Some recent research results and their implications for RPV irradiation surveillance under long term operation
During the last decade the irradiation behaviour of characteristic RPV steels used in Pressurized Water Reactors has been extensively investigated in the international research programs CARISMA, CARINA and LONGLIFE. Whereas the CARISMA and CARINA programs were mainly focused on material testing of German RPV steels and data base applications by the RTNDT and Master Curve concepts, the main emphasis of the LONGLIFE project was placed on microstructural examinations of a wide range of RPV steels used in European NPP. Atom Probe Tomography, Small Angle Neutron Scattering, Transmission Electron Microscopy and others belonged to the techniques applied. Four of those RPV steels which are particularly interesting under the point of view of long term irradiation behavior have been studied at different irradiation levels up to 8×10 n/cm (E > 1 MeV) in all three research programs. In this way it was possible to get a comprehensive understanding of the material behavior induced by neutron irradiation and the responsible mechanisms behind. By means of the material properties and microstructural data obtained, in particular the impact of chemical composition (copper and nickel), and neutron flux on the material’s fracture toughness was quantified. Moreover, the most important mechanisms such as formation of element specific precipitations, segregations, and matrix defects could be demonstrated in relation to the change of material properties. For one material the occurrence of late irradiation effects has been observed in both material properties and microstructural appearance. All the available data are discussed thoroughly by consulting the relevant literature in the light of the practical implications they have for RPV irradiation surveillance under long term operation of 60 years and beyond. Specific issues like material specific application of reference temperature concepts, data scattering, prediction of high fluence behavior and use of material test reactor data are addressed. Finally, based on the results obtained by the research programs concerned, best practices for RPV irradiation surveillance programs are suggested and exemplified by industrial experience and adopted measures already in use.
Revision of the Irradiation Embrittlement Correlation Used for the EDF RPV Fleet
Cinquante huit reacteurs a eau pressurisee sont en fonctionnement actuellement en France, dont trente quatre de 900 MWe, vingt de 1300 MWe et quatre de 1450 MWe. Un programme de surveillance des effets de l'irradiation est en cours pour tous ces reacteurs conformement a la reglementation. Il a fourni a ce jour des donnees de fragilisation pour des fluences superieures a celles attendues apres quatre periodes decennales de fonctionnement pour vingt sept reacteurs de 900 MWe. Jusqu'en 2008, la formule de prevision de la fragilisation utilisee par EDF etait la formule "FIS", qui a ete etablie en 1983 avec, pour l'essentiel, des donnees obtenues en reacteurs d'essais. Globalement, sa confrontation aux donnees de surveillance disponibles aujourd'hui montre qu'elle surestime l'evolution de la fragilisation en fonction de la dose a faibles fluences, et qu'elle tend a la sous-estimer a forte fluence. Pour cette raison, le developpement d'une formule amelioree est apparu necessaire dans la perspective d'une prolongation de duree de fonctionnement des reacteurs. L'homogeneite de la base de donnees francaise en termes de materiaux (faible teneur en cuivre, gammes de fabrication similaires) et son relativement grand nombre de donnees a fluence elevee ont motive l'etablissement d'une formule de prevision specifique plutot que l'utilisation de formules developpees dans d'autres pays a partir de bases de donnees presentant des caracteristiques differentes. Les heterogeneites metallurgiques des viroles forgees constitutives des cuves ont ete etudiees et leurs effets integres dans la calibration de la formule et dans son utilisation. Elles induisent des variations locales de teneurs en elements fragilisants et de temperatures de transition de resilience initiale, et sont par consequent une source de dispersion du programme de surveillance. Le premier type d'effet est pris en compte par des teneurs de calcul majorees pour couvrir celles des segregations positives maximales. Le second type d'effet est pris en compte dans la definition de la courbe de tenacite minimale, ce qui conduit a ne pas integrer toute la dispersion du programme de surveillance pour l'evaluation de l'enveloppe superieure de la fragilisation. Dans cet article, la constitution de la base de donnees, la selection du modele de correlation, la calibration obtenue et sa validation sont presentes. Des donnees obtenues en reacteurs d'essai ont ete maintenues dans la base d'ajustement pour eviter toute extrapolation en composition chimique au stade de l'application de la formule. Il n'a pas ete decele d'effet significatif du flux de neutrons sur les fragilisations par analyse statistique. La nouvelle formule de fragilisation est en cours d'insertion dans le code RSEM et dans le dossier d'analyse d'integrite des cuves presente par EDF.
Endodontic regeneration: hard shell, soft core
A loss of organs or the destruction of tissue leaves wounds to which organisms and living things react differently. Their response depends on the extent of damage, the functional impairment and the biological potential of the organism. Some can completely regenerate lost body parts or tissues, whereas others react by forming scars in the sense of a tissue repair. Overall, the regenerative capacities of the human body are limited and only a few tissues are fully restored when injured. Dental tissues may suffer severe damage due to various influences such as caries or trauma; however, dental care aims at preserving unharmed structures and, thus, the functionality of the teeth. The dentin–pulp complex, a vital compound tissue that is enclosed by enamel, holds many important functions and is particularly worth protecting. It reacts physiologically to deleterious impacts with an interplay of regenerative and reparative processes to ensure its functionality and facilitate healing. While there were initially no biological treatment options available for the irreversible destruction of dentin or pulp, many promising approaches for endodontic regeneration based on the principles of tissue engineering have been developed in recent years. This review describes the regenerative and reparative processes of the dentin–pulp complex as well as the morphological criteria of possible healing results. Furthermore, it summarizes the current knowledge on tissue engineering of dentin and pulp, and potential future developments in this thriving field.