Radionuclide transport

N.P. Dikiy, S.Yu.Sayenko, V.L. Uvarov, E.P. Shevyakova, The nuclear-physical methods application for a radionuclide transport in a granite rocks studies. VANT, Nuclear-Physical Researches Series, 2000. No. 2, p. 54-57. 

Chapter 6 was concerned, with determining the probability of various failures leading to insufficient core cooling of a nuclear reactor. This chapter describes how the accident effects are calculated as the accident progresses from radionuclide release, radionuclide migration within the plant, escape from retaining structures, atmospheric radionuclide transport and the public health effects. 

A general review of actinide transport on colloids, and how this may relate to radionuclide transport studies, is provided by Ivanovich (1991). It has been found that colloids can carry a large fraction of U (Dearlove et al. 1991). Due to the greater reactivity. 

Luo SD, Ku XL, Roback R, Murrell M, McLing XL (2000) In-situ radionuclide transport and preferential groundwater flows at INELL (Idaho) decay-series disequilibrium studies. Geochim Cosmochim Acta 64 867-881... 

Carroll J, Harms IH. 1999. Uncertainty analysis of partition coefficients in a radionuclide transport model. Water Res 33(11) 2617-2626. 

Janke DH, Arthur WJ. 1985. Radionuclide transport by cottontail rabbits at a radioactive waste disposal area. Northwest Sci 59(3) 221-229. 

MMT (32) is a 1- or 2-dimensional solute transport numerical groundwater model, to be driven off-line by a flow transport, such as VTT (Variable Thickness Transport). MMT employs the random-walk numerical method and was originally developed for radionuclide transport. The model accounts for advection, sorption and decay. 

Linkoff I, Burmistrov D, Kandlikar M, Schell WR. 1999. Reducing uncertainty in the radionuclide transport modeling for the Chernobyl forests using Bayesian updating. In Linkov I, Schell WR, editors. Contaminated forests. Dordrecht (DE) Kluwer, p 143-150. 

Read, D., Ross, D. Sims, R. J. 1998. The migration of uranium through clashach sandstone The role of low molecular weight organics in enhancing radionuclide transport. Journal of Contaminant Hydrology, 35, 235 -248. 

Smellie, J. A. T. Karlsson, F. 1999. The use of natural analogues to assess radionuclide transport. Engineering Geology, 52, 193-220. 

A major outcome of the abovementioned studies is the importance of pH and notably of the salinity of the groundwater controlling colloid concentrations and, consequently, the relevance of colloids for radionuclide transport. The pH-dependent colloid stability varies considerably for different colloid types. Experimental data for the relationship of the stability ratio W... 

Meier, H., Zimmerhackl, E. Zeitler, G. 2003. Modeling of colloid-associated radionuclide transport in porous groundwater aquifers at the Gorleben site, Germany. Geochemical Journal, 37, 325-350. 

This is not to say that all is doom and gloom. Although many of these tasks are formidable, the earth-science community believes them to be tractable and that a successful geologic repository for radioactive waste can be constructed. We only plead that our ignorance of earth s processes be considered in the development of a repository and that any repository constructed prior to the acquisition of the needed fundamental knowledge contain many independent natural and manmade barriers to radionuclide transport to compensate for our lack of knowledge. 

MPR Model for the Process of Radionuclide transport to foodchains (Krapivin, 1995). 

Local variations in the vertical distribution of radionuclides are determined by both hydrological and ecological conditions. The correlation between these conditions is a function of the season. Table 6.12 gives estimates of the role of ecological processes in the formation of the vertical distribution of the radionuclear pollution of Arctic seas. These estimates show that the biological community plays a minor role in radionuclide transport from upper layers to the deep ocean. 

Krapivin V.F. Cherepenin V.A. Nazaryan N.A. Phillips G.W. and Tsang F.Y. (1997). Simulation model of radionuclide transport in the Angara-Yenisey river system. Problems of the Environment and Natural Resources, 2, 41-58 [in Russian]. 

Radionuclide transport in natural waters is strongly dependent on sorption, desorption, dissolution, and precipitation processes. The first two sections discuss laboratory investigations of these processes. Descriptions of sorption and desorption behavior of important radionuclides under a wide range of environmental conditions are presented in the first section. Among the sorbents studied are basalt interbed solids, granites, clays, sediments, hydrous oxides, and pure minerals. Effects of redox conditions, groundwater composition and pH on sorption reactions are described. 

Field measurements of radionuclide migration can be used to help substantiate laboratory measurements of sorption, solubility, and identification of important chemical species. The fourth section describes three field investigations that provide information on the effects of organics, colloids and environmental conditions (Eh, pH, and temperature) on radionuclide transport. The chemical species of radionuclides that are mobile under specific field conditions are identified. 

Groundwater leaching of radionuclides from waste forms is the first step in radionuclide transport from a disposal site. The release rate of radionuclides from the waste form is dependent on the waste form s leaching behavior. The sixth section describes the factors that affect the leaching behavior of several potential waste forms and radionuclides. 

Sorption and desorption isotherms were obtained for sorption of radionuclides under oxidizing and reducing conditions. The Freundlich equation accurately describes most of these isotherms. Most radionuclides are apparently irreversibly sorbed on each of the geologic solids since the slopes of sorption and desorption isotherms for a given radionuclide are different. This hysteresis effect is very large and will cause a significant delay in radionuclide transport. It, therefore, should be included in modeling radionuclide transport to accurately assess the isolation capabilities of a repository in basalt. 

This equation can be used to describe one-dimensional transport of radionuclides through porous media (e.g. radionuclide elution curves from laboratory columns packed with interbed solids) assuming instantaneous sorption and desorption. Van Genuchten and coworkers have demonstrated the importance of using both sorption and desorption isotherms in this equation when hysteresis is significant. Isotherm data for sorption and desorption reactions of radionuclides with interbed materials are presented in this paper which can be used to predict radionuclide transport. 

Three interbed materials from the Columbia River Basalt Group have been investigated in the radionuclide sorption experiments. Interbeds are porous sedimentary layers located between many of the basalt flows in the Columbia River Basalt Group and comprise a potential preferential pathway for groundwater and, therefore, radionuclide transport. 

Sorption and Desorption Isotherms. To model radionuclide transport in groundwater through geologic media, it is necessary to mathematically describe sorption and desorption in terms of isotherms. The Freundlich isotherm was found to accurately describe sorption and desorption of all radionuclides studied in the interbed-groundwater systems, except when precipitation of the radionuclide occurred. 

This chemical hysteresis will, of course, affect radionuclide transport. For example, if hysteresis occurs during a column experiment in which a pulse of tracer is added to the influent, the effluent curve will show heavy tailing and a reduction in peak concentration. Ignoring hysteresis effects could cause serious errors in predicting radionuclide movement. 

Chemical components in the waste solutions potentially could affect radioelement solubility and sorption reactions, and thus enhance or reduce radionuclide transport. The effects of 12 chemical components on the solubility and sorption of cobalt, strontium, neptunium, plutonium, and americium were studied to... 

Investigations of redox processes in natural water systems have emphasized the disequilibrium behavior of many couples (e.g., 37). The degree of coupling of redox reactions with widely varying rates, and its effect on radionuclide transport in an NWRB needs to be considered. Because of the generally slow kinetics of autoxidation reactions, the potential surface catalyzed reduction of a radionuclide at low temperatures in the presence of trace levels of DO may explain certain sorption data (e.g., 38). 

Migration of contaminated groundwater has been identified as the principal mechanism for radionuclide transport from a repository to the biosphere. Over the lifetime of the repository, it is assumed that groundwater will become contaminated as the result of hydrothermal reactions and interactions within and near waste packages. 

---