Radioactive Waste Burial Ground Research Articles

A containment and disposition strategy for tritium-contaminated groundwater at the Savannah River Site, South Carolina, United States

A containment and disposition water management strategy has been implemented at the Savannah River Site to minimize the discharge of tritiated groundwater from the Old Radioactive Waste Burial Ground to Fourmile Branch, a tributary of the Savannah River. This paper presents a general overview of the water management strategy, which includes a two-component (pond and irrigation) system, and a summary of operations and effectiveness for the first 3 yr of operations. Tritiated groundwater seep discharge was impounded by a dam and distributed via irrigation to a 22-ac (8.9-ha) upland forested area comprised of mixed pines (loblolly and slash) and hardwoods (primarily sweetgum and laurel oak). As of March 2004, the system has irrigated approximately 133.2 million L (35.2 million gal) and prevented approximately 1880 Ci of tritium from entering Fourmile Branch via forest evapotranspiration, as well as via pond storage and evaporation. Prior to installation of the containment and disposition strategy, tritium activity in Fourmile Branch downstream of the seep averaged approximately 500 pCi mL1. Six months after installation, tritium activity averaged approximately 200 pCi mL1 in Fourmile Branch. After 1 yr of operations, tritium activity averaged below 100 pCi mL1 in Fourmile Branch, and a range of 100–200 pCi mL1 tritium activity has been maintained as of March 2004. Complex hydrological factors and operational strategies influence remediation system success. Analyses may assist in developing groundwater management and remediation strategies for future projects at the Savannah River Site and other facilities located on similar landscapes.

Routine dose estimates for the removal of soil from a basin to the burial ground at the Savannah River Site.

Worker dose estimates have been made for various exposure scenarios resulting from the relocation of soil from the H Area Retention Basin to the Old Radioactive Waste Burial Ground at the Savannah River Site. Estimates were performed by hand calculations and using RESRAD and MAXDOSE-SR. Doses were estimated for the following pathways: (1) shine and inhalation as a result of standing on contaminated soil at the H Area Retention Basin and the Old Radioactive Waste Burial Ground; (2) exposure to off-unit receptors due to soil disturbances from excavation type activities at the H Area Retention Basin and the Old Radioactive Waste Burial Ground; (3) exposure to off-unit receptors due to soil disturbances from dumping of soil from bucket and from roll-off pan; and (4) exposure to off-unit receptors from wind driven dust from contaminated area. The highest dose estimates (0.25 mSv h(-1)) resulted from the receptor standing on the H Area Retention Basin.

A 35-year history of 90 Sr releases from a radioactive-waste burial ground

Data from a radioactive waste disposal area at Oak Ridge National Laboratory suggest that releases depend on site hydrology and waste containment. Loss of packaging integrity has apparently caused episodic increases in 90Sr source strength, followed by gradual reduction as runoff carries contaminants away. Most flow and transport occurs during January–April storms in response to site hydrology. Diversion of runoff from undisturbed areas upstream of the waste site (1983) reduced flow through the site by more than 65% and annual 90Sr release by more than 45%. However, between 1983 and 1994, increases in 90Sr source strength have partially offset the diversion effectiveness. Selective source control in 1996 further reduced annual 90Sr releases by more than 30% in the first two years, compared with pre-treatment conditions. The effectiveness of the grouting treatment should increase over the next 5–10 years, if new 90Sr sources are insignificant.

Tritium Transport from a Solid Radioactive Waste Burial Ground Whose Heterogeneous Conductivity Field is Based on Site Lithologic Data: ABSTRACT

Tritium Transport from a Solid Radioactive Waste Burial Ground Whose Heterogeneous Conductivity Field is Based on Site Lithologic Data: ABSTRACT

The environmental biogeochemistry of chelating agents and recommendations for the disposal of chelated radioactive wastes

Chelating agents are used in nuclear decontamination operations because they form very selective and strong complexes with numerous radionuclides. However, if environmentally-persistent chelated wastes are disposed of without pretreatment to eliminate the chelating agents, increased radionuclide migration rates from the disposal sites may occur. The environmental chemistry of the three most common aminopolycarboxylic acid chelating agents, NTA (nitrilotriacetic acid), EDTA (ethylenediaminetetraacetic acid), and DTPA (diethylenetriaminepentaacetic acid) is reviewed. This review includes information on their persistence in the environment, as well as their tendency to form complexes with actinides. Data on the sorption of chelated actinides by geologic substrates and on the uptake of chelated actinides by plants are also presented. Increased solubility and/or migration of radionuclides by chelating agents used in decontamination operations have been observed at two different radioactive waste burial grounds. EDTA was found to be promoting the migration of 6OCo and possibly other radionuclides from liquid waste disposal sites at Oak Ridge National Laboratory (1). Recently EDTA has again been identified in radioactive wastes-this time in trench waters containing from 600–16,100 pCi 238Pu per liter from solid waste burial grounds in Maxey Flats, Kentucky (2). These observations at Oak Ridge and Maxey Flats suggest that the practice of disposing chelated radioactive wastes should be reevaluated. Three different technical options for disposing chelated low-level radioactive wastes are proposed: 1. [1] Bind the solidified chelated waste in some kind of solid matrix that has a slow leach rate and bury the waste in a “dry” disposal site. 2. [2] Substitute biodegradable chelating agents in the decontamination reagent for the chelating agents that are persistent in the environment. 3. [3] Chemically or thermally degrade the chelating agents in the waste prior to disposal. The relative advantages and disadvantages of each of these options are discussed. We feel that surprisingly little attention has been given to an obvious procedure for the disposal of chelated radioactive wastes: chemically or thermally degrading the chelating agent prior to disposal. Any of the above three options might in fact be a satisfactory approach to the disposal of chelated wastes. However, we suggest that the burial of chelating agents such as EDTA be avoided and that option [3] be given more consideration.

Adsorption of Co and selected actinides by Mn and Fe oxides in soils and sediments

Iron and Mn oxides and associated radionuclides in soils and sediments from the radioactive waste burial grounds at Oak Ridge National Laboratory have been selectively extracted using wet chemical techniques. Product-moment-correlation analyses have demonstrated that 60Co and various actinides, principally 244Cm, 241Am and 238Pu are dominantly associated with Mn oxides. Correlation coefficients between these radionuclides and Fe oxides and organic C are generally very low. The important role of Mn oxides in radionuclide adsorption is attributed to their unique surface and colloidal properties. The data illustrate the importance of the Mn oxide component of soils and sediments in controlling transition metal and actinide solubility. These results suggest two major implications for the disposal of radioactive waste. First, in order to minimize future 60Co and actinide mobilization from disposal sites, a chemical environment in which Mn oxides are least soluble should be maintained. Second, the liberal use of Mn oxides in waste management operations might improve long-term retention of these radionuclides. Deep-sea Mn modules, which may in the future be mined for their trace metal contents, could serve as a ready supply of Mn oxide for waste disposal applications.

Radionuclide adsorption by manganese oxides and implications for radioactive waste disposal

COBALT-60 and certain transuranics such as 244Cm, 241Am and 238Pu are migrating in trace amounts from original intermediate-level waste disposal pits and trenches in the radioactive waste burial grounds of Oak Ridge National Laboratory (ORNL) in Tennessee1. These radionuclides are transported in trace amounts from the trench 7 area and are to some extent adsorbed by soil and shale along the route of migration. We show here that the adsorbed radionuclides, which are very strongly bound in the soil, are being retained primarily by manganese oxides in the soils. Our data illustrate the importance of the manganese oxide component of soils and sediments in general in controlling 60Co and actinide mobility. Certain implications of these results for the field of radioactive waste management will also be discussed.