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Research Support Summaries 2022-2023

R656.2 - Licensing of safety critical software for nuclear reactors - Common position of international nuclear regulators and authorised technical support organisations

In Canada, regulatory document REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power Plants, is the Canadian Nuclear Safety Commission document focused on the regulation of the design of nuclear power plants. REGDOC-2.5.2 provides both requirements and guidance regarding design.  However, there is limited guidance regarding how to meet the requirements when computer-based systems are used to implement safety functions. In order to develop more comprehensive guidance for reviewing the safety critical software, CNSC joined the Regulator Task Force on Safety Critical Software with other regulators, including the major European regulators and US NRC.

A copy of the report can be downloaded here.

R691.2 - Natural analogues: Revisiting Cigar Lake

Used Nuclear Fuel (UNF) is considered to be high-level radioactive waste in Canada. The internationally recognized approach for disposal of UNF is a deep geological repository (DGR). The Nuclear Waste Management Organization is currently leading the process to select a UNF DGR site in Canada. As the regulator, the CNSC is engaging in research on the long-term safety of DGR’s and natural analogues.

UNF contains various long-lived radioactive isotopes that must be isolated and contained for an extended period of time, up to 1 million years. One of the most important radioactive isotopes present in these wastes is iodine-129 (129 I) due to its long half-life and high mobility.

Ensuring the long-term safety of a DGR is a regulatory requirement, this study was conducted by the University of Ottawa to measure the in-situ production of 129 I and determine its mobility within uranium deposit at Cigar Lake, a well-known natural analogue for a DGR.

Uranium ore bodies are helpful as natural analogues for studying the mobility of radionuclides in radioactive waste, including 129 I, which is the principle radioisotope of concern, over long periods in natural settings. Thus, the study selected Cigar Lake, located in Saskatchewan, Canada, as an analog for the DGR system due to the naturally occurring high uranium concentrations, the clay ap that mimics an engineered barrier and the high degree of characterization of the site as a natural analogue.

57 samples were collected from 9 boreholes in the Cigar Lake uranium deposit. Iodine was extracted from the rock samples via combustion and two isotopes analyzed using accelerator mass spectrometry (129I) and inductively coupled plasma mass spectrometry (127I). Both measurements and calculations were done to determine the in-situ production and migration of 129 I and to constrain the residence time of 129I in the Cigar Lake Natural Analogue site in order to provide the first empirical assessment of 129I mobility and residence time in a DGR natural analogue.

This work found that 129I produced in the ore body has migrated out of the system as 129I concentrations measured in the ore body were depleted relative the calculated secular equilibrium (the rate of production = the rate of loss) values and enriched outside of the ore zone showing 129I had been transported through the clay cap into the surrounding sandstone. Using the measured concentration of 129I, a mean residence time of 1 million years in the ore body was calculated, this result is far less than the minimum residence time of ~80 million years if the measured and calculated 129I were in secular equilibrium. This suggests that the clay halo overlying the ore body does not prevent 129I from diffusing out and does not constitute a significant barrier to its migration, which is counter to both the original hypothesis that 129I would be at secular equilibrium and previous studies of the Cigar Lake natural analogue that showed the clay cap was a barrier for the migration of uranium although these studies did not investigate the migration of 129I.

Nevertheless, this study suggests that a well-designed DGR, which includes a combination of natural and engineered barriers, could contain 129I for at least 1 million years, based on the ability of the Cigar Lake natural analogue to do so as a purely natural system.

R691.4 - Radionuclide transport in the arctic: quantifying the effects of glaciation on geological disposal projects

The science behind the safety of nuclear waste disposal in a Deep Geological Repository (DGR) derives from decades of research and technical assessment. In Canada, the Nuclear Waste Management Organization (NWMO) is in the process of selecting a site for the potential deep geological disposal of used nuclear fuel resulting from the operation of Canadian nuclear power plants. The NWMO plans to select one of the two sites by 2024, at which point the regulatory oversight process will begin.

Two sites remaining in the NWMO’s site selection process would be expected to be subject to future glacial events, based on the known geological history of Canada; the effect of glaciation on the future evolution of a Canadian DGR is an important aspect of CNSC’s regulatory research to prepare for a future licensing submission.

This research, conducted by the University of Manitoba, studied the Kiggavik uranium deposits in Nunavut, Canada. They are a series of high-latitude deposits that were glaciated multiple times in the Pleistocene. This project provided new insight on radionuclide migration over a large spatial and temporal scale.

This project identified key processes that influence radionuclide mobility, including estimates of the timing and duration of fluid events required to transport, concentrate, and modify radionuclides in the Canadian arctic.

The study also developed a new structural and alteration model of the study area, and a new interpretation of uranium deposit evolution, establishing relative and absolute chronologies of mineral formation.

This is a new Canada-relevant natural analogue for deep geological disposal representing a fractured, post-glacial eroded environment. The results of this study will be used by CNSC staff to develop and maintain independent scientific knowledge to support informed licensing decisions and to disseminate objective information to stakeholders.

R691.5 - Development of mathematical models of geomechanics of Cobourg Limestone and Lac du Bonnet granite based on microstructural characterization.

The Nuclear Waste Management Organization (NWMO) is currently in the process of selecting one among two sites in Ontario, South Bruce and Ignace, for the disposal of used nuclear fuel from Canadian nuclear power plants.  

At the South Bruce site, the potential host rock formation is the Cobourg limestone, a sedimentary rock formation dating back to the Ordovician period. The rock has high strength, low permeability and high sorption capacity, so that it would constitute an efficient barrier to radionuclide migration.

At the Ignace site, plutonic rock of the Revell batholith would be the potential host rock. Since geomechanical data from the Revell batholith was not available at the time this research project was conducted, the focus was on a similar formation, the Lac du Bonnet batholith. The latter is a late-tectonic granite in the western Superior Province of the Canadian Shield, which comprises several lithotectonic regions in northwestern Ontario and eastern Manitoba.

The purpose of this project is to formulate and numerically implement constitutive relations governing the hydro-mechanical response of the Cobourg limestone and Lac du Bonnet granite.

The main components of the project include:

  • Conducting an overview of basic trends in the hydro-mechanical behaviour of both types of rocks
  • The modelling of homogenous deformation as well as the onset and propagation of localized damage.
  • The formation of a continuum approach for the coupled hydro-mechanical analysis in the presence of discontinuities.
  • The verification of the performance of a constitutive law with embedded discontinuity approach in assessing the hydraulic properties and the coupled hydro-mechanical response of fractured crystalline rocks, such as Lac du Bonnet granite.

R719.2 - Federal Low Dose Radiation Program: An International Survey to Advance the Use of Adverse Outcome Pathway (AOPs)

Low-level radiation risks have important environmental and human health implications. For this reason, it is important to understand scientific data from multiple types of studies.

The Adverse Outcome Pathway (AOP) framework has been demonstrated to be an effective means to consolidate and structure multiple lines of evidence, spanning many levels of biological organization. The AOP framework facilitates access to and understanding of complex data for risk assessors and decision-makers involved in setting guidelines for the protection of human health and the environment.

The objective of the study was to conduct a ‘key questions’ exercise (a type of horizon scan) to identify 25 important research questions that could be supported by the AOP framework. If answered, these questions could improve the description of the radiation dose-response relationship for low dose and low dose-rate exposures as well as reduce uncertainties in estimating the risk of developing adverse health outcomes following such exposures.

The study was comprised of three main components:

  • An open solicitation phase requesting radiation researchers and regulators across the globe to submit candidate questions for subsequent consideration by members of the project Steering Committee (SC);
  • A collaborative SC review and, during a virtual 2-day workshop, refinement of candidate question submissions, which narrowed the list to 25 important research questions; and
  • An international survey of researchers and regulators, in which each respondent was asked to rank the relative importance of each of the 25 important questions.

R751.1 - Effect of Radioactive Contamination and Hot Particles on the Eye-Lens Dose

In 2012, the International Commission on Radiological Protection (ICRP) issued new

recommendations, in publication 118, regarding the dose limits to the lens of the eye. However, new analyses of historical exposure data indicated that radiation-induced cataracts may appear at lower doses than previously assumed. This spurred largescale efforts in a variety of fields including dosimetry, radiation effects simulations, and the review of national regulatory limits.

The aim of this work was to produce tabulated data of eye-lens dose rates, per activity (MBq), for a variety of radionuclides.

In this report, the dose to the eye-lens from contamination directly in contact with the cornea and on other parts of the eye, expressed in terms of Dose Rate Conversion factors (DRCFs) for eye-lens, in units of Gy h-1 MBq-1, are presented for 102 radionuclides of interest. These radionuclides were selected as they had been considered by the International Atomic Energy Agency (IAEA) of importance for skin dose.

The report describes the method used to separately simulate all emissions of the radionuclides of importance for all irradiation geometries of interest, a discussion of the results, and validation tests. The report also provides a complete set of DRCF tables for all radionuclides and geometries of interest. The results from this report will help health physics professionals, who are tasked with conducting a dose assessment, in the event of an exposure incident, who may not have the knowledge, the time, or access to the required computing facilities to perform these detailed simulations. The outcome of this work was published recently (January 3, 2023) in a peer reviewed journal titled “Eye-lens dose rate conversion factors due to hot particles and surface contaminations on the cornea”, J. Radiol. Prot., vol. 42(4) https://doi.org/10.1088/1361-6498/acad0e

R760.1 - A Study for the Canadian Nuclear Safety Commission on Artificial Intelligence Applications and Implications for the Nuclear Industry

CNSC engagement with the nuclear industry has revealed a desire to incorporate Artificial Intelligence (AI) into their regulated activities. As AI appears to offer the opportunity to accelerate technological development in the nuclear sector, regulators, industry, and stakeholders are evaluating the potential benefits of AI, from automating workflows and increasing efficiencies to design optimization.  However, the intersection of AI and safety significant applications poses a risk to the nuclear industry as the technology is difficult to audit and monitor.

The purpose of this report is to study potential AI applications and implications for the nuclear industry and to examine readiness for AI implementation, in various nuclear applications, within the current comprehensive and robust nuclear framework.

The scope of the study involved the following elements:

  • Identifying and comparing various definitions of AI in the government and regulatory sectors;
  • Reviewing relevant applications of AI in the nuclear industry;
  • Reviewing current regulatory activities to address AI applications in nuclear; and
  • Assessing the CNSC’s regulatory framework to determine AI's impact on safety significant applications, in terms of reliability, trustworthiness and security, and offering suggestions as to how the framework may be used for the potential operational implementation of AI by licensees in the conduct of their regulated nuclear activities. 

This review will help to inform the CNSC on how it might consider the potential implementation of AI in regulated nuclear activities. Additionally, as industry seeks to adopt AI, regulators, including the CNSC, are actively seeking opportunities to streamline their regulatory activities by also adopting AI into their internal processes, and the outputs of this project will also inform these objectives.

To obtain the full report, request the RSP-760.1 final report from cnsc.info.ccsn@cnsc-ccsn.gc.ca.

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