Abstract

A large database for fracture toughness data according to the standard ASTM E1921 in the brittle and brittle to ductile transition region was generated within the former research programs CARINA and CARISMA for materials used in western pressurized water reactor (PWR) reactor pressure vessels (RPV). These programs confirmed successfully the application of the Master Curve approach for German RPVs. With respect to the RPV proof of safety during plant operation, in particular for integrity assessments considering the event of a Pressurized Thermal Shock (PTS) further relevant issues appeared in terms of the use of suitable fracture toughness curves for components and of the quantification of safety margins for the irradiated material state:

• Validity of fracture toughness curve and Master Curve respectively in the irradiated state at higher test temperatures (ductile material region)

• Verification of the WPS effect (warm pre-stress) in the irradiated state for representative loading paths and materials

• Impact of material inhomogeneities on the fracture toughness

• Transferability of specimen-specific effects on the safety-related RPV integrity assessment

To address these open issues a follow-up project was initiated called CAMERA (Consideration of special effects for the application of an optimized fracture mechanics approach for the RPV safety assessment). One main aspect within this program is to assess the possibility of describing the whole fracture toughness curve including the upper shelf based on empirical T0 correlations and the effect of a load case related warm pre-loading.

Material tests are carried out and evaluated according to ASTM E1820 to get the crack extension resistance as a function of stable crack extension (J-R curves) in the transition to the ductile region and according to ASTM E1921 (WPS) in the lower shelf region and transition region. The least-square fit curves (J-R) as well as the effect of warm pre-stress are determined for several types of irradiated and unirradiated RPV base and weld metals.

The results serve to expand the application window of the Master Curve concept to the ductile region and to complete the fracture toughness curve over the entire temperature range from lower shelf until operating temperature also considering the load scenario based on the effect of warm pre-stress. This paper will summarize and discuss the results of the material tests performed.

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