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At the beginning of 1986, thirty-two 900-MWe and four 1300-MWe nuclear power stations were in service in France. A regulatory surveillance program is in progress concerning the base metal, weld metal, and heat affected zones of every nuclear pressure vessel; a reference metal sample is also present in each reactor. This surveillance program was implemented largely in accordance with U.S. rules. The specifications for the core shell forgings in MnNiMo low alloy steel and the associated welds require low contents in embrittling elements such as copper and phosphorus. The results presented here concern materials containing less than 0.08 wt% Cu and 0.011 wt% P, except for the welds of the first six reactor vessels, which have 0.13 wt% Cu and 0.019 wt% P maximum. The main aim is to obtain the RTNDT shift from Charpy-V tests, in relation to the fluence measured from fissile and activation dosimeters. Tensile, compact, and three-point bend specimens are also included in the capsules.
Results for the first capsules removed after up to four years of operation, corresponding to fluences (E > 1 MeV) less than 1.5 × 1019 n · cm−2 (2.9 × 10−2 dpa), are presented and evaluated. The mean and upper values of the RTNDT shift are about 20 and 40°C, respectively, and there is no significant difference between parent metal and weld. A new formula to predict embrittlement has been derived from test reactor experiments, because of the strict limits on the residual element contents in French materials when compared with materials for which other formulae have been established. The surveillance program results are discussed and compared with the predictions of these formulae.
irradiation embrittlement, surveillance program, pressure vessel steels, predictive formulae
Engineer, Electricité de France, SCMI (Service Contrôle de Matériaux Irradies), Avoine,
Electricité de France, SEPTEN (Service Etudes et Projets thermiques et Nucléaires), Lyon,
Framatome, Département Matériaux, Paris la Défense,