Accelerator-Driven Molten Salt Reactors: Studies on Neutron Efficiency and Multiplication Factor

At the Kyoto University Critical Assembly, a series of reactor physics experiments on the accelerator-driven system (ADS) coupled with the fixed-field alternating gradient (FFAG) accelerator are carried out, and the spallation neutrons generated by 100-MeV protons from the FFAG accelerator are successfully injected into the cores. In the ADS experiments, the neutron characteristics of the solid target are investigated through static and kinetic analyses, when the external neutron source of the neutron spectrum (the W, W-Be, or Pb-Bi target) is varied. The results demonstrate that the neutron yield is large with the W target, but a discrepancy is observed between the experiments and the calculations, because the experimental uncertainty of proton monitoring is attributable to defocusing of proton beams. With the use of reaction rate distribution in the core region, the static parameters are estimated fairly well in the analyses of the neutron multiplication and subcritical multiplication factor. In the kinetic experiments, the variation of the solid target used is clearly evident in the prompt neutron decay constant and the subcriticality.

Reactor physics analysis of a Source-driven TRIGA configuration in subcritical domain

Possible use of accelerator driven subcritical reactors for minor actinides incineration

At the University of Cincinnati Nuclear Engineering Program, the resurrection of a once moth-balled subcritical reactor facility now provides an ideal laboratory experience to its students. Its simplicity and accessibility are among its key features. This article focuses upon supplementing the experimental aspects of this facility via the development of a three-dimensional, full detail, MCNP model of this reactor, while emphasizing the validation of this computational tool against laboratory measurements. The subcritical reactor parameters herein compared include: neutron and photon flux distributions, fission rate, and the subcritical multiplication factor (k-effective), among other relevant parameters of interest.

While a considerable and world-wide growth of the nuclear share in the global energy mix is desirable for many reasons, there are also, in particular in the "old world" major objections. These are both concerns about safety, in particular in the wake of the Fukushima nuclear accident and concerns about the long-term burden that is constituted by the radiotoxic waste from the spent fuel. With regard to the second topic, the present contribution will outline the concept of Partitioning & Transmutation (P&T), as scientific and technological answer. Deployment of P&T may use dedicated "Transmuter" or "Burner" reactors, using a fast neutron spectrum. For the transmutation of waste with a large content (up to 50%) of (very long-lived) Minor Actinides, a sub-critical reactor, using an external neutron source is a most attractive solution. It is constituted by coupling a proton accelerator, a spallation target and a subcritical core. This promising new technology is named ADS, for accelerator-driven system. The present paper aims at a short introduction into the field that has been characterized by a high collaborative activity during the last decade in Europe, in order to focus, in its later part, on the MYRRHA project as the European ADS technology demonstrator.

Review of the European project — Impact of Accelerator-Based Technologies on nuclear fission safety (IABAT)

High-current proton accelerators are being researched at Los Alamos National Laboratory and other laboratories for accelerator production of tritium, transmuting long-lived radioactive waste into shorter-lived products, converting excess plutonium, and producing energy. These technologies make use of spallation neutrons produced in (p,xn) and (n,xn) nuclear reactions on high-Z targets. Through (p,xn) and (n,xn) nuclear reactions, neutrons are produced and are moderated by heavy water. These moderated neutrons are subsequently captured on 3He to produce tritium via the (n,p) reaction. Tritium self-sufficiency must be maintained for a commercial fusion power plant. Rubbia succeeded in a proposal of a full scale demonstration plant of the Energy Amplifier. This plant is to be known the accelerator-driven system (ADS). The ADS can be used for production of neutrons in spallation neutron source and they can act as an intense neutron source in accelerator-driven subcritical reactors, capable of incinerating nuclear waste and of producing energy. Thorium and Uranium are nuclear fuels and Lead, Bismuth, Tungsten are the target nuclei in these reactor systems. The spallation targets can be Pb, Bi, W, etc. isotopes and these target material can be liquid or solid. Naturally Lead includes the 204Pb (%1.42), 206Pb (%24.1), 207Pb (%22.1) and 208Pb (%52.3) isotopes. The design of ADS systems and also a fusion-fission hybrid reactor systems require the knowledge of a wide range of better data. In this study, by using Hartree–Fock method with an effective nucleon-nucleon Skyrme interactions rms nuclear charge radii, rms nuclear mass radii, rms nuclear proton, neutron radii and neutron skin thickness were calculated for the 204, 206, 208Pb isotopes. The calculated results have been compared with those of the compiled experimental and theoretical values of other studies.

Molten salt reactors (MSRs) are a class of Generation IV advanced reactor technologies aimed to enhance and improve the safety, fuel utilization and cost-effectiveness of nuclear power generation. MSR concepts are based on using a molten salt mixture as a primary nuclear reactor coolant, while the fuel can be either directly dissolved in the coolant (i.e., fluid-fueled) or can be in a separate solid form (i.e., salt-cooled solid-fueled). MSRs can be operated in either thermal or fast neutron spectra, as simple fissile convertors, or breeder reactors (e.g., utilizing both fissile and fertile fuels), as well as accelerator-driven sub-critical reactors or transuranic element burners. Operation of MSRs will necessitate management and treatment of the off-gas streams released to the headspace of the reactor where, in some designs, a cover gas can be circulated to remove certain fission products and maintain an inert atmosphere. An inert MSR cover gas swept over or sparged into the salt will confine radionuclides emerging from the free surface, including radioactive noble and non-noble gases, aerosols, and volatile species. The elements and compounds of these species will have a wide range of thermochemical and physical properties, some of which will decay to different products in the off-gas stream. Therefore, system components used to manage and treat MSR off-gas streams will need to be robust under dynamic reactor and chemistry conditions to support adequate reactor performance by managing the composition and species in the salt coolant and cover gas space. Off-gas system components would perform as a radionuclide boundary to the reactor vessel and a primary means for preventing radionuclide release; therefore, they are of high safety significance for MSR operations. This report reviews various technologies and materials for potential implementation in the design of an MSR off-gas system per a general conceptual framework. The reviewed technologies operate based on scrubbing, capture, delay, or separation of species in the off-gas stream. These include molten hydroxide scrubbers, solid sorbents, delay off-gas systems, particle traps, and cryogenic distillation. Since aspects of an off-gas system will be design-specific, the approach is to provide general discussions on attributes of these technologies and materials, including target off-gas stream species, operational parameters and conditions of importance to decontamination factors, implementation maturity, system component monitoring, potential off-normal conditions and considerations for waste products. The information aims to support the U.S. Nuclear Regulatory Commission in their safety evaluations for MSR designs.

Investigation of subcritical multiplication parameters in TRIGA Mark II accelerator driven system

Accelerator-Driven Systems (ADS) represent a transformative approach to nuclear waste management, offering the potential to reduce long-lived radiotoxicity while enhancing nuclear fuel utilization. This comprehensive review analyses global technological advancements in ADS development, with particular emphasis on China's pioneering CiADS (China Initiative Accelerator Driven System) project. The study synthesizes data from major international programs including MYRRHA (EU), J-PARC (Japan), and IAEA collaborative benchmarks, examining: 1) High-power proton accelerator reliability achieving more than 85% beam availability at 500 MeV/5 mA operation; 2) Spallation target innovations using Liquid Lead-Bismuth Eutectic (LBE) enabling 700 W/cm³ power density handling; 3) Subcritical core designs with minor actinide-bearing fuels demonstrating 98.7% transmutation efficiency over five recycling passes; and 4) Integrated safety validation confirming core damage frequencies less than 3×10⁻⁸/year through inherent subcriticality (effective multiplication factor, keff equal to 0.75) and passive decay heat removal. The fuel cycle in CiADS achieves breakthrough resource efficiency with 95% uranium utilization and waste volume reduction to less than 5% of conventional levels. Technological roadmaps indicate potential deployment of industrial-scale 300 MWth transmutation plants by 2035, supported by emerging regulatory frameworks. The analysis establishes ADS as a viable solution for closing the nuclear fuel cycle while providing a technical foundation for future sustainable nuclear energy systems.

A preliminary stability analysis of MYRRHA Primary Heat Exchanger two-phase tube bundle

Accelerator Driven Systems are innovative options in the field of nuclear fission energy, based on the use of neutrons produced in a spallation target to feed a sub-critical reactor. The nuclear physics reactions involved in these systems are described and it is shown that specific new nuclear data are needed, especially for the optimisation of the target-blanket assembly. Recent experimental programs raised by the recent interest in accelerator-driven systems are presented.

The reactor core of an accelerator driven sub-critical system has been physically analyzed by the MCNP code. Neutron flux density of different area within the reactor has been calculated, and the influence on its distribution has also been analyzed. Results show that there exists higher fast neutron flux variation at different element layer in fast region, and relatively lower thermal neutron flux variation at different element layer in thermal region. The calculated neutron flux meets the general design requirements in the reflector and shielding layer. Neutron multiplication factor is remarkable in the fast neutron spectrum area, and it realizes the energy amplification in the thermal spectrum area. The statistical particle number of code can influence the accuracy of the calculation and variation of the core design parameters can change the neutron flux distribution in the reactor core.

The article analyses the designs and fuel cycles of thorium nuclear reactors being developed in leading producing countries. Special attention is paid to molten salt reactors (MSR), advanced heavy water reactors (AHWR), high-temperature systems (HTR), and subcritical accelerator-driven systems (ADS). The physicochemical properties of thorium and its behaviour in different types of cores are reviewed. A comparative analysis with uranium fuel is carried out, and the advantages and limitations of the thorium cycle in terms of energy efficiency, radiation safety, and reproduction of fissile isotopes are disclosed. The main design approaches to the integration of thorium into existing and prospective reactor plants, including solid-fuel, liquid-salt and hybrid systems, are described. Possible coolants and external neutron sources as well as spent fuel reprocessing requirements are discussed. On the basis of review and experimental data, recommendations on further directions of scientific and technical research and international co-operation in the field of thorium energy are formulated.

For the first time, the double-differential and integral cross-sections of the reaction (p,xd) on the 120Sn nucleus were measured at the energy of the bombarding protons of 30 MeV. Tin is the structural material of the nuclear power plants being designed, in particular, the promising ADS (Accelerator Driven System) hybrid electro-nuclear installations consisting of a high-energy proton accelerator and a deeply subcritical nuclear reactor. The main idea is to use high-energy charged particle accelerators to produce neutrons in heavy element targets. For registration and identification of reaction products, the dE-E method was used, where two parameters of the detected particle are registered: specific ionization and total energy. The total error of the measured double-differential cross sections did not exceed 20%. After integrating the double-differential cross sections by angle, the integral energy spectrum was determined. The theoretical analysis is carried out within the framework of the TALYS calculation code, which is based on modern theoretical models of nuclear decay. The mechanisms of nuclear reactions responsible for the formation of the energy spectrum of outgoing deuterons are determined. The obtained experimental results fill in the missing values of the cross-sections of the studied reactions and can be used in the development of new approaches to the theory of nuclear reactions, as well as in the design of hybrid nuclear power plants.