Embrittlement trend curve for vessel steels with low copper content

Among the different requirements established in order to ensure the integrity of the components of the coolant pressure boundary in light water reactors are those referring to the fracture toughness of the materials used for these components. These requirements are especially important in the case of the material used for the reactor vessel since, given that it is subjected to neutron irradiation, it will progressively undergo embrittlement throughout its service life. Neutron irradiation gives rise to changes in the mechanical properties of the vessel steels and welds. The magnitude of these changes may be quantified using empirical models developed on the basis of data obtained from materials irradiated in research reactors or from the irradiation of surveillance capsules in commercial reactors. By using empirical and semi-empirical models, it is possible to determine the increase in the Reference Temperature, RTNDT, that the vessel material will undergo for a given neutron fluence. An own correlation has been obtained for the calculation of ΔRTNDT using the surveillance data of the Spanish PWR reactors, the expression of which is as follows: ΔRTNDT=(12.3+34.52.%Cu).f(0.44-0.1.logf). This report also presents a comparison between measured ΔRTNDT values and those obtained through the application of different correlations developed in other countries, with a view to checking the validity of ΔRTNDT predictions. (author)