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

Abstract

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 ( 3 H) or for radiocarbon ( 14 C). 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 3 H 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 Bq.L -1 thus demonstrating the transfer of 3 H between water and atmosphere. The mean flux of 3 H between the water and the atmosphere, calculated during these cruises was 2.4 10 7 Bq.km -2 .d -1 . For the Seine Bay area (4400 km 2 ) this flux represents 39 TBq.yr -1 and hence less than 0.3 % of 3 H discharged into the ocean from the COGEMA spent fuel reprocessing plant at La Hague.

Modelling tritium flux from water to atmosphere: application to the Loire River

“…Atmospheric water vapour was also sampled along the riverbanks. The water vapour was condensed on a cold trap (PREVAIR system) developed by IRSN in association with the French Navy (GEA) (Maro and Tenailleau, 2005). The sampling system allowed the 3 H limit of detection to be lowered by a factor of 3000 compared to sampling using impingers.…”

“…The second approach supposes that 3 H emission from water to atmosphere is similar to water evaporation. Such a method was considered in some models developed for the simulation of 3 H behaviour in the environment Maro and Tenailleau, 2005). Water vapour flux (L m À2 s À1 ) can be calculated with the following equation based on the Rohwer's formula:…”

Radionuclides transfer between water and atmosphere in the Loire estuary (FLORE project)

“…As the post atmospheric nuclear test activity reference value is less than 1.0 Bq.L -1 in air and 0,15 Bq.L -1 in water, all samples are clearly marked by 3 H from the nuclear industry [7]. The activities in water decrease linearly with the salinity reflecting the dilution and the mixing of fluvial effluent into marine water.…”

“…Recent studies around COGEMA La Hague nuclear reprocessing plant show that this area of high bacteriological activity generate high carbon dioxide flux marked by 14 CO 2 originating from liquid waste released of the plant [5] [6]. Similarly in the Bay of Seine evaporating process results in 3 H flux from sea to the atmosphere [7]. This indicates that part of volatile radionuclides ( 14 C, 3 H) of liquid waste released are recycled in the atmosphere.…”

“…14 C and 3 H activities in air and water samples were determined using the procedure defined by Maro et al, [5], and Maro et al, [7] respectively. 131 I concentration was measured by gamma spectrometry after precipitation of total iodine [9].…”