High-fidelity models for the online control of power ramps in fuel displacement systems – Revisiting the ISABELLE experiment in the OSIRIS Material Testing Reactor

The Jules Horowitz Reactor (JHR) is an MTR under construction at the CEA Cadarache, France. Its design and future operation build upon the lessons learned from the OSIRIS MTR. The CEA intends to transfer the knowledge accumulated with the ISABELLE1 loop of OSIRIS to the ADELINE loop of the JHR, both dedicated to power-ramp-type irradiation experiments, the purpose of which is to test the resistance of PWR fuel rod cladding under extreme levels of stress. In this article, we revisit the ETALISA experiment, a heat balance measurement experiment performed in 1992 for calibrating power ramps in ISABELLE1. We use high-fidelity modelling and simulation tools, especially the neutron-gamma TRIPOLI-4® Monte Carlo transport code, to calculate the detailed components of the heat balance, correction terms, and uncertainties. Comparisons between the simulations and the experiments show a very good agreement in the total linear heat generation rate of 400 W/cm at high power. The computed 2σ uncertainty is found to be 5%, a value essentially identical to the estimate derived in 1993 from an engineering approach. The use of modern simulation tools does not make it possible to improve upon this value, but provides a better understanding of the various components and corrections introduced in the total heat balance. The main limitations come from the ISABELLE1 online instrumentation, thermocouples and self-power neutron detectors, which set a limit on our very knowledge of the actual power ramp experimental conditions

Turbulent induced vibration of a guide tube in experimental reactor

The design of advanced experimental nuclear reactors consists in integrating safety and operational requirements as well as reaching targets in terms of thermal power and neutron spectrum. In order to meet theses constraints, slender structures with little supports and crossing the entire reactor vessel are implemented in the reactor and are subjected to an axial flow that generates flow-induced vibration (FIV). From the industrial point of view, the mastering of the occurrence of FIV and its associated wear in case of contacts is requested. The stationary fluid forces applying on slender tubular structure in response to its motion are of primary interest since they can significantly affect the vibration amplitudes and even the stability of the system, especially in case of confined axial flow with high velocities (typically higher than 10 m/s). In this study it proposed to compare two approaches to estimate the vibration induced by turbulent excitation of an industrial device encountered in a research nuclear reactor. The control-rod guide-tube mock-up of the Jules Horowitz Reactor, previously tested in an hydraulic channel at the Technical Center from Le Creusot in France, is retained for this benchmark. Two models are proposed, one based on derivation of leakage flow theory and the other one was based on potential flow theory with adjusted coefficients given by CFD simulations. The flow induced vibration amplitude is consistent with the experimental data. Also, the calculation and experiment provide similar trends when the boundary conditions are changed

Radiolysis of bituminized radioactive waste: a comprehensive review

In the realm of radioactive waste management, the impact of radiolysis on bitumen and bituminized radioactive waste also called bituminized waste product (BWP) is considered one of the most significant factors influencing structural changes and the generation of radiolysis gas bubbles. This review provides a comprehensive overview of several studies that have explored the intricate interaction between radiation and various types of bitumen, to gain a better understanding of how such waste ages when exposed to radiation. While these studies provide insights into the diverse effects of radiolysis on bitumen, they also highlight numerous unanswered questions. The absence of gas bubbles does not necessarily indicate an absence of gas production, leaving further research to be undertaken. The complexities of bitumen radiolysis offer multiple avenues for future investigation, aiming to enhance our understanding and provide comprehensive solutions for bituminous radioactive waste management. Among the studied types of bitumen, blown R85/40 bitumen and straight-run distilled bitumen with a penetration grade of 70/100 stands out due to their widespread use in immobilizing co-precipitated radioactive sludges. These bituminous matrices play an essential role in understanding the broader implications of radiolysis within the context of bituminous waste management. This review underscores the significance of further research into radiolysis and bitumen ageing, emphasizing the need for a more in-depth exploration of these complex phenomena and their implications for the long-term safety and efficacy of repositories and disposal facilities

Rheological investigation of bitumen, used for radioactive waste conditioning, with ultrasonic waves

In the context of bituminized radioactive waste storage and disposal, nucleation monitoring at room temperature and radiolysis bubbles migration at elevated temperature is crucial particularly in fire scenarios where bubble may impact thermal properties. Traditional methods are limited by the opacity of bitumen. To gain a deeper insight into bitumen rheology and ultrasonic wave propagation, we conducted a pilot study using ultrasonic testing cells spanning temperatures from 10°C to 60°C. Ultrasonic velocities and attenuations were measured at around 500 kHz in a 70/100 grade bitumen. Rheological information was deduced with the Time-Temperature Superposition principle and a behaviour model was proposed to describe bitumen across a wide frequency range. Notably, our study reveals a transition point around 50°C to 60°C, where bitumen’s liquid behaviour becomes dominant. The shear-thinning characteristics gradually give way to a more Newtonian response. Using the proposed model, ultrasonic attenuation and viscosity were estimated at 110°C. Acceptable ultrasonic frequencies for monitoring the nucleation and migration of radiolysis bubbles are discussed for future investigations. These findings have significant implications for safety measures and a deeper understanding of bitumen response within the realm of radioactive waste management

Templates of expected measurement uncertainties for average prompt and total fission neutron multiplicities

In this paper, we provide templates of measurement uncertainty sources expected to appear for average prompt- and total-fission neutron multiplicities, $\overline\nu_p$ and $\overline\nu_t$ , for the following measurement types: absolute manganese-bath experiments for $\overline\nu_t$ , absolute and ratio liquid-scintillator measurements for $\overline\nu_p$ . These templates also suggest a typical range of these uncertainties and their correlations based on a survey of available experimental data, associated literature, and feedback from experimentalists. In addition, the information needed to faithfully include the associated experimental data into the nuclear-data evaluation process is provided

UMAN – a pluralistic view of uncertainty management

Decisions associated with Radioactive Waste (RW) Management programmes are made in the presence of irreducible and reducible uncertainties. Responsibilities and roles of each actor, the nature of the RW disposal programme and the stage in its implementation influence the preferences of each category of actors in approaching uncertainty management. UMAN (UMAN – Uncertainties Management Multi-Actor Network is a Work Package of the European Radioactive Waste Management Programme – EURAD) carries out a strategic study about the management of uncertainties based on extended exchanges among actors representing Waste Management Organisations, Technical Support Organisations, Research Entities and Civil Society, a review of knowledge generated by past and ongoing R&D projects, and findings of international organisations. UMAN discusses the classification schemes and approaches applied in uncertainty management, and identifies possible actions to be considered in the uncertainty treatment. The relevance for the safety of the uncertainties associated with waste inventory, including spent fuel, near-field, site and geosphere and human aspects, as perceived by each type of actors, and approaches used in their management are explored with the aim to reach either a common understanding on how uncertainties relate to risk and safety and how to deal with them along the programme implementation, or at least arrive at a mutual understanding of each individual view. Finally, uncertainties assessed as highly significant and the associated R&D issues that can be further investigated are being identified

On the estimation of nuclide inventory and decay heat: a review from the EURAD European project

In this work, a study dedicated to the characterization of the neutronics aspect of the Spent Nuclear Fuel (SNF), as part of the European project EURAD (Work Package 8), is presented. Both measured nuclide concentrations from Post Irradiation Examination samples and decay heat from calorimetric measurements are compared to simulations performed by different partners of the project. Based on these detailed studies and data from the published literature, recommendations are proposed with respect to best practices for SNF modelling, as well as biases and uncertainties for a number of important nuclides and the SNF decay heat for a cooling period from 1 to 1000 years. Finally, specific needs are presented for the improvement of current code prediction capabilities

Reflections on achievements, activities, and emerging issues of strategic nature within the current and future EURATOM RTD programme on radioactive waste management

This paper provides a review of and some reflections on radioactive waste management activities (including disposal) at the strategic level in connection with the ongoing ‘European Joint Programme on Radioactive Waste management – EURAD’ and the European ‘PREDIS’ project on pre-disposal issues. The review took advantage of the large number of contributions made during the FISA 2022/EURADWASTE ’22 conference. The paper addresses the key characteristics of EURAD and PREDIS and highlights some of the key strengths of Joint Programming in supporting the member states with implementing waste management activities. Then, it discusses topics of strategic importance for waste management and the contributions of EURAD and PREDIS to these topics. This includes a summary of waste management strategies, the current status of implementing disposal solutions, the importance of knowledge management (taking the long duration of disposal programmes into account) and the importance of societal support of ongoing and future waste management activities. Finally, some remarks are made about issues of importance when organizing future joint activities on radioactive waste management at the European level

Templates of expected measurement uncertainties for neutron-induced capture and charged-particle production cross section observables

This paper provides a template of expected uncertainties and correlations for measurements of neutron-induced capture and charged-particle production cross sections. Measurements performed in-beam include total absorption spectroscopy, total energy detection, γ-ray spectroscopy, and direct charged-particle detection. Offline measurements include activation analysis and accelerator mass spectrometry. The information needed for proper use of the datasets in resonance region and high energy region evaluations is described, and recommended uncertainties are provided when specific values are not available for a dataset

Templates of expected measurement uncertainties for prompt fission neutron spectra

In this paper, we provide templates of uncertainty sources expected to appear for three measurement types of prompt fission neutron spectra (PFNS): (1) shape measurements, (2) clean-ratio shape, that is the monitor PFNS are measured in nearly exactly the same surrounding as the PFNS of interest, and (3) indirect ratios, where the detector efficiency is backed out from PFNS monitor measurements. Information is also listed that is needed to faithfully include PFNS in nuclear data evaluations to guide experimenters on how to best report data and metadata for their measurements. These templates also suggest a typical range of pertinent uncertainty values and their correlations in case realistic uncertainties cannot be estimated from information on the measurement itself. The templates were based on a literature review, information found in EXFOR for 252Cf, 235, 238U, and 239Pu PFNS, and enhanced by expertise from experimenters contributing to these PFNS templates