This paper provides an overview over the work of the European Network on Neutron Techniques Standardization for Structural Integrity (NeT). The network involves some 35 organisations from industry and academia and these partners undertake the application of modern experimental and numerical techniques to problems related to the structural integrity of components, mainly relevant to nuclear applications. While being built around neutron scattering techniques, which are predominantly applied for analyses of welding residual stresses, one of the major strengths of the consortium is the diversity in available experimental and numerical techniques. In the residual stress area, for example, many types of materials characterizations testing, several methods for residual stress analysis, including neutron and X-ray diffraction, deep hole drilling, the contour method and others, and many different ways of numerical analysis employing several commercially available FEM codes can be covered by the partners. Currently the network has embarked on five different Task Groups. Four of these are dealing with welding residual stress assessment, and one applies Small Angle Neutron Scattering for studying thermal ageing processes in duplex stainless steels used for reactor core internals. The work already performed in the context of NeT and the envisaged investigations for the ongoing Task Groups are briefly outlined in this paper. The aim is to give the reader a comprehensive overview of the work of NeT and to shed some light on the potential present in this kind of collaborative effort.
Neutron irradiation is known to have a considerable impact on the mechanical
characteristics and the behaviour of materials and components. The distribution of residual stresses
is one of the properties affected by irradiation. However, because of the difficulties in performing
measurements in radioactive components, not many experimental data have to date been collected.
At the High Flux Reactor (HFR) of the European Commission’s Joint Research Centre (JRC), a
facility has been developed for residual stress measurements in steel specimens subjected to longterm
irradiation. The objective of this development was to establish the neutron radiation induced
changes in the residual stresses around welds in test pieces representative of the core shroud of
boiling water reactors. Residual Stress measurements on such double-V butt welds in stainless steel
plates after irradiation exposure have been performed by neutron diffraction using this facility. The
comparison with measurements in non-irradiated companion specimens [1] showed that irradiation
changed the distribution of residual stresses. The results suggested that the impact of irradiation
varied with the distance of the test location from the specimen surface. On the basis of currently
measured data we could not draw definitive conclusion about the influence of neutron dose and
irradiation duration upon the stress modification.
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