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. From the analysis of the first capsules irradiated, considerable experimental data are now available on the dosimetry technique used, based on the experience of more than fifteen Electricité de France 900 MWe reactors.

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