Subjects Treated in Project Undertaken by Meulenbelt Nuclear Research
Reactor Monitoring Programme
In this project, a Reactor Monitoring Programme (RMP) was developed for the High Flux Reactor (HFR) in Petten to assess reactor fuel reliability. The programme employs gamma-ray spectrometry to establish isotopic baselines and identify measurable fuel defect indicators. It features three main components: the Isotopic Baseline, the Release Model, and Fuel Defect Indicators.
The Isotopic Baseline uses historical gamma-ray spectrometry data to define normal operational levels. This baseline, derived from steady-state operation data, serves as a reference for detecting anomalies in new weekly spectrometry results.
The Release Model is a Python-based tool that predicts the release of fission products from the fuel matrix. By modelling the diffusion and decay of these products, the model sets thresholds for normal release rates, helping to identify isotopic activities that may indicate fuel defects.
Fuel Defect Indicators are quantitative metrics for identifying potential fuel issues. These include changes in the Xe-133/Xe-135 ratio, detection of radioisotopes that should not be released under normal conditions, and overall increases in volatile fission product activity. Comparing current data against the baseline and model predictions allows the programme to flag potential anomalies.
This programme enhances the evaluation of reactor performance and facilitates early detection of anomalies. A detailed paper on the methodology and results, presented at the RRFM 2024 conference in Poland, is available for download and is published in the RRFM conference proceedings
Offshore Nuclear Power
Ime Meulenbelt is one of the Co-Founders of MarineFission. MarineFission focuses on harnessing offshore nuclear power by integrating compact nuclear reactors with offshore wind farms. The idea originated from the challenge of finding suitable locations for reactors in the densely populated Netherlands, where placing reactors inland would mean they are always near residential areas. Over time, this concept evolved into combining offshore nuclear reactors with wind farms to maximise the strengths of both technologies.
The integration of nuclear reactors within wind farms enhances grid stability and ensures a consistent energy supply by leveraging the ocean’s cooling capabilities for improved safety and efficiency. This innovative solution not only reduces operational costs but also enhances scalability and minimises environmental impact.
To validate this concept, Ime conducted technical feasibility studies, evaluating offshore platform design, oceanographic conditions, and the integration with wind infrastructure. Additionally, financial projections were developed using the real options approach, allowing for flexible and informed investment decisions. These analyses demonstrated the project’s potential for significant improvements in energy security and sustainability.
MarineFission presents a new approach to clean energy production, addressing the need for reliable, low-carbon power while mitigating the land use constraints in crowded regions like the Netherlands. For more details, visit MarineFission.
Fuel Incident Analysis
Here, the aim was to identify and analyse fuel defects using gamma-ray spectrometry (GRS) on weekly samples taken from the primary coolant water. By monitoring isotope releases from fuel elements, defects were detected through changes in isotopic ratios such as 133Xe to 135Xe. This detailed investigation enabled precise defect pinpointing, crucial for early detection and mitigation, ensuring reactor safety and efficiency.
GRS measured gamma rays from isotopes in the primary coolant water (PCW), identifying specific isotopes and noble gas ratios indicative of fuel defects. A key aspect was analysing defect size based on activity measurements in the coolant, determining if visual inspection methods were feasible for identifying defects.
The project also involved a sipping experiment to analyse suspected defective fuel elements (FEs). Sipping involves drawing water through FEs and analysing it for radioactive isotopes, identifying which FEs are defective. This provided insights into the stability of FEs over time and whether defects worsened or self-sealed due to oxidation.
The project highlighted the importance of refining detection methods to distinguish actual fuel defects from false positives, enhancing the reliability of GRS measurements. This ensured that increases in isotopic activity were correctly attributed to fuel defects and not to background fluctuations or measurement errors.
Predictive Modelling
Predictive Modelling was done for the High Flux Reactor in Petten. It uses Fick’s second law and a finite difference approach to simulate the release of isotopes from nuclear fuel plates under various conditions. These simulations provided insights into the expected behaviour of isotopes during both normal and defective states, allowing for accurate anticipation of potential issue.
The main difficulty lay in developing a comprehensive numerical model to estimate isotope release rates. This model accounted for the different mechanisms influencing isotope behaviour, including diffusion and fission product recoil. By incorporating variables such as the ‘release coefficients’ (similar to the diffusion coefficient) of noble gases like xenon and krypton, and other volatile fission products, the model could predict the release rates and activity levels of these isotopes in the reactor’s primary coolant water.
One significant aspect of the model was its ability to simulate various defect scenarios, ranging from minor cladding breaches to more significant fuel defects. The model used historical gamma-ray spectrometry (GRS) data to refine its predictions, ensuring high accuracy in identifying the presence and size of fuel defects based on isotopic signatures.
Primary Coolant Water Analysis
The “Primary Coolant Water Analysis” project involved a detailed examination of the isotopes present in the primary coolant water (PCW) of the reactor using gamma-ray spectrometry (GRS). This technique measures the gamma rays emitted by radioisotopes in the PCW, allowing for precise identification of the isotopes based on their distinct energy patterns.
Weekly GRS measurements of the PCW provided data that was crucial for establishing an isotopic baseline, reflecting the normal operational conditions of the reactor. This baseline was essential for detecting any deviations that might indicate anomalies. The isotopic baseline included a comprehensive analysis of both fission products released from the fuel and activation products from reactor structural components.
To accurately determine the isotopes in the PCW, each gamma ray peak detected was assigned a confidence value, which was adjusted using a penalty function considering the difference between reference and measured energies, branching ratios, and the presence or absence of expected peaks for specific isotopes. This process ensured the reliability of isotope identification and helped distinguish between true measurements and false positives.
The GRS data was also used to monitor fuel defect indicators by observing isotopic activities that deviated from the established baseline. Key isotopes monitored included noble gases like xenon and krypton, and fission products such as cesium-137. Any increase in the activity levels of these isotopes could signal a fuel defect, prompting further investigation.
Additionally, the project involved refining the GRS measurement techniques to enhance the detection capabilities and reduce the occurrence of false positives. By improving the confidence levels and verification algorithms, the analysis could reliably attribute isotopic activities to actual fuel defects rather than background fluctuations or contamination.
Fragments of creativity
The Reactor Monitoring Programme (RMP) was used to monitor the ageing of reactor components in the primary circuit. By utilising gamma-ray spectrometry (GRS) to track long-term trends in radioisotope activities, the project gained insights into corrosion processes and structural integrity.
The RMP employed weekly GRS measurements to establish a detailed isotopic baseline of the primary coolant water (PCW). This baseline, derived from historical data, served as a reference for identifying deviations that could indicate ageing or degradation of reactor components. By monitoring isotopes associated with structural materials, such as Na-24 from aluminium cladding, the project could detect increasing trends indicative of corrosion and material wear.
The programme was particularly effective in distinguishing between normal operational emissions and those signalling ageing-related issues. By analysing the isotopic activity profiles over extended operational cycles, the RMP could correlate increases in certain isotopes with ongoing ageing processes within the reactor. This capability supported proactive maintenance and reactor longevity, ensuring the continued safe operation of the nuclear reactor.
The research findings, presented at the European Research Reactor Conference (RRFM), highlight the importance of continuous monitoring and data analysis for effective ageing management. The detailed paper, available for download, provides comprehensive insights into the methodologies and outcomes of the project.
