Luka Snoj

As the primary coolant, water is used in most current fission reactors and is also a promising coolant for future fusion devices. During normal operation, the fusion device produces plasma discharges. The primary cooling water circulates through in-vessel cooling channels and thus passes through regions of high neutron flux ( E ∼ 14 MeV ) produced by D–T fusion. During this process, cooling water can be activated and produce radioactive nuclides that emit gamma rays and neutrons (neutron energy range 0.4–1.7 MeV). Predicting the dose-rate field—the spatial and temporal distribution of radiation dose rates ( Sv ⋅ h − 1 ) produced by activated nuclides in the flowing coolant—requires coupling computational fluid dynamics (CFD) with radiation-transport and activation calculations. To validate these coupled CFD + radiation-transport + activation models and to investigate how production, transport and decay of activation products together create the observed dose-rate field, the KATANA water-activation loop at the Jožef Stefan Institute Training, Research, Isotope production, General Atomics Mark II reactor was commissioned. This paper examines the newly established KATANA water-activation loop and evaluates the feasibility of using the neutron activation method for neutron measurements at the facility. The studies show that this method can be successfully applied to detect and quantify neutrons originating from 17 N decay. Furthermore, the measurements demonstrate that this technique is capable of characterising the neutron emission rate at the KATANA water-activation loop. Finally, the paper proposes a method for estimating the neutron fluence at selected sample positions. The results encourage further use of the neutron activation method to investigate neutrons emitted by activated water. Future experiments could determine the neutron fluence-rate profile, thereby validating fluid-activation codes for ITER, DEMO and other fusion devices. This would also contribute to reducing the uncertainty of the 17 O ( n , p ) 17 N reaction cross-section.

KATANA is a water activation facility located in the TRIGA Mark II reactor of the Jožef Stefan Institute in Ljubljana, Slovenia. Since its commissioning it has contributed to a better understanding of water activation processes and their modelling, which is important in the context of the future operation of the ITER tokamak. The facility is designed to provide a flexible, benchmark-quality environment for the validation of computational tools for the activation of water. It will also support shielding experiments, in particular for ITER-relevant materials, and serve as a stable source of high-energy gamma rays and neutrons. This paper presents the calibration of 3He and BF3 neutron detectors used to measure neutron emission from the decay of 17N. The calibration was performed at the Czech Metrology Institute using a well-characterized graphite-moderated thermal neutron reference field. The calibrated acquisition system is then used in conjunction with Monte Carlo particle transport simulations to obtain the total neutron emission within the measurement volume of the KATANA water activation facility. The results form a basis for the determination of the integral cross section of the 17O(n,p)17N reaction, a nuclear reaction that is still insufficiently described in the literature.

Accurate online in-core parameter measurements, such as neutron and photon fluxes and nuclear heating rates, are essential for fusion and fission applications. Wide bandgap semiconductors, particularly Silicon Carbide (SiC), have demonstrated strong potential for radiation detection over six decades. Despite this, challenges persist in optimizing detector performance under extreme in-core conditions. Our study focuses on 4H-SiC-based detectors, developed within a joint laboratory between Aix-Marseille University and the CEA, aiming to address these challenges and provide high-precision measurements for advanced nuclear facilities. Following previous measurements in ZPRs and with D-T neutron generators, this paper focuses on in-core experimental results obtained with such detectors in the Triangular Irradiation Channel (TIC) of the TRIGA Mark II-type research reactor at the Jožef Stefan Institute (JSI) in Slovenia. These in-core measurements were done by using two types of diodes. One with a Neutron Converter Layer (NCL) of Boron-10 for thermal neutron detection, and the other one without NCL in order to discriminate thermal and fast neutrons by studying ¹⁰B reaction versus scattering. Thanks to various Pulse Shape Analyses (PSA) and count rate studies the influence of bias voltage, NCL and neutron fluence on the detector performances were determined. The highest neutron flux and fluence for these detectors were reached: 1.2 × 10¹³ cm⁻²·s⁻¹ and 1.2 × 10¹⁷ cm⁻², respectively.

The TRIGA Mark II research reactor at the Jožef Stefan Institute in Slovenia achieved first criticality in 1966. Since then, the reactor has been playing an important role in developing nuclear technology. The reactor has been mainly used for research, education of university students, training of operators of the Krško nuclear power plant (start of operation in 1983) and other nuclear specialists, isotope production and beam applications. The reactor is experiencing a high level of activity today, engaging in a diverse range of experiments and studies across reactor physics, environmental research, radiation hardness testing as well training and education. The future of nuclear technology in Slovenia is focused on new NPPs, while the research community is looking forward to a possible new nuclear reactor. The basic initiatives are at a very preliminary stage: the primary choice is dual-core pool-type reactor, with a zero-power core and a separate MW-size core, cooled and moderated with light water. Such a dual-core configuration is designed to meet the varied requirements of the European Union member states. Another option would be hosting one or more micro-reactors with electrical and/or heating power producing capability that could offer stronger support toward demonstration of prototype small modular reactors in prototype future electrical grids.

ITER is of key importance in the European fusion roadmap as it aims to prove the scientific and technological feasibility of fusion as a future energy source. The EUROfusion consortium of labs within Europe is contributing to the preparation of ITER scientific exploitation and operation and aspires to exploit ITER outcomes in view of DEMO. The paper provides an overview of the major progress obtained recently, carried out in the frame of the new (initiated in 2021) EUROfusion work-package called ‘Preparation of ITER Operation’ (PrIO). The overview paper is directly supported by the eleven EUROfusion PrIO contributions given at the 29th Fusion Energy Conference (16–21 October 2023) London, UK [www.iaea.org/events/fec2023]. The paper covers the following topics: (i) development and validation of tools in support to ITER operation (plasma breakdown/burn-through with evolving plasma volume, new infra-red synthetic diagnostic for off-line analysis and wall monitoring using Artificial Intelligence techniques, synthetic diagnostics development, development and exploitation of multi-machine databases); (ii) R&D for the radio-frequency ITER neutral beam sources leading to long duration of negative deuterium/hydrogen ions current extraction at ELISE and participation in the neutral beam test facility with progress on the ITER source SPIDER, and, the commissioning of the 1 MV high voltage accelerator (MITICA) with lessons learned for ITER; (iii) validation of neutronic tools for ITER nuclear operation following the second JET deuterium–tritium experimental campaigns carried out in 2021 and in 2023 (neutron streaming and shutdown dose rate calculation, water activation and activated corrosion products with advanced fluid dynamic simulation; irradiation of several materials under 14.1 MeV neutron flux etc).

To computationally support hydrogen and helium plasma discharges in the early stages of tokamak operation and to support the commissioning of the neutron detectors during these operational phases, creation of a realistic neutron and gamma ray particle source for Monte Carlo simulations will be needed. One of the most important parts of creating the particle source is calculating the reaction rates of the particle-emitting reactions to determine the emission profile in the plasma and the energy spectra of the emitted particles. In this paper the analysis and evaluation of cross sections for important neutron-emitting reactions, namely, ⁹Be(p,nγ)⁹B, ⁹Be(³He,nγ)¹¹C, and charged-particle emission reactions ⁹Be(p,d)2α and ⁹Be(p,α)⁶Li that cause neutron emission in the next step of interactions are presented. The reaction cross sections were evaluated based on experimental measurements and empirical models describing the interaction of two charged particles. Evaluation of the associated uncertainties was also performed. The main goal of the work is to propose the newly evaluated cross sections for inclusion in the FENDL nuclear data library, thus making the cross section available to other researchers studying the above listed reactions.