BBER-500 reactor as a source of induced activity resulting from decommissioning

Abstract

The future development of nuclear power requires the development of a new of generation of reactors that meet the modern international reliability and safety requirements. An example of such reactors is the promising power-generating unit with enhanced safety with a 1800 MW(th) water-moderated water-cooled BBER-500 reactor [1]. This plant employs the principle of self-shielding and is a further development of the BBR (PWR) plants, widely used in the world, with the traditional loop arrangement of the first loop.After power plants have reached their service life, they must be decommissioned [2, 3]. According to estimates made by the IAEA, by the year 2010 approximately 200 of the currently operating power generating units with an equivalent electric power of 1000 MW each will be decommissioned and dismantled [4].The disassembly costs are equal to 20-30% of the total construction costs of the power plants [3]. All components, included in the dismantling process will be radioactive to a greater or lesser degree. For accident-free standard operation, the induced activity exceeds 99% of the total activity neglecting the activity of the fuel [5, 6]. Long-lived induced activity is of practical interest, since disassembly is performed at least no earlier than two years after the reactor is shut down.Our objective in this work is to make a two-dimensional investigation of the long-lived induced activity of the structures and materials of a BBER-500 reactor after decommissioning.The BBER-500 reactor consists of the following basic units: a thick-wall metallic vessel, the top block with the safety and control rod drives, intravessel units (shaft, recess), and a core with an equivalent radius of 158 cm and a height of 355 cm.The reactor vessel consists of a vertical vessel, whose inner surface is covered with a 0.7 cm thick stainless anticorrosion facing. In the horizontal plane, passing through the center of the core, the equivalent thickness of the recess is 15.5 cm, the thickness of the shaft is 6.5 cm, and the thickness of the reactor vessel walls is 19.25 cm. The shielding beyond the vessel consists of concrete. A dry side shielding, consisting of serpentinite concrete with a thickness of 73.85 cm with a lining, followed by the standard concrete shielding, is installed on the right side. in the radial direction, at the level of the core.The service life of the reactor is taken to be 50 years with a power utilization coefficient of 0.8. The construction of the main unit of the BBER-500 reactor is planned for the Leningrad nuclear power plant.The construction described above corresponds to the layout of the BBER-500 reactor displayed in Fig, 1. An approximation along the radius r in the horizontal plane is displayed in Fig. 2. Here. r = 0 is the center of the core.The induced activity in the (r, z) geometry was calculated using the AKTIVATSIYA-2 program-constant system [7, 8], which includes the KASKAD-1 program [9, 10] with the DLC-23/CASK library of constants [11]. This system is designed for computational investigati...