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.
Flux dependence of cluster formation in neutron-irradiated weld material
The effect of neutron flux on the formation of irradiation-induced clusters in reactor pressure vessel (RPV) steels is an unresolved issue. Small-angle neutron scattering was measured for a neutron-irradiated RPV weld material containing 0.22 wt% impurity Cu. The experiment was focused on the influence of neutron flux on the formation of irradiation-induced clusters at fixed fluence. The aim was to separate and tentatively interpret the effect of flux on the characteristics of the cluster size distribution. We have observed a pronounced effect of neutron flux on cluster size, whereas the total volume fraction of irradiation-induced clusters is insensitive to the level of flux. The result is compatible with a rate theory model according to which the range of applied fluxes covers the transition from a flux-independent regime at lower fluxes to a regime of decelerating cluster growth. The results are confronted with measured irradiation-induced changes of mechanical properties. Despite the observed flux effect on cluster size, both yield stress increase and transition temperature shift turned out to be independent of flux. This is in agreement with the volume fraction of irradiation-induced clusters being insensitive to the level of flux.
Complex thoracic vascular injury repair using deep hypothermia and circulatory arrest.
A 61-year-old man with a penetrating injury to the innominate artery, left common carotid artery, and left subclavian artery at their origins from the aortic arch with associated injuries to both innominate veins and an innominate artery to vein fistula after a single stab wound is described. The patient was managed successfully using cardiopulmonary bypass together with deep hypothermia and circulatory arrest. Presentation and management are discussed.