Pressure Vessel Steel Surveillance Program: Developments, Experience Feed-Back, and Perspectives

Aims of surveillance programs and the reactor operating scenarios which were used to establish them are recalled. The main characteristics of surveillance programs drawn up at the design of each series of French pressurized water reactor units are then presented. Developments in the cumulative dose rate at the design end of life have contributed to a reduction in the number of irradiation capsules. The withdrawal schedule not only takes into consideration the anticipation due to the irradiation location, but also takes into account real operating conditions. A large number of specimens and the presence of a dosimetric and thermal monitoring in each capsule play a great part in the quality of the results. Extensive work aimed at a more accurate definition of reference neutronic data were undertaken to improve the reliability of the results. Experience feed-back from the first capsules used confirms the interest of this work and the weight of parameters such as geometries, spectrum, fissile dosimeter, neutron filter, etc. Developments in fuel design and operation call into question some manufacturers' hypotheses of primary importance. This necessitates the reassessment of the damage to the vessel steel and the operator's becoming aware of the relevant risks and modification of the design of the next programs of reactor surveillance.