Inventory of Radionuclides in Bottom Sediment of the Clinch River Eastern Tennessee
GEOLOGICAL SURVEY PROFESSIONAL PAPER 433-1
Prepared in cooperation with the U.S. Atomic Energy Commission and the Oak Ridge National Laboratory Inventory of Radionuclides in Bottom Sediment of the Clinch River Eastern Tennessee By P. H. CARRIGAN, JR.
TRANSPORT OF RADIONUCLIDES BY STREAMS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 433-1
Prepared in cooperation with the U.S. Atomic Energy Commission and the Oak Ridge National Laboratory
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR
WALTER J. HICKEL, Secretary
GEOLOGICAL SURVEY
William T. Pecora, Director
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 35 cents (paper cover) CONTENTS
Abstract ______II Results continued Introduction. ______1 Retention factors.______112 Acknowledgments______3 Distribution of radionuclides______13 Coring procedures and results.. 4 Longitudinal distribution.______13 Selection of sampling sites. 4 Vertical distribution______14 Coring tools______5 Contribution to inventory from reaches outside of Results of coring. ______5 study reach______14 Core processing______7 Distribution of sediment..-______15 Computation of inventory. 9 Physical properties______16 Results. ______11 Future estimation of radionuclide loading-______16 Inventory of identified radionuelides __ 11 Conclusions.______17 Estimate of accuracy of inventory. 11 References..______18
ILLUSTRATIONS
FIGTJBE 1. Index map showing study area; low-level radioactive waste waters are released through Whiteoak Dam______12 2. Map showing 14 sampling sections in Clinch River______4 3. Graph of sampling sections located in reaches of high, low, and transitional levels of radioactivity. ______4 4. Graph of coring penetration, sample recovery, and distribution of sediment and of radioactivity at Clinch River mile 7.5__-______-______-____-______-______-_---__--______-_-____ 5. Photograph showing coring from barrel float-______---_-_-_---_-_--_----____ 6. Diagram showing scanner for detection of gamma radiation in core______-___-_-__-__---______8 7. Photograph showing masonry saw cutting frozen cores.______8 8. Diagram showing methods of determining length, width, and thickness of subvolumes______10 9-14. Graphs: 9. Similarities in longitudinal distribution of radionuclides______13 10. Longitudinal distributions of cesium-137, determined through different sampling techniques, are much alike______14 11. Concentration bears a nearly direct relationship to sediment thickness______14 12. Sediment thickness in the downstream direction______15 13. Cross-sectional area of radioactive sediment-______16 14. Time required to accumulate 2.6 feet of sediment over a given proportion of surface area. ______17
TABLES
TABLE 1. Yearly discharges of radionuclides to the Clinch River______13 2. Numbers of sampling sites, of samples used in computations, and of truncated cores used in computations for each sampling section-______7 3. Method of estimating depth of radioactivity of truncated cores collected in the Clinch River______11 4. Quantity of total identified radioactivity and volume of radioactive sediment in subreaches______12 5. Areal distribution of radioactive sediments, for selected thicknesses.______16
in
TRANSPORT OF RADIONUCLIDES BY STREAMS
INVENTORY OF RADIONUCLIDES IN BOTTOM SEDIMENT OF THE CLINCH RIVER EASTERN TENNESSEE
By P. H. CAKKIGAN, JK.
ABSTRACT posed of representatives of each of the participating An inventory has been made of the radionuclides associated agencies (Morton, 1963, p. 1) established the following with bottom sediment in the lower Clinch River. The reach in objectives: (1) To determine the fate of radioactive cluded in this inventory extends 21 miles from the mouth of materials currently being discharged to the Clinch the river to the mouth of Whiteoak Creek. River, (2) to determine and understand the mecha The source of the radionuclides in the sediments was the release of low-level-radioactive waste waters from the Oak nisms of dispersion of radionuclides released to the Ridge National Laboratory into Whiteoak Creek basin and river, (3) to evaluate the direct and indirect hazards of thence into the river via Whiteoak Lake. current disposal practices in the river, (4) to evaluate Results of the inventory indicate that the following quantities the overall usefulness of the river for radioactive waste of radioactivity were associated with the bottom sediment in disposal purposes, (5) to provide appropriate conclu July 1962: 150 curies of cesium-137; 18 curies of cobalt-60; 16 curies of ruthenium-106; at least 10 curies of rare earths; and sions regarding long-term monitoring procedures. 2.9 curies of strontium-90. Most of the radioactivity was found Work described in this report was part of a coopera to be downstream from mile 15; about 95 percent of the identi tive program with the Health Physics Division, ORNL; fied radioactivity was in this reach. Maximum concentration the Oak Ridge Operations Office, AEC; and the Divi of radioactivity occurred near the mouth of Whiteoak Creek. A high proportion of cesium-137 (21 percent), rare earths sion of Reactor Development and Technology, AEC. (about 25 percent), and cobalt-60 (9 percent) released to the The release of low-level-radioactive liquid waste to river are retained in bottom sediment of the study reach. Reten the basin of Whiteoak Creek, which drains the ORNL tion of ruthenium-106 and strontium-90 is minor--less than 1 area, was begun soon after establishment of the Labora percent each. tory in 1943 for the processing of radioactive materials. INTRODUCTION Radioactive liquids have entered Whiteoak Creek as a This report describes a contribution of the U.S. Geo result of direct releases of processed waste water from logical Survey to the Clinch Eiver Study. The Clinch the Laboratory, seepage from liquid waste holdup pits, River Study was a multiagency effort to evaluate the and drainage from solid-waste disposal trenches past, present, and future use of the Clinch Eiver for dis (Browder, 1959). posal of low-level-radioactive liquid waste from the Oak Throughout most of the Laboratory's history, the Ridge National Laboratory, which is in eastern Ten waters of Whiteoak Creek have been impounded in nessee (Morton, 1961, 1962b, 1963) and is operated by Whiteoak Lake by Whiteoak Dam, which is located 0.6 Union Carbide Corp. for the U.S. Atomic Energy Com mile upstream from the mouth of the creek. The lake mission. The agencies that participated in the study are: was created as a holdup facility for the radioactive Oak Ridge National Laboratory (ORNL); Tennessee waste carried in the creek water. Radioactive waste Game and Fish Commission; Tennessee State Depart waters in Whiteoak Creek flow into the Clinch River at ment of Public Health, Stream Pollution Control a point 3.3 miles downstream from fche Laboratory area. Board; Tennessee Valley Authority (TVA) ; U.S. The diluted wastes in the Clinch River flow into the Atomic Energy Commission (AEC); U.S. Geological Tennessee River 20.8 miles downstream from the entry Survey (USGS); and U.S. Public Health Service of Whiteoak Creek. (PHS). The continuous release of radioactive wastes to the When the study was begun in 1960, the Clinch River Clinch River during nearly 20 years of Laboratory op Study Steering Committee, an advisory group com erations has provided a unique opportunity for studying II 12 TRANSPORT OF RADIONTJCLIDES BY STREAMS the effects of such releases on the river and the effects of activity in surface layers of Clinch River bottom sedi the physical, chemical, hydrologic, and biological ment by Cottrell (1959) suggested that accumulation of characteristics of the river on the fate of the radio radioactive sediment might be occurring. active materials. In 1960, coring of the Clinch River bottom sediment Since 1943 part of the radioactive materials released was undertaken at selected sites to explore more fully from OENL through Whiteoak Dam (fig. 1) have be the possibility of accumulation of radioactive sedi come associated with bottom sediment of the Clinch ment. Variations in vertical distribution of radioac River. tivity in a few cores strongly implied accumulation of First indications of association of radionuclides with radioactive deposits in the riverbed (Carrigan and riverbed sediment came from work by Garner and others, (1967). Kochtitzky (1956). They made measurements, annually, Partial inventory (upper strata) of radionuclides in of levels of radiation from the surface of the bottom Clinch River bottom sediment, derived from analysis of sediment in the period 1951-53. Continued observation the 1960 cores, showed that retentions in the sediment of annual changes in longitudinal distribution of radio of cobalt-60, rare earths, and cesium-137 probably
7'30" 84°00'
TENNESSEE
_ - ''NORTH | CAROLINA
A Streamflow stations 1 Clinch River near Scarboro, Tenn. 2 Whiteoak Creek at Whiteofik Dam, near Oak Ridge, Tenn. 3 Whiteoak Creek below ORNL, near Oak Ridge, Tenn. 4 Whiteoak Creek at ORNL, near Oak Ridge, Tenn. oWater-sampling station at mile 5.5
Enlargement at right MELTON HILL DAM
10 MILES
FIGURE 1. Low-level-radioactive waste waters are released through Whiteoak Dam to the Clinch River, a tributary to the Tennessee River. INVENTORY OF RADIONUCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 13
TABLE 1. Yearly discharges of radfonuclides to the Clinch River [Results in curies. Results of total rare-earth (TRE) analysis include yttrium-90 content but exclude cerium-144 content. From Cowser and Snyder (1966, p. 6)J
Year Gross TRE Ce»« 1131 beta
1Q4Q 71 8 77 110 1 f»n 77 1 8 180 22 77 1950______.____.------______191 1Q OQ 00 on 1 P» 42 19 1951__.__ ___..._____.______101 20 18 on 11 _ 4. 5 2.2 18 1952______. ______._..______214 Q Q 1 P. 79 OR oo 1Q 18 20 1953___.______304 6.4 26 130 110 6.7 7.6 3.6 2. 1 _. 1954______°.P.4 22 11 140 160 24 14 9.2 3.5 _. 1955______437 63 31 93 150 85 5.2 5.7 7.0 6.6 1956_. ______582 170 29 100 140 59 12 15 3.5 46 1957 ______--_-____.______397 89 60 83 110 13 23 7.1 1.2 4.8 1958____.______.-_-______544 55 42 150 240 30 6.0 6. 0 8.2 8.7 1959 ______937 76 520 60 94 48 27 30 . 5 77 1960______2,190 31 1,900 28 48 27 38 45 5.3 72 1961______-______2,230 15 2,000 22 24 4.2 20 70 3.7 31 1962______1,440 5.6 1,400 9.4 11 1.2 2. 2 7.7 .36 14 1963______470 3.5 430 7.8 9.4 1.5 .34 .71 .44 14 ranged from 10 to 20 percent of the quantity released throughout the study reach. Once the radioactive length from ORNL (table 1; see Carrigan and others, 1967). of the core was determined, analyses for radionuclide A complete inventory could not be made because the content could be made, mass and volume of radioactive coring tool did not completely penetrate the radioactive sediments could be computed, and the quantity of radio sediment (Morton, 1962a, p. 45-60). nuclides in the sediments could be inventoried. Based on results of the partial inventory, the pro Cores were collected from preselected sections, ex portions of cobalt-60, rare earths, and cesium-137 re tending from near the mouth of the Clinch River up leases associated with the river bed deposits in 1960 stream to Melton Hill Dam (fig. 2). did not seem extraordinarily high. However, a com The cores, collected in the summer of 1962, were also plete inventory was needed to establish the quantity available for use in other studies. Pickering (1969) of radionuclides that had become associated with the made use of them in investigation of vertical distribu bed deposits of the 21-mile-long study reach since 1943. tion of radioactivity and of physicochemical properties Once the inventory was accomplished, the influence of of the sediment. the deposits on retention of these and other radioactive elements in the lower Clinch Kiver would be better ACKNOWLEDGMENTS understood. Inventory of radioactivity in Clinch River bottom, Information from the inventory of the radionuclides sediment was financed by the Division of Reactor De in Clinch River bottom sediment was obtained to meet velopment and Technology, AEC. A part of this financ the first objective of the Clinch River Study (see "In ing was used for particle-size analysis at laboratories troduction"). Also, the information is applied to meet of the Water Resources Division, USGS, in Raleigh, objectives 3,4, and 5 of the study. N.C., and for a variety of services furnished through Data from this inventory may be applied to further arrangements made by F. L. Parker, Health Physics refine safety analysis of current practices of radio Division, ORNL. active waste disposal (third study objective; see Cowser Services furnished at ORNL included a contract for and Snyder, 1966). coring with Sprague and Henwood, Inc., design and Estimates of the fraction of each radionuclide re fabrication of the core scanner and the core saw, radio- tained in the study reach may be used in forming a chemical analysis, use of a general purpose digital com predictive model to evaluate the capacity of the Clinch puter, laboratory technicians to assist in sample collec River to safely receive radioactive liquid wastes (fourth tion and in preparation of cores for physicochemical study objective). analysis, and consulting services. Techniques of collecting and analyzing samples, Design and fabrication of the core scanner and core methods of ascertaining total quantity of radioactivity, saw were by P. N. Hensley, Health Physics Division, and the accuracy of the inventory may suggest alternate and by C. D. Martin and W. F. Johnson, Instruments or additional procedures that may be applied to long- and Controls Division. Some radiochemical analyses term monitoring procedures (fifth study objective). were performed under the direction of C. L. Burros The bottom sediment was sampled by coring. Un and J. H. Moneyhun, Analytical Chemistry Division. disturbed cores were required in this inventory for use Advice in computer programing was given by M. T. in measuring vertical distribution of the radioactivity Harkrider, R. P. Leinius, and A. M. Craig, Jr., Mathe in order to define the base of the radioactive zone matics Division. 14 TRANSPORT OF RADIONUCLIDES BY STREAMS
MELTON HILL DAM
EXPLANATION pif' Sampling section; distance upstream from river mouth, 1 Vi 0 1 MILE' ' 3 in miles 2 Distance upstream from river mouth, in miles
FIGURE 2. Fourteen sampling sections were established in the Clinch River, downstream from Melton Hill Dam.
Persons making special contributions to this inves SELECTION OF SAMPLING SITES tigation were R. J. Pickering, USGS, who supervised coring operations and continually furnished valuable Locations of sampling sections were based on the and timely advice; E. Schonfeld, Chemical Technology longitudinal pattern of radionuclide distribution in the Division, ORNL, who made available the computer study reach. Sections were selected to sample reaches program for gamma spectrum analysis and supervised of high and low radioactivity, locations at which breaks computer processing of gamma spectrum data; and in the general trend of increasing or decreasing radio E. R. Eastwood, Health Physics Division, ORNL, who activity occurred, and reaches of transition from one was the major assistant in field and laboratory work. radiation level to another. Superposition of section loca tion (fig. 2) on the longitudinal distribution pattern of Data on annual monitoring surveys of radioactivity radioactivity (Carrigan and others, 1967, p. 24) in in bottom sediment of the Clinch and Tennessee Rivers figure 3 illustrates the relationship of location to varia were furnished by H. H. Abee and W. D. Cottrell, tion in radioactivity. Health Physics Division, ORNL; data on channel bed The two sections established on the Emory River and profiles at sediment ranges were furnished by J. W. on Poplar Creek (fig. 2) provided subsidiary informa Beverage, Chief, Hydraulic Data Branch, TVA. tion to health physicists at ORNL on possible upstream Many illustrations in this report were prepared by Graphic Arts, ORNL.
CORING PROCEDURES AND RESULTS Coring verticals were areally spaced to sample both ? Data from 1960 variations in (1) distribution of radioactivity and (2) ^monitoring survey volume of bottom sediment in the study reach. In selec tion of sampling sites, longitudinal variations in radio activity and in sediment volume and lateral vard'ations'in radioactivity were taken into consideration. Little was known of the thickness of the radioactive sediment. Therefore, the coring tool was driven to the maximum
depth possible with the equipment used; generally this CLINCH RIVER MILE depth was at the top of bedrock or at the top of in- FIGURE 3. Sampling sections were located in reaches of high, low, penetrable soil lying below the sediment. and transitional levels of radioactivity. INVENTORY OF RADIONUCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 15 movement of radioactive contaminants into streams above, the sediment surface as the head and barrel of tributary to the Clinch River. the sampler are pushed into the sediment. Spacing of coring verticals within a sampling sec Little or no compaction of sample apparently oc tion was chosen by combined assessment of transverse curred in the use of the Swedish Foil Sampler. Recovery distribution of sediment thickness and of radiation of cores was very satisfactory, especially if a basket shoe levels at the sediment surface. Relation of spacing of and a plastic sleeve were inserted as retainers in the verticals to variations in these variables for one sam sampler tip. pling section is shown in figure 4. A more complete description of the sampler, its use, and results of its application is given by Pickering CORING TOOLS (1965). The author and his associate, R. J. Pickering, USGS, The Swedish Foil Sampler could not be used in soupy selected the Swedish Foil Sampler as the primary sam sediments, in sandy sediments, and in sediments con pling tool after having made inquiries to other inves sisting mostly of pebbles and gravel. For soupy sedi tigators engaged in sampling of bottom sediments, par ments, SCUBA divers drove a thin-walled, 2^-inch ticularly marine sediments, and after having searched coring tube into the sediment. For sandy sediments, the literature on coring equipment. sampling was done with a split-barrel sampler, con Within the barrel of the Swedish Foil Sampler (fig. taining a basket shoe and a plastic sleeve for sample 5) are 16 steel foils (0.05 inch wide by 0.0005 inch thick) retention. Hand-operated clam-shell dredges were used which completely line the barrel. The foils prevent fric to collect gravel samples. tion between the sediment core and the walls of the RESULTS OF CORING barrel; as the sampler is pushed into the sediment, the foils unroll from coils stored in a magazine in the head In the summer of 1962, cores were collected at 135 of the sampler. Foils are pulled from the magazine be verticals in 14 sections in the Clinch River and in 4 cause one end is affixed to a piston within the barrel; sections in tributaries to the river (see fig. 2). The the vertical position of the piston is fixed at, or just number of verticals in a section ranged from 4 to 13.
SEDIMENT SURFACE ACTIVITY
0 100 200 300 400 500 600 700 800 DISTANCE FROM LEFT BANK, IN FEET *(CPM)= COUNTS PER MINUTE
FIGURE 4. Coring-tool penetration, sample recovery, transverse distribution of sediment thickness and of surface radiation levels, and verti cal distribution of gross gamma radioactivity at Clinch River mile 7.5 (from Pickering, 1969). 331-517 16 TRANSPORT OF RADIONUCLIDES BY STREAMS
FIGURE 5. Coring was done from a barrel float. Sampler head and part of the segmented barrel of the Swedish Foil Sampler are suspended from drilling tower. INVENTORY OF RADIONUCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 17
Relationships 'between depth of penetration, length procedures were undertaken, the cores (and dredge of core recovered, and thickness of the radioactive zone samples) were frozen. at CRM (Clinch River mile) 7.5, seen in figure 4, ex Cores were frozen shortly after collection for two rea emplify the success of coring operations generally ex sons: (1) To suppress biological and chemical action perienced throughout the study reach. The abbreviation and (2) to prevent distortion of the plastic cohesive CRM followed by a number has been used in this report samples. to designate distance, in miles, upstream from the mouth The frozen cores, still wrapped in steel foil and en of the river. This terminology is consistent with prior cased in a plastic tube, were placed in a specially fab usage in the Clinch River Study (Morton, 1961) . ricated radiation-counting apparatus called a core scan Results of coring at each section are summarized in ner (fig. 6). The core scanner was used to automatically table 2. Two situations of special significance to the measure the gross gamma radiation in 2-inch increments summary of coring results are emphasized by the table: along the full length of the core. For measurement of (1) 15 cores did not completely penetrate the radio distribution of gross gamma radiation, the electrical active zone, and (2) not all cores or dredge samples output from the photomultiplier tube was routed to a were found to contain significant quantities of radio sealer (Pickering, 1969). activity in subsequent analyses. Therefore, samples con Limitation of radiation detection to a 2-inch incre taining no radioactivity were excluded from further ment was improved by inclusion of a collimated detector direct consideration in computations. in the core scanner. However, the length of the collima- tor channel (2-in.) was too short for precise collimation, TABLE 2. Numbers of sampling sites, of samples used in compu and radiation from zones of core above and below the tations, and of truncated cores used in computations for each sampling section face of the collimator was detected. Through calibration [Length of truncated core recovered is less than thickness of radioactive zone] of the instrument, effects of imperfect collimation on radiation measurements were corrected. Location of sampling Used in computations section (miles Coring Dredge For accuracy and economy, the corrections due to im upstream from verticals samples Cores Dredge Truncated mouth) samples cores perfect collimation were applied to the counting data from the sealer by means of a computer program. Ex Clinch River amples of the bar-graph plots, derived from the com puter program and showing radiation distribution for 1.3 ____ 10 0 8 0 3 4.3 _.__ 13 0 12 0 3 2-inch incremental lengths of core, are given in figure 4. 7.5 __ 9 0 9 0 1 Corrected counting data for each 2-inch-high slice of 10.0______.______11 0 10 0 2 11.9______.__ __ 11 0 10 0 1 core were used to define the thickness of the radioactive 12.1 ______11 0 11 0 3 zone at each core vertical (see fig. 4). These data were 14.0-______5 0 5 0 0 16.0 ______.__ 7 0 7 0 0 also used as a guide in determining cores in which there 17.5______..__ 6 0 6 0 0 was no significant radioactivity. 19.2 ___ _ _.____ 5 0 4 0 0 20.5______8 6 8 6 1 After the counting of gross gamma radiation, each 20.8 1__-____,____ 5 7 3 7 1 core was cut longitudinally into halves and one of the 21.0 __ -.____ 4 0 2 0 0 22.8 ___ _ . 5 1 5 1 0 halves was divided longitudinally to provide a quarter- section sample for use in the inventory and to provide Emory River duplicate samples for use by Pickering (1969) in his studies of vertical distribution of radioactivity and the 1.9- 5.1. physicochemical characteristics of the sediments. Cut ting was done by placing the frozen core in a jig Poplar Creek and passing the jig through a carbide-tipped circular saw (fig. 7). The quarter-section core cylinders used 3.1- 4.5_ in this inventory were cut horizontally at the base of the radioactive zone, and the nonradioactive part was > Section 100 feet downstream from mouth of Whiteoak Creek. discarded. After cutting, the volume and weight of the cylinder CORE PROCESSING of radioactive sediment were measured for determina Core processing was divided into four major proce tion of specific bulk weight. The volume of the cylinder dures : measurement of gross gamma radiation distribu (including void space) was found by permitting the tion, longitudinal cutting, preparation of composite frozen material to melt in a calibrated vessel. For these samples for analyses, and physical and radiochemical volumetric measurements, voids in the sediment were analyses of composites. Until the final two processing assumed to be completely filled with water. 18 TRANSPORT OF RADIONUCLIDES BY STREAMS
Core in plastic tube 3- by 3-in. Nal crystal and 4-in. lead photomultiplier tube shielding
Multichannel analyzer Sealer and punch and printed tape readout tape readout
- Stepping pulley mechanism Stepping interval control 2-by .2-by 2-in. collimator
FIGURE 6. Core is hoisted through well in core scanner for detection of gamma radiation. Electric output from photomultiplier of detec tor may be routed to sealer or analyzer (from Pickering, 1969).
FIGURE 7. A masonry saw was modified to cut frozen cores, Jig holding core rolled under saw blade between guides on table. INVENTORY OP RADIONUCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 19
Next, a homogeneous composite of the quarter-section the study reach. Analysts at this facility found that con cylinder was prepared by using an electrically driven centrations of only two radioactive contaminants, eggbeater. Preliminary tests showed that sediments cesium-137 and cobalt-60, could be reliably determined ranging from highly cohesive to noncohesiv© could be by their method of hand computation of gamma spectra homogeneously mixed in 10 minutes. data produced from their pulse-height analyzer. Results A 1-gram aliquot was split from the composite for for concentrations of cobalt-60 and cesium-137 deter analysis of particle-size distribution at laboratories of mined by these analysts were slightly greater than those the USGrS in Raleigh, N.C. Then, the remaining com determined by computer program 7.8 and 13.8 percent posite was weighed, dried at 100° C (Celsius), and re- greater, respectively. weighed to provide data for computation of the dry- Differences in results between computer and hand to-wet weight ratio of the composite. processing of counting data are believed logical; but the The dry composite was split into aliquots for radio- computer-derived concentrations are considered to be chemical analyses using a Jones soil splitter. A 100- most accurate. Methods of hand computation do not ap gram aliquot (±0.01g) was prepared for gamma spec pear to be sufficiently sensitive and precise to detect, or trum analysis, and a 20-50 gram aliquot was prepared to compensate for, the presence of minor constituents for analyses of strontium-90 and trivalent rare-earth in a sample if the concentrations of these constituents contents. are 100 or more times less than concentrations of major Radiochemical analyses for strontium-90 and tri constituents. valent rare-earth contents of the 20-50 gram aliquots Cores presumptively containing no radioactivity were performed at the Low-Level Counting Facility, based on results of gross gamma core scanning were Analytical Chemistry Division, ORNL. Standard meth reevaluated by careful examination of results of gamma ods of chemical extraction of the specified elements and spectra analyses for cesium-137 and cobalt-60 contents. beta counting of the extracts were used in these analyses Cores which contained concentrations of these radio (Raaen and Cline, 1964). nuclides slightly greater than limits of detection were Analysis of concentrations of cesium-13Y, cobalt-60, included in the inventory. and mthenium-106 in composites of the bottom sediment was made by techniques of gamma spectrometry by COMPUTATION OF INVENTORY using a sodium iodide crystal, 4 inches high by 4 inches The volume of radioactive sediments is divided into in diameter, for a detector and by using a 512-channel subvolumes when computing the inventory. The quan pulse-height analyzer. Derivation of concentrations for tity of a radionuclide in a subvolume is equal to the the desired radionuclides from punch-taped data was product of its concentration (curies per unit weight) obtained by means of a computer program which uti and weight of sediment in the subvolume. Total quan lized a technique of least-squares resolution of the tity of the radionuclide in the study reach is the sum gamma-ray spectra (Schonfeld and others, 1965). In of its quantities in the subvolumes. put data for the computer program included the spectra Locations of sampling sections and of coring verticals for the sample, the background associated with the sam in the study reach serve as controls for dividing the ple, and known concentrations of selected radionuclides volume of sediment into subvolumes. Each subvolume (standards). Standards were selected on the basis of is associated with a specific coring vertical. records of releases of radionuclides from Whiteoak Shape of each subvolume is assumed to be prismatic; Lake, experience from other investigations of radio its length extends from midpoints between adjacent activity in bottom sediments (see Cottrell, 1959; Car- sampling sections; its width extends from midpoints rigan and others, 1967), and the knowledge that nat between adjacent coring verticals in the sampling sec urally occurring radionuclides are found in soil and tion ; and its depth is equal to the thickness of the radio rock of the area. Standards included were cesium-137, active zone for the specified core. These definitions of cobalt-60, ruthenium-106, cerium-144, zirconium-95, dimensions of a subvolume are modified for the two niobium-95, cesium-134, europium-152, europium-154, terminal subreaches and for terminal verticals (where potassium-40, uranium ore, and thorium ore. thickness of sediment is zero) in a sampling section. To assure that results of radionuclide analyses by The length of the terminal subreach for subvolumes gamma spectrometry were reasonably accurate, nine se associated with the sampling section at CRM 1.3 extends lected samples were reanalyzed at the Low-Level Count from CRM 0.0 to the midpoint between CRM 1.3 and ing Facility, ORNL. These samples were selected as 4.3. The length of the terminal subreach for subvolumes representative of the general range of radioactivity and associated with the sampling section at CRM 21.0 ex of sampling location for samples collected throughout tends from the midpoint between CRM 20.8 and 21.0 to 110 TRANSPORT OF RADIONUCLIDES BY STREAMS OEM 21.0. The widths of radioactive zones in the sam The width of the subvolume associated with a coring pling sections did not extend in every case from one vertical adjacent to a terminal vertical was computed edge of water to the other. Hence the transverse loca in the same manner as widths of other subvolumes. tions of 'at least two, and sometimes more, terminal verti A diagram of the methods of determining length, cals of radioactive zone(s) in a section had to be defined. width, and thickness of subvolumes is shown in figure 8. These terminal verticals were defined on the basis of Sediment weight in a subvolume is the product of its (1) locations of cores that contained no detectable radio volume and of the specific bulk weight and dry-to-wet activity, (2) rates of change of the gamma radiation weight ratio of its associated core. Specific bulk weight levels at the surface of the 'bottom sediment, (3) rates of is the wet weight per unit volume. Equations for change in thickness of the radioactive zone, (4) trans computations are as follows: verse slope of the streambed, and (5) limits of bedrock areas as determined by probing of the bed material. The Vs=xbt influence of some of these factors on location of terminal in which Vs= volume of subvolume in cubic meters, verticals is indicated in figure 4. x= length of subreach in meters, 6= width of subvolume in meters, and PLAN VIEW OF REACH IN VICINITY OF SECTIONS A.B.AND C t thickness of radioactive zone in meters.
in which V total volume of radioactive sediment in study reach in cubic meters.
in which Ws= weight of sediment in sub volume in grams, ovendry basis, s=specific bulk weight in grams per cubic meter, wet-weight basis, and = length of subreach associated with sampling section B ^= dry-to-wet weight ratio. RS=CWS
ELEVATION VIEW OF PART OF SECTION B IN VICINITY OF in which Rs= quantity of radionuclide in subvolume in CORING VERTICALS 3, 4, AND 5 picocuries (10~12 curies), C= concentration of radionuclide in compos ite in picocuries per gram, ovendry basis.
Cx=
in which Cx= mean concentration of radionuclide in sampling section in picocuries per gram.
t4 =thickness of subsection associated with in which R total quantity of radionuclide in study coring vertical 4 reach in picocuries.
fa< =width of subsection = V2 (63^ + fa 4_5 ) " B in which tx= average thickness of radioactive sediment FIGURE 8. Methods of determining length, width, and thickness of subvolumes. at sampling section in meters. INVENTORY OF RADIONTTCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 111
B total width of radioactive zone at sampling clides. Concentrations used in the computations were section in meters. adjusted to those at the time of sampling, except for rare earths. No adjustment for radioactive decay of rare earths was made because they are a mixture of radionuclides having a variety of radioactive half lives. in which Ax= cross-sectional area of radioactive zone at Methods of adjustment for effects of radioactive decay sampling section in square meters. on radiation have 'been described by the U.S. Public Computations using these equations were facilitated Health Service (1960). through use of a general purpose digital computer. All Depth of penetration of hand-operated dredges could dimensional units were converted to those commonly not be measured. Depths were computed by using used in American engineering practice for presentation information on volume of sample collected and on geo of results. metric characteristics of the sampler. Computed depth As shown in table 2, the recovered length of some of sampling was assumed to be the radioactive depth. cores was less than the thickness of the radioactive zone ; these cores are termed truncated. Thicknesses of radio RESULTS active sediment for truncated cores and dredge samples In the course of acquiring necessary data to inventory were estimated as follows: Distribution patterns of radioactivity in Clinch Eiver bottom sediment, infor gross gamma radiation were discernable in many trun mation has been gathered not only on quantities of cated cores; patterns of radioactivity distribution in radionuclides in the sediment but also on distribution such cores were compared to patterns for cores which of radionuclides in these sediments and distribution of penetrated the entire radioactive zone at nearby coring the sediments in the river. verticals; comparisons were made using correlation analyses developed in study of vertical distribution of INVENTORY OF IDENTIFIED RADIONUCLIDES radioactivity (Pickering, 1969) ; from results of these The following quantities of radionuclides are asso comparisons, the depth to which radioactivity extended ciated with bottom sediments of the Clinch Eiver be could be estimated for truncated cores. tween GEM 0.0 and 21.0 : 150 curies of cesium-137, 18 In some instances the truncated length was too short curies of cobalt-60, 16 curies of ruthenium-106, at least to clearly discern the distribution pattern of radioac 10 curies of rare earths, and 2.9 curies of strontium-90. tivity, in which case the radioactive thickness at the All quantities have been adjusted for effects of radio coring vertical was assumed to be equal to the depth of active decay to those quantities present at the time of penetration of the coring tool. Fortunately, the fraction sampling (July 1962), except for the rare earths (see of core recovered was large in most cases. "Computation of inventory"). Quantity of rare earths The scope of the adjustment procedures is summa reported is that present at the time of radiochemical rized in table 3. analysis. TABLE 3. Method of estimating depth of radioactivity of truncated Total inventoried and identified radioactivity is 200 cores collected in the Clinch River curies, of which cesium-137 constitutes 77 percent; [Length of truncated core recovered is less than thickness of radioactive zone] cobalt-60, 8.7 percent; ruthenium-106, 7.7 percent; rare earths, 5.1 percent; and strontium-90, 1.5 percent. Number of Adjustment based on depth of Location of sampling section cores adjusted coring-tool penetration (miles upstream from mouth) through About 95 percent of the identified radioactivity is in correlation ' Number Length of ratio 2 the reach of river downstream from CEM 15 (table 4) . of cores At least 50 percent of the identified radioactivity is 1.3 .______.______2 1 0 75 downstream from CEM 8.7. 4.3 _ ------3 0. 67, 0. 74, 0. 82 7.5 ___-___ .-_--_ 1 __. ESTIMATE OF ACCURACY OF INVENTORY 10.0-______-__..-____ 2 __. 11.9 ______..----_ 1 __. The quantity of a radionuclide in a volume of sedi 12.1... ______1 2 0. 42, 0. 68 ment, R, may be expressed by the equation 20.5__-_-__. ______1 0.50 20.8- ____ 1 0. 73 ww 1 Adapted from results of work by Pickering (1969). * Ratio of truncated length to depth of penetration (radioactive length). in which the independent variables are, respectively, Approximately 2 years elapsed between collection and concentration of a radionuclide, length of subreach, radiochemical analyses of cores. During this period, width of sampling section, mean thickness of radio decrease in radioactive content through the process of active sediment in sampling section, specific bulk radioactive decay was appreciable for some radionu- weight, and dry-to-wet weight ratio. The following 112 TRANSPORT OF RADIONUCLIDES BY STREAMS
expression is used to compute the level of expected error RETENTION FACTORS in R: The retention factor for a radionuclide is defined as the ratio, expressed in percent, of the quantity of the radionuclide in the sediment in July 1962 to that quan in which ratio are less than 5 and 2 percent, respectively. Kelative (* T errors in dimensions of sediment volume have been es 0= lodt, timated for each subreach downstream from CKM 15. Limitation in considered reach length has been made in which kr = retention factor, in percent, because 95 percent of the radioactivity is downstream /= inflow of radionuclide to study reach dur from CRM 15. Coefficients of variation for subreach ing time period T, in curies, length, width, and thickness are about 3, 5, and 15 per 0= outflow of radionuclide from study reach cent, respectively. Other independent sources of error during time period T, in curies, in the determination of radionuclide concentration are R= quantity of radionuclide in bottom sedi accuracy of radionuclide standards, counting errors in ment of study reach at end of period T, analysis, and sampling errors. Error in radionuclide in curies, content of standards is about 5 percent. Average levels X=radioactive decay constant for radio of counting errors for cesium-137, cobalt-60, ruthenium- nuclide, in seconds -1, 106, strontium-90, and rare earths are 2, 8, 23, 4, and 2 T duration of time period, in seconds, percent, respectively. i=rate of inflow of radionuclide to study The estimated errors in inventory sampling error reach, in curies per second, a function of being neglected and the foregoing expression for Only annual records of inflow are available so that it in most respects. Highest mean concentrations of radio is necessary to use numerical techniques to compute kr : nuclides are in the two sections immediately down stream from the mouth of Whiteoak Creek (CKM 20.8 R le-*T* kr=^f^ (100),»=1,2J . . .,T years (1) and CKM 20.5). Lowest concentrations generally are in sediments of the next downstream sampling section at CRM 19.2. Secondary peaks in the distribution (fig. 9) in which Rm =Re~*Ts= inventory of radionuclide at time occurred at CRM 17.5 and 14.0. Mean sectional concen of radiochemical analysis, in curies, trations for all but one radionuclide abruptly decreased X= radioactive decay constant, in years, between sections immediately upstream and downstream T^time between collection of cores and from the mouth of Poplar Creek (CRM 12.0). radiochemical analysis, in years, and Distribution of radioactivity in Clinch River bottom in= annual inflow of radionuclide to study sediment is controlled primarily by sedimentation (Car- reach during ^th year, in curies per year. rigan and others, 1967; Pickering, 1969). Radionuclides Pickering (1969) had previously evaluated the domina- in the bottom sediment become intimately associated tor in equation 1 . with suspended sediments passing through Whiteoak Dam. Patterns of radioactive deposits in the river result Using equation 1, the retention factors are computed from the combined interaction of lateral diffusion, char to be 21 percent for cesium-137, 9 percent for cobalt-60, acteristics of the flow pattern, and decreasing intensity, 0.4 percent for ruthenium-106, and 0.2 percent for stron- downstream, of turbulent forces acting to suspend the tium-90. Retention of the rare earths may approach, radioactive sediment particles from Whiteoak Creek. and possibly may exceed, 25 percent (see Struxness and Therefore, similarities in concentration distribution are Morion, 1961). A good estimate of the retention factor to be expected. for rare earths has not been obtained because mixtures Investigation of the movement of sediments has not of radioelements of undetermined composition are in been a part of the Clinch River Study. As a consequence, volved. The above estimate was derived from a con careful documentation of the effects of diffusion, flow servative consideration of the cerium- 144 and other distribution, and turbulence on sedimentation is not rare-earths contents of three samples. available. However, the influence of these three on the DISTRIBUTION OF RADIONTTCLIDES longitudinal distribution may be surmised from obser vation and general understanding of mechanics of fluid LONGITUDINAL DISTRIBUTION motion. Patterns of longitudinal variation in mean concen High concentrations of radioactivity in bottom sedi tration of principal radionuclides (fig. 9) are similar ments may be expected near the mouth of Whiteoak Creek. Dispersion of waters and suspended sediments 40,000 from the creek into the river is restricted because of in complete lateral diffusion (Morton, 1962b and 1963; Carrigan and others, 1967). Consequently, suspended sediments from Whiteoak Creek, which are rich in sorbed radioactivity, do not immediately became diluted with relatively uncontaminated river sediments. Abrupt changes in the momentum of the water enter ing the river from the creek tend to induce deposition. Eddy zones along the right bank of the river immedi ately downstream from the creek mouth are created as the two streams meet. The eddies and the restricted dis persion of sediments produce immediate concentrated deposition of suspended sediments rich in sorbed radio activity. Suspended sediments from the creek diffuse outward 50 into the river channel and mix with sediments carried in the river. This action prevents the formation of addi 22 20 18 16 14 12 10 8 6 4 2 0 CLINCH RIVER MILE tional pockets of deposited sediments containing high concentrations of radioactivity. FIGURE 9. Similarities in longitudinal distribution of radionuclides in bottom sediment are observed throughout study reach. Turbulence is of sufficient intensity in the upstream 114 TRANSPORT OF RADIONUCLIDES BY STREAMS part of the study reach to keep sediments in suspension thickness in the sampling section (shown in fig. 12); the through reaches such as those near CRM 19.2. ordinate is the ratio of the concentration of cesium-137 The abrupt decrease in concentration of radionuclides in the core to its mean concentration in the sampling sec in bottom sediment in the downstream direction at the tion (shown in fig. 9). mouth of Poplar Creek may be the result of dilution The increase in radionuclide concentration with rela of contaminated river sediments by uncontaminated tive thickness of sediment (fig. 12) may result from sediments from Poplar Creek. changes in the clay content of the sediment. Carrigan About the time cores were collected for use in this and others (1967) showed that the radionuclide concen inventory, the annual monitoring survey of radioac trations increase as the clay content of the sediment in tivity in Clinch River bottom sediment was 'being con creases. A linear regression analysis suggests that the ducted by personnel of the Applied Health Physics clay-silt ratio increases as the relative thickness of the Section, ORNL. In the monitoring surveys, attempts sediment increases (18 cores; correlation coefficient, are made to collect samples of the upper part of the 0.46; regression coefficient, 0.042). bottom sediment at equally spaced verticals in a sam pling section. Sampling is clone with a hand-operated CONTRIBUTION TO INVENTORY FROM REACHES dredge. All sediment collected at a section is composited OUTSIDE OF STUDY REACH and radiochemically analyzed (Cottrell, 1959). The lon- Some of the radioactivity in bottom sediments within gitudial distribution of cesium-137, determined from the study reach may have been contributed by fallout the 1962 monitoring survey, is compared to the distribu from weapons tests. Fallout is transported into the tion determined from this inventory in figure 10. study reach primarily by flow from parts of the Clinch VERTICAL DISTRIBUTION River basin upstream from the head of the study reach. Contributions to the radioactivity in bottom sediments Radionuclide concentrations are related to sediment of the study reach from fallout appear to be negligible. thickness and location in the study reach. This relation Concentrations of radionuclides in bottom sediment at ship is shown in figure 11. The abscissa in the figure is a sampling section 2.0 miles upstream from the study the ratio of the thickness at a coring vertical to mean 4 I . 1000 EXPLANATION Si O CRM 1.3 A CRN1 11.9 A 4.3 12.1 500 2 X 7.5 14.0 I3 A Xn/^y 9^ V 10.0 n 17.5 ^X 1 ' V X 200 A 0.8 - US JS X A L o 0.6 )< y loo O ' CL 1 13 0.4 ^ O V o V O 50 < A 0.2 / V 20 0.1 /"--Data from 1962 monitoring survey (Morton, 1965) / LJ / 10 0.08 / 0.06 / A 0.04 p = 0.661 SE = 0.348 log units 2 - A n 09 1 1 0.04 0.1 0.2 0.4 1 THICKNESS RATIO 22 20 18 16 14 12 10 8 FIGURE 11. Radionuclide concentration bears a nearly direct re CLINCH RIVER MILE lationship to sediment thickness at specific sampling sections. Individual sectional relationships are a function of location in FIGURE 10. Longitudinal distributions of cesium-137 in bottom study reach, p is the coefficient of correlation for the logarithms sediment, determined through different sampling techniques, are of the concentration ratio and thickness ratio. Sa is the standard much alike. error of estimate. INVENTORY OF RADIONUCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 115 reach, CRM 22.8, 'are below limits of detection. Concen 3.0 I r trations of cesium-137 and cobalt-60 in waters flowing General trend li past a water-sampling station at CKM 41.5 have been at 2.5 or below limits of detection. No rare earths have been detected in water samples collected at this station. z 2.0 Kuthenium-106 and strontium-90 have been detected regularly in water samples (Churchill and others, 1.5 1965); but these radionuclides constitute a minor frac /\ tion of the total inventory, and their retention factors 1.0 are low. Cores were collected in Poplar Creek and Emory 0.5 -\t Kiver to gage the extent of upstream movement of con taminated waters from the Clinch Kiver. Hydraulic 22 20 18 16 14 12 10 8 6 4 20 conditions are such in the study reach of the Clinch CLINCH RIVER MILE River that upstream movement of water from the river FIGURE 12. Radioactive sediment thickness increases in the down can occur in any tributary. stream direction as a result of increasing flow area. Examination of gross gamma radioactivity scans of of more than 50 percent occurs between sampling sec cores from Poplar Creek and from the section at mile 5.1 tions upstream at CRM 7.5, and downstream, at CRM on the Emory River indicates that the radionuclide con 4.3, from the mouth of the Emory River. This decrease tent in bottom sediments at these sampling sites (fig. 2) is negligible. in sediment thickness may be the result of a localized in Concentrations of radioactivity in some cores from crease in turbulence due to inflow from the Emory River mile 1.9 on the Emory River were above lower limits of and (or) the diversion of Clinch River upstream into detection. the Emory River (Elder and Dougherty, 1958). An Picketing, in a study of radioactivity in bottom sedi increase in turbulence would tend to keep sediment ments of sloughs adjacent to Clinch River (Carrigan particles in suspension. and others, 1967),'noted that radiation levels in some At the mouth of Poplar Creek (CRM 12.0), the areas approached levels measured at the surface of mean thickness of radioactive sediment sharply in Clinch River bottom sediment. creases. Probably the decrease in radionuclide concen trations observed in this part of the streambed is due to Collectively, the evidence of radioactivity in bottom sediments in the lowermost reaches of tributaries to the dilution of radioactive sediment with uncontaminated sediments issuing from the creek. Clinch River suggests that supplemental inventories might be undertaken. The section at which sediment transport capacity rapidly decreases is clearly indicated to be at CRM 14.0 DISTRIBUTION OP SEDIMENT in figure 13. From CRM 21.0 to 14.0, deposition is Ninety-five percent of the radioactive sediment in the limited to zones of the channel near bank(s) of the Clinch River is downstream from CRM 15, and at least river (Pickering, 1969). The sediment transport 60 percent is downstream from CRM 9 (table 4). capacity is of much greater magnitude i" the central A tendency for mean thickness of radioactive sedi core of flow in this reach than near the banks. Though ment to increase linearly from the head of the study the magnitude of transport capacity remains greater in reach to the mouth of the Emory River (CRM 21.0 to the central core of flow than elsewhere in the flow area 4.5) appears to exist (fig. 12). The general trend for throughout the study reach, its magnitude relative to increasing thickness may be explained by considering that near the banks drops sharply in the vicinity of hydraulic conditions in the study reach. Accretions to CRM 14.0. flow in the study reach are almost negligible except The cross-sectional area of radioactive sediment is at inflow from the Emory River (U.S. Geological Survey, a maximum at CRM 10.0 (fig. 13) because of the influ unpub. data, 1961). Flow area continuously increases ence of islands and submerged ridges on the flow pattern in the downstream direction (Morton, 1962a). Without in that vicinity (Carrigan and others, 1967, p. 27). accretions to flow and with increasing flow area, During the 191^-year period of waste disposal velocity and intensity of turbulence of the stream de (December 1943 to July 1962), 64 percent of the stream- crease and consquently sediment transport capacity bed has become covered with radioactive sediment. Areal decreases in the downstream direction. distribution of radioactive sediments, for selected A decrease in mean thickness of radioactive sediment thicknesses, is listed in table 5. 116 TRANSPORT OF RADIONUCLIDES BY STREAMS of releases, further estimation of radionuclide loading in the sediments is not needed. Waste disposal processes or quantities of wastes proc essed at ORNL could change such that releases to the river will increase. If releases of cesium-137, cobalt-60, and (or) rare earths should increase substantially above experienced levels for sustained periods, another safety analysis of radiation dosage from bottom sediment would be needed. Safety analysis may be undertaken at two times: (1) after a period of increased loading to determine result ant radiation dosage and (2) prior to increased loading to estimate concentration and duration of releases which will assure safety. For case 1, knowledge of retention factors would be an aid in estimating the magnitude of radiation dosage resulting from increased releases. The relationship of radiation dose to concentration of radionuclides in the 20 18 16 14 12 10 8 CLINCH RIVER MILE release is FIGURE 13. Cross-sectional area of radioactive sediment increases Z> = V2 (51.2) krCEf, most rapidly between CRM 14 and 10. Minor longitudinal varia tions occur upstream from this reach. An appreciable decrease in which D is the dose rate, in rad per day, for beta or in area begins at CRM 10. gamma radiation from an infinitely thick source uni TABLE 5. Areal distribution of radioactive formly spread over the bed of the study reach; kr is the sediments, for selected thicknesses retention factor in dimensionless units; G is the mean Proportion of radioactive surface concentration of the radionuclide released for a known Radioactive sediment area over which indicated thick thickness, in feet ness is equaled or exceeded duration, with effects of radioactive decay taken into 1. 0 0.57 account, in microcuries per gram (10-6 curies per 1. 5 .41 2.0 .31 gram); E is the effective absorbed radiation of beta 2.6 . 24 4.0 . 13 disintegration or maximum energy of gamma-ray emis sion, in million electron volts; and / is the fraction of PHYSICAL PROPERTIES disintegration of a particular energy, dimensionless. Three physical properties of Clinch River bottom This equation for dose rate is derived from those pro sediment that were measured are specific bulk weight, posed by Cowser and Snyder (1966; their eqs 14 and 17). dry-to-wet weight ratio, and particle-size classification. D is a nominal dose rate applicable to the study reach Measurements of these characteristics have been as a whole. As such, it is an indicator of relative hazard. restricted to radioactive zones in the sediment. If D approaches one-third of the critical dose rate, local Mean specific bulk weight for all core composites dose rates may be approaching critical levels. Especially is 100 pounds per cubic foot. Mean wet-to-dry weight critical areas of the riverbed are along the right bank ratio for all composites is 0.69. The dominant particle- between CRM 20 and 21 and also in the vicinity of CRM size classification is silty clay based on the triangular- 4.3, 14.0, and 17.5. plotting method of Shepard (1954). Results of exten For case 2, safety analysis would seek an estimate of sive physicochemical analyses of radioactive sediment the rate of buildup of radiation to the critical dose rate. samples obtained in the 1962 coring program are Radiation dose at the surface of the sediment increases, reported by Pickering (1967). in general, as the radioactive sediment becomes thicker. If the radionuclide releases are constant, this relation FUTURE ESTIMATION OF RADIONUCLIDE LOADING ship between radiation dose and thickness is an ex Continued decline of radionuclide releases to the ponential function. Cottrell (1959, fig. 17) indicated Clinch River in recent years (see table 1) indicates that that the dose asymptotically approached a maximum increasing radiation hazard in the future is unlikely. in Clinch River bottom sediment at a thickness of about Cowser and Snyder (1965) found that, even if releases 2.6 feet; Sayre and Hubbell (1965, p .47) found that continue indefinitely at the highest experienced levels this asymptote was somewhat less than 2.6 feet. This (in 1956 or 1959), bottom sediments will remain a minor thickness (2.6 ft) was called the infinite thickness and source of radiation exposure. With continuing decline its magnitude varied slightly with variations in physi- INVENTORY OF RADIONUCLIDES IN SEDIMENT, CLINCH RIVER, EASTERN TENNESSEE 117 cochemical properties of sediment and with energy In the study reach, at least 20 percent of the cesium- distribution of gamma-ray emissions. 137 and rare earths released to the river are retained in Rate of buildup of radiation dose depends on the rate the bottom sediment. Retention of cobalt-60 releases is 9 of accumulation of radioactiver deposits; rate of accu percent. Less than 1 percent each of the ruthenium-106 mulation, in turn, depends on location in the study and strontium-90 releases are retained in the bottom reach. sediment. Most of the radioactive sediment is down Data required to estimate radiation dose would be the stream from CRM 15. Because of downstream decreases rate of accumulation, or time to attain infinite thickness, in the turbulence of flow, the thickness, cross-sectional and the interrelationship of radionuclide concentrations area, and volume per unit length of radioactive sedi in releases and sediments throughout the study reach. ment are generally greater in the downstream parts of Information on sediment distribution is obtained the reach than in the upstream parts. Of these three from table 5 and from figure 12. Time required to attain geometrical variables, only thickness varies in a regu an overburden of infinite thickness may be estimated lar manner, showing a linear increase in the downstream by assuming that the rate of accumulation at a point direction. on the channel bed is constant. The rate is assumed to be The total inventory of principal radionuclides in equal to the ratio of the radioactive thickness observed bottom sediment (cesium-137, cobalt-60, and rare at the point in 1962 to the period of radionuclide releases earths) of the Tennessee River basin is undoubtedly from Whiteoak Creek 19.5 years. Using this estimate greater than that measured in the Clinch River. Radio of the rate of accumulation, the time required to attain nuclides have become associated with bottom sediment infinite thickness over various proportions of the river in sloughs and mouths of tributaries to the Clinch River bed is shown in figure 14. and in the bed of the Tennessee River downstream from From the relationship of concentration and thickness, the mouth of the Clinch River (see Carrigan and others, (fig. 11) the interrelationship of concentrations in 1967). releases and in sediment may be derived. Two methods of aiding future safety analyses are CONCLUSIONS suggested: (1) estimation of dose rates for individual radionuclides incorporated in bottom sediment by con The inventory of radionuclides in Clinch River sideration of mean concentration of radionuclides in bottom sediment provides strong insight to the fate of releases and of the retention factor, and (2) considera radioactive waste released to the Clinch River. The in tion of (a) rate of sediment thickness buildup in various ventory is a direct and the principal measure of the areas of the study reach, (£>) relation of concentration residual between the 20-year input and output loads of to sediment thickness, and (c) interelationship of the radionuclides to the study reach of the river. concentrations in releases and in sediments. ou Future use of the river for radioactive liquid-waste disposal is predicated on the safety of such practices. we s * u. usefulness of the river for such purposes. Continued i- z 40 / / 1 4 z decline in release of radionuclides would indicate that < UJ (/) P UJ / J--0 uj retention of radionuclides would not limit future use / z (T ^ *: fulness. However, the possibility of an increase in on y °0 / u.0 i radionuclide releases must be recognized. Assuming P UJ 9D / retention of 10 to 20 percent of some readionuclides in X < 3.0 t bottom sediment, a substantial increase in releases s/ 4.0 ~ ^^ 10 ~^ might be a factor leading to limited use of the stream UJ S for disposal of radioactive waste. Limitations resulting 1- from an increase in radionuclide content of bottom 0 (3 0. 10 0. 20 0 30 0. 40 0. 50 0. 60 sediment can be determined only through a safety PROPORTION OF SURFACE AREA OF RADIOACTIVE analysis in which all avenues of radiation exposure are SEDIMENT OVER WHICH THE INDICATED INITIAL THICKNESS IS EQUALED considered. OR EXCEEDED Water-sampling stations have value in obtaining con FIGURE 14. An estimate of time required to accumulate 2.6 tinuous and current records of radionuclide concentra feet of sediment over a given proportion of surface area tions at a site. However, measurements of small but is made by assuming that the observed net accumulation continues at the same rate. significant losses or gains in radionuclide loads, occur- 118 TRANSPORT OF RADIONUCLIDES BY STREAMS ring between stations of a network, are difficult and Garner, J. M., and Kochtitzky, O. W., 1956, Radioactive sedi costly. Inventory of accumulated radioactivity in sedi ments in the Tennessee River System: Am. Soc,. Civil Engineers Sanitary Engineering Div. Jour. Paper 1051, ment is inherently more accurate than determining a 20 p. small residual between large radionuclide loads meas Morton, R. J., ed., 1961, Status report No. 1 on Clinch River ured at two water-sampling stations. Cost of such an Study: U.S. Atomic Energy Comm. ORNL-3119, 81 p. inventory would be comparable to the annual cost of 1962a, Status report No. 2 on Clinch River Study: U.S. operating a two-station water-sampling network in the Atomic Energy Comm. ORNL-3202, 97 p. Clinch River study reach. The techniques of radioactive 1962b, Status report No. 3 on Clinch River Study: U.S. Atomic Energy Comm. ORNL-3370, 123 p. sediment inventory developed in this investigation can 1963, Status report No. 4 on Clinch River Study: U.S. be used for long-term surveillance of release of radio Atomic Energy Comm. ORNL-3409, 115 p. active material. And an inventory can be used in lieu 1965, Status report No. 5 on Clinch River Study: U.S. of water-sampling networks. Atomic Energy Comm. ORNL-3721, 149 p. Pickering, R. J., 1965, Use of Swedish Foil Sampler for taking REFERENCES undisturbed cores of river bottom sediments, in Proceed ings of Federal Inter-Agency Sedimentation Conference, Browder, F. N., 1959, Radioactive waste management at Oak 1963: U.S. Dept. of Agriculture Misc. Publ. 970, p. 586-589. Ridge National Laboratory, in Hearings on industrial radio 1969, Distribution of radionuclides in bottom sediment active waste disposal before the Special Subcommittee on of the Clinch River, eastern Tennessee: U.S. Geol. Survey Radiation of the Joint Committee on Atomic Energy: U.S. Prof. Paper 433-H. (In press.) 86th Gong., 1st sess., v. 1, p. 461-514. Raaen, H. P., and Cline, A. S., 1964, ORNL Master Analytical Carrigan, P. H., Jr., Pickering, R. J., Tamura, Tsuneo, and Manual, 1953-63: U.S. Atomic Energy Comm. TID-7015. Forbes, Robert, 1967, Radioactivity in bottom sediments of Sayre, W. W., and Hubbell, D. W., 1965, Transport and disper Clinch and Tennessee Rivers, Part A, Investigations of sion of labeled bed material, North Loop River, Nebraska: radionuclides in upper portion of sediment: U.S. Atomic U.S. Geol. Survey Prof. Paper 433-C, 48 p. Energy Comm. ORNL-3721, Supp. 2A, 82 p. Churchill, M. A., Cragwall, J. S., Jr., Andrew, R. W., and Jones, Schonfeld, Ernest, Kibbey, A. H., and Davis, Wallace, Jr., 1965, S. L., 1965, Concentrations, total stream loads, and mass Determination of nuclide concentrations In solutions con transport of radionuclides in the Clinch and Tennessee taining low levels of radioactivity by least-squares resolu Rivers: U.S. Atomic Energy Comm. ORNL-3721, Supp. 1, tion of the gamma-ray spectra: U.S. Atomic Energy Comm. 78 p. ORNL-3744, 57 p. Cottrell, W. D., 1959, Radioactivity in silt of the Clinch and Shepard, F. P., 1954, Nomenclature based on sand-silt-clay Tennessee Rivers: U.S. Atomic Energy Comm. ORNL-2847, ratios: Jour. Sed. Petrology, v. 24, p. 151-158. 50 p. Struxness, E. G., and Morton, R. J., 1961, Radioactive waste Cowser, K. E., and Snyder, W. S., 1966, Safety analysis of radio disposal, in Health Physics progress report, period ending nuclide release to the Clinch River: U.S. Atomic Energy July 31, 1961: U.S. Atomic Energy Comm. ORNL-3189, Comm. ORNL-3721, Supp. 3, 115 p. 80 p. Elder, R. A., and Doughtery, G. B., and 1958, Thermal density U.S. Public Health Service, 1960, Radiological health hand underflow diversion, Kingston Steam Plant: Am. Soc. Civil book [rev. ed.] : U.S. Dept. of Health, Education, and Engineers Hydraulics Div. Jour. Paper 1583, 20 p. Welfare, Public Health Service, 468 p. US. GOVERNMENT PRINTING OFFICE: 1969 O 331-517