One of the key issues concerning the structural integrity of a reactor pressure vessel (RPV) is the effect of neutron irradiation on fracture toughness. To assure the structural integrity of the RPV it is necessary to adjust the pressure-temperature operational limits. These limits depend on the fracture toughness of the RPV material, which is affected by the neutron irradiation.
The purpose of the material surveillance program, as established in ASTM E185, is to monitor changes in the fracture toughness properties of ferritic materials in the RPV. Under the surveillance program, Charpy-V notch specimens included in surveillance capsules are tested and the shift in impact energy due to irradiation is calculated. Due to the lack of standard fracture toughness specimens in the surveillance capsules, most of the codes assume that fracture toughness shift due to irradiation is the same as the Charpy-V notch shift. This correlation requires high conservative margins to reduce the uncertainty of the method. To avoid these uncertainties, several approaches have been developed during the last several years. One of the most innovative is the Master Curve approach developed by VTT, which has been adopted as a testing standard by ASTM.
In this paper, Master Curves are determined for IAEA reference material JRQ non-irradiated and irradiated on a commercial Nuclear Power Plant. Determination of the To reference temperature is done following single and multi-temperature techniques. Specimens used are pre-cracked Charpy and 1/2TCT type.