Analysis of the reasons for the scatter of the data on temperature reference specimens of VVER-1000 base metal

The distribution of material properties in a forged part used to make reference specimens was studied. The objective was to determine why the scatter of data was so large in tests of temperature reference specimens of VVER-1000 base metal on the metal of a sampling ring of a regular VVER-1000 casing. The tests were performed on Charpy and rupture samples, and the hardness was measured and the chemical composition studied. It is shown that the scatter is mainly due to the fact that the reference specimens of the VVER-1000 base metal were cut from the end of the forged part, where, characteristically, a property gradient exists along the vertical coordinate with the critical brittleness temperature decreasing significantly toward the top boundary of the forged part. The scatter of the initial critical brittleness temperature for the control and temperature groups was evaluated within the framework of a virtual experiment simulating a study of reference specimens with prescribed property variation.