Carbon 14 transfer from seawater to the atmosphere through degassing processes in the Bay of Seine (North-West of France)

¹ Laboratoire des Sciences du Climat et de l'Environnement, UMR 1572-CEA/CNRS, Domaine du CNRS, 91198 Gif-sur-Yvette, France
² Institut de Radioprotection et de Sûreté Nucléaire, Laboratoire de Radioécologie de Cherbourg-Octeville, 50130 Cherbourg-Octeville, France
³ Marine Nationale, Groupe d'Études Atomiques, BP. 34, 50115 Cherbourg Naval, France

Abstract

COGEMA La Hague nuclear reprocessing plant is located in the North West of Cotentin peninsula near Cherbourg (France). This nuclear plant releases radioelements in atmosphere and in the English Channel. About 8.5 TBq.year^-1 of radiocarbon are released as the liquid wastes through a pipe a few kilometres off sea shore, West of the reprocessing plant. Recent studies in the peninsula show anomalous higher radiocarbon contents in vegetation near the coast that have suggested a supplementary marine contribution through the degassing of the ¹⁴C excess supplied by liquid releases of the nuclear plant. Carbon dioxide partial pressure, ¹⁴C activities were measured in air and sea water in the Bay of Seine and around the COGEMA-La Hague nuclear reprocessing plant during three cruises in 2000 and 2002. Results show clearly that sea is a source of CO₂ and ¹⁴C to the atmosphere. Higher ¹⁴C concentrations in air and water related to the La Hague liquid wastes are clearly recorded. The aim of this paper is to show results of these oceanographic campaigns. Flux between seawater and atmosphere are calculated in the North-West Cotentin and in Bay of Seine.