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Research Support Summaries 2023-2024

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RSP-222.3 - Exposure to Radon Progeny and Mortality from Non-Respiratory Cancers among Newfoundland Fluorspar Miners between 1950 and 2016

Previous reports have documented increased risks of lung cancer from radon progeny – the radioactive elements produced by radon when it decays – among Newfoundland fluorspar miners. However, to date, there has been no internal cohort analysis to investigate whether radon progeny increases the risks of mortality from other cancers.

Associations between cumulative exposure to radon progeny and cancer mortality (excluding lung cancer) were evaluated for a cohort of 2055 miners. Mortality was followed up from 1950–2016. Individual-level radon progeny exposure in working level months (WLM) – a unit which describes one month’s worth of exposure to the maximum allowable concentration of radon gas – were determined for each miner during their employment. For those cancers with at least ten deaths, statistical models were used to estimate excess relative risks. Cancer site specific relative risks were derived for more common cancers, specifically for stomach, colorectal cancer, and all cancers (excluding lung cancer). Relative risks were adjusted for age, period effects, and average number of cigarettes smoked.

In total, 495 cancer deaths, excluding lung cancer, were identified during the 66-year follow up period. The relative risk of cancer mortality (excluding lung) was 2.33 (95% CI: 1.851, 2.927) among underground miners with a cumulative exposure of ≥ 50 WLM when compared to those who were unexposed. There were no statistically significant increases in risk for any of the other specific cancer sites examined, however, the analysis is constrained by a small sample size.

RSP-675.1 - Development of Empirical correlation Models for Hydrogen Production due to Steel Oxidation in CANDU Feeder and End fitting Materials

The reaction of steam with six steels and ductile iron used in Canada Deuterium Uranium (CANDU) reactors were evaluated at temperatures from 900 K to 1600 K. Sample weight gain with time was measured by Thermogravimetric Analysis (TGA) at 900 K. At higher temperatures, the generation of hydrogen, carbon monoxide and carbon dioxide were measured directly using the Ultra High Temperature (UHT) test rig as well as the change in mass at the end of the steam exposure. The steam reactions enabled prompt hydrogen generation such that a representative Severe Accident scenario resulting in a Loss of Coolant Accident (LOCA) could be modeled.

Hydrogen generation as a function of time and temperature was modeled assuming parabolic kinetics. At temperatures of 1300 K and above and times later than 30 minutes, the data conformed well to expected kinetics of hydrogen generation rates and consistent activation energies were obtained over the 1300 K to 1600 K range, consistent with increasing diffusion through a growing oxide layer being the reaction limiting step. X-ray diffraction analysis determined that FeO, and Fe3O4 were the dominant oxide types for all the tested materials. At lower temperatures, the kinetics were more material dependent, suggesting that the presence of chromium and the development of chromium-containing oxides played an important role.

The results of this study were consistent with studies performed by the Canadian Nuclear Laboratories.  In addition, the parabolic behaviour of steam oxidation of the metals was true for zirconium alloy corrosion using well-known correlations in literature.

RSP-736.1 - Conversion factor determination of radon and external gamma radiation exposures and calculation of organ specific doses for Port Hope radium and uranium refining and processing workers based on the iPAUW harmonized dosimetry protocol

This project provides doses to specific organs for an epidemiological study of 2,995 uranium workers from the Port Hope Conversion Facility (PHCF) from 1930–1999, who never worked in mines. The PHCF’s raw products varied by period, from the ore originally being processed at the site, followed by uranium either being uranium concentrate (e.g., yellow cake) or refined. The type of job activities also changed throughout the period, as well as radiation measurement practices, such as increased monitoring and safety protocols. Products ranged from radium to various forms of uranium, largely for fuel purposes.

Dose conversion factors (DCFs) allow organ-specific radiation doses to be calculated from a total amount of radiation absorbed. This study used the approach to harmonize the DCFs, proposed by the international Pooled Analysis of Uranium Workers (PAUW), in order to address the differences in exposure within the facility and to be consistent with the international study. Data available included personal information, years worked, and exposure to gamma radiation and radon gas on a yearly basis. Staff who provided the exposure inputs for the 2013 epidemiology study (1) considered the type of raw product (ore, uranium concentrate, refined) and the type of measurements to determine the harmonized DCFs. This is Part 1 of the study that estimates doses from the gamma and radon. Part 2 will estimate internal doses arising from the inhalation of uranium.

The exposure rates showed substantial decreases over the period as the exposure to ore decreased with process improvements. Many of the workers in this study had no reportable exposure. The exposures were multiplied by the harmonized DCF to estimate yearly organ doses. Overall, 90% of the dose is from gamma radiation with 10% of the dose from radon: most of the dose, more than 90%, was received prior to 1951.

  • Zablotska LB, Lane RSD, Frost SE. Mortality (1950-1999) and cancer incidence (1969-1999) of workers in the Port Hope cohort study exposed to a unique combination of radium, uranium and γ-ray doses. BMJ Open. 2013;3(2).

RSP-763.1 - Methodology for Developing Power Reactor Regulatory Program (PRRP) Risk Significance Insights

Regulatory inspections are carried out by teams of inspectors with relevant educational backgrounds and training, who record their collective observations and determine risk findings in accordance with licence conditions and regulatory requirements. Inspectors may draw on their expertise and experience to supplement their familiarity with written requirements, as they interpret observations and estimate their risk significance in the context of CNSC regulatory priorities.

The purpose of the Artificial Intelligence / Machine Learning methodology project is to design a methodology for the later development of an AI/ML system that can model the reasoning processes used by inspectors to determine the risk significance of non-compliant observations in inspections of nuclear power plants. This system could provide insights into effective decision making that can further improve decision making guidance. Such insights may include the implicit and explicit reasoning processes by which inspectors assign risk rankings, as well as particular factors, or combinations of factors, that may be associated with a non-compliant finding and a particular risk rating.

This study reviews the literature on the types of machine learning technologies, outlines an approach for designing a feasible AI/ML classification system as well as a possible implementation strategy. All of this is in the light of information obtained from CNSC guidelines and interviews with inspectors. Five recommendations are made to bridge existing gaps in documentation and establish the foundation for a successful integration of AI/ML. These include standardizing terminology and documentation practices, enhancing documentation content for AI/ML suitability, identifying skills and resources necessary for AI/ML implementation, attempting a proof of concept for different approaches, and establishing feedback mechanisms.

RSP-765.1 - Load Carrying Capacities of Small-Diameter Pipe Bends Under Internal Pressure: Analytical and Computational Predictions

The performance and embedded conservatism of common modeling approaches used for predicting load carrying capacities were evaluated for feeder bends in CANDU reactors. Comprehensive analyses were conducted using both an analytical approach and detailed finite element modelling with commercial code ABAQUS. Small diameter feeder bends, with and without local wall thinning, under loading by internal pressure were investigated. The adopted modelling approach incorporated variability in feeder bend geometry and the characterization of feeder material properties.

The results obtained indicate that load carrying capacities of feeder bends, either with or without local wall thinning but characterized with uniform wall thickness and single parameter material strength, are conservatively predicted with analytical models in principle based on limit load method adopting small strain approach. However, detailed finite element modelling is necessary for obtaining more accurate predictions of plastic instability pressure for feeder bends with local wall thinning.

The reported investigation provides technical insights into modelling approaches used for predicting load carrying capacities of feeders under internal pressure. In addition, it has explored embedded conservatism while recognizing the existence of involved uncertainties. The results obtained emphasize the importance of detailed characterization of feeder wall thickness and feeder material strength in such engineering predictions.

RSP-768.1 - The Social Component of Deep Geologic Repository Safety: Public Trust and the Canadian Nuclear Regulator

From the siting stage onward, the development of a deep geologic repository (DGR) for high-level nuclear waste is a long and complicated process at the intersection of technical and social issues. This challenges the traditional social-technical divisions common in nuclear regulation. Public engagement is a key component for DGR development, and directly impacts and is impacted by trust in the regulator, confidence in the regulatory process, and public perceptions of risk and safety. This report examines the process of public engagement carried out by the regulator and considered how the licensing process for a DGR might impact public trust in the nuclear regulator. This report contains recommendations for CNSC developed as a result of our research and endeavours to provide a context based on theories in social science studies for those recommendations. This report in informed by 34 in-depth interviews with CNSC staff, members of the public, public interest groups, and impacted Indigenous nations, as well as foreign experts at nuclear regulatory agencies who have experience with licensing deep geologic repositories for high-level waste. It also contains information gained from in-person engagement events, public hearings, relevant hearing transcripts, and a review of existing literature. In light these findings, the CNSC should consider how public engagement directly impacts nuclear regulation, improve public accessibility to the regulatory process, and improve transparency in decision-making. The CNSC should also consider how its organizational structure is negatively affecting the success of public engagement and how a cohesive strategy could bridge existing gaps. The process of establishing a DGR affords a unique opportunity to either lose or gain public trust and that opportunity should be prioritised within the institution.

RSP-769.2 - GE Hitachi BWRX-300 Executive Training Seminar (PSPC)

Ontario Power Generation has applied to construct one small modular reactor, the BWRX-300 designed by GE Hitachi Nuclear Energy (GEH), at the existing Darlington Nuclear Generating Station.

In preparation for reviewing this small modular reactor, the CNSC contracted GEH to provide training for CNSC staff in leadership roles to become better prepared to review Ontario Power Generation’s application and to increase CSNC knowledge of boiling water reactors.

This training consisted of a 4-day course in San Jose, California in early 2023. It was held at the contractor’s location, where equipment for demonstration and mock-ups were available. The course covered:

  • Reactor Physics
  • Thermal hydraulics design
  • Accident mitigation
  • Means of shutdown
  • Emergency core cooling
  • Containment
  • Fuel Handling
  • Operating Economics

as they relate to boiling water reactors and the BWRX-300 in particular. This course provided CNSC staff with better awareness and understanding of boiling water reactors which will help inform future regulatory decisions.

RSP-771.1 - Geoscientific Considerations for a Deep Geological Repository in the Canadian Shield

Geoscientific information is central for understanding potential Deep geological repository (DGR) sites, and is required for demonstrations of long-term safety. The Revell batholith in the Canadian Shield of Ontario remains one of two potential candidate host rock types for a national deep geological repository (DGR) for Canada’s used nuclear fuel, in a site selection process being carried out by the Nuclear Waste Management Organization.

This project synthesizes existing information from Canadian, and other well-studied crystalline host rock DGR sites from Finland and Sweden, in the context of how geological information is being used to support evaluations of safety over geologically long time frames.

This report reviews the characteristics of crystalline rock settings in the Canadian and Fennoscandian shields as potential repository hosts. Selected DGR sites in Finland (Olkiluoto) and Sweden (Forsmark) underwent extensive characterization work over 20-years to develop comprehensive descriptive geosphere site models. Work on the Revell crystalline site is still preliminary, though it follows from previous studies at different Canadian Shield locations and could benefit from that earlier work.

RSP-784.1 - Canadian Archive of Women in STEM – oral history interviews and data entry

In 2023, the Canadian Nuclear Safety Commission funded a project lead by the University of Ottawa Library’s Archives and Special Collections for the Canadian Archive of Women in STEM initiative. This initiative aims to increase awareness and access to the historical record of the accomplishments of women in STEM in Canada. The project consisted of two parts. The first was improving and updating the [Canadian Archive of Women in STEM Portal], a database of information related to archival holdings held by Canadian memory institutions. The second was the production of a series of ten, 60- to 90-minute oral history interviews of prominent Canadian women in STEM. The subjects were:

  • Dr. Monique Frize, the first woman to graduate from the University of Ottawa with an engineering degree
  • Dr. Tyseer Aboulnasr, the second-ever female Dean of Engineering in Canada
  • Dr. Claire Deschenes, the first female professor of engineering at Laval University
  • Rumina Velshi, former President and CEO of the CNSC
  • Dr. Kim TallBear, the current Canada Research Chair in Indigenous Peoples, Technoscience, and Society
  • Dr Karen Messing, a geneticist and ergonomist specializing in women’s occupational health
  • Dr. Veronica Dahl, an Argentine Canadian computer-scientist who has been recognized as one of the 15 founders of the field of logic programming
  • Dr. Nikki Colodny, a medical practitioner who openly provided women with abortions in contravention of the Criminal Code
  • Dr. Louise Lafortune, an expert in STEM education who has studied the relationship between gender, science, and mathematics
  • Dr. Maydianne Andrade, co-founder of the Canadian Black Scientists Network (CBSN)

The two components of the project were completed in December 2023.

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