Tritium transfer between sea and atmosphere in the English Channel (North Cotentin and Bay of Seine)

Abstract

Oceans, seas, estuaries and rivers represent a vast sink for many substances of anthropic origin (metals, radionuclides, etc...). Depending on their chemical form, artificial radionuclides discharged into the sea by the nuclear industry can be carried onto land in marine aerosols, as well as by degassing seawater as is the case for tritium (³H) or for radiocarbon (¹⁴C). Three oceanographic cruises in the English Channel: TE-SEA, TRANSAT 1 and 2 have been performed on R.V. “Côtes de la Manche" to quantify the flux of ³H in gaseous form, from the sea into the atmosphere, following particular discharge into the sea from the COGEMA spent fuel reprocessing plant at La Hague (North West France). During cruises, the maximum concentration measured in the air was 10.6 Bq.L^-1, which is distinctly higher than the background of 1$^{\circ}$Bq.L^-1 thus demonstrating the transfer of ³H between water and atmosphere. The mean flux of ³H between the water and the atmosphere, calculated during these cruises was 2.4 10⁷ Bq.km^-2.d^-1. For the Seine Bay area (4400 km²) this flux represents 39 TBq.yr^-1 and hence less than 0.3 % of ³H discharged into the ocean from the COGEMA spent fuel reprocessing plant at La Hague.