Accelerator-driven Subcritical System Research Articles

Production cross sections of 102mRh and 108mAg in proton bombed natPb target with 400 MeV energy

The accelerator-driven subcritical system (ADS) is a competitive option for next-generation nuclear energy systems. Production cross sections of long-lived residual radioactive nuclides in a proton-nuclide reaction are basic quantities for the calculation of accumulated radioactivity in the use of ADS systems. This work presents the production cross sections of 102mRh and 108mAg in a natural lead (natPb) target activated by 400 MeV protons. The natPb target was irradiated by a 400 MeV proton beam in NRC “Kurchatov Institute” and measured two decades later by a low background gamma spectrometer in China Jinping Underground Laboratory (CJPL). A spectrum analysis method based on simulated single-isotope spectrum and Bayesian peak fitting was employed to compute the activities and production cross sections of the residual nuclides. The experimentally measured cross-sections for 102mRh and 108mAg were 0.72 ± 0.05 mb and 0.76 ± 0.09 mb respectively. These values are approximately twice as high as those predicted by the QGSP_INCLXX_HP model and fall within the range predicted by the INCL4+ABLA and LAQGSM+GEM2 models for mass numbers A=102 and A=108. These findings offer new experimental insights for ADS research and provide a practical benchmark for theoretical models concerning proton-lead interactions.

Enhanced transmutation of minor actinides by incorporation of multi-beam design in Accelerator-Driven subcritical system

This study aims to identify the optimal beam design for incinerating the long-lived minor actinides in Accelerator-Driven System (ADS). All the analyses were performed using the MCNP6.1 code with cross-section library ENDF/B-VII. In this study, a depletion method for ADS was conducted and analyses were exercised to investigate the burnup performances for the various arrangements of a three-proton beam design. The influences of the various arrangements of the three-proton beam design were used as a criterion for comparison. It was found that the dual proton beam arrangement demonstrated the best depletion result for the incineration of minor actinides.

Beam physics design of a superconducting linac

The China initiative Accelerator-Driven subcritical System (CiADS) project aims to design and build the world’s first accelerator-driven subcritical system demonstration facility. The facility will attain 2.5 MW thermal power in 2026 to realize accelerator-target-reactor coupling experiments. As the first approved accelerator-driven subcritical system facility, the CiADS driver linac will adopt cutting-edge accelerator technologies to achieve the challenging goals of high beam power and high reliability. The accelerator will operate in cw mode to produce a 500 MeV, 5 mA proton beam. To meet the extremely high demands on beam availability, the linac design lays strong emphasis on beam loss control and increased fault tolerance via a novel fault-compensation method. The accelerator complex consists of a room temperature front-end section, a main linac that employs superconducting accelerator technologies, and a high-energy beam transport line. The beam-loss-oriented beam dynamics design of the driver linac complex is presented in the paper. Published by the American Physical Society 2024

Study on the corrosion behavior of laser surface remelted and laser cladding of ferritic/martensitic steels after exposure to lead-bismuth eutectic at 700 °C

This study explores two vital structural materials, T91 (Fe-9Cr) and SIMP (Fe-11Cr) steels, in the context of lead-cooled fast reactors and accelerator-driven sub-critical systems (ADS). Lead-bismuth eutectic (LBE) functions as a key coolant and spallation target material due to its impressive thermal conductivity, neutron yield, and chemical properties. Unfortunately, materials in contact with LBE are prone to severe corrosion at elevated temperatures (T>500 °C), compromising their integrity. To bolster corrosion resistance, we utilized laser remelting and laser cladding to apply FeCrAl/TiN coatings on the steel surfaces. Our study scrutinizes the corrosion behavior of steel in LBE saturated with oxygen at 700 °C and investigates the underlying causes. Following 240 h of exposure to corrosion, T91 and SIMP steels subjected to laser remelting displayed substantial oxide scale formation. Lead-bismuth atoms infiltrated the outer oxide layer (Fe3O4), diminishing adhesion between the inner and outer oxide layers, leading to the detachment of the outer oxide layer. The inner oxide layers, composed of Fe-Cr spinel, were approximately 123 μm thick for T91 steel and 77 μm for SIMP steel, underscoring SIMP steel's superior corrosion resistance. For T91 steel treated with laser cladding FeCrAl/TiN coating, a characteristic duplex oxide layer with a total thickness of around 83 μm was formed, with noticeable deposition of Pb-Bi atoms at the interface between the outer and inner oxide layers. Conversely, only a protective alumina layer safeguarded SIMP steel from LBE corrosion. This outcome emphasizes the efficacy of laser cladding FeCrAl/TiN coating in providing superior protection for SIMP steel over T91 steel. Our research significantly contributes to the development of anti-corrosion coatings for high-temperature LBE environments.

Studying on failure compensation in low-energy region of superconducting cavity in CAFe2

The high availability of Accelerator-Driven Sub-critical system (ADS) facilities poses a major challenge for the accelerators, which sets stringent requirements on the beam trip rate. However, beam trips caused by component failures in the low-energy region of the superconducting (SC) radio-frequency (RF) cavity are always a bottleneck for the long-term stable operation of high-power beams. In this paper, we present a compensation method. This method can be used to compensate for cavity faults that occur at low-energy ([Formula: see text][Formula: see text]MeV). The compensation is achieved by rematching the beam with nearby components and compensating for energy using all cavities. The new Epeak and RF phases of the remaining components are calculated in the simulation environment using a multi-objective genetic algorithm. The compensation scheme is then tested on the super-heavy element research accelerator II (CAFe2). The experimental results show that the scheme can compensate for the energy, maintaining the same level as the normal operation status, while keeping the transmission efficiency [Formula: see text]. The entire compensation process takes only 36[Formula: see text]s. This is the first compensation experiment in the low-energy region, and it demonstrates the feasibility of long-term stable operation.

Preparation and thermal physical properties of MgO-(Nd1-xYx)2(Zr1-xCex)2O7 composite ceramics as a candidate for inert matrix fuel

In recent years, the MgO-Nd2Zr2O7 composite ceramics inert matrix (IM) was proposed as a candidate for the transmutation of Pu and minor actinides (MA) in light water reactors (LWR) or accelerator driven sub-critical system (ADS). To take full advantage of the pyrochlore structure of Nd2Zr2O7 to accommodate different types of MA and Pu, in this work, Y and Ce co-doped ωMgO-(1-ω)(Nd1-xYx)2(Zr1-xCex)2O7 (M-NYZC) composite ceramics used as a candidate IM for inert matrix fuel were prepared by solid-state one-step sintering method at 1500 °C for 3 h. The phase structure and microstructure of M-NYZC composite ceramics were characterized by XRD and SEM-EDS. Also, the thermal physical properties of M-NYZC composite ceramics including the thermal expansion coefficient and thermal conductivity were investigated systematically. Results from XRD and SEM-EDS showed that the magnesium oxide and NYZC pyrochlore solid solution are intermixed well with each other, and the M-NYZC samples present uniform element distribution with a grain size of about 1 μm. Also, the as-prepared samples possessed well densified microstructure, and the average relative density of all samples could exceed 95 %. Moreover, the thermal expansion coefficient and thermal conductivity of 0.5M-0.5NYZC (x = 0, 0.15, 0.2, 0.5, 0.9) samples were located in the range of 13.4 × 10-6–14.4 × 10-6 K-1 and 16.34–3.70 W·m-1·K-1 respectively. By comparison, the thermal physical properties of 0.5M-0.5NYZC samples are superior to that of traditional UO2 and MOX fuels. It is suggested that the M-NYZC composite ceramics prepared in this study can meet the thermal physical performances of inert matrix fuel.

Availability and reliability statistics at ISIS and at other high-power proton accelerators

Detailed availability statistics, and reliability statistics in terms of trip rates, between 1994 and 2021 at the ISIS Spallation Neutron Source are presented. The average of the availabilities for 121 irradiation campaigns spanning the better part of three decades is 86% with a standard deviation of 7%. Trip rates at ISIS are very similar to trip rates at high-power proton machines of different accelerator ‘architecture’ elsewhere, and altogether these trip rates can be fitted quite well over several orders of magnitude by the simple power law Ṅ=6t−0.75 where Ṅ is the number of trips per day longer than time t (t in minutes). Typical trip rates for present-day accelerator systems would appear to be too high to be suitable for acceptable operation of accelerator-driven subcritical reactor systems.

Applicability of RANS models and pressure drop in edge subchannels for 19-pin wire-wrapped fuel bundle channel in CiADS

The accelerator-driven subcritical system has a strong transmutation ability and high inherent safety, and it is internationally recognized as the most promising long-life nuclear waste disposal device. This study involves the construction of a Visual Hydraulic ExperimentaL Platform (VHELP) for the purpose of evaluating the applicability of Reynolds-averaged Navier–Stokes (RANS) models and analyzing the pressure distribution within the fuel bundle channel of China initiative accelerator-driven system (CiADS). Measurements of thirty differential pressures in edge subchannels within a 19-pin wire-wrapped fuel bundle channel were obtained under different conditions using deionized water. The pressure distribution in the fuel bundle channel at Reynolds numbers of 5000, 7500, 10,000, 12,500, and 15,000 was simulated using Fluent. The results show that RANS models obtained accurate results, and the shear stress transport k-ω model provided the most accurate prediction of the pressure distribution. The difference between the results of the Shear stress transport (SST) k-ω model and experimental data was the smallest, and the maximum difference was ±5.57%. Moreover, the error between the experimental data and numerical results of the axial differential pressure was smaller than that of the transverse differential pressure. The pressure periodicity in axial and transverse directions (one pitch) and a relatively three-dimensional pressure measurements were studied. The static pressure fluctuated and decreased periodically as the z-axis coordinate increased. These results can facilitate research on the cross-flow characteristics of liquid metal-cooled fast reactors.

Design and Development of the 200-kW Beam Dump

The Chinese Accelerator Front end (CAFe) is a demo superconducting proton linac for an accelerator-driven subcritical system (ADS). It includes an electron-cyclotron resonance ion source, a low-energy transport line, a radio-frequency quadrupole, a medium-energy transport line, a superconducting section, a high-energy transport line, and a beam dump. The design energy and current are 20 MeV and 10 mA, with a beam power of 200 kW. The goal of the CAFe is to demonstrate the 10-mA ability of a full superconducting linac, especially in the low-energy region. In previous beam commissioning, the maximum beam power achieved was 34 kW, which was limited by the capacity of the beam dump. Thus, for the high-power beam commissioning of CAFe, a new 200-kW beam dump has been designed and developed. Based on the thermal analysis, a maximum power density of 200 W/cm2 is adopted for the dump. To avoid a high-level residual dose, the material of the dump is aluminum alloy (Al6063). The dump is a conical structure, with water flow in the interlayer. During beam commissioning, the dump withstood 200-kW proton beam power and collected a total charge of 2049 mAh.

The Influence Mechanism of Space-Time Kinetics of ADS Subcritical Reactor under Beam Transients

The space-time kinetics of ADS Subcritical Reactor (ADSR) under beam transients play an important role in ensuring the reliability of the control and safety system of the accelerator-driven subcritical system (ADS). In order to elucidate the effect of high heterogeneity of neutron flux density in space-time on the neutron space-time kinetics of ADSR under different subcriticality and beam transients, in this paper, the multimode core few-group constants, which is more adaptable to the beam transients, is used to investigate the mechanism of neutron flux density, core few-group constants, and kinetic parameters of ADSR under the synergistic effect of external neutron source, subcriticality, and the beam transients. The results show that with the deepening of the subcriticality, with the increasing role of external neutron source, the neutron flux density of the ADSR has a higher heterogeneity of space-time, which leads to a larger difference in the core few-group constant library of different modes, and thus a larger difference in the kinetic parameters (especially the neutron generation time) of different modes. Therefore, in the study of the influence mechanism of neutron space-time kinetics of ADSR under beam transients, the multimode core few-group constants should be used, and the influence of external neutron source and subcriticality on the kinetic parameters, especially the neutron generation time, should be emphasized.

Strategies of eliminating nuclear waste using accelerator-driven system in the transition stage for sustainable and clean nuclear energy in China

Based on the current situations and development tendencies of nuclear energy in China, three scales of nuclear-energy development are predicted. This work explores the strategies of transmuting the Minor Actinides (MAs) in the spent nuclear fuel using Accelerator-Driven Subcritical systems (ADS) to achieve the transition to sustainable and clean nuclear fission energy. The mass-flow data of fuel cycle with time for ADS transmutation system is obtained through simulations, which provides the basic reference for the fuel fabrication, the reprocessing scale and the interim storage of discharged fuel in Chinese ADS systems arranged in different stages. The time required for eliminating over 95% MAs inventory from Pressurized Water Reactor (PWR) spent fuel is discussed. The mass and toxicity of final high-level waste in different stages are analyzed to demonstrate the excellent ability of ADS to eliminate the mass of MAs and the inventory of high-level waste.

Benchmark shielding calculations for fusion and accelerator-driven sub-critical systems

We conducted benchmark calculations of neutron-shielding experiments for fusion applications such as (1) Neutron spectra in iron shields with 14 MeV neutrons; and (2) Leakage neutron spectra from various sphere piles by 14 MeV neutrons, and for Accelerator-Driven Sub-Critical system (ADS) such as (3) Neutron energy spectra after transmission through iron and concrete shields using a quasi-monochromatic neutron source, (4) Thick target neutron yield produced by high-energy heavy ion incidence on a thick target, and (5) Induced radio activity in concrete exposed to secondary particles produced by heavy-ion incident reaction on an iron target by using the Particle and Heavy Ion Transport code System (PHITS). For case (1), the calculated neutron energy spectra using the nuclear data libraries, JENDL-4.0, agreed with the experimental data in iron shields. For the cases (2) of Al, Ti, Cr, and As piles, the neutron energy spectra calculated with JENDL-4.0 agreed with the experimental results well. For the case (3), the neutron spectra calculated with JENDL-4.0/HE reproduced the experimental data because the proton data library of7Li can produce source neutrons for proton incident reactions. For the case (4), calculated results for thick target neutron spectra produced by a 400 MeV per nucleon carbon incident reaction on lead reproduced the experimental data well. For the case (5) with a neutron source produced by the 200–400 MeV per nucleon heavy-ion incident reaction, the calculated results of the reaction rate depth profiles of197Au (n, γ)198Au reactions reproduced the experimental results within a factor of 2. Overall, PHITS with nuclear data libraries reproduced the experimental data sufficiently well. Thus, PHITS has a potential application in the design of advanced reactor systems, such as fusion and ADS facilities. This experimental data are also useful in validating nuclear reaction models in other Monte Carlo codes and evaluating nuclear data libraries for advanced reactor systems.

Thorium as an abundant source of nuclear energy and challenges in separation science

Abstract Today about 440 nuclear power plants, with total installed capacity of 390 GW(e) are in operation worldwide generating around 10% of global electricity which are largely fuelled by enriched uranium oxide [Nuclear Power in the World Today. https://world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx]. Thorium is 3–4 times more abundant than uranium and needs to be exploited by countries with limited stock of uranium. Historically, there have been several attempts to develop Th based reactors, but none has reached commercial scale. In recent years, High Temperature Reactor based on thorium has gained prominence for production of hydrogen with long term goal of complete carbon neutrality. However, unlike natural uranium, which contains ∼0.7% fissile 235U isotope, natural thorium does not contain any ‘fissile’ material and is made up exclusively of the ‘fertile’ 232Th which can be converted to ‘fissile’ 233U, thereby enlarging the fissile material resources. However, there is a need to develop robust closed fuel cycle to address to the challenges of high gamma dose due to the presence of decay products of 232U. It is necessary to gain more experience with promising THOREX process to achieve the desired recovery and D.F. of 233U from the irradiated 232Th. There is also scope to have a close look at some of the alternative extractants and emerging separation techniques for the reprocessing of spent Th based fuels. In view of the distinct advantages of non aqueous reprocessing over aqueous reprocessing, there is need to intensify the efforts to develop the former on a commercial scale. Molten Salt Breeder Reactor (MSBR) is particularly promising in this context. There is a need to investigate Th as energy amplifier under Accelerator Driven Sub-critical System (ADSS) which has potential to burn long lived radio nuclides, considered as a threat to environment over million of years.

Application of the improved quasi-static coupled probability theory method to transient safety analysis of an experimental facility

The accelerator-driven sub-critical system is driven by external neutron sources, which are generated by the spallation reaction and maintain the stable operation of the sub-critical core, while the external neutron source increases the complexity of reactor neutron kinetic processes. This article focuses on simulation analysis of neutron space–time kinetics with a dynamic analysis code, which is developed based on the improved quasi-static approximation and Monte Carlo neutron transport method. The amplitude function and shape functions are solved to achieve the dynamics simulation process. Then, the transient responses of beam interruptions and reactivity insertions are calculated and analyzed for an experimental facility. To further verify the correctness and reliability of dynamic behavior, the simulation results are compared with experimental values, and the results show that the normalized neutron fluxes varying with time are in good agreement with the corresponding values. It can be concluded that the improved quasi-static coupled probability theory method can be used to solve the neutron space–time kinetic problem of the experimental facility, and the results are reliable.

DEVELOPMENT AND VALIDATION OF FIXED-SOURCE DEPLETION METHOD FOR ACCELERATOR-DRIVEN SUB-CRITICAL SYSTEM

DEVELOPMENT AND VALIDATION OF FIXED-SOURCE DEPLETION METHOD FOR ACCELERATOR-DRIVEN SUB-CRITICAL SYSTEM

Preliminary Neutronics Study of an Accelerator-Driven Molten Spallation Target–Molten Lithium Source of Tritium

Current tritium production might not be enough for all future fusion research reactors. Different approaches for tritium production have been studied in the past, one of which was tritium production using the accelerator-driven subcritical systems. This idea was dismissed in the 1990s as uneconomical when compared to using existing commercial light water reactors. This paper presents changes to the basic idea, mainly the use of a molten spallation target and molten lithium breeding volume. This advanced design is described, optimized for tritium yield using the MCNP 6.2.0 code, and compared between different accelerators. The optimized configuration consists of a 1-GeV, 200-mA proton accelerator, a molten Pb-Bi eutectic spallation target with a length of 60 cm and a diameter of 75 cm, and molten lithium breeding volume with dimensions of 500 cm in length and 900 cm in diameter. As calculated, the annual production of the proposed accelerator-driven tritium production system could be as high as 350 g of tritium with the optimized configuration.

Analysis of representative unprotected accidents for a sub-critical lead–bismuth eutectic reactor using IMPC-transient

For an accelerator driven sub-critical system (ADS), the transient analysis of the sub-critical reactor is very important. It is better to use the 3D neutron transport kinetic model rather than the 0D point reactor kinetic model due to the change of the neutron spatial distribution in some conditions. The code IMPC-transient has been developed to provide an effective system safety analysis tool for Chinese ADS project, in which3D neutron transport kinetics is available. A 10 MW ADS conceptual scheme, in which the target power is 2.5 MW and the reactor power is 7.5 MW, was proposed to test the applicability of IMPC-transient in sub-critical lead-bismuth eutectic (LBE) reactor. The steady state and three accident cases including unprotected loss of flow(ULOF), unprotected beam overpower(UBOP) and unprotected beam-trip(UBT) have been simulated, and the dynamic thermal-hydraulic response was focused on. The results show that IMPC-transient has the function of analyzing the ULOF, UBOP and UBT conditions for the sub-critical LBE reactor, and the 7.5 MW reactor conceptual scheme is feasible under steady state and has remarkable resistance against ULOF, UBOP and UBT.

Evaluation of OpenMC calculations coupling with PHITS, FLUKA, and GEANT4 for ADS study

The Accelerator-Driven Subcritical system (ADS) is a subcritical reactor driven by the spallation neutrons generated in a spallation target under the bombardment of proton beam from an accelerator. To study ADS neutronics, the external spallation neutrons should be investigated carefully for coupling with a reactor core. This work focuses on the investigation into the OpenMC calculations by using different nuclear data libraries coupling with different high-energy Monte Carlo programs such as PHITS, FLUKA, and GEANT4 for ADS neutronics simulation. MCNPX direct calculations is performed as the baseline to compare to coupling-calculations. Firstly, the information of leaking neutrons from a spallation target are calculated with different codes and physical models to evaluate difference from the direct calculations to the coupling-calculations. Secondly, the neutronics characteristics of OECD-ADS model are calculated by using OpenMC calculations coupling with a surface-source from three high-energy codes to compare to MCNPX direct calculations. The neutronics parameters of mono-energy neutron for OECD-ADS evaluated from OpenMC and MCNPX with ENDF/B-VII.0 data library or only from OpenMC with different libraries are found to be in good agreement. The effect of high-energy neutrons is evaluated to be difference of around 25% in beam requirements by MCNPX direct calculations with INCL model and PHITS-OpenMC coupling-calculation with ENDF/B-VII.0 below 20 MeV. The differences in beam requirements between different coupling-calculations with the same library are compared. Moreover, the discrepancies in beam requirements from PHITS-OpenMC with JENDL-4.0/HE from 20 MeV to 200 MeV are around 15%. Finally, both neutron profiles and neutron spectra from coupling-calculations agree well with these from MCNPX direct calculations outside the coupling region of target.

Corrosion Behavior of Ti3SiC2 in Flowing Liquid Lead-Bismuth Eutectic at 500 °C.

MAX phases are promising candidate structural materials for lead-cooled fast reactors (LFRs) and accelerator-driven sub-critical systems (ADSs) due to their excellent corrosion resistance in liquid LBE. In this work, one of the typical MAX phases, Ti3SiC2, was exposed to the flowing LBE with a saturated oxygen concentration at 500 °C for up to 3000 h. The corrosion behaviors, including the evolution of the corrosion layer, mechanical properties and wettability, were evaluated via X-ray diffraction, a scanning electron microscope equipped with an energy-dispersive X-ray, a microhardness test and contact angle measurement. The results reveal that a corrosion structure with a duplex layer was formed on the sample surfaces. The outer layer was a diffusion layer, which always remained thin (<3 μm) during the whole test due to the erosion effect caused by the flowing LBE. The inner layer was the stable protective oxide layer, and its thickness increased with exposure time. The growth of the corrosion structure improved the microhardness and reduced the wettability with regard to LBE, which was beneficial to inhibiting further surface corrosion of Ti3SiC2.

Beam physics design of a 30-MW beam transport to the target for an accelerator-driven subcritical system

The Japan Atomic Energy Agency's accelerator-driven subcritical system (JAEA-ADS) proposes the reduction of nuclear waste through the transmutation of minor actinides. The JAEA-ADS drives a 30-MW proton beam to a spallation target to produce neutrons for a subcritical 800-MWth reactor. The beam must be transported from the end of the linear accelerator (linac) to the target located inside the reactor core with high beam power stability and low peak density to ensure beam window integrity, which is a primary concern for the ADS project. Additionally, the design of the beam transport to the target (BTT) must be compatible with the established reactor design, and the elements that comprise the BTT must facilitate the maintenance and replacement of the fuel and the beam window. To this end, a robust-compact BTT design was developed through massive multiparticle simulations. First, the beam optics was optimized to guarantee beam window feasibility requirements by providing a low peak density of less than 0.3 μA/mm2. Then, beam stability was evaluated and improved by a simultaneous application of input beam and element errors. The input beam errors were based on the beam degradation obtained by implementing fast fault compensation in the linac, which is a key strategy to attain high-reliability operation. The results show that the BTT design fulfills reactor and beam window requirements for JAEA-ADS.