Each year, the Student and Young Professionals Committee organizes the Anthony J. MacKay Student Paper Contest in conjunction with the CRPA annual conference. The contest is open to all students enrolled full time in a Canadian college or university program related to the radiation sciences.

Entrants must submit an abstract of no more than 750 words on a topic that is related to some aspect of radiation; the topic is intentionally kept broad to encourage participation from a wide range of students.

Three finalists are selected to present their work at the conference in a plenary session. Here are the abstracts submitted by this year’s finalists.

• RDS-112 Cyclotron Facility Decommissioning by Meghan Sanderson, Medical and Biological Physics, McMaster University
• Estimation of Effects of Filtration and Ventilation on Worker Inhalation Dose from Aerosols During Nuclear Dismantlement by Nicholas Somer, Nuclear Engineering, Ontario Tech University
• Ionizing Radiation Exposure Effects Across Multiple Generations in Non-Human Biota by Shayenthiran (Shayen) Sreetharan, Radiation Sciences, McMaster University

 

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RDS-112 Cyclotron Facility Decommissioning

Meghan Sanderson
Medical and Biological Physics, McMaster University

Background

The RDS-112 cyclotron facility, consisting of an 11 MeV self-shielded cyclotron, was located in the McMaster University Medical Centre in Hamilton, ON. This facility was in operation from 1990 to 2018, producing radioisotopes for medical imaging and research (primarily fluorine 18, along with carbon 11, nitrogen 13, and oxygen 15). The McMaster University Health Physics Department provided radiation safety support throughout the lifetime of the facility.

By 2018, when all operations ceased, the cyclotron was owned by the Centre for Probe Development and Commercialization. All sealed and unsealed radioactive material was removed, and it was determined that the facility would be decommissioned. The problem was determining the process, as the option to remove the cyclotron as a whole was expensive and not feasible. The final decision was to dismantle the cyclotron and its related components, with the work being planned and led by McMaster Health Physics.

Methods

Samples and measurements of the internal components and the surrounding concrete shielding were taken to characterize and estimate the extent of activation. From this data, the decommissioning plan was created. 

In April 2023, researchers at King’s College London identified 82 components of the RDS cyclotron that they could use for their own cyclotron. These components were removed, surveyed, and cleared for release for shipment. All 82 components showed activation below exemption quantities or below minimum detection limits.

In June 2023, an opening was created in the exterior wall of the building that housed the cyclotron and the demolition commenced. Air sample measurements were taken during the demolition of the concrete shields to determine if this generated any airborne contamination. Daily contamination surveys were performed to ensure no loose contamination was generated.

The demolition began with the six surrounding concrete shields, which contained most of the material, working toward the central components of the cyclotron. The shields were demolished in sections, from which representative samples were taken and analyzed. All samples were surveyed for both loose and fixed contamination using contamination and dose rate meters prior to being removed from the building. Further analysis was performed using low-energy gamma spectroscopy along with liquid scintillation to characterize and quantize what, if any, activation products were present.

Results

The pre-demolition samples showed that the activation was mostly localized to the metal components around the ion source, extraction ports, and target stations. The inner six inches of the concrete shields also showed low levels of activation.

As demolition proceeded, the analysis confirmed that the activity levels of majority of the material were well below the exempt and unconditional clearance limits and could be unconditionally released. The lead shielding surrounding the targets also showed no activity above the minimum detectable limits.

Approximately 56,600 kg of material was exempt or unconditionally cleared, and approximately 5,700 kg is considered to be potentially radioactive. The activated components not able to be unconditionally released were parts of the more centralized components, consisting of a small section of the north and bottom steel shields surrounding the magnet, two floor tracks, I-beams, and a localized portion of the upper and lower magnets near the targets. These remaining materials will be kept under McMaster’s consolidated licence until a plan for conditional release or radioactive waste disposal is finalized.

Conclusion

This project was the first of its kind in Canada completed under a Canadian Nuclear Safety Commission (CNSC) licence to decommission an isotope production accelerator facility. The decision to dismantle the cyclotron resulted in most of the materials being unconditionally released, in addition to many of the parts being reused in the RDS cyclotron at King’s College. This proved to be a viable alternative to the expensive option of removing the cyclotron as a whole.

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Estimation of Effects of Filtration and Ventilation on Worker Inhalation Dose from Aerosols During Nuclear Dismantlement

Nicholas Somer
Nuclear Engineering, Ontario Tech University

Coauthors

• Glenn Harvel, Ontario Tech University
• Ed Waller, Ontario Tech University

Background

During the decommissioning of nuclear power plants, radioactive contaminants may be released into the work environment in the form of aerosols, which can expose workers through inhalation, ingestion, and submersion pathways. Workers often perform dismantlement work in confined spaces and sealed-off environments. Typical engineering controls to reduce concentrations include air exchange as well as air filtration, which captures aerosols at their source. The dose reduction from these engineering controls is generally not well understood. Given that a variety of filtration methods of varying efficiencies and throughputs exist, a method of estimating dose reduction for a variety of work scenarios is desirable.

Methods

This work presents a model of radioactive aerosol concentration. It is used to estimate worker committed effective dose. The model considers dismantlement work parameters, such as work time, aerosol source rate, and air exchange, along with air filtration and air filtration efficiency. The concentration over time is compared to a worst-case aerosol buildup based on no filtration nor air exchange. 

The committed effective dose (CED) due to inhalation from the aerosols is calculated by applying the approach of International Commission on Radiological Protection (ICRP) 119: the dose is proportional to the inhaled activity. The rate of activity inhalation is proportional to the concentration of aerosols in the air. By integrating the concentration over time for an entire shift, the dose to a worker can be estimated. These calculations involve integrations of elementary functions, which allows for scaleability of the model and calculations that are easily done on spreadsheets.

Results

Aerosol concentration over time is not dictated exclusively by the filter flow rate, the filter’s capture efficiency, and the air exchange rate of the room. Instead, it is dictated by a combination of all these factors, referred to as the cleaning period τ. The cleaning period identifies the trade-offs that can be made between air exchange and filtration. Further, this is an engineering parameter that applies to any workspace size.

By comparing the worst case of no ventilation or filtration, the reduction of worker dose over a 10-hour shift can be determined. The dose reduction is exclusively a function of the cleaning period τ and dismantlement shift structure (i.e., when work is and is not being performed). The dose reduction is independent of scenario-specific parameters such as workspace volume, aerosol source rate, personal protective equipment (PPE), etc., and so can be used to model aerosol dose reduction in different dismantlement scenarios.

This paper produces two useful charts for filter selection. The first chart outlines the required cleaning period τ for a desired dose reduction for the modelled 10-hour worker shift. The second chart outlines the necessary combination of filter efficiency and flow rate for a single filter to achieve the cleaning period for such a space. These types of charts are a tool for engineers and health physicists to consider when building work packages, selecting engineering controls for dismantlement work, and so on.

Conclusion

This paper presents a mathematical model of the evolution of aerosol concentrations over time during dismantlement work using various dismantlement work parameters, such as aerosol source rates, workspace size, air exchange and filtration, and so on.

The engineering parameter referred to as a cleaning period τ, which emerges from the model, determines the growth or reduction in aerosol concentrations over time, and ultimately the worker dose.

For a desired dose reduction, charts to select for cleaning period and associated filtration parameters can be generated for work package design. The models suggest that filtration systems, which often tout their capture efficiencies, should also have their specified flow rates considered.

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Ionizing Radiation Exposure Effects Across Multiple Generations in Non-Human Biota

Shayenthiran (Shayen) Sreetharan
Radiation Sciences, McMaster University

Coauthors

• Sandrine Frelon, Institute for Radiation Protection and Nuclear Safety (IRSN), Cadarache, France
• Patrick Laloi, Université de Lyon, Villeurbanne, France
• Nele Horemans, Belgian Nuclear Research Centre (SCK CEN), Mol, Belgium / University of Hasselt, Diepenbeek, Belgium
• Sisko Salomaa, University of Eastern Finland, Kuopio, Finland
• Christelle Adam-Guillermin, Institute for Radiation Protection and Nuclear Safety (IRSN), Cadarache, France

Background

The potential for radiation-induced harmful effects in progeny, and thus in next generations, is a major concern for parents exposed to ionizing radiation from occupational, medical, or environmental sources. To date, the systems of radiological protection do not quantify or consider the possibility for effects that may manifest in subsequent generations following the initial exposure.

A Task Group (TG121) of the International Commission on Radiological Protection (ICRP) Committee 1 was launched in 2021 to study the effects of ionizing radiation in offspring and next generations. One of TG121’s goals was to review the literature on the effects on both

• multi-generational non-human biota (in which the exposure continues across multiple generations) and
• trans-generational non-human biota (in which later generations are not exposed during a recovery period).

Because of shorter generation times in these non-human species, they offer a unique tool to monitor and study generational effects following radiation exposure; however, the underlying biological and physiological differences amongst these species must be carefully considered.

Methods

A review of multiple online databases (Google Scholar, PubMed, Scopus) was completed in 2022 by performing keyword searches related to the topics of multi-generational and trans-generational effects of ionizing radiation in non-human species. Both laboratory-controlled experiments and field studies were considered, with the latter typically containing ecological studies from either the Chernobyl Exclusion Zone or the Fukushima-Daiichi prefecture. In addition to studies identified from online databases, we also included published reviews, conference proceedings, and expert reports in our review.

Results

Studies were grouped into categories based on the model organism used, which included species of bacteria, nematodes and annelids (largely Caenorhabditis elegans), crustaceans (largely Daphnia magna), insects, amphibians, birds, fish, mammals, and plants. 

Details regarding exposure schedule (multi-generational, trans-generational or environmental exposure), generation numbers studied, endpoints monitored, and results were summarized in a table. 

Effects on altered reproductive parameters were reported in offspring, with this observation present in different study models. In some studies, decreased survival in offspring was also observed; however, these studies typically involved chronic, persistent exposure of numerous generations to a radiation field or following very large acute doses in trans-generational studies.

There was also a number of studies involving different species that reported changes in genetic and epigenetic endpoints, with transmission of epigenetic changes into subsequent generations previously described as a possible mechanism for multi- and trans-generational irradiation effects. Changes in genome methylation, histone modifications, chromosomal aberrations, and other mutations were reported in plants (Arabidopsis thaliana and flax), nematodes (Caenorhabditis elegans), insects (Drosophila melanogaster), and amphibian (Japanese tree frogs and Eastern tree frogs) species.

Overall, the diversity of available non-human biota data brings complexities regarding the application of any reported results into the systems of radiological protection. We propose that differences in radiation sensitivity between species, transferability of data between different species, the presence of adaptation and adaptive responses, dose reconstruction across subsequent generations, and, finally, extending knowledge to humans represent key knowledge gaps within
this field.

Conclusion

The goal of this paper was to perform a literature review of studies that investigated multi- and trans-generational effects in non-human biota, and to consider the incorporation of this evidence into the systems of radiological protection. The reported effects in altered reproduction represent an area of potential concern, due to the importance of population and ecosystem structure within ecological radiation protection. This is in contrast to human radiation protection, which considers effects at an individual level.

ICRP Task Group 121 will continue to review this literature and will ultimately report our findings in an ICRP publication for the radiation protection community.

 

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See related articles:

2024 Anthony J. MacKay Student Paper Contest: Meet This Year’s Finalists, June 7, 2024

2023 Anthony J. MacKay Student Paper Contest, May 17, 2023

2022 Anthony J. Mackay Student Paper Contest Winners, February 16, 2023

2019 Anthony J. MacKay Student Paper Contest, June 7, 2019

2018 Anthony J. MacKay Student Paper Contest, May 8, 2018