Evaluation of the Non-Transient Hydrologic Source Term from the CAMBRIC Underground Nuclear Test in Frenchman Flat, Nevada Test Site PDF Download
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Author: R. M. Maxwell
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Languages : en
Pages : 67
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Hydrologic Source Term (HST) calculations completed in 1998 at the CAMBRIC underground nuclear test site were LLNL's first attempt to simulate a hydrologic source term at the NTS by linking groundwater flow and transport modeling with geochemical modeling (Tompson et al., 1999). Significant effort was applied to develop a framework that modeled in detail the flow regime and captured all appropriate chemical processes that occurred over time. However, portions of the calculations were simplified because of data limitations and a perceived need for generalization of the results. For example: (1) Transient effects arising from a 16 years of pumping at the site for a radionuclide migration study were not incorporated. (2) Radionuclide fluxes across the water table, as derived from infiltration from a ditch to which pumping effluent was discharged, were not addressed. (3) Hydrothermal effects arising from residual heat of the test were not considered. (4) Background data on the ambient groundwater flow direction were uncertain and not represented. (5) Unclassified information on the Radiologic Source Term (RST) inventory, as tabulated recently by Bowen et al. (2001), was unavailable; instead, only a limited set of derived data were available (see Tompson et al., 1999). (6) Only a small number of radionuclides and geochemical reactions were incorporated in the work. (7) Data and interpretation of the RNM-2S multiple well aquifer test (MWAT) were not available. As a result, the current Transient CAMBRIC Hydrologic Source Term project was initiated as part of a broader Phase 2 Frenchman Flat CAU flow and transport modeling effort. The source term will be calculated under two scenarios: (1) A more specific representation of the transient flow and radionuclide release behavior at the site, reflecting the influence of the background hydraulic gradient, residual test heat, pumping experiment, and ditch recharge, and taking into account improved data sources and modeling approaches acquired or developed since the previous work (as in Pawloski et al., 2001, at the CHESHIRE site). This will be referred to as the transient CAMBRIC source term. (2) A generic release model made under steady-state flow conditions, in the absence of any transient effect, at the same site with the same RST for use in the development of simple release models at the other nine underground test sites in the Frenchman Flat CAU. This will be referred to as the steady state (non-transient) source term. The purpose of this report is to summarize the results of our steady state source term simulations. Additional details pertaining to these results, the transient model results, and the overall strategy, rationale, and assumptions used in the models will be documented in a separate report.
Author: R. M. Maxwell
Publisher:
ISBN:
Category :
Languages : en
Pages : 67
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Book Description
Hydrologic Source Term (HST) calculations completed in 1998 at the CAMBRIC underground nuclear test site were LLNL's first attempt to simulate a hydrologic source term at the NTS by linking groundwater flow and transport modeling with geochemical modeling (Tompson et al., 1999). Significant effort was applied to develop a framework that modeled in detail the flow regime and captured all appropriate chemical processes that occurred over time. However, portions of the calculations were simplified because of data limitations and a perceived need for generalization of the results. For example: (1) Transient effects arising from a 16 years of pumping at the site for a radionuclide migration study were not incorporated. (2) Radionuclide fluxes across the water table, as derived from infiltration from a ditch to which pumping effluent was discharged, were not addressed. (3) Hydrothermal effects arising from residual heat of the test were not considered. (4) Background data on the ambient groundwater flow direction were uncertain and not represented. (5) Unclassified information on the Radiologic Source Term (RST) inventory, as tabulated recently by Bowen et al. (2001), was unavailable; instead, only a limited set of derived data were available (see Tompson et al., 1999). (6) Only a small number of radionuclides and geochemical reactions were incorporated in the work. (7) Data and interpretation of the RNM-2S multiple well aquifer test (MWAT) were not available. As a result, the current Transient CAMBRIC Hydrologic Source Term project was initiated as part of a broader Phase 2 Frenchman Flat CAU flow and transport modeling effort. The source term will be calculated under two scenarios: (1) A more specific representation of the transient flow and radionuclide release behavior at the site, reflecting the influence of the background hydraulic gradient, residual test heat, pumping experiment, and ditch recharge, and taking into account improved data sources and modeling approaches acquired or developed since the previous work (as in Pawloski et al., 2001, at the CHESHIRE site). This will be referred to as the transient CAMBRIC source term. (2) A generic release model made under steady-state flow conditions, in the absence of any transient effect, at the same site with the same RST for use in the development of simple release models at the other nine underground test sites in the Frenchman Flat CAU. This will be referred to as the steady state (non-transient) source term. The purpose of this report is to summarize the results of our steady state source term simulations. Additional details pertaining to these results, the transient model results, and the overall strategy, rationale, and assumptions used in the models will be documented in a separate report.
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Languages : en
Pages : 32
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Pages : 2
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Vining speaks of translating his work The mystery of Hamlet into German.
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Frenchman Flat is one of several areas of the Nevada Test Site (NTS) used for underground nuclear testing (Figure 1-1). These nuclear tests resulted in groundwater contamination in the vicinity of the underground test areas. As a result, the U.S. Department of Energy (DOE), National Nuclear Security Administration Nevada Site Office (NNSA/NSO) is currently conducting a corrective action investigation (CAI) of the Frenchman Flat underground test areas. Since 1996, the Nevada Division of Environmental Protection (NDEP) has regulated NNSA/NSO corrective actions through the ''Federal Facility Agreement and Consent Order'' ([FFACO], 1996). Appendix VI of the FFACO agreement, ''Corrective Action Strategy'', was revised on December 7, 2000, and describes the processes that will be used to complete corrective actions, including those in the Underground Test Area (UGTA) Project. The individual locations covered by the agreement are known as corrective action sites (CASs), which are grouped into corrective action units (CAUs). The UGTA CASs are grouped geographically into five CAUs: Frenchman Flat, Central Pahute Mesa, Western Pahute Mesa, Yucca Flat/Climax Mine, and Rainier Mesa/Shoshone Mountain (Figure 1-1). These CAUs have distinctly different contaminant source, geologic, and hydrogeologic characteristics related to their location (FFACO, 1996). The Frenchman Flat CAU consists of 10 CASs located in the northern part of Area 5 and the southern part of Area 11 (Figure 1-1). This report documents the evaluation of the information and data available on the unclassified source term and radionuclide contamination for Frenchman Flat, CAU 98. The methodology used to estimate hydrologic source terms (HSTs) for the Frenchman Flat CAU is also documented. The HST of an underground nuclear test is the portion of the total inventory of radionuclides that is released over time into the groundwater following the test. The total residual inventory of radionuclides associated with one or more tests is known as the radiologic source term (RST). The RST is comprised of radionuclides in water, glass, or other phases or mineralogic forms. This evaluation was conducted in support of the development of a CAU contaminant transport model for the Frenchman Flat CAU.
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The objectives of this report are to develop, summarize, and interpret a series of detailed unclassified simulations that forecast the nature and extent of radionuclide release and near-field migration in groundwater away from the CHESHIRE underground nuclear test at Pahute Mesa at the NTS over 1000 yrs. Collectively, these results are called the CHESHIRE Hydrologic Source Term (HST). The CHESHIRE underground nuclear test was one of 76 underground nuclear tests that were fired below or within 100 m of the water table between 1965 and 1992 in Areas 19 and 20 of the NTS. These areas now comprise the Pahute Mesa Corrective Action Unit (CAU) for which a separate subregional scale flow and transport model is being developed by the UGTA Project to forecast the larger-scale migration of radionuclides from underground tests on Pahute Mesa. The current simulations are being developed, on one hand, to more fully understand the complex coupled processes involved in radionuclide migration, with a specific focus on the CHESHIRE test. While remaining unclassified, they are as site specific as possible and involve a level of modeling detail that is commensurate with the most fundamental processes, conservative assumptions, and representative data sets available. However, the simulation results are also being developed so that they may be simplified and interpreted for use as a source term boundary condition at the CHESHIRE location in the Pahute Mesa CAU model. In addition, the processes of simplification and interpretation will provide generalized insight as to how the source term behavior at other tests may be considered or otherwise represented in the Pahute Mesa CAU model.
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The purpose of this report is to provide an approach for the development of a simplified unclassified hydrologic source term (HST) for the ten underground nuclear tests conducted in the Frenchman Flat Corrective Action Unit (CAU) at the Nevada Test Site (NTS). It is being prepared in an analytic form for incorporation into a GOLDSIM (Golder Associates, 2000) model of radionuclide release and migration in the Frenchman Flat CAU. This model will be used to explore, in an approximate and probabilistic fashion, sensitivities of the 1,000-year radionuclide contaminant boundary (FFACO, 1996; 2000) to hydrologic and other related parameters. The total inventory (or quantity) of radionuclides associated with each individual test, regardless of its form and distribution, is referred to as the radiologic source term (RST) of that test. The subsequent release of these radionuclides over time into groundwater is referred to as the hydrologic source term (HST) of that test (Tompson, et al., 2002). The basic elements of the simplified hydrologic source term model include: (1) Estimation of the volumes of geologic material physically affected by the tests. (2) Identification, quantification, and distribution of the radionuclides of importance. (3) Development of simplified release and retardation models for these radionuclides in groundwater. The simplifications used in the current HST model are based upon more fundamental analyses that are too complicated for use in a GOLDSIM sensitivity study. These analyses are based upon complex, three-dimensional flow and reactive transport simulations summarized in the original CAMBRIC hydrologic source term model (Tompson et al., 1999), unclassified improvements of this model discussed in Pawloski et al. (2000), as well as more recent studies that are part of an ongoing model of the HST at the CHESHIRE test in Pahute Mesa (Pawloski et al., 2001).
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Pages : 21
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The U.S. Department of Energy, Nevada Operations Office (DOE/NV) Environmental Restoration Division is seeking to evaluate groundwater contamination resulting from 30 years of underground nuclear testing at the Nevada Test Site (NTS). This evaluation requires knowledge about what radioactive materials are in the groundwater and how they are transported through the underground environment. This information coupled with models of groundwater flow (flow paths and flow rates) will enable predictions of the arrival of each radionuclide at a selected receptor site. Risk assessment models will then be used to calculate the expected environmental and human doses. The accuracy of our predictions depends on the validity of our hydrologic and risk assessment models and on the quality of the data for radionuclide concentrations in ground water at each underground nuclear test site. This paper summarizes what we currently know about radioactive material in NTS groundwater and suggests how we can best use our limited knowledge to proceed with initial modeling efforts. The amount of a radionuclide available for transport in groundwater at the site of an underground nuclear test is called the hydrologic source term. The radiologic source term is the total amount of residual radionuclides remaining after an underground nuclear test. The hydrologic source term is smaller than the radiologic source term because some or most of the radionuclide residual cannot be transported by groundwater. The radiologic source term has been determined for each of the underground nuclear tests fired at the NTS; however, the hydrologic source term has been estimated from measurements at only a few sites.
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Pages : 15
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It has been proposed that unclassified source terms used in the reactive transport modeling investigations at NTS CAUs should be based on yield-weighted source terms calculated using the average source term from Bowen et al. (2001) and the unclassified announced yields reported in DOE/NV-209. This unclassified inventory is likely to be used in unclassified contaminant boundary calculations and is, thus, relevant to compare to the classified inventory. They have examined the classified radionuclide inventory produced by 10 underground nuclear tests conducted in the Frenchman Flat (FF) area of the Nevada Test Site. The goals were to (1) evaluate the variability in classified radiological source terms among the 10 tests and (2) compare that variability and inventory uncertainties to an average unclassified inventory (e.g. Bowen 2001). To evaluate source term variability among the 10 tests, radiological inventories were compared on two relative scales: geometric mean and yield-weighted geometric mean. Furthermore, radiological inventories were either decay corrected to a common date (9/23/1992) or the time zero (t0) of each test. Thus, a total of four data sets were produced. The date of 9/23/1992 was chosen based on the date of the last underground nuclear test at the Nevada Test Site.
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This report documents the evaluation of the information and data available on the unclassified source term and radionuclide contamination for CAU 97: Yucca Flat/Climax Mine. The total residual inventory of radionuclides associated with one or more tests is known as the radiologic source term (RST). The RST is comprised of radionuclides in water, glass, or other phases or mineralogic forms. The hydrologic source term (HST) of an underground nuclear test is the portion of the total RST that is released into the groundwater over time following the test. In this report, the HST represents radionuclide release some time after the explosion and does not include the rapidly evolving mechanical, thermal, and chemical processes during the explosion. The CAU 97: Yucca Flat/Climax Mine has many more detonations and a wider variety of settings to consider compared to other CAUs. For instance, the source term analysis and evaluation performed for CAUs 101 and 102: Central and Western Pahute Mesa and CAU 98: Frenchman Flat did not consider vadose zone attenuation because many detonations were located near or below the water table. However, the large number of Yucca Flat/Climax Mine tests and the location of many tests above the water table warrant a more robust analysis of the unsaturated zone.
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Pages : 53
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Effective management of available groundwater resources and strategies for remediation of water impacted by past nuclear testing practices depend on knowledge about the migration of radionuclides in groundwater away from the sites of the explosions. A primary concern is to assess the relative mobilities of the different radionuclide species found near sites of underground nuclear tests and to determine the concentration, extent, and speed of this movement. Ultimately the long term transport behavior of radionuclides with half-lives long enough that they will persist for decades, their interaction with groundwater, and the resulting flux of these contaminants is of paramount importance. As part of a comprehensive approach to these assessments, more than three decades of site-specific sites studies have been undertaken at the Nevada Test Site (NTS) which have focused on the means responsible for the observed or suspected movement of radionuclides away from underground nuclear tests (RNM, 1983). More recently regional and local models of groundwater flow and radionuclide transport have been developed as part of a federal and state of Nevada program to assess the long-term effects of underground nuclear testing on human health and environment (e.g., U.S. DOE/NV, 1997a; Tompson et al., 1999; Pawloski et al., 2001). Necessary to these efforts is a reliable measure of the hydrologic source term which is defined as those radionuclides dissolved in or otherwise transported by groundwater (Smith et al., 1995). Measurement of radionuclides in waters sampled near the sites of underground nuclear test provides arguably the best opportunity to bound the hydrologic source term. This empirical approach was recognized early and concentration data has been collected annually since mid-1970's. Initially three sites were studied at the NTS; over the years the program has been expanded to include more than fifteen study locations. As part of various field programs, Lawrence Livermore National Laboratory and Los Alamos National Laboratory have annually returned water samples from wells in near-field locations at the NTS for radiochemical analyses. This report makes the distinction between samples taken in the near-field and the far field. The near-field includes the area extending radially (almost equal to)300 meters from surface ground zero (the firing point of an underground nuclear test projected upwards on ground surface). Over the years this sampling program has also been refereed to as the ''hot-well monitoring program'' because these water samples contained concentrations of tritium above natural background (tritium concentrations in southern Nevada precipitation are 0.5 to 2.0 Bq/L, Farmer et al., 1998). A majority of the hot wells contain tritium in excess of the 741 Bq/L (20,000 pCi/L) drinking water standard (Smith et al., 1996a; Smith et al., 1997). The sites which comprise our current hot well sampling network are plotted on a map of the NTS in Figure 1.
