High fast neutron fluence in RPV internals can change the ductility and fracture resistance of the material. Cracking has been detected in some RPV internal components such as the core shrouds and top guides of BWRs and this has resulted in the need for more data on the irradiated material properties. A concern has also been expressed as to whether high neutron doses could cause void swelling and, therefore embrittlement induced by the voids. These phenomena could clearly impact on the life of a plant. In order to address these issues, the EC PRIS project has been set up to examine the properties of irradiated stainless steels for predicting the lifetime of such nuclear power plant components (Nordgren et al., 2001).

The project involves the procurement of representative top parts of BWR control rods blades of type AISI 304L and type AISI 316L stainless steel with fast neutron fluences in the range 2 X 1021 -5 X 1021 ncm~2. These specimens are being examined, mechanical properties are being determined and the microstructure is being characterised.

A thimble tube of type AISI 316 stainless steel from the Swedish Ringhals 2 plant that has been irradiated for 23 years to between 0 and 70 dpa is also being examined. Tensile and hardness properties, fracture properties and radiation-induced micro-structural and micro-chemical changes will be determined. Fracture properties will be determined using previously established pin-loading fracture toughness test techniques (Grigoroev et al., 1995, 1997).

The properties of both the BWR — and PWR-irradiated materials will be compared with non-irradiated archive materials.

Stress corrosion cracking in PWR and BWR shroud internals are also under study in the EC INTERWELD project (Youtsos et al., 2001). The objective of this project is to define better the radiation-induced material changes in the heat-affected regions of austenitic stainless steels.

Test welds of stainless steel type 304 and type 347 are being produced with weld residual stresses, microstructure and properties that are representative of core shroud applications. These are being irradiated to two neutron fluence levels in the HFR at Petten, the low level at 0.3 dpa and the high level in the range 0.8-1.2dpa. These levels are representative of LWR internal irradiations. The results will be compared with an in­service weld from the BR3 reactor. This weld has been irradiated from 1962 to 1987 in a coolant of temperature 260-300°C with maximum dose irradiation of 2.4 X 1020 n cm-2.

The weld residual stresses of the irradiated materials are being measured by neutron diffraction and the corrosion characteristics of the material will be determined by further tests. Mechanical properties are being determined for both the test specimens and the in-service material. The microstructure and microchemistry properties are being obtained by optical, EPMA and other techniques.