[en] When it was decided, in January, 1960, to make a major effort in the research and development of coated particles for the first charge of the reactor experiment, it was obvious that in order to find out what kind of particles should be used, an extensive programme had to be mounted to evaluate fuel for the development laboratory and for use in the irradiation tests. A selection amongst the numerous tests possible had to be made in order to determine the more realistic ones to be applied on the particles. The second urgent task was to find out the limit values within which the results of these tests must lie, that is to say, to give criteria defining the best particles. But these limits depend on irradiation results, and an extensive programme is now being carried out to give the best value of each variable. It has been necessary at this stage to take into account the greatest number of parameters possible. Another important part of the work consisted in developing methods for use in process control.