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Title: THE TRITIUM UNDERFLOW STUDY AT THE SAVANNAH RIVER SITE

Abstract

An issue of concern at the Savannah River Site (SRS) over the past 20 years is whether tritiated groundwater originating at SRS might be the cause of low levels of tritium measured in certain domestic wells in Georgia. Tritium activity levels in several domestic wells have been observed to occur at levels comparable to what is measured in rainfall in areas surrounding SRS. Since 1988, there has been speculation that tritiated groundwater from SRS could flow under the river and find its way into Georgia wells. A considerable effort was directed at assessing the likelihood of trans-river flow, and 44 wells have been drilled by the USGS and the Georgia Department of Natural Resources. Also, as part of the data collection and analysis, the USGS developed a numerical model during 1997-98 (Ref. 1) to assess the possibility for such trans-river flow to occur. The model represented the regional groundwater flow system surrounding the Savannah River Site (SRS) in seven layers corresponding to the underlying hydrostratigraphic units, which was regarded as sufficiently detailed to evaluate whether groundwater originating at SRS could possibly flow beneath the Savannah River into Georgia. The model was calibrated against a large database of water-level measurements obtainedmore » from wells on both sides of the Savannah River and screened in each of the hydrostratigraphic units represented within the model. The model results verified that the groundwater movement in all hydrostratigraphic units proceeds laterally toward the Savannah River from both South Carolina and Georgia, and discharges into the river. Once the model was calibrated, a particle-track analysis was conducted to delineate areas of potential trans-river flow. Trans-river flow can occur in either an eastward or westward direction. The model indicated that all locations of trans-river flow are restricted to the Savannah River's floodplain, where groundwater passes immediately prior to discharging into the river. Whether the trans-river flow is eastward or westward depends primarily on the position of the Savannah River as it meanders back and forth within the floodplain and is limited to narrow sections of land adjacent to the river. With respect to ''westward'' trans-river flow, the model indicates that it primarily occurs in locations south of SRS and within the deeper aquifers (Crouch Branch and McQueen Branch). Particle-tracking analysis of westward trans-river flow in these aquifers indicates that the groundwater crossing from South Carolina into Georgia originates as recharge in upland areas well to the east and south of SRS. The model identified one location (an area of less than one square mile) where westward trans-river flow originating as recharge within the boundaries of SRS and which could conceivably receive tritium or other contaminants from SRS as a result. The one-square-mile area occurs immediately adjacent to the Savannah River, where groundwater within the Gordon Aquifer flows immediately prior to discharging into the river and is indicated in Figure 1. Reverse particle tracking indicates that recharge zones associated with the one square mile are located in the upland areas between D-Area and K-Area. There is no known subsurface contamination at these recharge zones. The travel times associated with the particles were calculated to range from 90 to 820 years, although these estimates are shorter than actual travel times since no accounting of groundwater transit time across the uppermost aquifer was included in the model. It is important to note that the range of travel times represents seven to 66 half-lives of tritium (12.33 years), suggesting that even if tritium contamination existed at the recharge areas, it likely would decay away prior to discharging into the Savannah River.« less

Authors:
;
Publication Date:
Research Org.:
SRS
Sponsoring Org.:
USDOE
OSTI Identifier:
908026
Report Number(s):
WSRC-STI-2007-00272
TRN: US200721%%595
DOE Contract Number:
DE-AC09-96SR18500
Resource Type:
Conference
Resource Relation:
Conference: AMERICAN NUCLEAR SOCIETY-DECOMMISSIONING, DECONTAMINATION AND REVTILIZATION TECHNOLOGY EXPO
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; ACTIVITY LEVELS; AQUIFERS; CONTAMINATION; DECAY; DECONTAMINATION; RIVERS; TRITIUM

Citation Formats

Hiergesell, R, and Daniel Kaplan,D. THE TRITIUM UNDERFLOW STUDY AT THE SAVANNAH RIVER SITE. United States: N. p., 2007. Web.
Hiergesell, R, & Daniel Kaplan,D. THE TRITIUM UNDERFLOW STUDY AT THE SAVANNAH RIVER SITE. United States.
Hiergesell, R, and Daniel Kaplan,D. Mon . "THE TRITIUM UNDERFLOW STUDY AT THE SAVANNAH RIVER SITE". United States. doi:. https://www.osti.gov/servlets/purl/908026.
@article{osti_908026,
title = {THE TRITIUM UNDERFLOW STUDY AT THE SAVANNAH RIVER SITE},
author = {Hiergesell, R and Daniel Kaplan,D},
abstractNote = {An issue of concern at the Savannah River Site (SRS) over the past 20 years is whether tritiated groundwater originating at SRS might be the cause of low levels of tritium measured in certain domestic wells in Georgia. Tritium activity levels in several domestic wells have been observed to occur at levels comparable to what is measured in rainfall in areas surrounding SRS. Since 1988, there has been speculation that tritiated groundwater from SRS could flow under the river and find its way into Georgia wells. A considerable effort was directed at assessing the likelihood of trans-river flow, and 44 wells have been drilled by the USGS and the Georgia Department of Natural Resources. Also, as part of the data collection and analysis, the USGS developed a numerical model during 1997-98 (Ref. 1) to assess the possibility for such trans-river flow to occur. The model represented the regional groundwater flow system surrounding the Savannah River Site (SRS) in seven layers corresponding to the underlying hydrostratigraphic units, which was regarded as sufficiently detailed to evaluate whether groundwater originating at SRS could possibly flow beneath the Savannah River into Georgia. The model was calibrated against a large database of water-level measurements obtained from wells on both sides of the Savannah River and screened in each of the hydrostratigraphic units represented within the model. The model results verified that the groundwater movement in all hydrostratigraphic units proceeds laterally toward the Savannah River from both South Carolina and Georgia, and discharges into the river. Once the model was calibrated, a particle-track analysis was conducted to delineate areas of potential trans-river flow. Trans-river flow can occur in either an eastward or westward direction. The model indicated that all locations of trans-river flow are restricted to the Savannah River's floodplain, where groundwater passes immediately prior to discharging into the river. Whether the trans-river flow is eastward or westward depends primarily on the position of the Savannah River as it meanders back and forth within the floodplain and is limited to narrow sections of land adjacent to the river. With respect to ''westward'' trans-river flow, the model indicates that it primarily occurs in locations south of SRS and within the deeper aquifers (Crouch Branch and McQueen Branch). Particle-tracking analysis of westward trans-river flow in these aquifers indicates that the groundwater crossing from South Carolina into Georgia originates as recharge in upland areas well to the east and south of SRS. The model identified one location (an area of less than one square mile) where westward trans-river flow originating as recharge within the boundaries of SRS and which could conceivably receive tritium or other contaminants from SRS as a result. The one-square-mile area occurs immediately adjacent to the Savannah River, where groundwater within the Gordon Aquifer flows immediately prior to discharging into the river and is indicated in Figure 1. Reverse particle tracking indicates that recharge zones associated with the one square mile are located in the upland areas between D-Area and K-Area. There is no known subsurface contamination at these recharge zones. The travel times associated with the particles were calculated to range from 90 to 820 years, although these estimates are shorter than actual travel times since no accounting of groundwater transit time across the uppermost aquifer was included in the model. It is important to note that the range of travel times represents seven to 66 half-lives of tritium (12.33 years), suggesting that even if tritium contamination existed at the recharge areas, it likely would decay away prior to discharging into the Savannah River.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 21 00:00:00 EDT 2007},
month = {Mon May 21 00:00:00 EDT 2007}
}

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  • Temperature coefficients of reactivity have been calculated for the Mark 22 assembly in the K-14 charge at the Savannah River Site. Temperature coefficients are the most important reactivity feedback mechanism in SRS reactors; they are used in all safety analyses performed in support of the Safety Analysis Report, and in operations to predict reactivity changes with control rod moves. The effects of the radial location of the assembly in the reactor, isotope depletion, and thermal expansion of the metal components on the temperature coefficients have also been investigated. With the exception of the dead space coefficient, all of the regionalmore » temperature coefficients were found to be negative or zero. All of the temperature coefficients become more negative with isotopic depletion over the fuel cycle. Coefficients also become more negative with increasing radial distance of the assembly from the center of the core; this is proven from first principles and confirmed by calculations. It was found that axial and radial thermal expansion effects on the metal fuel and target tubes counteract one another, indicating these effects do not need to be considered in future temperature coefficient calculations for the Mark 22 assembly. The moderator coefficient was found to be nonlinear with temperature; thus, the values derived for accidents involving increases in moderator temperature are significantly different than those for decreases in moderator temperature, although the moderator coefficient is always negative.« less
  • A study was conducted to determine whether acoustic emission monitoring would be feasible in monitoring the solid-state resistance pinch weld used to seal tritium reservoirs at the Savannah River Site. Experiments were performed using a commercially available acoustic emission detection system, with a transducer mounted on a flat milled onto one of the pinch weld electrodes. Welds were made using a wide range of weld power, from very cold, with no metallurgical bond, to hot, with local fusion and excessive material injection into the tube bore. The tubes were drawn type 316L stainless steel. The welds were confined (anvils preventedmore » material flow outward from the sides of the tube not being forced inward by the electrodes) and all were made using the same electrode force. The total number of ringdown counts for each weld was more correlated with weld power and bond length than total energy counts or total number of hits. The onset of large acoustic emission at higher weld power coincides with the injection of material into the tube bore, termed extrusion if arising from a solid state weld or spitting if arising from a weld with local fusion. Since large extrusions and spits, identified by radiography, cause rejection of production welds, a useful function of acoustic emission monitoring of pinch welding might be to detect the onset of extrusion or spitting. The low level of acoustic emission at production weld power levels (and below), the variability of acoustic emission at power levels causing extrusion and spitting, and the inability of acoustic emission to distinguish welds made with oxidized stems indicates that acoustic emission monitoring would not be a useful nondestructive evaluation of reservoir pinch welding at the Savannah River Site. 3 refs., 3 figs.« less
  • Temperature coefficients of reactivity have been calculated for the Mark 22 assembly in the K-14 charge at the Savannah River Site. Temperature coefficients are the most important reactivity feedback mechanism in SRS reactors; they are used in all safety analyses performed in support of the Safety Analysis Report, and in operations to predict reactivity changes with control rod moves. The effects of the radial location of the assembly in the reactor, isotope depletion, and thermal expansion of the metal components on the temperature coefficients have also been investigated. With the exception of the dead space coefficient, all of the regionalmore » temperature coefficients were found to be negative or zero. All of the temperature coefficients become more negative with isotopic depletion over the fuel cycle. Coefficients also become more negative with increasing radial distance of the assembly from the center of the core; this is proven from first principles and confirmed by calculations. It was found that axial and radial thermal expansion effects on the metal fuel and target tubes counteract one another, indicating these effects do not need to be considered in future temperature coefficient calculations for the Mark 22 assembly. The moderator coefficient was found to be nonlinear with temperature; thus, the values derived for accidents involving increases in moderator temperature are significantly different than those for decreases in moderator temperature, although the moderator coefficient is always negative.« less
  • An issue of concern at the Savannah River Site (SRS) over the past 20 years is whether tritiated groundwater originating at SRS might be the cause of low levels of tritium measured in certain domestic wells in Georgia. Tritium activity levels in several domestic wells have been observed to occur at levels comparable to what is measured in rainfall in areas surrounding SRS. Since 1988, there has been speculation that tritiated groundwater from SRS could flow under the river and find its way into Georgia wells. A considerable effort was directed at assessing the likelihood of trans-river flow, and 44more » wells have been drilled by the USGS and the Georgia Department of Natural Resources. Also, as part of the data collection and analysis, the USGS developed a numerical model during 1997-98 to assess the possibility for such trans-river flow to occur. The model represented the regional groundwater flow system surrounding the Savannah River Site (SRS) in seven layers corresponding to the underlying hydrostratigraphic units, which was regarded as sufficiently detailed to evaluate whether groundwater originating at SRS could possibly flow beneath the Savannah River into Georgia. The model was calibrated against a large database of water-level measurements obtained from wells on both sides of the Savannah River and screened in each of the hydrostratigraphic units represented within the model. The model results verified that the groundwater movement in all hydrostratigraphic units proceeds laterally toward the Savannah River from both South Carolina and Georgia, and discharges into the river. Once the model was calibrated, a particle-track analysis was conducted to delineate areas of potential trans-river flow. Trans-river flow can occur in either an eastward or westward direction. The model indicated that all locations of trans-river flow are restricted to the Savannah River's flood plain, where groundwater passes immediately prior to discharging into the river. Whether the trans-river flow is eastward or westward depends primarily on the position of the Savannah River as it meanders back and forth within the flood plain and is limited to narrow sections of land adjacent to the river. With respect to the only location of westward trans-river flow that has a recharge area within the SRS, the new evaluations of hypothetical pumping scenarios indicated that only a very slight impact is incurred, even under the most extreme groundwater extraction scenario. The updated model did not result in a significant change in the location of the recharge areas at SRS and the only impact was measured in slight changes in the travel times associated with the travel path. The median groundwater travel times for particles released under each of the 4 groundwater extraction scenarios ranged from 366 to 507 years while. Under the most extreme scenario, that under which SRS groundwater extraction is discontinued, the shortest travel time was reduced from 90 to 79 years. It should be emphasized that the groundwater transit times do not include the time required for groundwater to migrate vertically downward across the uppermost aquifer (i.e. at the recharge area), thus the actual groundwater travel times could be up to several decades longer than what was calculated in the model. The exhaustive evaluations that have been conducted indicates that it is highly unlikely that tritiated groundwater originating at the SRS could migrate into Georgia and explain the low tritium activity levels that were originally observed in certain domestic water supply wells. Considering that those wells were located at some distance (several km) from the Savannah River, a far more likely explanation is that tritiated rainfall infiltrated the subsurface and recharged the shallow aquifer within which the well was finished.« less
  • This paper discusses a new tritium processing facility, named the Replacement Tritium Facility (RTF), nearing completion and being prepared for startup at the Savannah River Site (SRS). The RTF has the capability to load and unload tritium from gas containers and to recover, purify and separate hydrogen isotopes. A multilayered confinement system is designed to reduce tritium losses t the environment. This confinement system is expected to confine and recover any tritium that might escape the process equipment, and to maintain the tritium concentration in the nitrogen glovebox atmosphere to less than 10{sup {minus} 1} {mu}Ci/cc tritium during normal operation.