Artificial radionuclides in waters of the lower section of the river Ebro (Northeast Spain)

The river Ebro, in Northeast Spain, discharges into the Mediterranean Sea a fter flowing through several large cities and agricultural, mining and indu strial areas. The Asco nuclear power plant (NPP) is located in the lower ri ver section and comprises two pressurised-water reactor (PWR) units, from w hich low-level liquid radioactive waste is released to river waters under a uthority control. During the period 1989 to 1993, we carried out 29 samplin g campaigns in order to determine H-3, Sr-90, Cs-134, Cs-137, Pu-238 and Pu -239,Pu-240 in Ebro river waters at different locations, both upstream and downstream from the Asco NPP. H-3, Cs-134 and Cs-137 activities showed larg e variability as they ranged from < 1.4 to 117 +/- 3 Bq L-1, < 0.27 to 22 /- 1 mBq L-1 and < 0.36 to 35 +/- 1 mBq L-1, respectively. This behaviour, especially remarkable for tritium, was due to the detection of tank release s travelling downstream. The characteristic NPP Cs-134/Cs-137 ratio was fou nd to be 0.61 +/- 0.02 (N = 22). In the estuarine area, Cs-137 traces from Mediterranean waters were observed and relatively enhanced tritium activiti es might possibly be present due to the accumulation of activity in the est uary. Sr-90 and Pu-239,Pu-240 activities were homogeneous both in respect t o time and space, showing mean activities 6.9 +/- 0.2 mBq L-1 (N = 10) and 1.36 +/- 0.10 mBq m(-3) (N = 3), respectively. These levels could only be a ttributed to nuclear weapons fallout leached by continental waters, as the impact from the plant appears to be negligible and no other sources are pre sent in the area.