Analysis of the Difference Between the Reference Temperature Values Derived From Conventional and Mini-C(T) Specimens: Effect of the Number of Valid Fracture Tests

The long-term-operation of nuclear power plants (NPPs) requires a precise knowledge of the fracture toughness of the reactor pressure vessel (RPV) materials. This property decreases with the irradiation level, so surveillance programs measure it throughout the NPP operational life by testing materials placed inside the RPV which were initially designed to cover the initial lifespan. Therefore, the amount of available material to be tested during the life extension of NPPs may be scarce, and it is not possible to perform fracture tests using conventional specimens (e.g., 1T or 25.4 mm thick). In this context, mini-C(T) specimens (0.16T) appear as a key technology. Generally, mini-C(T) specimens provide similar results to those generated by using conventional specimens. However, there are situations where the deviations between the T₀ predictions of conventional and mini-C(T) specimens are negligible, and situations where such deviations are as high as 40C. This work provides a comprehensive literature review of experimental T₀ results obtained using conventional fracture specimens and mini-C(T) specimens, analyzing how the corresponding deviations are affected by the number of valid tests used to define T₀. The research includes a total of 140 datasets, covering base, heat affected zone (HAZ), and weld materials, and both irradiated and unirradiated conditions. With all this, the paper finally provides insights into how the mentioned deviations depend on the extent of the experimental program performed for the characterization of T₀, revealing that larger experimental programs tend to provide smaller discrepancies.