CONTAMINANT TRANSPORT IN BIDIMENSIONAL POROUS-MEDIA VIA BIASED MONTE-CARLO SIMULATION

One of the most vulnerable spots of nuclear power systems is the hazar d posed by the radioactive wastes at the end of the fuel cycle. Curren tly, the most widely pursued end solution consists of disposing the ra dioactive wastes in repositories buried in deep geologic formations of presumed high stability. Licensing of such repositories is conditiona l on the assessment of the reliability of such confinement for quite e xtensive periods of time ranging from 10 000 to 1 million years. Over such long time scales the repositories may leak, thus releasing contam inants to the surrounding medium. The released contaminant may reach t he groundwater and be transported for substantial distances, eventuall y returning to the biosphere, where it poses a hazard for human health and the environment. In the present paper, we propose a phenomenologi cal model based on the Kolmogorov-Dmitriev theory of branching stochas tic processes in which a distributed source releases contaminant which is transported over a bidimensional medium whose physical properties are stochastic in space. The proposed model is implemented within a Mo nte Carlo scheme which exploits variance reduction techniques. (C) 199 8 Elsevier Science Ltd. All rights reserved.