All safety relevant limits and parameters of various TLK systems are, in addition, surveyed by a safety system. This system monitors these parameters and brings automatically those components or entire systems that show exceeded limit values into a safe condition. The safety system is subdivided into an excitation level, an interconnection level, an actuating level, an operator level, and an information and registration level. The excitation level transform signals from all safety relevant sensors to standardized analog signals. After passing a limit comparator, they are converted into binary output signals. The interconnection level connects the binary signals to predetermined signal chains, which activate the relevant procedures in the next level. The actuating level switches off the power supply of all safety relevant mechanical and electrical components and instruments in order to bring the system into a safe condition. The operator level allows manual intervention into the safety circuits. The operator can activate the safe condition of individual systems as well as of the entire laboratory from the main control room. Individual systems can also be switched off locally. The information and registration level displays events and system status on a display screen, by optical signals on an indicator board, and by acustical signals, as well as recording on a printer. 3.5. Operation
A trained staff is responsible for tritium supply, tritium purification, isotope separation, safety, and waste disposal, and also supports the installation and operation of experiments.
Acknowledgments
We gratefully acknowledge many valuable comments from S. Huber, H.R. Ihle, P. Schira and D. Stiinkel.