Hydrogeology Journal

, Volume 12, Issue 6, pp 688–697 | Cite as

Radionuclides transport at the site of a low- and intermediate-level waste repository, Saligny, Romania

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Abstract

The site of the future Saligny low- and intermediate-level waste repository presents a rather deep unsaturated zone consisting of a pile of loess and clay, underlain by a calcareous aquifer. Van Genuchten parameters were first estimated in laboratory on samples collected from all the horizons, at different depths. In a second kind of test, moisture parameters were estimated from the natural water content profiles, observed in some wells, by inversion of the unsaturated flow equation. Based on the solution of the inverse problem as well as of the sensitivity analyses a simple physical model of the vadose zone was determined, consisting of a layered sequence that was subjected to a constant infiltration flux. Radionuclide migration was simulated in a vertical cross section made along the most probable path from the repository towards the surface water discharge zone. For radionuclide release, a source term was evaluated by ensuring a conservative estimate of cell inventory during the cell-filling operation. According to the simulation results, for the medium half-life nuclides, the unsaturated zone is a perfect barrier, whereas the long half-life isotopes break through in the aquifer at significant concentrations.

Keywords

Nuclear waste management Numerical simulation Parameter identification Radionuclides transport Unsaturated zone 

Résumé

Le futur stockage de déchets radioactifs de faible et moyenne activité de Saligny est caractérisé par une zone non-saturée assez profonde qui consiste dans des dépôts de loess et d’argile qui couvrent un aquifère calcaire. Dans une première étape, les paramètres de van Genuchten ont été déterminés en laboratoires sur des échantillons prélevés de toutes les couches, à des profondeurs différentes. Dans une seconde étape les mêmes paramètres ont été estimés, comme un solution du problème inverse à partir de profils de la saturation en eau, mesurés dans des forages. Les résultats du problème inverse, ainsi que l› analyse de sensibilité ont mené à un modèle multi- couches de la zone non-saturé, rechargé par un flux constant. On a simulé le transport des radionucléides dans une coupe verticale, construite au long du trajet le plus probable entre le stockage et les eaux de surface. Le flux de radionucléides relâchés a été estimé en considérant une valeur consevative pour la masse totale stocké. D› après les résultats de la simulation la zone non saturée forme une barrière presque parfaite pour les radionucléides de période moyenne, d’environs de 30 ans, tendis qu’elle est traversée avec des concentrations assez importantes par des isotopes à grande période.

Resumen

El sitio del futuro repositorio para desechos de nivel bajo e intermedio, denominado Saligny, presenta una zona no saturada bastante profunda, consistente en un depósito de loess y arcilla, subyacido por un acuífero calcáreo. Los parámetros de Van Genuchten se estimaron por primera vez en laboratorio, a partir de muestras recolectadas de todos los horizontes, a diferentes profundidades. En un segundo tipo de prueba se estimaron los parámetros de humedad a través de la inversión de la ecuación de flujo no saturado, a partir de los perfiles naturales que contienen agua, observados en algunos pozos. Con base en la solución del problema inverso, así como también en análisis de sensibilidad, se determinó un modelo físico simple de la zona vadosa, el cual consiste de una secuencia estratificada sometida a un flujo de infiltración constante. La migración del radioisótopo fue simulada en una sección vertical, hecha a lo largo del camino más probable entre el repositorio y la zona de descarga en el agua superficial. Para la liberación del radioisótopo se evaluó la fuente, asegurando un estimativo conservador del inventario de celdas durante la operación de llenado de celdas. De acuerdo con los resultados de la simulación, para los isótopos con vida media intermedia, la zona no saturada es una barrera perfecta; mientras que los isótopos con vida media larga irrumpen en el acuífero con concentraciones importantes.

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References

  1. Bouver H (1978) Groundwater hydrology. McGraw-Hill, New YorkGoogle Scholar
  2. Chavent G (1987) Identifiability of parameters in the output least square formulation: in: Walters E (ed) Identifiability of parametric models. Pergamon, NYGoogle Scholar
  3. Didiţa L, Danchiv A, Ilie P, Pavelescu M (2000) Radioactive release and transport through the unsaturated zone. Proc Int Conf Safety Radioactive Waste Management, Cordoba, SpainGoogle Scholar
  4. Didiţa L, Ilie P, Pavelescu M, Danchiv A, Martac E (2001) Simulation of radionuclide release and transport for LILW new Romanian repository. The 8th Int Conference on Environmental Management. Bruges, BelgiumGoogle Scholar
  5. Durdun I (1995) Disposal of radioactive waste discharged by the Romanian nuclear power generation program: final disposal for low and medium radioactive waste: a geological approach (in Romanian). Energia Nucleară 6–7Google Scholar
  6. Gheorghe A, Danchiv A, Mãrunţeanu C, Scrãdeanu D (1995) Hydrogeological assessment of LILW Saligny and Cernavoda sites (in Romanian). Trans Romanian Assoc HydrogeolGoogle Scholar
  7. IAEA (Institute of the Atomic Energy Authority) (1997) ISAM, The international program for improving long term safety assessment methodologies for near surface radioactive waste disposal facilities. Final version. IAEA, ViennaGoogle Scholar
  8. Knopmann D, Voss C (1987) Behavior of sensitivities in the one-dimensional advection-dispersion equation: Implication for parameter estimation and sampling design. Water Resour Res 23:2Google Scholar
  9. Knopmann D, Voss C (1989) Multiobjective sampling design for parameter estimation and model discrimination in groundwater solute transport. Water Resour Res 25:10Google Scholar
  10. Kool JB, Parker JC (1988) Analysis of the inverse problem for transient unsaturated flow. Water. Resour Res 24:6Google Scholar
  11. Kool JB, Parker JC, Van Genuchten MT (1987) Parameter estimation for unsaturated flow and transport models: a review. J Hydrol 91:2CrossRefGoogle Scholar
  12. McDonald MG, Harbaugh AW (1988) A modular three-dimensional finite-difference ground-water flow model. Techniques of water-resources investigations of the US Geological Survey, Geraghty and Miller, Inc.Google Scholar
  13. Mualem YA (1976) A new model for predicting the hydraulic conductivity of unsaturated porous media. Water Resour Res 12:12Google Scholar
  14. Simunek J, Vogel T, van Genuchten MT (1994) The SWMS_2D code for simulating water flow and solute transport in two-dimensional variably saturated media. Version 1.2, Res. Rap No 132. US Salinity Laboratory, Riverside, CaliforniaGoogle Scholar
  15. Sullivan TM (1993) Disposal unit source term (DUST), data input guide, NUREG/CR-6041, BNL-NUREG-52375, Brookhaven National LaboratoryGoogle Scholar
  16. Sun N, Sun N-Z, Elimelech M, Ryan JN (2001) Sensitivity analysis and parameter identifiability for colloid transport in geochemically heterogeneous porous media. Water Resour Res 37:2Google Scholar
  17. van Genuchten MT (1980) A closed form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci Am J 44:3Google Scholar
  18. van Genuchten MT, Leij FJ, Yates SR (1991) The RETC code for quantifying the hydraulic functions of unsaturated soils. IAG-DW12933934. US Salinity Laboratory, Riverside, CaliforniaGoogle Scholar
  19. Yeh WWG (1986) Review of parameter identification procedures in groundwater hydrology: the inverse problem. Water Resour Res 22:2Google Scholar

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.University of Bucharest Faculty of Geology et GeophysicsBucharestRomania
  2. 2.Nuclear Research InstitutePitestiRomania
  3. 3.Nuclear Research InstitutePitestiRomania

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