In the vessel surveillance program of each French pressurized water reactor, four to eight in-reactor irradiation capsules are equipped with activation and fission dosimeters. Analysis of the first capsules irradiated has brought considerable data on the dosimetry process used. This experience comes from more than fifteen 900 MWe reactors of electricité de France.

In this paper, problems encountered after dismantling of the capsule are examined: activity measurements, data corrections, inconsistency in the results, etc. From these experimental results, proposals are made to improve accuracy, availability, and ease of use, for both short and long term applications. This analysis has led to better specification of the material composition with respect to impurities and, as a result, to changes in the number, design, and materials, both of the fissile dosimeter box and of the neutron filter. Moreover, niobium dosimetry has been added to the process.