Disposal Of Transuranic Waste Research Articles

Difference in expansion and dehydration behaviors between NH4- and K-montmorillonite

Montmorillonite (Mt) expansion and swelling are key factors determining the barrier performance of bentonite in trans-uranic (TRU) and high-level radioactive waste disposal. In the case of co-located geological disposal of TRU and high-level waste, NH4+ ions formed from NO3− ions leached from TRU waste may contact bentonite, exchanging with interlayer cations of Mt. to form NH4-Mt, with a reduction in barrier performance. Because of the similar hydration energies of NH4+ and K+, NH4-Mt may have less expandability or even change to a non-expandable mineral such as K-Mt. An understanding of the expansion and alteration behavior of NH4-Mt, especially in comparison with K-Mt, is thus necessary in waste-disposal safety assessment. Here, the hydration behavior of NH4-Mt was investigated by X-ray diffraction (XRD) analysis and molecular dynamics (MD) simulation and compared with that of K-Mt. XRD profiles under relative humidity (RH) control indicate that expansion of NH4-Mt is similar to that of K-Mt at >40% RH with slightly different d-values. However, NH4-Mt expansion is kept at ∼20% RH, while K-Mt tends to dehydrate. MD simulations indicate that hydrogen bonding with NH4+ ions causes the differences in hydration behaviors of NH4- and K-Mt, increasing basal spacing in dehydrated states and promoting hydration. This “hydration gap” may be attributed to differences in alteration to non-expandable minerals by dehydration, with NH4+ having less tendency for alternation and less of an effect on the barrier performance of bentonite than K+.

Influence of ethylenediaminetetraacetic acid on the long-term oxidation state distribution of plutonium

Spectrophotometry was used to study the effect of EDTA on plutonium oxidation state distribution as a function of time, pH, and ligand-to-metal ratio (L/M) under anoxic conditions. Novel Pu(V)-EDTA absorption bands were identified at 571, 993, 1105, and 1150 nm with molar absorption coefficients of 15 ± 1, 6 ± 1, 10 ± 1, and 10 ± 1 cm−1M−1, respectively. Pu(V)-EDTA spectral changes occurred at L/M < 1, indicating only PuVO2(EDTA)3- formed with logK = 3.6 ± 0.3. Time-resolved experiments showed EDTA drastically increased the Pu(V/VI) reduction rate, which we propose is driven by amine lone-pair electron donation and the oxidative decarboxylation of EDTA. Oxidation of Pu(III)-EDTA to Pu(IV)-EDTA occurred on a slower time scale (110–237 days) than previously reported (<15 min) and is hypothesized to be radiolysis driven. Pu(V/VI)-EDTA and Pu(III)-EDTA both approached Pu(IV)-EDTA stabilization over time, yet Pu(V/VI)-EDTA solubility data was ≥ 1.0 log10 units higher than predicted by Pu(IV)-EDTA solubility models, indicating that current thermodynamic models are incomplete. Ultimately, the data show EDTA preferentially stabilizes Pu(IV) over time regardless of initial oxidation state, but Pu(V)-EDTA can persist under environmentally-relevant conditions, emphasizing the need to continue investigating redox reactions, speciation, and behavior of these complexes to support the transuranic waste disposal and surface remediation/containment efforts.

Microscopic structural analysis of lead borate-based glass

The development of an iodine immobilization technique that can retain radioactive iodine in a waste form for a long period and constrain its leaching into pore water is necessary in order to secure the long-term safety of geological disposal of transuranic waste. Lead borate glass vitrified at a low temperature is regarded as a promising material for immobilizing the Iodine-129 that is recovered from spent AgI filters used in reprocessing plants in Japan.Structural models of lead borate-based glass were constructed by the Reverse Monte Carlo (RMC) method based on experimental information from such sources as neutron and high-energy X-ray diffraction, XAFS, and 11B MAS NMR spectroscopic analyses.The neutron structure factors [SN(Q)] and X-ray structure factors [SX(Q)] that were calculated by RMC and measured by J-PARC/MLF-BL20 and SPring-8/BL04B2 suggest that RMC results are consistent with experimental measurements and reveal that structural information of neutrons is indispensable for analyzing the surrounding boron structures.

Improvement of Inventory and Leaching Rate Measurements of C-14 in Hull Waste, and Separation of Organic Compounds for Chemical Species Identification

ABSTRACTIn order to analyze the C-14 inventory and leaching rate for safety evaluation of transuranic waste disposal, it is necessary to establish an analytical method that can measure C-14 with sufficient precision [1]. Oxidative decomposition of organic compounds containing C-14 is carried out to absorb carbon dioxide (CO2) in an alkaline solution, which is mixed with a liquid scintillation cocktail, and the amount C-14 is quantified by measuring a beta ray spectrum with a liquid scintillation counter. It has been difficult to completely decompose carbon compounds in a sample, even to CO2, by using conventional oxidizing agents. In the work described here, we improved the method of oxidative decomposition used to completely decompose carbon compounds using peroxydisulfuric acid (K2S2O8). When C-14 in the form of CO2 was absorbed in a sodium hydroxide (NaOH) aqueous solution, only 80% of the actually used quantity was detected. Total organic carbon measurements showed that the entire quantity of CO2 was absorbed by NaOH. When NaOH aqueous solution was used, it was found that only the analytical value was 80%. The entire quantity of the actually used carbon could be measured by absorbing the CO2 in Carbo-Sorb®. An anion form and a neutral molecule exist in the organic compound released from activated metals. In order to identify organic compounds efficiently, fractionation into an anion and a neutral molecule and separation by high performance liquid chromatography (HPLC) are necessary. Here, we propose the combined use of an ion exchange resin and HPLC as an improved technique for identification of the chemical species.

A new assessment method for demonstrating the sufficiency of the safety assessment and the safety margins of the geological disposal system

A new method for demonstrating the sufficiency of the safety assessment and safety margins of the geological disposal system has been developed. The method is based on an existing comprehensive sensitivity analysis method and can systematically identify the successful conditions, under which the dose rate does not exceed specified safety criteria, using analytical solutions for nuclide migration and the results of a statistical analysis. The successful conditions were identified using three major variables. Furthermore, the successful conditions at the level of factors or parameters were obtained using relational equations between the variables and the factors or parameters making up these variables. In this study, the method was applied to the safety assessment of the geological disposal of transuranic waste in Japan. Based on the system response characteristics obtained from analytical solutions and on the successful conditions, the classification of the analytical conditions, the sufficiency of the safety assessment and the safety margins of the disposal system were then demonstrated. A new assessment procedure incorporating this method into the existing safety assessment approach is proposed in this study. Using this procedure, it is possible to conduct a series of safety assessment activities in a logical manner.

Safety assessment methodology focused on response characteristics of the disposal system and safety assessment for TRU waste in Japan

ABSTRACTIn order to enhance the safety of geological disposal and the reliability of the safety assessment carried out for each stage of the geological disposal project, an assessment methodology focused on a sensitivity analysis and an evaluation of importance, which incorporates “system understanding” and “information feedback” into the existing assessment approach, has been developed in this study. In this paper, the assessment methodology and the assessment results as applied for the transuranic (TRU) waste disposal system in Japan will be described. In the sensitivity analysis, an approximate analytical solution was used in order to understand the response characteristics of the engineered barrier system (EBS). In the importance evaluation, important factors relating to the robustness of system safety were identified based on the response characteristics. Furthermore, important features, events, and processes (FEPs) related to such factors and high-impact scenarios were identified based on the information accumulated through “system understanding” and “information feedback”. Based on this approach, the robustness of the TRU waste disposal system was assessed and measures for improving the robustness were identified.

Environmental monitoring of radioactive and non-radioactive constituents in the vicinity of WIP

Abstract The Waste Isolation Pilot Plant (WIPP), a US Department of Energy (DOE) facility, is a deep geologic transuranic waste disposal site designed for the safe disposal of transuranic (TRU) wastes generated from the US defense program. Monitoring is a key component of the development and operation of any nuclear repository and is important to the WIPP performance assessment. Initial concerns over the release of radioactive and chemical contaminants from the WIPP led to various monitoring programs, including the independent, academic-based WIPP environmental monitoring (WIPP-EM) program conducted by the New Mexico State University (NMSU) Carlsbad Environmental Monitoring and Research Center (CEMRC) located in Carlsbad, NM. The mission of CEMRC is to develop and implement an independent health and environmental monitoring program in the vicinity of WIPP and make the results easily accessible to the public and all interested parties. Under the WIPP-EM program constituents monitored include: (1) selected radionuclides, elements, and ions of interest in air, soil, vegetation, drinking water, surface water and sediment from within a 100-mile radius of WIPP as well as in the air exiting the WIPP exhaust shaft, and (2) internally deposited radionuclides in the citizenry living within a 100-mile radius of WIPP. This article presents an evaluation of more than tens years of environmental monitoring data that informed the public that there is no evidence of increases in radiological contaminants in the region that could be attributed to releases from the WIPP. Such an extensive monitoring program and constant public engagement is an ideal model for all nuclear waste repositories anywhere in the world.

Measurement of the fate of acetic acid form carbon in soil solution of flooded soils using high performance liquid chromatography coupled with isotope ratio mass spectrometry

Carbon-14 ( 14C) which can be taken into low molecular weight organic compounds (e.g. acetic acid, formic acid, methanol and ethanol) is one of the most important radionuclides released from transuranic waste disposal sites. To understand the fate of organic compounds in the soil environment, a stable carbon isotope, 13C, can be used as a tracer of 14C. In this study, 13C-labeled acetic acid was added to six soil–water mixture samples and the chemical form changes in the soil solutions were measured by high performance liquid chromatography coupled with isotope ratio mass spectrometry. The 13C-labeled acetic acid in the soil solutions was detected for the first 24 h, but could not be detected afterwards for any soil samples. Thus, in any soils that have similar properties to the soil samples used in the present study, most of the 13C-labeled acetic acid would likely be changed to other physico-chemical forms and be removed from the soil solutions in a very short time period. Less than 3% of the carbon added as acetic acid remained in the soil solutions, and was possibly mainly in inorganic forms. Carbon from acetic acid would not be retained in soil solutions for 48 h.

Bacteria contributing to behaviour of radiocarbon in sodium acetate

An acetate-utilising bacterium was isolated and identified from deionised water that was used for flooding of paddy soils in this study's batch culture experiments. Bacteria in the deionised water samples formed colonies on agar plates containing [1,2-(14)C] sodium acetate, and the autoradiograms showed that all the colonies were positive for (14)C utilisation. Then one of the acetate-utilising bacteria was isolated. The isolate was characterised by phylogenetic analysis, cell morphology, Gram staining and growth at 30 °C. Phylogenetic analysis based on 16S rRNA sequencing showed that the isolate belonged to the genus Burkholderia. The bacterium was gram-negative rods and grew at 30 °C under aerobic conditions. Based on these characteristics, the isolate was identified as Burkholderia gladioli. Because B. gladioli is often found in soil, water and the rhizosphere, attention must be paid to the relationships between bacteria and the behaviour of (14)C to for the safety assessment of geological disposal of transuranic waste.

The long-term behaviors of passivation and hydride layer of commercial grade pure titanium in TRU waste disposal environments

Preservation of the passivity under reducing environmental conditions for extended periods of time and the behavior of hydrogen evolution as the results of the preservation of the passivity of several candidate commercial grade pure titanium related to the small amount of palladium addition, such as Ti–Gr.17 for metallic containers to be buried under deep ground for disposing of transuranic (TRU) waste is investigated. The present investigation has revealed the following corrosion paths for the titanium alloys investigated. The passivity of the alloys is preserved as the result of repeated destruction and recovery of the surface films on the alloys. The long-term corrosion rate under the preserved passivity is of the order of 10 −6–10 −8 my −1 with evolution of hydrogen. The substrate alloys absorb parts of the hydrogen generated to form lath-type hydride phase before forming hydride layers at the final stage.

Sustainability of humic acids in the presence of magnesium oxide

The Waste Isolation Pilot Plant (WIPP) is a U.S. Department of Energy (DOE) repository for the disposal of transuranic waste generated from the U.S. defense program. Humic acids (HA), known to strongly bind to actinides and which may be generated by the degradation of organic materials present in the waste, may influence the performance of the WIPP. This work presents experimental results on the effect of WIPP brines, ERDA-6 and GWB, and of the WIPP engineered barrier, Premier Chemicals magnesium oxide, on the solubility of HA. In the absence of MgO, a portion of HA initially precipitates, but a constant concentration of HA remains in solution: over a 60 day period of time, at least 290 ± 10 mg/L HA can remain soluble in de-ionized (DI) water, 30 ± 4 mg/L in 95% ERDA-6, and 31 ± 4 mg/L in 95% GWB. For solutions initially containing from 0 to 400 mg/L HA, the ratio of the initial HA concentration and the soluble HA concentration is 1.3 in DI water, 13 in 95% ERDA-6, and 11 in 95% GWB. In the presence of MgO, all HA precipitate within 60 days in systems with a high liquid-to-solid ratio (10.0 g/g) or a low ratio (2.4 g/g). This phenomenon is due to HA precipitation and/or sorption on the surface of MgO.

The Nuclear Energy Debate and the Importance of Radioactive Waste Management

The preparation of this special issue dedicated to the topic of radioactive waste management coincides with some notable milestones. The year 2004 marks the 50th anniversary of the world’s first nuclear power plant in the town of Obnisk, near Moscow, which initiated the use of nuclear energy for civilian applications by providing power to residences and businesses. This year also marks the 25th anniversary of the Three Mile Island accident, which occurred at a nuclear power plant near Harrisburg, Pennsylvania, and effectively halted any new nuclear power plant considerations in the United States. A clean and sustainable energy source is nearly universally accepted as a necessity for our future, and the issues of radioactive waste management and permanent disposal solutions are inextricably linked to the exploration of nuclear power as a viable energy option. The actual and perceived risks associated with nuclear energy as well as radioactive waste—its generation, transportation, and disposal—pervade every aspect of the nuclear debate. Nearly all debate participants can concur with the commonly referenced mission of radioactive waste management programs: protection of the environment and human health and safety. However, structuring such programs and successfully executing them is a complex and lengthy process generally spanning several decades. For example, in the U.S., achieving operational status for the Waste Isolation Pilot Plant (WIPP), a deep geologic repository for the permanent disposal of transuranic wastes, involved more than four decades from concept to completion. The regulations governing the permanent disposal of radioactive waste at WIPP require demonstration of safe repository performance for a period of 10,000 years. A defining characteristic of the complexity associated with radioactive waste management programs is the wide spectrum of participants involved, each with strongly anchored and unique perspectives. Technical debate and discussion alone cannot resolve the divergent viewpoints and convictions of the various stakeholders, which may be grounded in technical, social, political, economic, or cultural backgrounds and interests. As an example, with respect to the disposition of radioactive waste, scientific and technical communities generally agree that radioactive waste can be disposed of by deep burial in suitable geologic formations that safely isolate the waste for time-frames of tens of thousands of years. An obvious challenge to scientists and engineers is defining the logic by which long-term predictions of geologic and weather conditions, groundwater behavior, and human activity covering these time-frames can be made and evaluated for repository performance. The inherent uncertainty associated with such predictive science complicates the public acceptance of

Unfavorable Conditions for Nuclear Criticality Following Disposal of Transuranic Waste at the Waste Isolation Pilot Plant

Modeling of nuclear criticality was omitted from performance assessment calculations for the Waste Isolation Pilot Plant (WIPP), a repository for waste contaminated with transuranic radioisotopes, located in southeastern New Mexico, based on arguments of low probability and low consequence. Low-probability arguments are presented here. Guidance provided by the Environmental Protection Agency (EPA) - the regulator of WIPP - allowed either qualitative “credibility” arguments or quantitative probability estimates when screening features, events, and processes such as criticality. Although information to quantitatively evaluate the probability of a criticality event was mostly lacking, qualitatively reasoned discussion of the inability to assemble a critical configuration of fissile material was accepted by the EPA. Specifically, after disposal and prior to an inadvertent human intrusion into the repository, there is no credible mechanism to move radioisotopes (and particularly, fissile material) since only small amounts of brine enter the repository, as adequately demonstrated in calculations over the years. An inadvertent human intrusion (an event that must be considered because of safety regulations) might allow a large pressure gradient to move more brine through the repository, but there is still no credible mechanism to counteract the natural tendency of the material to disperse during transport. Unfavorable physical conditions on concentrating fissile material include low initial solid concentration of fissile material, small mass of fissile material transported over 10 000 yr, and insufficient physical compaction; unfavorable hydrologic conditions include the limited amount of brine available to transport fissile material. Unfavorable geochemical conditions on concentrating the fissile radioisotopes include lack of sufficient adsorption and water chemistry conducive to precipitation.

The 1996 performance assessment for the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) is under development by the US Department of Energy (DOE) for the geologic disposal of transuranic (TRU) waste that has been generated at government defense installations in the United States. The WIPP is located in an area of low population density in southeastern New Mexico. Waste disposal will take place in excavated chambers in a bedded salt formation approximately 655 m below the land surface. This presentation describes a performance assessment (PA) carried out at Sandia National Laboratories (SNL) to support the Compliance Certification Application (CCA) made by the DOE to the US Environmental Protection Agency (EPA) in October, 1996, for the certification of the WIPP for the disposal of TRU waste. Based on the CCA supported by the PA described in this presentation, the EPA has issued a preliminary decision to certify the WIPP for the disposal of TRU waste. At present (April 1998), it appears likely that the WIPP will be in operation by the end of 1998.

Summary discussion of the 1996 performance assessment for the Waste Isolation Pilot Plant

Abstract The Waste Isolation Pilot Plant (WIPP) is under development by the US Department of Energy (DOE) for the geologic disposal of transuranic waste. The construction of complementary cumulative distribution functions (CCDFs) for total radionuclide release from the WIPP to the accessible environment is described. The resultant CCDFs (i) combine releases due to cuttings and cavings, spallings, direct brine release, and long-term transport in flowing groundwater; (ii) fall substantially to the left of the boundary line specified by the US Environmental Protection Agency's (EPA's) standard 40 CFR 191 for the geologic disposal of radioactive waste; and (iii) constitute an important component of the DOE's successful Compliance Certification Application to the EPA for the WIPP. Insights and perspectives gained in the performance assessment (PA) that led to these CCDFs are described, including the importance of: (i) an iterative approach to PA; (ii) uncertainty and sensitivity analysis; (iii) a clear conceptual model for the analysis; (iv) the separation of stochastic (i.e. aleatory) and subjective (i.e. epistemic) uncertainty; (v) quality assurance procedures; (vi) early involvement of peer reviewers, regulators, and stakeholders; (vii) avoidance of conservative assumptions; and (viii) adequate documentation.

Review and perspectives on spallings release models in the 1996 performance assessment for the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant was licensed for disposal of transuranic wastes generated by the US Department of Energy. The facility consists of a repository mined in a bedded salt formation, approximately 650 m below the surface. Regulations promulgated by the US Environmental Protection Agency require that performance assessment calculations for the repository include the possibility that an exploratory drilling operation could penetrate the waste disposal areas at some time in the future. Release of contaminated solids could reach the surface during a drilling intrusion. One of the mechanisms for release, known as spallings, can occur if gas pressures in the repository exceed the hydrostatic pressure of a column of drilling mud. Calculation of solids releases for spallings depends critically on the conceptual models for the waste, for the spallings process, and assumptions regarding driller parameters and practices. The paper presents a review of the evolution of these models during regulatory review of the Compliance Certification Application for the repository. A summary and perspectives on the implementation of conservative assumptions in model development are also provided.

Development of the conceptual models for chemical conditions and hydrology used in the 1996 performance assessment for the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) is a US Department of Energy (DOE) facility for the permanent disposal of defense-related transuranic (TRU) waste. US Environmental Protection Agency (EPA) regulations specify that the DOE must demonstrate on a sound basis that the WIPP disposal system will effectively contain long-lived alpha-emitting radionuclides within its boundaries for 10,000 years following closure. In 1996, the DOE submitted the 40 CFR Part 191 Compliance Certification Application for the Waste Isolation Pilot Plant (CCA) to the EPA. The CCA proposed that the WIPP site complies with EPA's regulatory requirements. Contained within the CCA are descriptions of the scientific research conducted to characterize the properties of the WIPP site and the probabilistic performance assessment (PA) conducted to predict the containment properties of the WIPP disposal system. In May 1998, the EPA certified that the TRU waste disposal at the WIPP complies with its regulations. Waste disposal operations at WIPP commenced on 28 March 1999. The 1996 WIPP PA model of the disposal system included conceptual and mathematical representations of key hydrologic and geochemical processes. These key processes were identified over a 22-year period involving data collection, data interpretation, computer models, and sensitivity studies to evaluate the importance of uncertainty and of processes that were difficult to evaluate by other means. Key developments in the area of geochemistry were the evaluation of gas generation mechanisms in the repository; development of a model of chemical conditions in the repository and actinide concentrations in brine; selecting MgO backfill and demonstrating its effects experimentally; and, determining the chemical retardation capability of the Culebra. Key developments in the area of hydrology were evaluating the potential for groundwater to dissolve the Salado Formation (the repository host formation); development of a regional model for hydrologic conditions; development of a stochastic, probabilistic representation of hydraulic properties in the Culebra Member of the Rustler Formation; characterization of physical transport in the Culebra; and, the evaluation of brine and gas flow in the Salado. Additional confidence in the conceptual models used in the 1996 WIPP PA was gained through independent peer review in many stages of their development.

The geologic and hydrogeologic setting of the Waste Isolation Pilot Plant

Abstract The Waste Isolation Pilot Plant (WIPP) is a mined repository for the permanent disposal of transuranic wastes. It has been constructed by the United States Department of Energy (DOE) in semiarid, sparsely inhabited rangeland in southeastern New Mexico. The disposal area is 655 m below the land surface, in bedded salt of the Late Permian (approximately 255 million-years-old) Salado Formation. The extremely low permeability of the halite and other evaporite rocks provide the primary geologic barrier assuring long-term (10,000-year-plus) isolation of the radioactive waste from the accessible environment. Extensive geologic investigations during site characterization have provided information on the stratigraphy, structure, and natural resources of the region (including hydrocarbons, potash, and groundwater), and have investigated the potential for disruption by processes such as dissolution, salt deformation, tectonic activity, and climate change. Hydrogeologic investigations have documented the physical properties of the evaporite rocks, and have identified the Culebra Dolomite Member of the overlying Rustler Formation as the most transmissive water-bearing unit in the region. If the evaporite barriers are breached by accidental drilling intrusion, the Culebra would provide the most likely pathway for radionuclide transport away from the site. Although water in the Culebra is of poor quality and none is currently used for human consumption, groundwater flow and potential radionuclide transport in the unit have been studied in detail. Results of geologic and hydrogeologic studies of the WIPP region indicate that the geologic and hydrogeologic features of the site will provide effective long-term containment of radionuclides. Geologic and hydrogeologic information is used in the performance assessment that supported the DOE’s compliance certification application to the United States Environmental Protection Agency.

Software quality assurance in the 1996 performance assessment for the Waste Isolation Pilot Plant

The US Department of Energy (DOE) Waste Isolation Pilot Plant (WIPP), located in southeast New Mexico, is a deep geologic repository for the permanent disposal of transuranic waste generated by DOE defense-related activities. Sandia National Laboratories (SNL), in its role as scientific advisor to the DOE, is responsible for evaluating the long-term performance of the WIPP. This risk-based Performance Assessment (PA) is accomplished in part through the use of numerous scientific modeling codes, which rely for some of their inputs on data gathered during characterization of the site. The PA is subject to formal requirements set forth in federal regulations. In particular, the components of the calculation fall under the configuration management and software quality assurance aegis of the American Society of Mechanical Engineers(ASME) Nuclear Quality Assurance (NQA) requirements. This paper describes SNL's implementation of the NQA requirements regarding software quality assurance (SQA). The description of the implementation of SQA for a PA calculation addresses not only the interpretation of the NQA requirements, it also discusses roles, deliverables, and the resources necessary for effective implementation. Finally, examples are given which illustrate the effectiveness of SNL's SQA program, followed by a detailed discussion of lessons learned.

Computational environment and software configuration management of the 1996 performance assessment for the Waste Isolation Pilot Plant

The US Department of Energy (DOE) Waste Isolation Pilot Plant (WIPP), located in southeast New Mexico, is a deep geologic repository for the permanent disposal of transuranic waste generated by DOE defense-related activities. Sandia National Laboratories (SNL), in its role as scientific advisor to the DOE, is responsible for evaluating the long-term performance of the WIPP. This risk-based Performance Assessment (PA) is accomplished in part through the use of numerous scientific modeling codes, which rely for some of their inputs on data gathered during characterization of the site. The PA is subject to formal requirements set forth in federal regulations. In particular, the components of the calculation fall under the configuration management and software quality assurance aegis of the American Society of Mechanical Engineers (ASME) Nuclear Quality Assurance (NQA) requirements. This paper describes SNL's implementation of the NQA requirements regarding configuration management. The complexity of the PA calculation is described, and the rationale for developing a flexible, robust run-control process is discussed. The run-control implementation is described, and its integration with the configuration-management system is then explained, to show how a calculation requiring 37,000 CPU-hours, and involving 225,000 output files totaling 95 GB, was accomplished in 5 months by two individuals, with full traceability and reproducibility.