Strategic Approach to the Nuclear Legacy Problem (by the Example of Techa Cascade of Reservois of the Mayak Plant)

Sergey V. Kazakov, Federal Centre for Nuclear and Radiation Safety, 5, Pyzhevskiy per., Moscow, 119017, Russia; Tel.: +7 (495) 924-51-19, Email: s.kazakov@fcnrs.ru
Sergey S. Utkin, Federal Centre for Nuclear and Radiation Safety, 5, Pyzhevskiy per., Moscow, 119017, Russia; Tel.: +7 (495) 955-23-77, Fax +7 (495) 958-00-80, Email: uss@ibrae.ac.ru

Decommissioning of «nuclear legacy» objects is a complex of complicated and interrelated legal, scientific and engineering solutions directed to substantiation and ensuring of safety during and after completing the preservation of large-scale nuclear and/or radiation hazardous sources. One of the main problems is that the solutions are often unique, unobvious in advance and, consequently, cause active and not always fruitful discussions concerning their adequacy.

In the Russian Federation the question of Techa cascade of reservoirs (TCR) protection is of high importance nowadays. TCR was constructed in the period of 1950-1960 to solve defensive problems. In actual fact, TCR is open radioactive waste storage (total mirror area of reservoirs – 66 km2; total activity in water and sediments – 320 kCi) but at the same time it has all features of water object. Current safety and environment protection legislation of the Russian Federation doesn’t permit the possibility of existing of such an object but it materially exists. At present there are no specific approved engineering solutions of its liquidation (moreover, TCR is important part of radioactive waste management technology functioning at «Mayak» plant).

In the paper strategic approach to the «nuclear legacy» problem is considered. By the example of TCR of the «Mayak» plant principles of methodology of compound natural-technogenic objects safety are discussed (standard argumentation «from human exposure to discharge standards» is invalid) taking into account the necessity of the complex solution of the environmental problems in the region. Safety requirements of TCR are formalized taking into consideration legislation of the Russian Federation and biospheric approach to radiation protection of environment.

Assessment of Stream Fish Mortality from Short-term Exposure to Illite Clays Used as an In Situ Method for Remediating ¹³⁷Cs Contaminated Wetlands
Bon-Jun Koo, Ph.D., Department of Natural and Mathematical Sciences, California Baptist University, Riverside, CA 92504, Tel: 951-343-4621, Fax: 951-343-4584, Email: bonjunkoo@calbaptist.edu
Dean E. Fletcher, M.Sc., Savannah River Ecology Laboratory, University of Georgia, Aiken, SC  29802, Tel: 803-725-2472, Email: flectcher@srel.edu
Thomas G. Hinton, Ph.D,. Savannah River Ecology Laboratory, University of Georgia, Aiken, SC  29802, Tel: 803-725-7454, Email: thinton@uga.edu
Christopher D. Barton, Ph.D., Department of Forestry, University of Kentucky, Lexington, KY 40546, Tel: 859-257-2099, Email: barton@uky.edu
Daniel I. Kaplan, Ph.D. Savannah River National Laboratory, Aiken, SC 29802, Tel: 803-725-6211, Email: dkaplan@srnl.org

Due to their physical properties, illite clays can sorb cesium-137 almost irreversibly and, therefore, sequester the contaminant from the environment.  However, applying large amounts of clay to natural aquatic habitats for in situ remediation purposes may create deleterious conditions for stream biota due to high turbidity and sedimentation.  To evaluate potential effects of turbidity from illite application on fish survivorship, yellowfin shiners (Notropis lutipinnis) and tessellated darters (Etheostoma olmstedi) were subjected to treatment with illite clays of differing moisture content in flow-through simulated stream raceways. Air-floated illite containing 1 to 3% moisture was compared to semi-dry illite containing 8 to 12% moisture. Turbidity and fish mortality was subsequently monitored for seven days.  At 2-m downstream from the application point, mean turbidity peaked during clay application at 525 and 72 nephelometric turbidity units (NTU) in the air-floated illite and semi-dry illite treatments, respectively.  Turbidity returned to levels similar to that of the controls (4-6 NTU) after four hours in the air-floated illite raceways and one hour in the semi-dry illite raceways.  Although the majority of the suspended clay was quickly flushed from the system and the remaining settled to the bottom, turbidity did continue to fluctuate, because of fish movements and sediment resuspension. Fish mortality did not significantly differ among control and illite treated raceways.

Imitation Models of ⁹⁰Sr Behaviour in Soil and Stand of Forest Ecosystems
Sergey V. Mamikhin, Soil Science Faculty, Lomonosov Moscow State University, Vorobjevy Gory, Moscow, 119992 Russia, Tel: (495) 939-50-09, Email: mam@soil.msu.ru
Dmitriy V. Manakhov, Soil Science Faculty, Lomonosov Moscow State University, Vorobjevy Gory, Moscow, 119992 Russia, Tel: (495) 939-50-09, Email: dman@soil.msu.ru

The algorithm of display of ⁹⁰Sr behaviour in forest ecosystems by method of imitating modeling is developed. It was success to adapt earlier designed algorithm of long-term ¹³⁷Cs dynamics, that allows to speak about particular universality of the given algorithm in relation to both radionuclides. Algorithm is based mainly on the results of our division researches on Ural and in Chernobyl 30-km zone. The additional researches have confirmed statistically, that ¹³⁷Cs, ⁹⁰Sr and their chemical analogues K, Ca behave equally in a status of quasie-equilibrium.

Distinctive features of algorithm: the ⁹⁰Sr contents in vegetation is subdivided into two parts (outside and internal pollution), which dynamics is considered separately; dynamics of a radionuclide is considered in connection with dynamics of organic substance; it is supposed, that ⁹⁰Sr behaviour in plants is similar to Ca behaviour; the biological availability ⁹⁰Sr, contained in a soil, is integrated function of time and physico-chemical properties of the given soil. On the basis of offered algorithm the models are constructed which were used for realization of a number of numerical experiments, including reconstruction of a situation of pollution of pine forest ecosystem on grey forest soils in result of Kyshtym accident. The quantitative estimations of intensity of ⁹⁰Sr redistribution between stand components and soil are received.

The modern problems of creation of prognostication models of ⁹⁰Sr dynamics in the forest ecosystems are discussed. Necessary condition of success is the developing of various versions of algorithms by independent groups of the contributors with their subsequent analysis and generalization as the library of algorithms.

Development of a Uranium Transport Model for Assessment of Long Term Plume Stability
Thomas J. Phelan, Geosyntec Consultants, Inc., 289 Great Road, Suite 105 , Acton , MA 01720 , USA , Tel: 978-263-9588, Fax: 978-263-9594, Email: tphelan@geosyntec.com
Benjamin Bostick, Dartmouth College, Department of Earth Science, 6105 Fairchild Hall, Hanover, NH 03755, Tel: 603-646-3624, Fax: 603-646-3922, Email: benjamin.c.bostick@dartmouth.edu
Doug Larson, Geosyntec Consultants, Inc., 289 Great Road, Suite 105 , Acton , MA 01720 , USA , Tel: 978-263-9588, Fax: 978-263-9594, Email: dlarson@geosyntec.com
Robin Swift, Geosyntec Consultants, Inc., 289 Great Road, Suite 105 , Acton , MA 01720 , USA , Tel: 978-263-9588, Fax: 978-263-9594, Email: rswift@geosyntec.com
Peter Zeeb, Geosyntec Consultants, Inc., 289 Great Road, Suite 105 , Acton , MA 01720 , USA , Tel: 978-263-9588, Fax: 978-263-9594, Email: pzeeb@geosyntec.com

Uranium migration through saturated overburden materials is often strongly influenced by the adsorption of uranium onto aquifer materials.  While adsorption is most rigorously described using surface complexation modeling, it traditionally has been quantified in transport models using a linear sorption isotherm (i.e., k_d) approach.  The k_d approach requires fewer input parameters than surface complexation modeling and is computationally simple.    Data in the literature, however, demonstrate a three-to four-order-of-magnitude range in k_d values for uranium and other metals, suggesting a strong dependence of k_d on groundwater and matrix geochemistry/mineralogy.  The Generalized Composite Approach, as described by James Davis and Gary Curtis of the United States Geological Survey, has been offered as an alternative modeling method that reduces the equilibrium data requirements of a full surface complexation model while allowing for a more deterministic incorporation of geochemical variability in the subsurface.  This presentation will highlight a combined laboratory and numerical modeling study of depleted uranium fate and transport at the Nuclear Metals, Inc. Superfund Site in Concord , Massachusetts .  Data from adsorption experiments performed on overburden material sampled from several locations on site were used to develop surface complexation equilibrium constants for a small subset of iron oxide and oxyhydroxide surface sites with varying binding strengths.  These data were incorporated into flow and transport simulation that incorporates variability in matrix properties and groundwater chemistry, and allows predictions of transport behavior.

Evaluation of Indoor Radon Potential in Northern Virginia Using Spacial Autocorrelation, GIS Application and 3-D Visualization
George Siaway, Ph.D., Vikas Chandhoke, Ph.D., George Mushrush, Ph.D., and Douglas Mose, Ph.D., College of Science, George Mason University, Fairfax, VA 22030, Tel: 703-993-1068, Fax: 703-273-2282, Email: dje42@aol.com 

Studies by associates at the Virginia Center of Basic and Applied Science (CBAS,INC) have archived over 4000 seasonal (3-month) indoor radon measurements from a small (about 1000 square miles) but populous (over 1 million population) area in northern Virginia. About half of the residents live in single family homes, most of which have basements, and many new homes are built each year. The close proximity of a U.S. Geological National Center, offices of the State Geological Survey and several University geoscience departments have resulted in an abundance of geotechnical information. Scientists and citizen interest in indoor radon, and its influence on home value, resulted in several attempts to find the cause(s) of areas with high and low indoor radon. Most of these attempts are based on comparisons of indoor radon with geotechnical information (usually radioactivity of the soil or bedrock, or permeability differences between areas of high and low slope or between areas of high and low elevation). Our approach has shown that these geotechnical variables can be used to predict indoor radon in untested or not-yet-constructed homes, but not as definatively as previous reports suggest.

Modeling Radionuclide Transfer in Bottom Sediments of Water Bodies
Sergey V. Kazakov, Federal Centre for Nuclear and Radiation Safety, 5, Pyzhevskiy per., Moscow , 119017, Russia ; Tel.: +7 (495) 924-51-19, Email: s.kazakov@fcnrs.ru
Sergey S. Utkin, Federal Centre for Nuclear and Radiation Safety, 5, Pyzhevskiy per., Moscow , 119017, Russia ; Tel.: +7 (495) 955-23-77, Fax +7 (495) 958-00-80, Email: uss@ibrae.ac.ru

Concerning radionuclide migration in the ecosystem of water bodies, one of the main processes is the behavior of radionuclides in bottom sediments. In the case of single entry of radionuclides in a water object, the influence of bottom sediments on radiation conditions of the reservoir can be described in the following way: initially, during a relatively short time interval, bottom sediments appear to be a radionuclide storage and then, during a long period, they become a source of water and groundwater secondary pollution.

At present, there is certain experimental data of radionuclide distribution in the «water – biota – bottom sediments» system. There is also some data in the qualitative description of migration processes of radionuclides in bottom sediments and water. But the level of formalization of the processes is too low to use the mathematical modeling as a reliable tool to predict and control the radiation condition of water bodies.

The aim of the work is to investigate long-term effects of industrial plant accidents leading to water object radioactive pollution. We have developed a mathematical model of radionuclide migration dynamics in bottom sediments due to diffusion and convective transfer, taking into account the complicated formation of bottom sediments.

A structure of model equations has been developed. The numerical method solution and the analysis of results are given. It is shown that:

-        The content of radionuclides in the solid phase of bottom sediments, mainly in fixed form, is extremely important when we consider radionuclide distribution in bottom sediments and their removal to a lower layer.

-  The diffusion, including molecular diffusion and hydrodynamic dispersion, accelerates the radionuclide transfer in bottom sediments and promotes earlier and more intensive removal of radionuclides. The higher seepage velocity the higher the influence of dispersion.

-  It is determined that radionuclides can be accumulated in bottom sediments without further removal and can decay there when the content of radionuclides in fixed form and their decay constant are both relatively high. Relations between input data leading to such radiological safety conditions are defined.

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