Analysis of the Phenix fuel assembly and core performance

Since start-up the behaviour of the fuel assemblies and core of Phenix has been highly satisfactory. The performance levels set initially for this reactor have therefore been improved. After briefly describing some recent operating characteristics of the Phenix core, the paper shows how it was possible to increase the lifetime of fuel assemblies by analysing the measurements made in the reactor and the results of post-irradiation examinations. New solutions regarding the material used for fuel pin cladding and hexagonal tubes are presented. There is also a discussion of the procedures by which the core thermal power was increased, namely, adjustment of the loading schedule, flattening of the neutron flux by control rods and application of methods of thermohydraulic calculation. All the improvements referred to are optimized by use of the CAPHE code system, the data of which are being constantly refined by new experiments. In this connection, a recent result obtained in the measurement of the breeding gain of Phenix is discussed. (author)