THE MATERIALS CONCEPT FOR VVER PLANTS IN COMPARISON WITH SPECIFICATIONS IN GERMAN NUCLEAR SAFETY STANDARDS

During the course of safety analyses, the materials concept of VVER pl ants was evaluated and compared with that of Konvoi plants based on th e KTA nuclear safety standards. The general materials and toughness co ncept is outlined using the example of reactor coolant system main com ponents. The types of steel used are not directly comparable to the ma terials used in Konvoi plants. The specified examination coverage of i ndividual parts is generally not as detailed as that stipulated in KTA , and corresponds more closely with the specifications of other nuclea r engineering codes and standards such as the ASME code. In contrast t o Western codes and standards, the toughness of ferritic materials use d in VVER plants is determined within the framework of the RT(NDT) con cept solely on the basis of Charpy impact tests and not by means of Pe llini drop weight testing. A correlation between these two techniques still remains to be developed. The chemical analysis limits in the cor e region for Cu, P and Ni for newer plants correspond to the specifica tions laid down in the KTA standards. As the values are considerably h igher than these limits in older VVER plants, particularly in the weld metal, recovery annealing is necessary in these plants.