Chalk River Research Articles

A Novel In-Beam Delayed Neutron Counting Technique for Characterization of Special Nuclear Materials

A delayed neutron counting (DNC) system, where the sample to be analyzed remains stationary in a thermal neutron beam outside of the reactor, has been developed at the National Research Universal (NRU) reactor of the Canadian Nuclear Laboratories (CNL) at Chalk River. The new in-beam DNC is a novel approach for non-destructive characterization of special nuclear materials (SNM) that could enable identification and quantification of fissile isotopes within a large and shielded sample. Despite the orders of magnitude reduction in neutron flux, the in-beam DNC method can be as informative as the conventional in-core DNC for most cases while offering practical advantages and mitigated risk when dealing with large radioactive samples of unknown origin. This paper addresses (1) the qualification of in-beam DNC using a monochromatic thermal neutron beam in conjunction with a proven counting apparatus designed originally for in-core DNC, and (2) application of in-beam DNC to an examination of large sealed capsules containing unknown radioactive materials. Initial results showed that the in-beam DNC setup permits non-destructive analysis of bulky and gamma shielded samples. The method does not lend itself to trace analysis, and at best could only reveal the presence of a few milligrams of 235U via the assay of in-beam DNC total counts. Through analysis of DNC count rates, the technique could be used in combination with other neutron or gamma techniques to quantify isotopes present within samples.

Assessment of major causes: nuclear power plant disasters since 1950

Purpose This paper aims to investigate the major causes of the nuclear power plant (NPP) disasters since 1950, elucidates the commonalities between them and recommends strategies to minimize the risk of NPP disasters. Design/methodology/approach This paper analyzes facts from five case studies: Chernobyl disaster, USSR 1986; Fukushima Daiichi disaster, Japan 2011; Three Mile Island incident, USA 1979; Chalk River Accident, Canada 1952; and SL-1 Accident, USA 1961. A qualitative approach is adopted to compare and contrast the major reasons that led to the accidents, and consequent social and technological impacts of the disasters on environment, society, economy and nuclear industry are analyzed. Findings Although each of the nuclear accidents is unique in terms of its occurrence and impacts, this research study found some common causes behind the accidents. Faulty system design, equipment failure, inadequate safety and warning systems, violation of safety regulations, lack of training of the nuclear operators and ignorance from the operators and regulators side were found to be the major common causes behind the accidents. Originality/value This paper recommends some of the nuclear disaster risk reduction strategies in terms of “lessons learned from the past accidents”. The findings of the research paper would serve as an information tool for the nuclear professionals for informed decision-making and planning for proper preventive measures well in advance so that the mistakes which led to the occurrence of accidents in the past are not repeated in the future.

ONE-SIDED MUON TOMOGRAPHY—A PORTABLE METHOD FOR IMAGING CRITICAL INFRASTRUCTURE WITH A SINGLE MUON DETECTOR

High-energy muons generated from cosmic-ray particle showers have been shown to exhibit properties ideal for imaging the interior of large and dense structures. This paper explores the possibility of using a single portable muon detector in conjunction with image reconstruction methods used in nuclear medicine to reconstruct a 3-D image of the interior of critical infrastructure such as the Zero-Energy Deuterium (ZED-2) research reactor at Canadian Nuclear Laboratories’ Chalk River site. The ZED-2 reactor core and muon detector arrangement are modeled in GEANT4 and Monte Carlo measurements of the resultant muon throughput and angular distribution at several angles of rotation around the reactor are generated. Statistical analysis is then performed on these measurements based on the well-defined flux and angular distribution of muons expected near the surface of the earth. The results of this analysis are shown to produce reconstructed images of the spatial distribution of nuclear fuel within the core for ...

Changes in HTO and OBT activity concentrations in the Perch Lake aquatic ecosystem

Perch Lake, a small shallow shield lake located on the Chalk River Laboratories (CRL) site, contains elevated levels of tritium due to inputs from a nearby nuclear waste management area. The releases have been going on for many years but tritium levels in Perch Lake have been gradually decreasing since about year 2000. Lake water, sediments, aquatic plants, clams and fish were collected during the summer and fall of 2003 and 2013 at three locations in the lake. HTO activity concentrations were measured in all samples and OBT activity concentrations were measured in sediments, plants, clams and fish. In 2003, 2013, HTO activity concentrations in lake water were roughly uniform in time and space, except close to the shoreline where concentrations were fluctuating according to stream water and groundwater tritium levels in streams entering the lake. HTO activity concentrations of biota were similar to concentrations in lake water at the site where they were collected. OBT activity concentrations in biota were not always correlating with the lake water HTO levels. OBT to HTO ratios were found to be less than 1 for aquatic plants, around 1 for clams and fish and above 1 for birds reared on the shore of the lake.

The chalk hyporheic zone: a true ecotone?

This review summarises the main ecotonal properties of chalk hyporheic zone (CHZ), using a holistic approach on both structure and functionality of this habitat. The corroborated results suggest that the CHZ represents a typically shallow habitat (approx. 40–50 cm deep), with a homogenous distribution of both fauna and chemistry between heads and tails of riffles (putative down and, respectively, upwelling zones). Despite being groundwater fed, the CHZ is equally influenced by surface waters, chemically and biologically. However, despite its shallowness, the CHZ plays a very important role in nutrients (re)cycling and in the energy flux towards river ecosystems, fuelling benthic food webs with surface-derived macronutrients and subsurface chemosynthetic C. Although groundwater variation influences strongly the river flow during winter, the effects on interstitial fauna dynamic are limited, suggesting the active role of CHZ played in the stochastic events of down/upward migration of fauna across habitats. Overall, the CHZ represents a confined, but critical habitat in the structure and functionality of chalk river ecosystems and fulfils most properties of a true ecotone.

Distribution of radionuclides between atmosphere and ash during combustion of contaminated vegetation

A series of laboratory-scale combustion tests were conducted under well-controlled conditions to measure the release of 90Sr and 137Cs nuclides to the atmosphere (air) from combustion of vegetation and organic soil samples contaminated with radioactivity. These vegetation and soil samples were collected from a controlled contaminated forest area within the Canadian Nuclear Laboratories – Chalk River site. The combustion products including ash and smoke particulates, along with gaseous emissions, were collected and then analyzed for 137Cs and 90Sr concentrations by radiometric techniques. The experimental results reveal that the releases of 90Sr to the atmosphere (air) from combustion of vegetation are very low with most of the 90Sr activity remaining in ash residues, even at a temperature of 800 °C. The detailed combustion experiments with surface litter and twigs, alder twigs, alder leaves, and organic soil indicate that 0.5 ± 0.1%, 0.3 ± 0.1%, 0.9 ± 0.1%, and 0.3 ± 0.1% of 90Sr is released to the atmosphere (air), respectively. On the other hand, the releases of 137Cs are found to be highly dependent on the combustion temperature as well as the nature of vegetation. The releases of 137Cs obtained at 800 °C are 45 ± 7%, 77 ± 9%, 92 ± 5%, and 2.4 ± 0.5% for surface litter and twigs, alder twigs, alder leaves, and organic soil, respectively. The mechanism associated with the high release of 137Cs at a high temperature of 800 °C was explored.

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...

Trace levels of sewage effluent are sufficient to increase class 1 integron prevalence in freshwater biofilms without changing the core community

Most river systems are impacted by sewage effluent. It remains unclear if there is a lower threshold to the concentration of sewage effluent that can significantly change the structure of the microbial community and its mobile genetic elements in a natural river biofilm. We used novel in situ mesocosms to conduct replicated experiments to study how the addition of low-level concentrations of sewage effluent (nominally 2.5 ppm) affects river biofilms in two contrasting Chalk river systems, the Rivers Kennet and Lambourn (high/low sewage impact, respectively). 16S sequencing and qPCR showed that community composition was not significantly changed by the sewage effluent addition, but class 1 integron prevalence (Lambourn control 0.07% (SE ± 0.01), Lambourn sewage effluent 0.11% (SE ± 0.006), Kennet control 0.56% (SE ± 0.01), Kennet sewage effluent 1.28% (SE ± 0.16)) was significantly greater in the communities exposed to sewage effluent than in the control flumes (ANOVA, F = 5.11, p = 0.045) in both rivers. Furthermore, the difference in integron prevalence between the Kennet control (no sewage effluent addition) and Kennet sewage-treated samples was proportionally greater than the difference in prevalence between the Lambourn control and sewage-treated samples (ANOVA (interaction between treatment and river), F = 6.42, p = 0.028). Mechanisms that lead to such differences could include macronutrient/biofilm or phage/bacteria interactions. Our findings highlight the role that low-level exposure to complex polluting mixtures such as sewage effluent can play in the spread of antibiotic resistance genes. The results also highlight that certain conditions, such as macronutrient load, might accelerate spread of antibiotic resistance genes.

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.

Reactor shutdown threatens world’s medical-isotope supply

Canada’s Chalk River reactor, which makes large amounts of technetium-99m, will end production next month.

Hydrodynamic cavitation characteristics of an orifice system and its effects on CRUD-like SiC deposition

In a nuclear power plant, chalk river unidentified deposit (CRUD) is known as a deposit that is composed of corrosion and oxidation materials. It has a porous structure, which combines with boron that is injected into the coolant for controlling power levels. The buildup of corrosion products on the fuel cladding surface has proven to be particularly significant for both BWRs and PWRs. The high temperature of the cladding surface attracts impurities and chemical additives in the reactor coolant that deposit on the fuel rod surface in a process. The deposits on a fuel rod, known as CRUD, can be tenacious, insulative compounds capable of increasing the local clad temperature and accelerating clad corrosion—sometimes to the point of fuel failure.The deposition of CRUD on fuel cladding surfaces causes uneven heating of the reactor core. The situation is exacerbated by boron, which is added to the coolant to control power levels. However, boron becomes concentrated and is deposited within thick CRUD deposits. Ultrasonic mechanisms were developed but they have limitations for decontamination. In this experiment, a decontamination test was conducted using a sample sheet that was composed of SiC/water nanofluids. In addition, it was exposed to swirl flow and common flow for checking enhanced cavitation. It is measured by a pressure film, as shock pressure is associated with cavitation number. As a pressure film is wetted easily in water, it was injected into a holder. In the experiment, the maximum shock pressure was obtained during swirl flow at a low cavitation number. This indicates that pressure was concentrated on the pressure film. Consequently, cavitation can get rid of CRUD layers partially.

Quantitative phase analysis of challenging samples using neutron powder diffraction. Sample #4 from the CPD QPA round robin revisited

Quantitative phase analysis (QPA) using neutron powder diffraction more often than not involves non-ambient studies where no sample preparation is possible. The larger samples and penetration of neutrons versus X-rays makes neutron diffraction less susceptible to inhomogeneity and large grain sizes, but most well-characterized QPA standard samples do not have these characteristics. Sample #4 from the International Union of Crystallography Commission on Powder Diffraction QPA round robin was one such sample. Data were collected using the POWGEN time-of-flight (TOF) neutron powder diffractometer and analysed together with historical data from the C2 diffractometer at Chalk River. The presence of magnetic reflections from Fe3O4 (magnetite) in the sample was an additional consideration, and given the frequency at which iron-containing and other magnetic compounds are present during in-operando studies their possible impact on the accuracy of QPA is of interest. Additionally, scattering from thermal diffuse scattering in the high-Q region (<0.6 Å) accessible with TOF data could impact QPA results during least-squares because of the extreme peak overlaps present in this region. Refinement of POWGEN data was largely insensitive to the modification of longer d-spacing reflections by magnetic contributions, but the constant-wavelength data were adversely impacted if the magnetic structure was not included. A robust refinement weighting was found to be effective in reducing quantification errors using the constant-wavelength neutron data both where intensities from magnetic reflections were ignored and included. Results from the TOF data were very sensitive to inadequate modelling of the high-Q (low d-spacing) background using simple polynomials.

Draft Genome Sequence of a Thermophilic Cyanobacterium from the Family Oscillatoriales (Strain MTP1) from the Chalk River, Colorado

The draft genome (57.7% GC, 7,647,882 bp) of the novel thermophilic cyanobacterium MTP1 was determined by metagenomics of an enrichment culture. The genome shows that it is in the family Oscillatoriales and encodes multiple heavy metal resistances as well as the capacity to make exopolysaccharides.

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.

Characterization of crud deposited on fuel rods under HWC environment in Kuosheng Nuclear Power Plant

Under normal water chemistry conditions, the oxygen and hydrogen peroxide produced by water radiolysis in the coolant of boiling water reactors (BWRs) can lead to intergranular stress corrosion cracking in the constituent materials of plant components. This fact has led to the wide-scale adoption of hydrogen water chemistry (HWC) in the nuclear industry to counteract these effects. This study seeks to characterize the metallic composition and the surface properties of the constituent materials of plant components in order to determine their effects on the accumulation of chalk river unidentified deposits (crud) on fuel rods in the BWR Unit-1 of the Kuosheng Nuclear Power Plant in Taiwan. Inductively coupled plasma-atomic emission spectroscopy was used to calculate the concentrations of surface crud and gamma spectrometry was used to determine the radioactivity of the corrosion products, as well as their axial distribution across the surface of the fuel rods. X-ray diffraction analysis and scanning electron microscopy/energy-dispersive X-ray spectroscopy were used to identify the crystalline phase and morphology of the crud as irregular shapes and flakes. The amount of crud deposited during the fourth fuel cycle exceeded that of the third fuel cycle due to extended burn-up time. Our analytical results indicate that the implementation of HWC had no significant effect on the characteristics of subsequent crud.

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.

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.

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.