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 installed in the vacuum vessel. 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 order to gain timely information on the introduction of tritium into the tokamak, including retention of tritium in wall materials, operation of diagnostics, radiation monitoring and waste handling, it was decided in early 1991 to prepare for an experiment which would involve the use of a small quantity of tritium. It is also important to note that although tritium technology has become an important component of fusion development programmes worldwide, tritium has never been used so far in a tokamak or in any controlled fusion device.