Supplementary Surveillance Program for Reactor Pressure Vessels of VVER-440/V-213C Type Reactors in NPP Dukovany

Abstract

Standard surveillance specimen programs for materials in the reactor pressure vessels of VVER-440/V-213 type reactors were designed with a high lead factor (approx. equal to 12 for base metal and 18 for weld metal). Thus, end-of-life neutron fluence levels are obtained within the first three years of operation. The maximum irradiation time is five years after which there is no active monitoring of neutron fluence inside reactor pressure vessels. Also, the distribution of neutron flux along surveillance specimen chains creates a large difficulty in grouping of specimens for static fracture toughness testing. A reevaluation of the standard surveillance program for NPP Dukovany has been performed. This reevaluation includes additional irradiations and a very detailed analysis of all results, and provides a basis for a design of a Supplementary Surveillance Program. Its realization started in 1997 by loading the first chains with specimens. The principles of this Program are explained in this paper. This program will provide: 1) new results under a realistically low lead factor, 2) new data on cladding properties under irradiation as well as after annealing and re-irradiation, and 3) data on the re-irradiation rate of vessel materials. Also the fourth part of the Program will provide a permanent neutron monitoring through the real vessel end-of-life. Within the whole program, the IAEA reference material JRQ will be also used, and this material will serve as a correlation monitor with other irradiation experiments.