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Title: Radionuclide distributions and migration mechanisms at shallow land burial sites

Abstract

During the past several years, Pacific Northwest Laboratory (PNL) has conducted research at the Maxey Flats Disposal Site (MFDS) for the US Nuclear Regulatory Commission (NRC). This work has identified the spectrum of radionuclides present in the waste trenches, determined the processes that were occurring relative to degradation of radioactive material within the burial trenches, determined the chemical and physical characteristics of the trench leachates and the chemical forms of the leached radionuclides, determined the mobility of these radionuclides, investigated the subsurface and surface transport processes, determined the biological uptake by the native vegetation, developed strategies for environmental monitoring, and investigated other factors that influence the long-term fate of the radionuclide inventory at the disposal site. This report is a final summary of the research conducted by PNL and presents the results and discussions relative to the above investigative areas. 45 refs., 31 figs., 17 tabs.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Nuclear Regulatory Commission, Washington, DC (USA). Div. of Engineering; Pacific Northwest Lab., Richland, WA (USA)
Sponsoring Org.:
USNRC
OSTI Identifier:
6267453
Report Number(s):
NUREG/CR-4670
ON: TI91008555; TRN: 91-008406
DOE Contract Number:
AC06-76RL01830
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 54 ENVIRONMENTAL SCIENCES; 63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; CHEMICAL WASTES; GROUND DISPOSAL; GROUND WATER; RADIONUCLIDE MIGRATION; LOW-LEVEL RADIOACTIVE WASTES; ORGANIC COMPOUNDS; ENVIRONMENTAL TRANSPORT; PLANTS; RADIONUCLIDE KINETICS; SOILS; CARBON 14; CESIUM 137; COBALT 60; FOOD CHAINS; KENTUCKY; LEACHATES; PLUTONIUM; POTASSIUM 40; PROGRESS REPORT; RADIOACTIVE WASTE DISPOSAL; SITE SURVEYS; STRONTIUM 90; TREES; TRITIUM; ACTINIDES; ALKALI METAL ISOTOPES; ALKALINE EARTH ISOTOPES; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; BETA-PLUS DECAY RADIOISOTOPES; CARBON ISOTOPES; CESIUM ISOTOPES; COBALT ISOTOPES; DISPERSIONS; DOCUMENT TYPES; ELECTRON CAPTURE RADIOISOTOPES; ELEMENTS; EVEN-EVEN NUCLEI; FEDERAL REGION IV; HYDROGEN COMPOUNDS; HYDROGEN ISOTOPES; INTERMEDIATE MASS NUCLEI; INTERNAL CONVERSION RADIOISOTOPES; ISOMERIC TRANSITION ISOTOPES; ISOTOPES; LIGHT NUCLEI; MANAGEMENT; MASS TRANSFER; MATERIALS; METALS; MINUTES LIVING RADIOISOTOPES; MIXTURES; NORTH AMERICA; NUCLEI; ODD-EVEN NUCLEI; ODD-ODD NUCLEI; OXYGEN COMPOUNDS; POTASSIUM ISOTOPES; RADIOACTIVE MATERIALS; RADIOACTIVE WASTES; RADIOISOTOPES; SOLUTIONS; STRONTIUM ISOTOPES; TRANSURANIUM ELEMENTS; USA; WASTE DISPOSAL; WASTE MANAGEMENT; WASTES; WATER; YEARS LIVIN; YEARS LIVING RADIOISOT; YEARS LIVING RADIOISOTOPES; 052002* - Nuclear Fuels- Waste Disposal & Storage; 540330 - Environment, Aquatic- Radioactive Materials Monitoring & Transport- (1990-); 540230 - Environment, Terrestrial- Radioactive Materials Monitoring & Transport- (1990-); 560162 - Radionuclide Effects, Kinetics, & Toxicology- Animals, Plants, Microorganisms, & Cells; 540220 - Environment, Terrestrial- Chemicals Monitoring & Transport- (1990-); 540320 - Environment, Aquatic- Chemicals Monitoring & Transport- (1990-)

Citation Formats

Kirby, L.J., Toste, A.P., Thomas, C.W., Rickard, W.H., Nielson, H.L., Campbell, R.M., McShane, M.C., Wilkerson, C.L., and Robertson, D.E. Radionuclide distributions and migration mechanisms at shallow land burial sites. United States: N. p., 1991. Web.
Kirby, L.J., Toste, A.P., Thomas, C.W., Rickard, W.H., Nielson, H.L., Campbell, R.M., McShane, M.C., Wilkerson, C.L., & Robertson, D.E. Radionuclide distributions and migration mechanisms at shallow land burial sites. United States.
Kirby, L.J., Toste, A.P., Thomas, C.W., Rickard, W.H., Nielson, H.L., Campbell, R.M., McShane, M.C., Wilkerson, C.L., and Robertson, D.E. 1991. "Radionuclide distributions and migration mechanisms at shallow land burial sites". United States. doi:.
@article{osti_6267453,
title = {Radionuclide distributions and migration mechanisms at shallow land burial sites},
author = {Kirby, L.J. and Toste, A.P. and Thomas, C.W. and Rickard, W.H. and Nielson, H.L. and Campbell, R.M. and McShane, M.C. and Wilkerson, C.L. and Robertson, D.E.},
abstractNote = {During the past several years, Pacific Northwest Laboratory (PNL) has conducted research at the Maxey Flats Disposal Site (MFDS) for the US Nuclear Regulatory Commission (NRC). This work has identified the spectrum of radionuclides present in the waste trenches, determined the processes that were occurring relative to degradation of radioactive material within the burial trenches, determined the chemical and physical characteristics of the trench leachates and the chemical forms of the leached radionuclides, determined the mobility of these radionuclides, investigated the subsurface and surface transport processes, determined the biological uptake by the native vegetation, developed strategies for environmental monitoring, and investigated other factors that influence the long-term fate of the radionuclide inventory at the disposal site. This report is a final summary of the research conducted by PNL and presents the results and discussions relative to the above investigative areas. 45 refs., 31 figs., 17 tabs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1991,
month = 2
}

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  • Subsurface waters at Maxey Flats are anoxic systems with high alkalinity and high concentrations of dissolved ferrous ion. Americium and cobalt in these trench waters are made more soluble by the presence of EDTA, while strontium and cesium are unaffected under the same conditions. EDTA is the major organic complexing component in waste trench 27 leachate, but other polar, water-soluble organics are also present. Evidence points to the migration of plutonium between waste trench 27 and inert atmosphere wells as an EDTA complex. Polar organic compounds may influence the migration of /sup 90/Sr and /sup 137/Cs. The primary pathway ofmore » water entry into the waste burial trenches is through the trench caps, but major increases in water level have occurred in an experimental trench by subsurface flow. The areal distribution of radionuclides at Maxey Flats has been influenced by surface runoff, deposition from the evaporator plume, subsurface flow and the actions of burrowing animals or deep-rooted trees. Vegetal and surface contamination on site and near site are quite low, and only /sup 60/Co exceeds commonly observed fallout levels. Radionuclide concentrations in surface soil at Maxey Flats are comparable to concentrations resulting from normal fallout in other areas of high rainfall.« less
  • Subsurface waters at Maxey Flats are anoxic, have a high alkalinity and contain high concentrations of ferrous, sulfide and ammonium ions and organic carbon. The trench leachates are extremely variable in composition. Prominent radionuclides include /sup 3/H, /sup 60/Co, /sup 90/Sr, /sup 137/Cs, /sup 238/ /sup 239/ /sup 240/Pu and /sup 241/Am. A wide spectrum of dissolved organic compounds is present in the leachates, including EDTA, polar organics and decomposition products from the waste forms. Cobalt-60 and plutonium are present as EDTA complexes and /sup 90/Sr and /sup 137/Cs are associated with carboxylic acid type compounds. The chemistry of thesemore » waters changes drastically as they become oxic and plutonium becomes less mobile under these new conditions. Water enters the trenches by infiltration through the trench caps, through subsidence areas, and through interfaces between new landfill and the original soil. Lateral flow is very complex and slow, and apparently occurs mainly by fracture flow. The plastic infiltration barrier installed in 1981 to 1982 has been effective in reducing soil moisture if cracks and leaks are eliminated. To date, no direct evidence of radionuclide transport to offsite locations by subsurface flow has been confirmed. The offsite distribution of radionuclides, except for tritium, is comparable to the ambient fallout from nuclear weapons testing. Tritium concentrations in water offsite are orders of magnitude below MPC levels. 24 figures, 31 tables.« less
  • The impact of the SRP Solid Radioactive Waste Burial Ground on the environment has been studied since the early 1970s in four subtasks: subsurface monitoring of groundwater, lysimeter tests of waste, soil-water chemistry effects, and radionuclide transport modeling. This document summarizes and integrates the results of the four subtasks. More information has been gathered on the behavior of radionuclides in a solid waste disposal facility located in a humid region than from any other waste disposal site in the world. The design of closure for the SRP Burial Ground has been given a firm technical basis. The limiting pathways formore » radionuclide migration have been determined to be infiltrating rainwater and root penetration. Closure designs must therefore address both these factors. The designs for new storage/disposal facilities have also been given a firm technical basis. The major conclusions are that tritium will be stored for decay and not allowed to contact the groundwater, waste containing long-lived radionuclides such as iodine-129 must be stored for later geologic disposal, and above and below ground concrete vaults should be used for disposal of other low-level radioactive waste. 61 refs., 18 figs. 8 tabs.« less
  • The impact of microbial metabolism of the organic substituents of low level radioactive wastes on radionuclide mobility in disposal sites, the nature of the microbial transformations involved in this metabolism and the effect of the prevailing environmental parameters on the quantities and types of metabolic intermediates accumulated were examined. Since both aerobic and anaerobic periods can occur during trench ecosystem development, oxidation capacities of the microbial community in the presence and absence of oxygen were analyzed. Results of gas studies performed at three commercial low level radioactive waste disposal sites were reviewed. Several deficiencies in available data were determined. Furthermore » research needs are suggested. This assessment has demonstrated that the biochemical capabilities expressed within the low level radioactive waste disposal site are common to a wide variety of soil bacteria. Hence, assuming trenches would not be placed in sites with such extreme abiotic conditions that all microbial activity is precluded, the microbial populations needed for colonization and decomposition of the organic waste substances are readily provided from the waste itself and from the soil of existing and any proposed disposal sites. Indeed, considering the ubiquity of occurrence of the microorganisms responsible for waste decomposition and the chemical nature of the organic waste material, long-term prevention of biodecomposition is difficult, if not impossible.« less
  • Before a license can be obtained to construct a facility for the shallow-land burial of low-level wastes, the US Nuclear Regulatory Commission must be assured that the facility will meet both performance objectives and prescriptive requirements set forth in 10CFR61, Licensing Requirements for Land Disposal of Radioactive Waste. Subpart D of 10CFR61 states that a disposal site shall be capable of being characterized, modeled, analyzed and monitored. To test the concept of site modelability, a 30-year old low-level radioactive waste disposal site at Chalk River Nuclear Laboratories (CRNL), Canada, was used as a field location for evaluating the process ofmore » site characterization and the subsequent modeling prediction of radionuclide transport from the site by groundwater. The radionuclide source term was a limestone-lined pit (since covered with soil) which in 1953 to 1954 received approximately 3800 liters of aqueous waste containing 1000 to 1500 curies of aged, mixed fission products, including 700 to 1000 curies of /sup 90/Sr and 200 to 300 curies of /sup 137/Cs. This evaluation was performed by comparing the actual measured radionuclide migration with predicted migration estimated from hydrologic/radionuclide transport models. This comparison provided valuable insights into the applicability of transport modeling, and to determining what level of effort is needed in site characterization at locations similar to the Nitrate Disposal Pit to provide the desired degree of predictive capabilities. 47 refs., 42 figs., 7 tabs.« less