Modelling The Transport Of Sediment AndPlutonium From The Mururoa Lagoon

Abstract

Between 1966 and 1996 the French Government carried out a programme of nuclear weapons testing at Mururoa and Fangataufa atolls in the Tuamotu Archipelago in French Polynesia. In 1997/98 an international study was elaborated with the goal to show the impact of the testing on the environment. One of the aspects of this study was also to study the possible future outflow of radioactively contaminated sediments from the Mururoa lagoon into the Pacific Ocean. A 3D hydrodynamic (HD) and sediment transport model was used to calculate the circulation and the sediment outflow from the lagoon. The model is shortly described in the paper. Two scenarios were simulated: (a) Normal conditions, where tidal forcing and easterly trade wind of 8 m/s were taken into account. The outflow of sediment through the pass in the lagoon rim was determined to be about 80 000 tons/year; (b) Storm conditions, with wind from NW, max. speed of 150 km/h were calculated. Frequency of these storms (tropical cyclones) is about 0.1 storm/year. The sediment outflow through the pass in these conditions would be about 720 000 tons/storm. A large amount of sediments would also be outwashed by waves over the south rim of the atoll, i.e. about 3 200 000 tons/storm. Taking into account both normal and storm conditions, the average annual outflow of sediment-bound Plutonium would be about 77 Gbq/year. 1 Problem description At the Mururoa and Fangataufa Atolls in French Polynesia, the French government conducted 46 atmospheric and 147 underground nuclear experiments between the years 1966 and 1996. Recent measurements in both lagoons have shown that the sediment is partly contaminated, primarily by Environmental Coastal Regions III, C.A. Brebbia, G.R. Rodriguez & E. Perez Martell (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-827-9