ULTRA-TRACE DETERMINATION OF NEPTUNIUM-237 AND PLUTONIUM ISOTOPES IN URINE SAMPLES BY COMPACT ACCELERATOR MASS SPECTROMETRY

Ultra-trace analysis of actinides, such as Pu isotopes and 237Np, in bioassay samples is often needed for radiation protection programs at nuclear facilities. Accelerator mass spectrometry (AMS), particularly the compact ETH Zurich system “Tandy”, has evolved over the years as one of the most sensitive, selective, and robust techniques for actinide analysis. Employment of the AMS technique can reduce the demands on sample preparation chemistry and increase sample analysis throughput, due to very low instrumental detection limit, high rejection of interferences, and low susceptibility to adverse sample matrices. Initial research and development tests were performed to explore and demonstrate the analytical capability of AMS for Pu and Np urine bioassay. In this study, urine samples spiked with femtogram levels of Np and Pu isotopes were prepared and measured using compact ETH AMS system and the results showed excellent analytical capability for measuring Np and Pu isotopes at femtogram/litre levels in urine.

NON-DESTRUCTIVE EXAMINATION USING NEUTRONS: A NUCLEAR WASTE AND ORPHANED SOURCE CHARACTERIZATION CASE STUDY APPLICABLE TO NUCLEAR FORENSICS

Found unknown radioactive material is often contained in a package so the chemical and physical form of the material itself is unknown, and the detail of the packaging is likewise unknown. Together, these present a significant risk on how to handle the package for destructive examination of its contents. Whether of nefarious origin or the result of less stringent practices of yesteryear the material needs to be properly identified and characterized for appropriate disposition. Results of neutron imaging, neutron diffraction, and delayed neutron analysis as applied to an examination of sealed capsules containing unknown radioactive materials are presented. The results demonstrate that neutron-based non-destructive examination techniques can be employed for inspecting encapsulated radioactive samples to identify the materials, to elucidate the internal physical structure of the radioactive material and encapsulation, and to estimate the mass of fissile and fissionable materials within. This characterization of orphaned radioactive special nuclear material illustrates the potential for these techniques in nuclear forensics investigations.

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.

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.

SHORT-TERM STORAGE CONSIDERATIONS FOR SPENT PLUTONIUM–THORIUM FUEL BUNDLES

To support the development of advanced pressurized heavy water reactor (PHWR) fuel cycles, it is necessary to study short-term storage solutions for spent reactor fuel. In this paper, some representational criticality safety and shielding assessments are presented for a particular PHWR plutonium–thorium based fuel bundle concept in a hypothetical aboveground dry storage module. The criticality assessment found that the important parameters for the storage design are neutron absorber content and fuel composition, particularly in light of the high sensitivity of code results to plutonium. The shielding assessment showed that the shielding as presented in the paper would need to be redesigned to provide greater gamma attenuation. These findings can be used to aid in designing fuel storage facilities.

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.

SITE SELECTION FOR CANADA’S NATIONAL REPOSITORY FOR USED NUCLEAR FUEL

In 2007, the Government of Canada selected Adaptive Phased Management as Canada’s plan for the long-term management of Canada’s used nuclear fuel. The approach provides for containment and isolation of the material in a deep geological repository at a safe site with an informed and willing host. The Nuclear Waste Management Organization is tasked through federal legislation with selecting the site and developing and managing all aspects of the plan. In May 2010, the organization published and initiated the site selection process that serves as a road map for decision making on the location for the deep geological repository. It continues to lead the site selection process for the repository and an associated Centre of Expertise. The screening process is advancing and, from an initial starting point of 22 communities expressing interest in learning about the project; as of September 2015, 9 communities are the focus of more detailed technical and community well-being studies. Preliminary Assessments, the third step in the 9-step site selection process are underway in these communities. The Assessments involve preliminary technical and social desktop and field assessments, engagement activities within and beyond each interested community, and involvement of Indigenous peoples and nearby municipalities in the planning and conduct of the work. This paper provides an update on the advancement of the site selection process. It describes the nature of the technical and social studies being conducted at this phase of work, including the progressively more detailed field studies that are the focus of technical work at the current stage, the approach to engagement and collaboration with communities to direct these studies, and the work underway to ensure the framework used for this assessment and engagement includes the range of priorities and perspectives of First Nations and Métis peoples and communities in the broader area.

OPTIMIZATION AND VALIDATION OF A CHEMICAL PROCESS FOR URANIUM, MERCURY AND CESIUM LEACHING FROM CEMENTED RADIOACTIVE WASTES

Canadian Nuclear Laboratories (CNL) is developing a treatment and long-term management strategy for a legacy cemented radioactive waste that contains uranium, mercury, and fission products. Extracting the uranium would be advantageous for decreasing the waste classification and reducing the cost of long-term management. The chemical leachability of 3 key elements (U, Hg, and Cs) from a surrogate cemented waste (SCW) was studied with several lixiviants. The results showed that the most promising approach to leach and recover U, Hg, and Cs is the direct leaching of the SCW with H2SO4 in strong saline media. Operating parameters such as particle size, temperature, pulp density, leaching time, acid and salt concentrations, number of leaching/washing steps, etc. were optimized to improve key elements solubilization. Sulfuric leaching in saline media of a SCW (U5) containing 1182 ppm of U, 1598 ppm of Hg, and 7.9 ppm of Cs in the optimized conditions allows key elements solubilisation of 98.5 ± 0.4%, 96.6 ± 0.1%, and 93.8 ± 1.1% of U, Hg, and Cs, respectively. This solubilization process was then applied in triplicate to 7 other SCWs prepared with different cements, liquid ratios, and at different aging times and temperatures. Concentrated sulfuric acid is added to the slurry until the pH is about 2, which causes the complete degradation of cement and the formation of CaSO4. Sulfuric acid is particularly useful because it produces a leachate that is amenable to conventional ion exchange technology for the separation and recovery of uranium.

ASSESSMENT OF THE EFFECT OF WATER QUALITY ON COPPER TOXICITY INHYALELLA AZTECA

The objective of this study was to test the hypothesis that when standard artificial media 5-salt culture water (SAM-5S) is used to test sediment toxicity of much lower ionic-strength aquatic ecosystems, the resulting toxicity estimates are lower than if the tests had been conducted in water of comparable ionic strength. Results showed that this concern was unfounded for testing of copper toxicity to Hyalella azteca (H. azteca) in Ottawa River water. Sediment testing is often conducted using a standard water that is prepared in the laboratory. However, this water may have an ionic strength that is different than local water bodies. It follows that laboratory results using the standard water may be unrepresentative. A study was undertaken to assess the copper tolerance of 2 strains of H. azteca in SAM-5S, diluted SAM-5S (similar in electrical conductivity to Ottawa River water), and Ottawa River water. Acute (96 h) copper toxicity tests were conducted with 9–16 day-old H. azteca. For a given water type, the 2 strains of H. azteca yielded comparable responses to copper. The highest copper tolerance was found in Ottawa River water (closely followed by SAM-5S), whereas the lowest copper tolerance was found in diluted SAM-5S. Our results suggest that sediment toxicity is not lowered by the higher ionic strength of SAM-5S and that sediment toxicity tests of Ottawa River sediments, conducted with SAM-5S, can be used to estimate the in situ toxicity of the sediments.