The JET neutral beam injection system has proved to be both effective and reliable as a plasma heating device. The ion heating and plasma fuelling characteristics of the system are ideally suited to ...the production of high fusion performance plasmas while the flexibility in the choice of beam species (H, D, T,
3He or
4He) and the ability to inject into almost any JET plasma configuration allows a wide variety of related physics experiments to be carried out. The capability to inject (for the first time) tritium beams was essential to the successful execution of the first tritium experiments in which 1.7 MW of power from DT fusion reactions was generated.
The Joint European Torus (JET) Active Gas Handling System (AGHS) will store and process the tritium required for the active phase operation of JET. Numerous types of secondary containments are used ...to house the process components necessary for this processing and storage. Secondary containments are a key safety feature of the plant's design and provide a defence-in-depth against the release of tritium. The secondary containment designs, features, operating conditions and integrity monitoring and the role that they play in mitigating releases from the AGHS are discussed.
Status and Prospects of JET Tritium Operation Haange, R; Ballantyne, P; Bell, A C ...
Fusion Technology; (United States),
19/3/1/, Letnik:
21, Številka:
2P2
Journal Article, Conference Proceeding
The present schedule of JET includes an experimental campaign with D-T plasmas at the end of the Project programme. A dedicated facility, the Active Gas Handling System (AGHS), has been designed and ...is being commissioned to process the torus exhaust streams and to recycle tritium and deuterium. The AGHS is expected to process a maximum throughput of 30g tritium daily and total tritium inventory will not exceed 90g. The design is subject to a comprehensive safety analysis which must show that stringent safety criteria are met. In parallel to the AGHS installation, the JET torus and its auxiliary systems are being analysed for compliance with the same safety criteria. Modifications are being implemented where required. The AGHS installation is nearing completion and non-tritium commissioning is underway. The JET D-T phase will be preceded by a very short campaign of a few D-T pulses which can be conducted with a very small inventory of tritium, thus allowing this to be undertaken at an early stage in order to obtain important data prior to the start of the full D-T phase. JET will be the first experimental facility where the tritium fusion fuel processing cycle will be closed (albeit without breeding) and hence important experience and experimental data are expected to be gained for the next generation of fusion devices.
Metastable calcium atoms, produced in a magneto-optic trap (MOT) operating within the singlet system, are continuously loaded into a magnetic trap formed by the magnetic quadrupole field of the MOT. ...At MOT temperatures of 3 mK and 240 ms loading time we observe 1.1 x 10^8 magnetically trapped 3P2 atoms at densities of 2.4 x 10^8 cm^-3 and temperatures of 0.61 mK. In a modified scheme we first load a MOT for metastable atoms at a temperature of 0.18 mK and subsequently release these atoms into the magnetic trap. In this case 240 ms of loading yields 2.4 x 10^8 trapped 3P2 atoms at a peak density of 8.7 x 10^10 cm^-3 and a temperature of 0.13 mK. The temperature decrease observed in the magnetic trap for both loading schemes can be explained only in part by trap size effects.
The Joint European Torus (JET) Active Gas Handling System (AGHS) is a complex interconnection of numerous subsystems. While individual subsystems were assessed for their risk of operation, an ...assessment of the effects of inadvertent interconnections was needed. A systematic method to document the assessment was devised to ease the assessment of complex plant and was applied to the AGHS. The methodology, application to AGHS, the four critical issues and required plant modifications as a result of this assessment are briefly discussed.
The different subsystems of the JET Active Gas Handling System (AGHS) are equipped with sufficient instrumentation for process monitoring and control during normal operations. In addition, especially ...for the commissioning phase and in case of process malfunctions a central facility was designed which is connected to all subsystems of AGHS and uses mass spectroscopy, gas chromatography and ionisation chambers for characterisation of the various gas mixtures. Furthermore, a simple oxygen monitor is presented which works reliably in gas mixtures containing mainly hydrogen at low pressures.
The principle of temperature stabilization by inertial feedback control was further developed to provide a stable base for a thermoelectric calorimeter. Noise and long-term drift of the base ...temperature have been reduced to /spl plusmn/3/spl times/10/sup -10/ Ks/sup -1/. With this temperature stability, samples with large heat capacities, such as Amersham MKIV uranium getter beds for tritium transport and storage (total heat capacity of calorimeter chamber, uranium bed secondary containment and getter bed itself is 1370 JK/sup -1/), can be measured with a reproducibility of /spl plusmn/2 /spl mu/W. During a 14-day campaign, all Amersham getter beds presently held by JET were measured. The bed with the highest tritium content (22,40Ci) was repeatedly measured in 2-day intervals, and the results were found to follow the trend of the tritium decay well within the error band of /spl plusmn/0.4%, (/spl plusmn/0.3% due to tritium decay heat uncertainty, and /spl plusmn/0.1% due to calorimeter calibration accuracy). Tritium-free getter beds showed a power output of 7.5/spl plusmn/2 /spl mu/W, due to the decay heat of the total sum of all isotopes contained in their depleted uranium inventory of 320 g. This compares reasonably well with subsequent measurements on a 4 kg depleted uranium test sample of certified composition, procured from British Nuclear Fuels Limited.
The Active Gas Handling System (AGHS) of JET was designed to provide a closed loop for the supply and recovery of tritium during torus operations. The AGHS carried out this function during the 1997 ...tritium experiment DTE1 and provided detritiation of the torus ventilation air during the subsequent Remote Tile Exchange (RTE). At the end of the RTE approximately 3.6 g of tritium remained within the torus and although only D-D operations were to be carried out during the experimental campaign, the AGHS was still required to continue to support the machine operations. At the end of this experimental campaign (May 1999) the torus and neutral beam boxes were vented to atmosphere in order to install an inboard pellet injector track. Again the Exhaust Detritiation (ED) system was used to detritiate the ventilation air from the machine.
The JET experimental programme has been extended from its former formal closing date, end of 1992, to the end of 1996. The extension allows the study of plasma operation with a pumped divertor to be ...installed in the JET vacuum vessel during a shutdown in 1992-19931. As a consequence the final phase of JET, which involves the use of tritium to study D-T plasmas, will be delayed to 1996.
In view of this delay it was decided to adopt a stepwise approach to the introduction of tritium in JET and to carry out a tritium experiment within limits imposed by restrictions on vessel activation and tritium usage. The objectives were:
To establish a firm basis for prediction of the performance of future JET D-T pulses, including the question of fuel mixing;
To carry out accounting on tritium utilisation, including the assessment of tritium holdup in various components, especially in-vessel components;
To demonstrate the production of about 1MW of fusion power for approximately 1 second.
Preparations for the experiment included a physics programme to define the optimum plasma parameters, method of injection and diagnostics requirements, as well as a technical programme to design and install special equipment to inject tritium and recover tritiated exhaust gases. Safety aspects included the preparation of an overall probabilistic safety assessment and obtaining the requisite statutory and other approvals for the first tritium experiment. The experiment took place in two steps, firstly with a very weak tritium mixture to check all system, and secondly with a concentration of about 11% tritium in deuterium. The total fusion releases were 1.7 MW at peak power and 2 MJ of energy. The integrated total neutron yield was 7.2 10
17
neutrons. This paper reports the technical and safety aspects of the experiment.
