Avaliação do fluxo de nêutrons e da taxa de dose durante o funcionamento nominal do ITER

Abstract

The ITER (International Thermonuclear Experimental Reactor) is a tokamak with elongated plasma and single null poloidal divertor. The nominal inductive operation produces a DT fusion power of 500 MW for a burn length of 400 s, with a pulse repetition period as short as 1,800 s. The main goal is to exhibit the use of fusion energy for peaceful purposes. The tokamak will perform DT plasma experiments and theproduction rate of 14.1 MeV neutrons will achieve the level of 1020 n.cm-2.s-1. In this study of initial nature will be done primarily a description of the main reactor components intended mainly determine the spatial distribution of the neutrons flux and calculate the dose rates associated with normal ITER operation. Was used a onedimensionalmodeling technique with the code MCNP5 (Monte Carlo N- Particle). Thetransport of particles in MCNP5 was conducted based on FENDL/MC-2.1 data library and the dose rates were calculated using the conversion factors of the IRCP-21. In the model are included the most important shielding components of the reactor, namely the blanket, the vacuum vessel, the toroidal field coils, cryostat and the shielding hall with2.0 m concrete side walls. Calculations for two different concrete compositions were performed to investigate the influence of different filling materials of bioshield on the dose rate. Radiological source terms with an important dose rate impact as airborne tritium and activated corrosion products were not considered. The results confirm thatpersonnel access into the tokamak hall must be prohibited during operation. Taking into consideration the use of large boron concentration in the biological shield concrete (0.029 weight fraction), it was achieved a dose rate reduction by one order of magnitude. The dose rate is dominated by the secondary gamma ray. The dose rate during operation on the outside of the tokamak was determined and its value is around1.0 Sv/h.