Volume 5, Issue 3 (March 2008)
Using Subsize Impact Bend Specimens for Estimation of Irradiation and Re-Irradiation Embrittlement of VVER RPV Steels
Results of impact bend tests of subsize Charpy V-notch-type (CVN) specimens are used in Russia for monitoring both re-irradiation embrittlement of the first generation of VVER-440 (including VVER-440/179 and VVER-440/230, i.e., projects B-179 and B-230) reactor pressure vessel (RPV) steels and irradiation embrittlement of VVER-440/213 RPV steels. For the first generation of VVER-440 RPVs, no surveillance program was foreseen and only subsize specimens (5 by 5 by 27.5 mm and 3 by 4 by 27 mm) can be manufactured from samples taken from the inner surface of the RPV for radiation embrittlement monitoring. For VVER-440/213 RPVs, 80 % of the surveillance specimens are irradiated with a lead factor greater than 20. Only four specimens of base metal and four specimen halves of weld seam material are irradiated with a lead factor less than 3. Taking into account that full-size (10 by 10 by 55 mm) CVN specimens were used in surveillance programs, using subsize specimens enables to solve the flux effect problem for VVER-440/213 RPV beltline materials and ensure representativity of surveillance programs. Application of subsize specimens for the estimation of radiation embrittlement requires developing a correlation between transition temperature values evaluated using test results of standard (full-size) and subsize CVN specimens. Such a correlation is discussed.