Chalk River Laboratories Research Articles

SYNTHESIS OF GEOCHEMICAL AND FRACTURE MINERAL STUDIES RELEVANT TO A DEEP GEOLOGICAL REPOSITORY FOR NONFUEL WASTES AT CHALK RIVER

As part of a feasibility study under the Nuclear Legacy Liabilities Program, the geochemistry of the crystalline bedrock at the Chalk River Laboratories site has been investigated to examine the suitability of the bedrock to host a potential deep geologic repository, termed a Geologic Waste Management Facility, for the long-term management of intermediate-level radioactive wastes for Canadian Nuclear Laboratories, formerly Atomic Energy of Canada Limited. Characterization of the groundwater and fracture-filling minerals are important considerations in assessing how the geochemical environment would affect the performance and safety of such a facility. Regional groundwater chemistry at the site has evolved over time by groundwater mixing and by rock–water interactions. Collaborative studies with the University of Waterloo and the United States Geological Survey have provided data for whole-rock, fracture minerals, and groundwater isotope systematics. The sampled groundwaters appear in general to be geologi...

DEMONSTRATION OF CULTIVABILITY FOR A LOW IONIC STRENGTH WATERHYALELLA AZTECASTRAIN

The in-lab reproductive success of a strain of Hyalella azteca collected from Twin Lake, a water body located on the Canadian Nuclear Laboratories Chalk River Laboratories site, is sufficient to be used for effluent and (or) sediment toxicity assessments. This strain of Hyalella azteca enhances our capabilities to evaluate ecological risks in low ionic strength waters.

Isotopic signature of selected lanthanides for nuclear activities profiling using cloud point extraction and ICP-MS/MS

The presence of fission products, which include numerous isotopes of lanthanides, can impact the isotopic ratios of these elements in the environment. A cloud point extraction (CPE) method was used as a preconcentration/separation strategy prior to measurement of isotopic ratios of three lanthanides (Nd, Sm, and Eu) by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). To minimise polyatomic interference, the combination of interferents removal by CPE, reaction/collision cell conditions in He and NH3 mode and tandem quadrupole configuration was investigated and provided optimal results for the determination of isotopic ratio in environmental samples. Isotopic ratios were initially measured in San Joaquin soil (NIST-2709a), an area with little contamination of nuclear origin. Finally, samples collected from three sites with known nuclear activities (Fangataufa Lagoon in French Polynesia, Chernobyl and the Ottawa River near Chalk River Laboratory) were analysed and all exhibited altered isotopic ratios for 143/145Nd, 147/149Sm, and 151/153Eu. These results demonstrate the potential of CPE and ICP-MS/MS for the detection of altered isotopic ratio in environmental samples collected in area subjected to nuclear anthropogenic contamination. The detection of variations in these isotopic ratios of fission products represents the first application of CPE in nuclear forensic investigations of environmental samples.

Isotope hydrology of the Chalk River Laboratories site, Ontario, Canada

This paper presents results of hydrochemical and isotopic analyses of groundwater (fracture water) and porewater, and physical property and water content measurements of bedrock core at the Chalk River Laboratories (CRL) site in Ontario. Density and water contents were determined and water-loss porosity values were calculated for core samples. Average and standard deviations of density and water-loss porosity of 50 core samples from four boreholes are 2.73 ± 12 g/cc and 1.32 ± 1.24 percent. Respective median values are 2.68 and 0.83 indicating a positive skewness in the distributions. Groundwater samples from four deep boreholes were analyzed for strontium (87Sr/86Sr) and uranium (234U/238U) isotope ratios. Oxygen and hydrogen isotope analyses and selected solute concentrations determined by CRL are included for comparison. Groundwater from borehole CRG-1 in a zone between approximately +60 and −240 m elevation is relatively depleted in δ18O and δ2H perhaps reflecting a slug of water recharged during colder climatic conditions. Porewater was extracted from core samples by centrifugation and analyzed for major dissolved ions and for strontium and uranium isotopes. On average, the extracted water contains 15 times larger concentration of solutes than the groundwater. 234U/238U and correlation of 87Sr/86Sr with Rb/Sr values indicate that the porewater may be substantially older than the groundwater. Results of this study show that the Precambrian gneisses at Chalk River are similar in physical properties and hydrochemical aspects to crystalline rocks being considered for the construction of nuclear waste repositories in other regions.

A WEIGHT-OF-EVIDENCE APPROACH TO THE ASSESSMENT OF ECOLOGICAL RISK FROM HISTORICAL CONTAMINATION OF OTTAWA RIVER SEDIMENTS NEAR CHALK RIVER LABORATORIES

Canadian Nuclear Laboratories’ Chalk River Laboratories (CRL) site is situated on the banks of the Ottawa River, about 180 km northwest of the City of Ottawa. Since 1947, the Ottawa River has received effluent from CRL’s operations. Since this time, and in particular during the operation of the national research experimental research reactor (1947–1992), radionuclides (mainly 60Co and 137Cs) and mercury released in effluents have accumulated in deep-water sediments downstream of CRL. In the following, we present a holistic summary of characterization of the historical contamination and ecological risk assessment work completed to date. The evaluation included (i) comparisons of recommended benchmark dose and screening levels with concentrations in water and sediment, (ii) determination of relevant exposure pathways and biological receptors, (iii) measured and (or) modelled contaminant exposure to benthic receptors and trophic transfer of contaminants to upper trophic level receptors, (iv) whole-sediment laboratory toxicity tests using benthic invertebrates and fish, and (v) field studies assessing possible intermediate or long-term effects on aquatic biota at the population and community levels. The ecological risk related to the contaminated sediment site was assessed using multiple lines of evidence and a weight-of-evidence approach. Despite concentrations of anthropogenic radionuclides and mercury above screening levels in Ottawa River sediments near CRL, the laboratory toxicity tests, radiological dose and mercury bioaccumulation modelling, and biological surveys of benthic invertebrates and fish indicated no significant adverse effects. Ecological risk to Ottawa River benthic invertebrates, fish, fish-eating birds and mammals from historical sediment contamination near CRL is low-to-negligible, and levels of risk will continue to decline as sediment-bound radionuclides decay and contamination is buried by new sediment.

APPLICATION OF THE ADVANCED ATMOSPHERIC PLUME PROFILER TO CURRENT CHALK RIVER LABORATORIES MONITORING SYSTEMS

The Advanced Atmospheric Plume Profiler (AAPP) was used to model emissions from facilities at Canadian Nuclear Laboratories (CNL, formerly Atomic Energy of Canada Limited). The model results were found to compare well with results from the current atmospheric monitoring program at the Chalk River Laboratories (CRL). The AAPP is a dispersion model designed and developed by CNL to model multiple emission sources from CRL operations. The AAPP used in conjunction with in-situ sampling can also estimate emissions from sources that are difficult to access or directly measure.

Operational Characterization of a Combined Electrolysis Catalytic Exchange Process

Many current CECE systems, which are used to extract harmful tritium from heavy water nuclear reactors, operate with inefficient alkaline electrolyzers that contain dangerous caustic chemicals. Thus the Hydrogen Isotope Branch at Chalk River Laboratories developed and integrated a safer and more efficient PEM electrolyzer to replace the alkaline electrolyzer. In this research, a bench-scale CECE system with a PEM type electrolyzer at Chalk River Laboratories was tested at LPCE column temperatures of 20°C, 40°C and 60°C to determine baseline operational parameters and conditions for optimal isotopic exchange. Increased operational temperature led to greater isotopic exchange across the PEM electrolyzer but not the LPCE column, an irregularity likely caused by an insufficient amount of catalyst in the column. Increased LPCE temperature also led to a decrease in overall system flow stability. Finally, the PEM electrolyzer voltage exhibited an unusual sharp rise throughout testing, indicating the membrane's susceptibility to damage if used without proper conditioning. Research conclusions will be taken into consideration in setting up a new bench-scale CECE process that more accurately models tritium extraction using a PEM electrolyzer.

DEVELOPMENT OF VERY LOW-LEVEL RADIOACTIVE WASTE SEQUESTRATION PROCESS CRITERIA

Segregating radioactive waste at the source and reclassifying radioactive waste to lower waste classes are the key activities to reduce the environmental footprint and long-term liability. In the Canadian Standards Association’s radioactive waste classification system, there are 2 sub-classes within low-level radioactive waste: very short-lived radioactive waste and very low-level radioactive waste (VLLW). VLLW has a low hazard potential but is above the Canadian unconditional clearance criteria as set out in Schedule 2 of Nuclear Substances and Devices Regulations. Long-term waste management facilities for VLLW do not require a high degree of containment and isolation. In general, a relatively low-cost near-surface facility with limited regulatory control is suitable for VLLW. At Canadian Nuclear Laboratories’ Chalk River Laboratories site an initiative, VLLW Sequestration, was implemented in 2013 to set aside potential VLLW for temporary storage and to be later dispositioned in the planned VLLW facility. As of May 2015, a total of 236 m3 resulting in approximately $1.1 million in total savings have been sequestered. One of the main hurdles in implementing VLLW Sequestration is the development of process criteria. Waste Acceptance Criteria (WAC) are used as a guide or as requirements for determining whether waste is accepted by the waste management facility. Establishment of the process criteria ensures that segregated waste materials have a high likelihood to meet the VLLW WAC and be accepted into the planned VLLW facility. This paper outlines the challenges and various factors which were considered in the development of interim process criteria.

PRELIMINARY METHODOLOGY FOR THE ANALYSIS OF THE NATIONAL RESEARCH UNIVERSAL REACTOR USING INTEGRATED SEVERE ACCIDENT MODELLING CODES

The National Research Universal (NRU) Reactor is a multi-purpose research reactor located at Atomic Energy of Canada Limited (AECL) Chalk River Laboratories. The severe accident case for the NRU has been explored through deterministic and probabilistic safety analysis (PSA) including multi-level PSAs that detail the progression and consequences of a severe accident in the NRU. These previous calculations lack the interconnected and comprehensive features of a full severe accident modelling code that is now the standard for severe accident analysis of power reactors. It was of interest within AECL to evaluate modern severe accident modelling codes to the NRU reactor case to enhance the understanding of accident progression and predict the system damage and radiation release consequences of a severe accident, which is a very low probability event. The NRU is smaller and operates at a lower power than the large scale power reactors (e.g., pressurized heavy water reactors, pressurized water reactors, and boiling water reactors) that these codes were designed to analyze. Additionally, the NRU has a unique design different from the power reactors and several features relevant to severe accidents including filtered venting, large passive heat sinks, and a dispersion fuel design of uranium-silicide in an aluminum matrix. The major severe accident analysis codes available to AECL and their applicability to the NRU are explored in this paper. In addition, a preliminary strategy for employing the most applicable codes to the NRU for the purposes of severe accident modelling is proposed.

OBT analysis method using polyethylene beads for limited quantities of animal tissue

This study presents a polyethylene beads method for OBT determination in animal tissues and animal products for cases where the amount of water recovered by combustion is limited by sample size or quantity. In the method, the amount of water recovered after combustion is enhanced by adding tritium-free polyethylene beads to the sample prior to combustion in an oxygen bomb. The method reduces process time by allowing the combustion water to be easily collected with a pipette. Sufficient water recovery was achieved using the polyethylene beads method when 2 g of dry animal tissue or animal product were combusted with 2 g of polyethylene beads. Correction factors, which account for the dilution due to the combustion water of the beads, are provided for beef, chicken, pork, fish and clams, as well as egg, milk and cheese. The method was tested by comparing its OBT results with those of the conventional method using animal samples collected on the Chalk River Laboratories (CRL) site. The results determined that the polyethylene beads method added no more than 25% uncertainty when appropriate correction factors are used.

Production of Highly Tritiated Water for Tritium Exposure Studies

From inception to completion, this paper provides a brief description of the design and processes used in the production and dispensing of highly tritiated water in the Tritium Facility at Chalk River Laboratories.

Regional transport of radioxenon released from the Chalk River Laboratories medical isotope facility

An examination of proposed sampling sites near Chalk River Laboratories in Ontario, Canada is performed by considering the regional transport of radioxenon using atmospheric dispersion modeling. The local geography is considered, as are the local meteorological conditions during the summer months. In particular the impacts of predicted conditions on the imprinting of atmospheric radioxenon into the subsurface are considered and weighed against site proximity, geography, and geology.

Study on Specifics of Forced-Convective Heat Transfer in Supercritical Carbon Dioxide

The appropriate description of heat transfer to coolants at the supercritical state is limited by the current understanding. Thus, this poses one of the main challenges in the development of supercritical-fluids applications for Generation-IV reactors. Since the thermodynamic critical point of water is much higher than that of carbon dioxide (CO2), it is more affordable to run heat-transfer experiments in supercritical CO2. The data for supercritical CO2 can be later scaled and used for supercritical water-based reactor designs. The objective of this paper is, therefore, to discuss the basis for comparison of relatively recent experimental data on supercritical CO2 obtained at the facilities of the Korea Atomic Energy Research Institute (KAERI) and Chalk River Laboratories (CRL) of the Atomic Energy of Canada Limited (AECL). Based on the available instrumental error, a thorough analysis of experimental errors in wall- and bulk-fluid temperatures and heat transfer coefficient was conducted. A revised heat-transfer correlation for the CRL data is presented. A dimensional criterion for the onset of the deteriorated heat transfer in the form of a linear relation between heat flux and mass flux is proposed. A preliminary heat-transfer correlation for the joint CRL and KAERI datasets is presented.

ICONE23-2018 INNOVATIVE APPROACH TO CORRELATE HEAT-TRANSFER DATA TO SUPECRITICAL CARBON DIOXIDE FLOWING UPWARD IN A BARE TUBE

Existing literature on problems of heat transfer to fluids at supercritical pressures distinguishes three heat-transfer regimes: 1) Deteriorated, 2) normal, and 3) enhanced. Conventional approach to correlate forced-convective heat transfer to supercritical fluids is applied to the normal and enhanced heat-transfer regimes. Although, there were recent attempts to correlate data for the deteriorated heat-transfer regime at mixed convection, currently there are no heat transfer correlations for DHT occurring at pure forced convection at high heat fluxes. Thus, an innovative approach was developed to correlate data without distinguishing heat transfer regimes. The approach is discussed in this paper. Using this approach, the heat transfer data to supercritical CO2 in forced convection regime, which were obtained at MR-1 Loop at Chalk River Laboratories, were correlated with an RMS of approximately 10% (corresponds to approximately 20% spread based on the 2σ-level). This result is twice less than that previously obtained at the University of Ontario Institute of Technology. The paper covers the following major topics: thermal properties of supercritical fluids, specifics of heat transfer to fluids at supercritical state, overview of existing types of correlations, conventional methodology for the development of heat transfer correlations, and innovative methodology for the development of heat transfer correlations.

Development and testing of the FAST fuel performance code: Transient conditions (Part 2)

This paper documents the extension of the Fuel And Sheath modeling Tool (FAST) for modeling transient conditions and presents a proof of concept validation exercise. This validation compares the predictions of FAST and ELESTRES/ELOCA fuel performance codes against experimental measurements from a simulated loss of coolant test conducted at Chalk River Laboratories. The comparison includes in reactor measurements of fuel temperature and internal gas pressure along with post irradiation (hot-cell) measurements of cladding deformation and oxidation. The results of this comparison show that the single pellet version of the FAST code was insufficient to fully account for strong axial dependence along an element. This was addressed by modifying the FAST code geometry to allow an arbitrary number of pellets in the fuel-stack. This full element version demonstrated improved agreement with measured cladding deformation, including circumferential ridging effects.

Bayesian Inference for Source Reconstruction: A Real-World Application.

This paper applies a Bayesian probabilistic inferential methodology for the reconstruction of the location and emission rate from an actual contaminant source (emission from the Chalk River Laboratories medical isotope production facility) using a small number of activity concentration measurements of a noble gas (Xenon-133) obtained from three stations that form part of the International Monitoring System radionuclide network. The sampling of the resulting posterior distribution of the source parameters is undertaken using a very efficient Markov chain Monte Carlo technique that utilizes a multiple-try differential evolution adaptive Metropolis algorithm with an archive of past states. It is shown that the principal difficulty in the reconstruction lay in the correct specification of the model errors (both scale and structure) for use in the Bayesian inferential methodology. In this context, two different measurement models for incorporation of the model error of the predicted concentrations are considered. The performance of both of these measurement models with respect to their accuracy and precision in the recovery of the source parameters is compared and contrasted.

Spatial analysis of Carbon-14 dynamics in a wetland ecosystem (Duke Swamp, Chalk River Laboratories, Canada)

A detailed survey was conducted to quantify the spatial distribution of 14C in Sphagnum moss and underlying soil collected in Duke Swamp. This wetland environment receives 14C via groundwater pathways from a historic radioactive Waste Management Area (WMA) on Atomic Energy Canada Limited (AECL)'s Chalk River Laboratories (CRL) site. Trends in 14C specific activities were evaluated with distance from the sampling location with the maximum 14C specific activity (DSS-35), which was situated adjacent to the WMA and close to an area of groundwater discharge. Based on a spatial evaluation of the data, an east-to-west 14C gradient was found, due to the influence of the WMA on 14C specific activities in the swamp. In addition, it was possible to identify two groups of sites, each showing significant exponential declines with distance from the groundwater source area. One of the groups showed relatively more elevated 14C specific activities at a given distance from source, likely due to their proximity to the WMA, the location of the sub-surface plume originating from the WMA, the presence of marsh and swamp habitat types, which facilitated 14C transport to the atmosphere, and possibly, 14C air dispersion patterns along the eastern edge of the swamp. The other group, which had lower 14C specific activities at a given distance from the groundwater source area, included locations that were more distant from the WMA and the sub-surface plume, and contained fen habitat, which is known to act as barrier to groundwater flow. The findings suggest that proximity to source, groundwater flow patterns and habitat physical characteristics can play an important role in the dynamics of 14C being carried by discharging groundwater into terrestrial and wetland environments.

THE DEEP RIVER SCIENCE ACADEMY: A UNIQUE AND INNOVATIVE PROGRAM FOR ENGAGING STUDENTS IN SCIENCE

For 28 years, the Deep River Science Academy (DRSA) has been offering high school students the opportunity to engage in the excitement and challenge of professional scientific research to help nurture their passion for science and to provide them with the experience and the knowledge to make informed decisions regarding possible future careers in the fields of science, technology, engineering, and mathematics (STEM). The venue for the DRSA program has been a six-week summer science camp where students, working in pairs under the guidance of a university undergraduate tutor, contribute directly to an on-going research program under the supervision of a professional scientist or engineer. This concept has been expanded in recent years to reach students in classrooms year round by engaging students via the internet over a 12-week term in a series of interactive teaching sessions based on an on-going research project. Although the research projects for the summer program are offered primarily from the laboratories of Atomic Energy of Canada Limited at its Chalk River Laboratories site, projects for the year-round program can be based, in principle, in laboratories at universities and other research institutes located anywhere in Canada. This paper will describe the program in more detail using examples illustrating how the students become engaged in the research and the sorts of contributions they have been able to make over the years. The impact of the program on the students and the degree to which the DRSA has been able to meet its objective of encouraging students to choose careers in the fields of STEM and equipping them with the skills and experience to be successful will be assessed based on feedback from the students themselves. Finally, we will examine the program in the context of how well it helps to address the challenges faced by educators today in meeting the demands of students in a world where the internet provides instant access to information.

HT to HTO conversion and field experiments near Darlington Nuclear Power Generating Station (DNPGS) site

The Canadian input parameters related to tritiated hydrogen gas (HT) used in tritium dose models are currently based on experiments performed at the Chalk River Laboratories (CRL) site in 1986, 1987 and 1994. There is uncertainty in how well other sites experiencing atmospheric HT releases are represented by these data. In order to address this uncertainty, HT to HTO conversion factors were evaluated at different locations near the Darlington Nuclear Power Generating Station (DNPGS) site using various experimental approaches. These were D2 gas exposure chamber experiments, atmospheric tritium measurements, and HTO and OBT measurements in vegetation and soil. In addition to these field experiments, chamber experiments were conducted using HT gas on field soil samples. The suggested Canadian input parameters for atmospheric tritium releases estimate the total fraction of HT oxidized in air and in soil, at the site, to be up to a maximum of 2.4%. Based on the more limited data obtained near DNPGS in early spring, this fraction would likely be closer to 0.5%. The result suggests that current parameters provide a conservative estimate for the DNPGS site.

OBT/HTO ratio in agricultural produce subject to routine atmospheric releases of tritium

The mean expected value of the OBT/HTO ratio (i.e. generic ratio) is derived in this study on the joint basis of a long-term study conducted at Atomic Energy of Canada Limited (AECL)'s Chalk River Laboratories (CRL), model simulations targeted at filling gaps in a yet incomplete timeline of CRL measurements and a reference dataset comprised of numerous experiments reported in the literature. Cultivar variability and disparity in site-specific settings are covered by the reference dataset. Dynamical variability caused by meteorology has been a specific target of the long-term experimental campaign at CRL, where the former two types of variability were eliminated. The distribution of OBT/HTO ratios observed at CRL appears to be a fairly good match to the distribution of OBT/HTO ratios from the literature. This implies that dynamical variability appears important in both cases. Dynamics of atmospheric HTO at CRL is comprised of a sequence of episodes of atmospheric HTO uptake and re-emission of plant HTO. The OBT/HTO ratio appears sensitive to the proportion of the duration of these two episodes: the lesser the frequency (and duration) of plume arrivals, the higher the expected mean OBT/HTO ratio. With the plume arrival frequency defined by the typical wind rose, one would encounter a mean OBT/HTO ratio close to 2. It is important to note that this number is seen both in the reference dataset, and in the continuous timeline of HTO and OBT reconstructed from CRL observations by dynamical interpolation (modelling). Many datasets (including that of CRL) targeted at the OBT/HTO ratio are biased high compared to the suggested number. This could be explained by scarce measurements of the low OBT/HTO ratios in the short phase of uptake of atmospheric HTO by the plant.