ANALYSIS AND PREDICTION OF RADIOELEMENT D ISPERSION IN THE MARINE-ENVIRONMENT BY THE PULSE RESPONSE METHOD

This work presents analysis and prediction of the dispersion of radioe lements in the marine environment based on the pulse response theory. The analysis is made on three data sets over the period 1984-1988 : th e amounts of gamma-emitting radioelements contained in controlled rele ases from the nuclear reprocessing plant of La Hague (=signal emission point), and gamma-emitting radionuclide concentrations in sea water a t two stations (=signal reception points), situated at 8 and 35 km dis tance from the release point. Using this data base, the pulse response is determined for each station and for each element. This allows us t o estimate the mean delay and the amplitude of the reception signal (i .e. the concentrations of radioelements) and its sensitivity to wind f orcing. We then demonstrate that the convolution of the pulse response and released radionuclide time-series is capable of yielding a fairly good prediction of the concentrations at each station. Some particula rities of the behaviour of Cs-137, Ru-106 and Co-60 are evidenced by c omparison with that of Sb-125, assumed to be a conservative element in sea water: adsorption of Ru-106 and Co-60 on to particles, additional sources of Cs-137. The mean delays calculated for Sb-125 at each stat ion are close to each other (28-30 days) despite their different dista nces from the release point, and are explained by the specific hydrody namics of the studied area.