Statistical Simulation in Determination of the Critical Temperature of Metal Brittleness of the VVER-1000 Reactor Shell from Data of Bending Impact Test
Method of statistical simulation (Monte Carlo method) is used to determine the brittleness transition temperature Tk according to the procedures PNAE G-7-002-86 and RD EO 0598-2004 in the numerical experiments. Data of bending impact test of Charpy specimens (with V-notch) used in the calculation are obtained on an array of more than 1200 steel samples (15H2NMFAA) cut from different (in thickness, height and in the circumferential direction) zones of the VVER-1000 reactor shell within a temperatures range of -95 to +20°C. Data of statistical tests indicate that the material of the reactor shell can be considered homogeneous. It is found that the values of sample fracture in the brittle-ductile transition region obey the bimodal law, parameters ofthe distributions being determined at different temperatures. Statistical modeling revealed the laws of the transition temperature distribution. It is shown that the average Tk values determined from PNAE G-7-002-86 exceed the values determined from RD EO 0598-2004 approximately by 10°C. The boundaries of the intervals wherein the values of the transition temperature are located with 90% probability depending of the number of tested samples and test pattern are determined. Recommendations for improving the methodology of the transition temperature determination are specified.