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 1992–1993[1]. 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:

  1. To establish a firm basis for prediction of the performance of future JET D-T pulses, including the question of fuel mixing;
  2. To carry out accounting on tritium utilisation, including the assessment of tritium holdup in various components, especially in-vessel components;
  3. 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 1017 neutrons. This paper reports the technical and safety aspects of the experiment.