Short and long-lived radium isotopes in surface waters from Ilha Grande bay, Angra dos Reis, Brazil

¹ Programa de Engenharia Nuclear, COPPE/UFRJ, Cidade Universitária, Caixa Postal 68.509, 21945-970 Rio de Janeiro, Brazil
² Instituto de Radioproteção e Dosimetria (IRD), Caixa Postal 37750, Barra da Tijuca, 22642-970 Rio de Janeiro, Brazil
³ Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rua Marquês de São Vicente 225, 22453-900 Rio de Janeiro, Brazil

Abstract

The Angra dos Reis nuclear power plant site is located 130 km south from Rio de Janeiro city. Seawater is used as cooling water for both units; the cooling water is pumped from Itaorna Bay and discharged into Piraquara de Fora Bay, together with the liquid effluents from the two NPPs. Piraquara de Fora Bay belongs to a large bay system, Ilha Grande Bay and, therefore, conservative radionuclides in seawater will reach this bay with the tidal movement and, at the end, exported to open sea. Radium isotopes behave conservatively in seawater and can be applied as natural tracers to carry out dispersion studies. Two transets involving eight sampling points each were performed in Ilha Grande bay and ²²⁸Ra, ²²⁶Ra, ²²⁴Ra and ²²³Ra determination realized. The results have shown that the conservative radionuclide dispersion is controlled by eddy diffusion with negligible net offshore advection. The calculated eddy diffusion coefficient was 26 km² ⋅ d^-1 and 25 km² ⋅ d^-1, based on ²²³Ra and ²²⁴Ra respectively.