Subcritical Reactor Research Articles

Parametrical Choice of the Optimized Fusion System for a FFHR

Fusion–fission hybrid reactors are concepts of subcritical reactors based on the coupling of fusion and fission devices. In this case, the fusion reactor would work as an external neutron supplier for the fission core of the machine. Such systems could, in principle, operate as multi-purpose machines, such as energy generators, breeders and waste burners. The large availability of fusion and fission technologies makes the choice of devices to couple quite chaotic. In fact, most of the concepts proposed in the literature are based on attempts without real optimization. The purpose of this paper is to propose a parameter which could provide practical information regarding the choice or the design of the fusion system of an FFHR. An engineering approach based on the estimation of the energy efficiency of FFHRs was used. An evaluation of the parameter and some of its possible practical applications are shown. Obtained results indicate that, from a geometrical point of view, compact machines would need lower Q-values to reach high neutron source performance.

Real-time monitoring and protection strategies for dense granular flow spallation target in Accelerator-Driven System

An innovative concept of a high-power, gravity-driven, dense granular spallation target has been integrated into the prototype design of the China initiative Accelerator-Driven System (CiADS), which is envisioned as a promising nuclear demonstration facility aimed at converting long-lived fission products and minor actinides into short-lived isotopes. This spallation target system, bridging the proton beam accelerator and the subcritical reactor, plays a crucial role in ensuring safety control and facilitating dynamic operational strategies. In this study, we have developed a system design for an online detector array, incorporating several neutron fission chambers and thermocouples installed in the gap between the spallation target and the subcritical reactor to monitor operations. Furthermore, we have devised real-time monitoring and protection methods to tackle the challenges of measuring beam position and the blockage condition associated with granular flow, considering the distribution of neutron flux and heat deposition under abnormal irradiation conditions. Monte Carlo simulations have demonstrated the applicability and feasibility of the control system for the dense granular spallation target in the accelerator-driven system. The numerical results confirm that the proposed control system meets the requirements for stable measurement with acceptable accuracy.

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.

Nuclear Transmutation of 99Tc Utilizing Proton Spallation and Compact Subcritical Assembly

An innovative design is introduced for neutron transmutation employing a proton accelerator in conjunction with a compact subcritical system. The transmutation converter comprises a spherical target enveloped by a subcritical assembly. The subcritical assembly consists of a moderator and low-enriched uranium in shell plates. The subcritical assembly has an inner radius of 10 cm and a thickness of 40 or 55 cm. The material used for the target is lead, and beryllium or beryllium oxide is used as a moderator. Low-enriched uranium in the subcritical assembly contains 5% 235U. The transmutation half-life is inversely proportional to the integral of epithermal 99Tc capture rates. The MCNP6 simulation demonstrates that the transmutation half-life is less than 1 year when exposed to 1-GeV protons at 5 mA. Additionally, it is notable that this half-life can be further reduced with increased proton energies and currents. Previous studies have reported that the 99Tc transmutation half-life using fast reactors and an accelerator-driven system ranges from tens to hundred years; this design concept represents a substantial advancement to previous research efforts.

Production Cross Sections of Residual Nuclides from 93Zr + p at 27 MeV/Nucleon

Abstract Nuclear transmutation emerges as a promising approach for reprocessing high-level waste, specifically treating long-lived nuclides like 93Zr from spent fuel. It is essential to accumulate reaction data for these nuclei to advance this prominent treatment and to build a comprehensive understanding of reaction mechanisms. In this study, the residual production cross sections resulting from proton-induced reactions on 93Zr were measured at 27 MeV/nucleon in inverse kinematics. At the RI Beam Factory (RIBF) the OEDO beamline was used to deduce production cross sections for isotopes, 91 − 93Nb, 91, 92Zr, and 88, 89Y. Comparing the results from this study and prior research with calculated excitation functions, a moderate agreement is found with theoretical predictions derived from TALYS and CCONE. The measured cross sections offer valuable insights for future considerations in nuclear-waste treatment facilities. This is particularly relevant for facilities exploring innovative methods, such as accelerator-driven systems.

Properties of W–Ta Materials of the Neutron-Producing Target of the Subcritical Assembly at the National Scientific Centre ‘Kharkiv Institute of Physics and Technology’ of the National Academy of Sciences of Ukraine

The works in the field of radiation materials science of target materials of neutron sources based on the subcritical assemblies controlled by linear accelerators of electrons or protons, so-called accelerator driven systems (ADS), are reviewed. Now, electronuclear ADS systems are the prototype of safe nuclear reactors of the 5th generation. In connection with the physical start-up of the neutron source facility of the National Scientific Centre ‘Kharkiv Institute of Physics and Technology’ of the N.A.S. of Ukraine (NSC ‘KhIPT’ NASU), the target of which is fabricated from powdered tungsten covered with tantalum, the issues of preparation technology, construction, and physical and mechanical properties of W–Ta materials of targets in non-irradiated and irradiated states are considered. The nuclear-physical processes of radiation damage to the target during co-irradiation of it with both neutrons of a subcritical assembly and high-energy e- and γ-beams are analyzed. The target resources of ADS systems are estimated. As noted, the difficulty of predicting the ‘survivability’ of the W–Ta target also relates to the fact that, except for the works carried out at the NSC ‘KhIPT’ NASU in 70–90th of the last century, there are no experimental works in the world on the radiation damage of reactor materials by high-energy electrons with an energy of 100 MeV and above.

Baseline design of laser fusion research reactor with MW class laser facility

We propose a sub-ignition/burning reactor which is named the Laser-fusion Subcritical Power Reactor Engineering Method (L-Supreme). The reliabilities of L-Supreme in a MW class laser facility are assessed with respect to the following points: a reactor core, a target chamber, a target delivery system, an Exhaust Detritiation System (EDS), and neutron shielding. The Japan Establishment for Power-laser Community Harvest (J-EPoCH) would be applied as a MW class laser facility. A non-cryogenic glass balloon target filled with gaseous deuterium-tritium (DT) is contained in a target capsule. A chain-type magazine system might be used for a mass supply of the target capsules. Each target capsule is delivered to the center of a reactor core at 1 Hz. A batch of 10 000 laser shots would realize 0.22 MJ fusion power. The amount of tritium per batch is 1.51 × 1012 Bq. During laser experiments, unburned tritium is evacuated and transferred into an Exhaust Detritiation System (EDS). An evacuation rate of more than 0.1 m3 s−1 is required in order to recover less than 5000 Bq m−3 of the threshold of tritium concentration within 1 h. For safety, emergency situations such as tritium leakage in facilities are examined. The EDS works by internal circulation processes. Assuming leakage of tritium for a batch, an air circulation flow rate of 4100 Nm3 h−1 is required in an experimental hall for recovering less than 5000 Bq m−3 within 48 h. A primary and secondary neutron shield concept are proposed and would provide full neutron shielding. We conclude that it is possible to construct the L-Supreme system by marshalling current technologies.

A PHITS based-computational model of a TRIGA-fueled subcritical reactor for gamma dose mapping

Since 1988, the Philippines lacked local access to a nuclear facility, creating a significant void in this field of study for Filipinos. However, after a hiatus of 34 years, this gap was addressed with the recent authorization granted to Philippine Research Reactor 1 (PRR-1) Subcritical Assembly for Training, Education, and Research (SATER), allowing it to resume operations. In this work, a PHITS-based computational model was developed for the recently commissioned PRR-1 SATER. The model utilized a simplified model of the Training, Research, Isotope, General Atomics (TRIGA) fuel that releases photons with 0.6617 MeV energy from the Cs-137 fission product in the fuel. Compared to previous works on photon transport mapping, which utilized average source definition, this study employed individually defined fuel intensities and compared them with the averaged source definition for the fuel. The two fuel source definitions showed noticeable differences inside the reactor tank which is relevant for mixed-field irradiation applications of a research reactor. However, defining the fuel rods by their average strength is sufficient for radiation protection purposes. Simulations were also performed for fuel source definitions based on the average and ±1 standard deviation of the gamma intensity. Gamma doses received by cylindrical phantoms positioned at 0.5 m from the surface of the reactor tank for 500 h were found to be 1 % of the radiation dose limits per year and 4 % of the average dose limit for 5 years as stipulated by the Code of Philippine Nuclear Research Institute (PNRI) Regulations. Loss of water accident was also analyzed based on a conservative exposure time of 500 h. This resulted in a dose value that is only 45.5 % of the dose identified as the emergency turnback guidance of the IAEA. Lastly, PHITS calculated values of gamma doses were found to agree well, with 0.98 ratio, when compared with gamma doses measured at specified locations in the reactor. Results of this study confirm the inherent safety of the PRR-1 SATER in terms of radiological shielding for Cs-137 photons.

Cladding fatigue analysis under frequent beam trips for China initiative Accelerator Driven System

China initiative Accelerator Driven System (CiADS) is a 10 MW lead–bismuth eutectic (LBE) cooled subcritical reactor, which is designed to demonstrate the engineering feasibility of the ADS concept. An elaborated methodology was developed to deal with the nonlinear mechanical behaviors of fuels under transients. Based on this methodology, the fuel mechanical module was accomplished and coupled with the neutron dynamics module and thermo-hydraulics module in the extended BELLA code. The cladding mechanical simulation under frequent beam trips for CiADS was carried out using BELLA, and fatigue analysis based on the experimental data was discussed. Combined with the CiADS beam-trip transients, it is concluded that the tolerance of the CiADS cladding to beam trips is between 1000 and 11,000 cycles.

Simulation of the Measured Reactivity Distributions in the Subcritical MYRRHA Reactor

Simulation of the Measured Reactivity Distributions in the Subcritical MYRRHA Reactor

Optimization of photoneutron source for use in subcritical reactors

This work is an effort to maximize the number of output neutrons of a photoneutron target for 100 MeV incident electrons. The work steps were; to select the appropriate material, select the appropriate shape, and find the optimized dimensions. The simulations of this work were done with MCNPX2.6 simulation code. At first, U-235 was selected as the best material for the target, among some heavy atoms from the number of outlet neutron point of view. Then the best shape for the target was selected from geometric shapes that have been considered for the target and the dimensions of the target were optimized. After these parts, the energy spectrum of outlet neutrons was estimated and after that, the deposited energy of neutrons, electrons, and photons in the target was estimated and drowned with Tec plot.

Design, fabrication and validation of an electrical conductivity principle based two-phase detection sensor array for molten lead (Pb) based heavy metal coolants up to 600°C

Molten lead (Pb) and its alloys (PbBi and PbLi) are of immense interest for various nuclear engineering applications, including but not limited to advanced Lead-cooled Fast Reactors (LFRs), tritium Breeding Blankets (BBs) of fusion power plants and spallation targets for Accelerator-Driven Systems (ADS). Owing to their attractive thermophysical properties, these advanced fluids assert their candidacy to address the critical requirements of neutron multiplication, neutron moderation, high temperature coolants and tritium breeders, enabling the operation of next generation nuclear systems at high temperatures with better efficiencies. However, for numerous reasons such as a compromise of structural integrity at the heat transfer interface, presence of an inert cover gas during charging of molten metal in the loop, and the fusion fuel cycle itself may lead to molten metal-gas two-phase flows with high density ratios. At present, no effective diagnostics exist to detect such operational and accidental occurrences in high temperature molten metal systems resulting in a severe lack of relevant experimental studies. To address these limitations and to advance the current understanding toward two-phase regimes in high temperature Pb-based melts, the present work focuses on the design and assembly aspects of an electrical conductivity-based two-phase detection sensor array, utilizing high purity α-Al2O3 coatings with AlPO4 binder as electrical insulation layers. This paper discusses the design considerations, thermal analysis, systematic selection of structural/functional components along with preliminary results from the probe performance tests in very high temperature (600°C) static molten Pb column for real time detection of argon gas bubbles rising within the melt. Quantitative estimations of time-averaged void fraction, average bubble impaction frequency and average bubble residence time are presented from the preliminary experimental investigations.

Status of the MINERVA cryomodules and associated cryogenic system (MYRRHA phase 1)

MYRRHA at SCK CEN in Mol/Belgium will be a pre-industrial large-scale Accelerator Driven System for unparalleled research opportunities in spent nuclear fuel, nuclear medicine, and fundamental and applied physics. In 2018 the Belgian government released funding for MYRRHA’s first phase, MINERVA, for a staged implementation and operation. It covers the design, construction, and commissioning of the continuous-wave superconducting RF proton linac up to 100 MeV, as well as dedicated user target stations. The MINERVA proton linac will accommodate 30 identical cryomodules to boost the beam energy delivered by the normal-conducting frontend from 16.6 MeV to 100 MeV. Each cryomodule will contain two superconducting RF single-spoke cavities immersed in a superfluid Helium bath at 2 K. The design and architecture of the associated cryogenic system is derived from the stringent linac reliability requirements imposed by the future subcritical nuclear reactor. We present the architecture, design, and development status of the MINERVA cryomodules and associated cryogenic system towards the implementation phase of the project as part of a collaboration between ACS, CEA/DSBT, IJCLab, and SCK CEN. We also provide an overview of the initial outcomes of cryogenic and RF tests for the prototype MINERVA cryomodule, which are still ongoing at IJCLab.

Preliminary studies of the MINERVA cryogenic supply system

MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) will be composed of a 600 MeV LINear ACcelerator (LINAC) with a large number of cryomodules and a 100 MW thermal power subcritical nuclear reactor cooled by lead-bismuth. The MINERVA MYRRHA Isotopes productioN coupling the linEar acceleRator to the Versatile proton target fAcility) project is the first phase of the MYRRHA project composed of a 100 MeV, 4 mA continuous-wave proton LINAC. The MINERVA LINAC takes advantage of 60 superconducting radiofrequency (RF) cavities cooled at 2 K by saturated superfluid helium (He II). The MINERVA cryoplant will supply the required cryogenic cooling power of the LINAC through cryogenic lines and cryogenic valve boxes. This paper describes the LINAC cryogenic system supply architecture, the different operating modes, the heat loads, the cryoplant main requirements and the strategy to comply with high reliability requirements. The MINERVA cryoplant shall provide helium flows at 40 K for the thermal shielding, at 5 K for the cooling of the RF couplers and at 2 K for the 60 superconducting cavities installed in 30 cryomodules. The total equivalent refrigeration power of the MINERVA cryoplant is about 3.5 kW at 4.5 K. The cryoplant is composed of a warm compression station including sub-atmospheric volumetric compressors, helium gas storages and a refrigeration cold box with cold centrifugal compressors.

Comparative study on responses of three candidate materials for ADS beam/target windows to proton irradiation: T91, SIMP and Ti-6Al-4V

Accelerator-Driven System (ADS) represents an advanced nuclear energy system designed for the purpose of transmuting and eliminating nuclear waste. The irradiation tolerance of a material stands out as a critical factor in determining its availability for ADS beam/target windows. This study delves into the response of three promising candidates (T91, SIMP, and Ti-6Al-4V) for ADS beam/target windows to proton irradiation, as investigated by a 1.4 MeV H2+ irradiation experiment to dose of 1.5 peak dpa at 460 °C. Their cavity swelling and hardening behavior were estimated using Transmission Electron Microscope (TEM) and Nanoindentation, respectively. It was demonstrated that SIMP steel shows lower cavity swelling but slightly higher irradiation hardening compared to T91. Notably, no cavity swelling is observed in Ti-6Al-4V, but it experiences a higher level of irradiation hardening. The nucleation and evolution mechanisms of irradiation-induced defects (including cavities, dislocation loops, and precipitates) and their contributions to the proton irradiation response are discussed. Furthermore, a summary of the advantages and disadvantages of the three materials as candidates for proton beam/target windows is provided.

Burnup study on the effective transmutation of minor actinides based on multi-enrichment fuel in the ADS subcritical reactor

In order to solve the problem that the single-enrichment core parameters of the ADS subcritical reactor exceed the safety limit and to improve the MAs effective transmutation in the ADS system, short-term and long-term burnup calculations are carried out based on multi-enrichment fuel and the physical parameters of the sub-critical reactor are calculated and filtered throughout the calculation process. The MAs effective transmutation of the ADS subcritical reactor is calculated using the double-layer nested MAs effective transmutation calculation method. The short-term case is obtained for the target parameters, different fuel partitioning methods, and different fuel composition; long-term burnup calculations are conducted under different refueling methods; finally, a recommended case is given. The ADSOC code, coupled with FLUKA and OpenMC codes, can realize the multi-enrichment fuel refueling, as well as tracking and screening of physical parameters during burnup calculations in the ADS subcritical reactor.

Changes in chemical composition of TixAl1−xN coatings immersed in oxygen-saturated Lead–Bismuth Eutectic at low and moderate temperatures (250 °C ≤ T ≤ 410 °C)

Lead–Bismuth Eutectic (LBE) will serve as a liquid metal coolant in accelerator-driven systems, posing a corrosive threat to exposed materials. To address this challenge, TixAl1-xN coatings (0.38 ≤ x ≤ 0.58) were applied onto AISI 316 L austenitic stainless steel using the reactive bipolar magnetron sputtering technique. These coated samples underwent immersion in static oxygen-saturated LBE at temperatures of 250 °C and 360 °C for durations of 500 h and 1000 h, and at 410 °C for 500 h. XPS depth profiles revealed minimal oxidation at 250 °C even after 1000 h. However, at 360 °C, a mixed oxide layer of (Ti, Al)Ox was formed on the coating's surface. Exposure to LBE at 410 °C for 500 h led to the creation of an oxide bilayer comprising TiO2 (outer sublayer) and (Ti, Al)Ox depleted of Ti (inner sublayer). A model is proposed to illustrate the oxidation mechanism.

Energy Amplifier Systems as Sustainable Nuclear Reactors: An Overview

One of the present major issues for industrialised societies is the environmental impact of energy production. Nuclear power is identified as a possible sustainable opportunity to provide a technological answer to this problem. This review aims to overview the physical bases of accelerator-driven systems, focusing on spallation and transmutation phenomena. A discussion on the possible use of these nuclear devices is developed in the context of sustainable energy production, showing a possible new approach to nuclear energy, based on the developments of accelerator physics and technology during the last century.

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.

The influence of source locations of different multi-beam concept on the power density distribution and nuclear waste transmutation performance for ADS–NWT

The multi-beam concept for the accelerator driven subcritical reactor (ADS) has the advantages in reducing the requirements for the accelerator and can flatten the power distribution of the core. However, the layout of the multi-beam should meet the goal of balancing the relationship between the total power density, the neutron leakage, and the nuclear waste transmutation performance. For the further study of the multi-beam concept for the ADS, this paper focuses on the influence of the source locations of different multi-beam concept on the power density distribution, the neutron leakage, and the nuclear waste transmutation performance for the ADS for a nuclear waste transmutation reactor (ADS–NWT). The different variations on the radial power density distribution and the nuclear waste transmutation performance for the three-, four-, six-, and seven-beam concept for ADS–NWT were analyzed. The results show that the related neutronics performance for the multi-beam concept for ADS-NWT is not only affected by the external source locations and the core geometry, but also affected by the keff and the interference effect between the spallation targets. Moreover, the fission reaction ratio and the fission reaction / (n, gamma) absorbtion ratio for minor actinides (MA) and plutonium (Pu) for the few beams concept are both higher than that for the many beams concept. Based on the analysis of the influence of source locations on the neutron spectrum, the total neutron flux, and the nuclear waste transmutation performance for MA and Pu, the related conclusions about how to arrange the best beam position from the perspective of nuclear waste transmutation and production capacity are provided.