Modelling the Dispersion of Radionuclides in the Marine Environment

Miró

2009

Abstract.A numerical model that simulates the dispersion of radionuclides in the English Channel has been applied to study the dispersion of conservative and non-conservative radionuclides released from La Hague nuclear fuel reprocessing plant. The model is based upon previous work and now is able to simulate dispersion over long time scales (decades), explicitly including transport by instantaneous tidal currents and variable wind conditions. Wind conditions are obtained from meteorological statistics using a stochastic method. Outputs from the model are treated using time-series analysis techniques. These techniques allow the determination of characteristic times of the system, transport velocities and dispersion factors. This information may be very useful to support the decision-making process after an emergency situation. Thus, we are proposing that time-series analysis can be integrated with numerical modelling for helping decision-making in response to an accident. The model is first validated through its application to actual releases of 99-Tc and 125-Sb, and characteristic times for several radionuclides (a conservative one, 137-Cs and 239,240-Pu) are given next. Characteristic transport velocities and dispersion factors have been calculated as well.

Section: Methodsmentioning

confidence: 99%

Time scales for conservative and non-conservative radionuclide transport in the English Channel

Miró

2009

“…This method, standard in rapid-response models, allows a fast determination of tidal currents at any time and position [1]. The 2D depth-averaged hydrodynamic equations are standard and may be seen elsewhere [2]. They are solved by means of explicit finite difference schemes with appropriate boundary conditions in each domain.…”

Section: Model Descriptionsmentioning

confidence: 99%

“…The maximum sizes of the horizontal and vertical steps given by each particle due to turbulent diffusion are [2]:…”

Section: Model Descriptionsmentioning

confidence: 99%

See 1 more Smart Citation

Models for radioactivity dispersion assessments in Andalusian coastal waters: Gulf of Cádiz and Alborán Sea

2009

Abstract. Rapid response models for the assessment of the consequences of a radioactive spill in the coastal waters of Andalusia (south of Spain) have been developed. These waters comprise the Gulf of Cadiz, GoC, (Atlantic Ocean) and the Alborán Sea, AS, (Mediterranean Sea) and two models are described, covering both sectors. This subject is of high relevance since these waters are the only connection between the Atlantic and the Mediterranean. Thus, there are intense shipping activities that for instance include the transit of nuclear submarines. The models include hydrodynamic sub-models appropriate to describe the water circulation in each area. Results from the hydrodynamic models have been carefully tested through comparisons with observed tides and currents. The dispersion models are based upon a particle-tracking technique. Thus, the radioactive spill is simulated by a number of discrete particles, each one equivalent to a number of units, whose paths are computed. Turbulent diffusion and radioactive decay are calculated using a stochastic Monte Carlo method. The radionuclide concentrations may be obtained at the desired time from the density of particles per water volume. Some applications and examples of results are given.

“…Tidal and residual currents are obtained from two hydrodynamic models working on the same domain: a 2D depth-averaged model [1] is used for calculating tides and a two-layer model [2] is applied to obtain the residual flow. These are reasonable approaches, as discussed earlier [2].…”

Section: Model Descriptionmentioning

confidence: 99%

Modelling radioactivity dispersion in the Alborán Sea, western Mediterranean

2009

Abstract.A numerical model which simulates the dispersion of non-conservative radionuclides in the Alboran Sea has been developed. Water currents are obtained from two hydrodynamic models working on the same domain: a 2D depth-averaged model is used two calculate tides and a 2-layer has been applied to obtain the residual (mean) circulation. The output of the hydrodynamic models is first applied to calculate suspended particle concentrations and sedimentation rates over the domain, which are also required by the radionuclide transport model. This assumes that radionuclides may be present in three phases: dissolved, suspended matter and bed sediments. Exchanges between the liquid and solid phases are described through kinetic transfer coefficients. The model has been applied to simulate the dispersion of 137-Cs and 239,240-Pu introduced in the sea from atmospheric fallout. Measured and computed radionuclide concentrations in the water column and in bed sediments are, in general, in good agreement.