Accelerator-Driven Subcritical Research Articles

Precipitation characteristics and growth mechanism of Fe and Cr from liquid lead-bismuth eutectic by quenching in liquid nitrogen

The compatibility of structural steels with liquid lead-bismuth eutectic (LBE) restricts the development of the lead-cooled fast reactor (LFR) and the accelerator driven sub-critical (ADS) system. During the reactor operation, alloying elements in steel can dissolve into LBE. The dissolved alloying elements could precipitate in cold parts of the reactor due to the decrease in solubility, which can cause pipe clogging and worsen heat transfer. Therefore, it is necessary to study their precipitation characteristics to provide a reference for the filtration process. In this paper, Fe, Cr, and a mixture of Fe and Cr were added to liquid LBE at 1173 K and quenched in liquid nitrogen to study their precipitation characteristics. The scanning electron microscope (SEM) and field-emission scanning electron microscope (FESEM) were used to analyze the morphology, and the phase structure was identified by an X-ray diffractometer. The chemical compositions of precipitates were analyzed by an energy dispersive spectrometer (EDS, Esprit Compact, Bruker) and an electron probe microanalyzer (EPMA, EPMA-8050 G, Shimadzu). The solid-liquid interface structure and growth mechanism of precipitates were also discussed. The difference in growth mechanisms resulted in various morphologies for the precipitates. There were three morphologies of precipitates: faceted dendrite, polyhedron (cube, octahedron, and hopper), and seaweed dendrite. All the precipitates in LBE have a faceted growth character except the seaweed dendrites, irrespective of their morphology. The growth of Fe, Cr, and Cr-Fe faceted dendrites originated from continuous growth followed by lateral growth. On the contrary, the cubic and octahedral precipitates were controlled by the spiral growth mechanism, and the growth mechanism of hopper crystals was two-dimensional nucleation. The formation of seaweed dendrites was caused by a strong local undercooling of nonfaceted dendrites.

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

Study Analysis of Multiplication Factor on ADS Transmutation System

New research technology for partition and transmutation (P-T) of minor actinide (MA) contained in high-level waste (HLW) has been carried out to design accelerator-based transmutation system or commonly known as Accelerator Driven Subcritical (ADS) device. The objective of this system is to eliminate or minimize high-level radioactive waste that has long half-life and to develop long-term safety assurance in HLW management. Analysis done by using Origen2.1 and mCnP6 codes. As matrix, Th-232 with optimum weight 75% is used.. Comparing with , analysis results using MCNP shows that the use of PWR nuclear spent fuel for ADS device can be done by reprocessing to eliminate U-238 nuclide, which is the source of the formation of plutonium nuclide and minor actinides. From the results and discussion, it can be concluded that observation on transmutation of transuranic nuclides using ORIGEN2.1 Code on ADS device has been conducted successfully with LMFBR library. 15%-Th232 fuel has been justified as the most optimum ADS fuel based on K-inf reached at EOC on various fuel types. Mass reduction occurs at EOC for U-236, U-235, U-234, Th-232, Np-237, Pu-238, Am-241, Pu-242, and Cm 244. Radionuclides that experience mass changes during cooling time are Pu-238, Pu-240, Am-241, Pa-233, and Cm-244.

Beam-target configurations and robustness performance of the tungsten granular flow spallation target for an Accelerator-Driven Sub-critical system

The dense granular flow spallation target is a new target concept proposed for an Accelerator-Driven Sub-critical (ADS) system. In this paper, the beam-target configurations of a tungsten granular flow target for the ADS with a thermal power of 1 GW is explored. The beam profile options using different scanning methods are discussed. The critical geometry parameters are adjusted to investigate the performance of the granular target from the aspects of neutron efficiency, stability and temperature distribution in target medium. To figure out how the target under accident conditions would behave, different clogging conditions are induced in the simulation. The dynamic processes are analyzed and some important parameters such as abnormal temperature rise and beam cutoff time window are obtained. The response of the sub-critical reactor to a clogging accident is also investigated. It is indicated that the monitoring of the granular flow by the neutron detectors in the sub-critical core will be effective.

ADS design concept for disposing of the U.S. spent nuclear fuel inventory

The United States inventory of the spent nuclear fuel (SNF) is ~80,000 metric tons of heavy metal (MTHM) at the end of 2018, which contains ~131 tons of minor actinides (MAs) and ~669 tons of plutonium. This paper describes a conceptual design of an accelerator-driven subcritical (ADS) system for disposing of this SNF inventory by utilizing the 131 tons of MAs inventory and a fraction of the plutonium inventory for energy production and transmuting some long-lived fission products.An ADS system with a homogeneous subcritical fission blanket was first examined to define the main system parameters. A spallation neutron source is used to drive the fission blanket and it is generated from the interaction of a 1-GeV proton beam with a lead–bismuth eutectic (LBE) target. The fission blanket has a liquid mobile fuel using LBE as the fuel carrier. The fuel materials are dissolved, mixed, or suspended in the liquid fuel carrier. Monte Carlo simulations were performed for three fission blankets to determine the main concept parameters. The loaded amount of actinide materials in the LBE carrier is either 5, 7, or 10% of the total volume of the fission blanket, respectively. The plutonium fraction in the MAs of each fission blanket was selected so that the neutron multiplication factors of the three fission blankets are ~0.980. In addition, Monte Carlo burnup simulations using the MCB5 computer program were performed to analyze the performance of the three conceptual ADS systems. During operation, fresh fuel is fed into the fission blankets to adjust its subcriticality and to control the system power. The burnup results show that the total MA materials consumed are about 30.6, 35.3, and 37.2 tons, after operating the three fission blankets for 35 full-power years with 25-MW 1-GeV proton beam. Thus, the corresponding numbers of ADS systems to utilize the 131 tons of MA materials of the SNF inventory are 4.3, 3.7, or 3.5, respectively.ADS systems with tube bundles inserted in the fission blanket were analyzed to overcome the disadvantages of the homogeneous fission blanket concept. The liquid lead is used as the target material, the mobile fuel carrier, and the primary coolant to avoid the polonium production from bismuth. Physics and thermal–hydraulic analyses were coupled to determine the parameters of the heterogeneous fission blanket. The engineering requirements for a satisfactory performance of the HT-9 ferritic steel structure material have been realized. Two heterogeneous fission blanket concepts with the liquid lead mobile fuel inside or outside the tube bundles were considered. The heterogeneous fission blanket with the mobile fuel inside the tubes shows better performance than the fission blanket with mobile fuel outside the bundle tubes and it is presented in this paper. MCB5 and Serpent, the Monte Carlo burnup computer programs were both used to simulate the fuel burnup in the ADS concept with the mobile fuels inside the tubes for 35 full power years. The results show that five ADS systems can dispose of the total United States inventory of the spent nuclear fuel.

Simulating the Production of Medical Radioisotopes in a Fast Thorium-Cycle ADS with SERPENT

Radiopharmaceuticals are used in nuclear medicine for diagnostic or therapeutic acts. The short decay half-lives of medical radioisotopes, especially those used for diagnostics, imply that they should be produced continuously and transported as quickly as possible to the medical units where they are used. Neutron-rich medical radioisotopes are generally produced in research reactors, like technetium-99m, lutetium-177, holmium-166 and iodine-131. On the other hand, proton-rich radioisotopes are produced via reactions with charged particles from accelerators like fluorine-18, gallium-67, iodine-123 and thallium-201. Beside this, innovative nuclear reactors are advocated as solutions to the issues of nuclear waste production and proliferation threats. Fast neutron, thorium-cycle and accelerator-driven subcritical (ADS) reactors are some of the most promising of them, proposed as safer fuel breeders and “waste burners”. This article examines the use of a fast thorium-cycle ADS with liquid lead-bismuth eutectic coolant for the production of molybdenum-99/technetium-99m and lutetium-177. Burnup simulation has been made with the Monte-Carlo (MC) code SERPENT. It is demonstrated that MC codes can advantageously be used to determine the optimal irradiation time for a given radioisotope in a realistic reactor core. It is also shown that fast thorium-cycle ADS is an economical option for the production of medical radioisotopes.

Study of the Effects of Moderators on ADS System Performance Based on UN-ThO2 Fuel

The neutron spectrum is an essential factor in making possible the increase of 233U isotope breeding from thorium fuel in an accelerator-driven subcritical (ADS) system; therefore, studying the effects of various moderators and coolants on 233U breeding is an important step in ADS performance. This study aims to evaluate the effect of using different moderators and coolants on the ADS system characteristics. Sodium, which was the most common coolant used in ADS reactors, was replaced by light water (LW) and graphite + CO2, separately. In this study, we used uranium nitride as the seed fuel associated with ThO2 as the blanket fuel for all cases. The Monte Carlo transport code MCNPX 2.7.0 was used to calculate neutronic parameters such as effective multiplication factor (Keff), power peaking factor (Pmax/Pav) in the radial direction of the ADS reactor core, actinide isotope evolution during fuel burnup, and power fraction from each fuel type for all cases. The results show that the utilization of graphite as the moderator with CO2 as the coolant allows more 233U production in thorium fuel compared with sodium and LW. On the other hand, LW showed great ability for plutonium and minor actinide transmutation and for energy generation.

ADS Injector-I 2 K superfluid helium cryogenic system

The Accelerator Driven Sub-critical (ADS) system is a strategic plan to solve the nuclear waste problem for nuclear power plants in China. High-energy particle accelerators and colliders contain long strings of superconducting devices, superconducting radio frequency cavities, and magnets, which may require cooling by 2 K superfluid helium (Helium II). 2 K superfluid helium cryogenic system has become a research hot spot in the field of superconducting accelerators. In this study, the ADS Injector-I 2 K cryogenic system is examined in detail. The cryogenic system scheme design, key equipment, and technology design, such as the 2 K Joule–Thomson (J–T) heat exchanger and cryomodules CM1 + CM2 design, are examined, in addition to the commissioning and operation of the cryogenic system. The ADS Injector-I 2 K cryogenic system is the first 100 W superfluid helium system designed and built independently in China. The ADS proton beam reached 10 MeV at 10 mA in July 2016 and 10 MeV at 2 mA in continuous mode in January 2017 and has been operated reliably for over 15,000 h, proving that the design of ADS Injector-I 2 K cryogenic system, the key equipment, and technology research are reasonable, reliable, and meet the requirements. The research into key technologies provides valuable engineering experience that can be helpful for future projects such as CI-ADS (China Initiative Accelerator-Driven System), SHINE (Shanghai High Repetition Rate XFEL and Extreme Light Facility), PAPS (Platform of Advanced Photon Source Technology), and CEPC (Circular Electron-Positron Collider), thereby developing national expertise in the field of superfluid helium cryogenic systems.

Monte Carlo fuel burnup analyses of the Accelerator-Driven Subcritical systems

This paper describes the Monte Carlo fuel burnup analysis performed for the Argonne National Laboratory (ANL) Accelerator-Driven Subcritical (ADS) conceptual design. The ANL ADS conceptual design was developed to dispose of the 131 tons of Minor Actinides (MA) fuel of the current United States Spent Nuclear Fuel (SNF) inventory. It uses a neutron source from 1 GeV 25 MW proton beam with the liquid lead target to drive the subcritical fission assembly. It utilizes the liquid metal slurry fuel concept to load the MAs fuel. The subcritical fission assembly has a neutron multiplication factor of 0.98. The total fission power generated in the system is about 2.67 GW. The system is designed to operate for 35 full power years. Monte Carlo fuel burnup analyses were performed to calculate the amount of MAs consumed by the ANL ADS conceptual design. The MCNP6 computer program was used to simulate the high energy physics of the protons striking the liquid lead target for generating the neutron source. The MCB5 and SERPENT Monte Carlo burnup computer programs were used to simulate the fuel burnup during the ADS operation. In the ANL ADS conceptual configuration, the reactivity loss during the fuel burnup is compensated by adding fresh fuel into the subcritical assembly. In this paper, both batch and continuous fueling modes are examined. The fresh fuel particles are loaded into the slurry fuel carrier at the beginning of each burnup step of the batch-fueling mode and loaded continuously into the slurry fuel carrier during the operation in the continuous fueling mode. Monte Carlo fuel burnup analyses show that one ANL ADS conceptual design can consume about 25.7 tons of MAs fuel during the 35 full power years with the continuous fueling mode. About five units is required to dispose of the 131 tons of MAs.

Proton-induced spallation of mercury and xenon targets for neutron flux produced between CEM03.01 and INCL4-ABLA spallation packages

Accelerator-Driven Subcritical (ADS) reactors are one of the pathways considered for the incineration of minor actinides. They use a proton beam accelerator up to a GeV energy, bombarding a spallation target, usually made of a material of high atomic number (W, Pb, Ta or U). The neutrons generated during the spallation reactions are then multiplied. The main goal of this study is to make a comparison between two models of physical packages via the Monte Carlo code MCNP6. The first package is the INCL4-ABLA and the second one is the CEM03.01, and we have deduced the best package according to the neutron production rate. In this study, we are interested in two cylindrical targets of natural mercury and xenon 20cm in height and 20 in diameter and a proton beam varies from 0.1 to 1.5 GeV.

Proton-induced spallation of mercury and xenon targets for neutron flux produced between CEM03.01 and INCL4-ABLA spallation packages

Accelerator-Driven Subcritical (ADS) reactors are one of the pathways considered for the incineration of minor actinides. They use a proton beam accelerator up to a GeV energy, bombarding a spallation target, usually made of a material of high atomic number (W, Pb, Ta or U). The neutrons generated during the spallation reactions are then multiplied. The main goal of this study is to make a comparison between two models of physical packages via the Monte Carlo code MCNP6. The first package is the INCL4-ABLA and the second one is the CEM03.01, and we have deduced the best package according to the neutron production rate. In this study, we are interested in two cylindrical targets of natural mercury and xenon 20cm in height and 20 in diameter and a proton beam varies from 0.1 to 1.5 GeV.

Research of coupled wall conduction effects on forced and natural circulation of LBE in CLEAR-S

The lead based reactor concept is considered to be the most promising reactor option for the Accelerator Driven Subcritical (ADS) system. Lead based reactor engineering validation facility CLEAR-S is a large scale integrated non-nuclear pool type facility which has been built to provide a unique experimental platform for full-scale prototype components test of lead based reactors. In this article, three-dimensional steady state analysis of flow in the hot and cold pools of CLEAR-S was carried out by using computational fluid dynamics (CFD) code FLUENT during forced and natural circulation conditions. The results showed that the simulation had a good agreement with the design parameters of CLEAR-S and the temperature profile was uniform in the whole domain of the hot and cold pools without considering any conduction through the coupled walls. The temperature distribution in the hot and cold pools became non-uniform with the coupled wall conduction and thermal stratification was observed in the cold and hot pools near the bottom wall of the hot pool. This non-uniform distribution of temperature could cause thermal stresses on equipment, which is dangerous for the integrity of the system. During natural circulation conditions, the coupled wall conduction enhanced the natural circulation and kept the hot pool at a relatively low temperature because the cold pool cooled the hot pool through heat transfer between the walls of the hot and cold pools. Therefore, wall conduction has some advantages and disadvantages as it enhances the natural circulation on one hand but disturbs temperature uniformity on the other hand.

RF tuning and beam commissioning of CW RFQ for China-ADS Injector-I

A 325-MHz continuous-wave (CW) four-vane radiofrequency quadrupole (RFQ) is employed in Injector-I of the China Accelerator-Driven Subcritical System. The radiofrequency tuning and beam commissioning were performed from January 2014 to January 2017. In a cold test, a stability study showed that the design of the segmented resonantly coupling and dipole stabilizer rods can shift the harmful quadrupole and dipole mode from the fundamental mode to above 2.6 MHz. We also found a simplified tuning method for the field unflatness, involving changing the inserted length of a few plug tuners. For achieving CW-beam commissioning, two full-size RFQs were constructed successively. The commissioning results indicate that the beam transmission rate decreased by approximately 3% as the normalized field unflatness decreased by 1%. A 10-MeV CW proton beam with an average beam current of 2.1 mA was achieved at the target of Injector-I, and the output beam energy of the RFQ was 3.18 MeV.

Balanced design and commissioning of a 500W/4.5K helium refrigerator and its liquefier

A 500W/4.5K helium refrigerator for ADS (Accelerator Driven Subcritical) project of CAS (Chinese Academy of Sciences) has been designed. The functional requirements and process analysis of this helium refrigerator are described. Based on the regulation of the high pressure, a balanced design between refrigeration capacity and liquefaction capacity for equal Carnot work with the same high efficiencies is presented. The constraints of components and operation strategies in refrigeration mode and liquefaction mode are discussed. Commissioning results indicated that this 500W/4.5K helium refrigerator can provide 5.74g/s (or 165L/h) liquid helium in liquefaction mode or 550W at 4.5K in refrigeration mode with the respective FOM (Figure of Merit) of 14% or 13.2%. Existing problems were analyzed and discussed through comparing the theoretical calculation and experimental data, and some suggestions are given at the end of this paper.

Toward high-efficiency and detailed Monte Carlo simulation study of the granular flow spallation target

The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed.

Parallel GPU-based collision detection of irregular vessel wall for massive particles

In this paper, we present a novel GPU-based limit space decomposition collision detection algorithm (LSDCD) for performing collision detection between a massive number of particles and irregular objects, which is used in the design of the Accelerator Driven Sub-Critical (ADS) system. Test results indicate that, the collisions between ten million particles and the vessel can be detected on a general personal computer in only 0.5 s per frame. With this algorithm, the collision detection of maximum sixty million particles are calculated in 3.488030 s. Experiment results show that our algorithm is promising for fast collision detection.

Beam commissioning for a superconducting proton linac

To develop the next generation of safe and cleaner nuclear energy, the accelerator-driven subcritical (ADS) system emerges as one of the most attractive technologies. It will be able to transmute the long-lived transuranic radionuclides produced in the reactors of today's nuclear power plants into shorter-lived ones, and also it will provide positive energy output at the same time. The prototype of the Chinese ADS (C-ADS) proton accelerator comprises two injectors and a 1.5 GeV, 10 mA continuous wave (CW) superconducting main linac. The injector scheme II at the C-ADS demo facility inside the Institute of Modern Physics is a 10 MeV CW superconducting linac with a designed beam current of 10 mA, which includes an ECR ion source, a low-energy beam transport line, a 162.5 MHz radio frequency quadrupole accelerator, a medium-energy beam transport line, and a superconducting half wave resonator accelerator section. This demo facility has been successfully operating with an 11 mA, 2.7 MeV CW beam and a 3.9 mA, 4.3 MeV CW beam at different times and conditions since June 2014. The beam power has reached 28 kW, which is the highest record for the same type of linear accelerators. In this paper, the parameters of the test injector II and the progress of the beam commissioning are reported.

CFD Analysis and Design of Detailed Target Configurations for an Accelerator-Driven Subcritical System

High-fidelity analysis has been utilized in the design of beam target options for an accelerator-driven subcritical system. Designs featuring stacks of plates with square cross section have been investigated for both tungsten and uranium target materials. The presented work includes the first thermal-hydraulic simulations of the full, detailed target geometry. The innovative target cooling manifold design features many regions with complex flow features, including 90° bends and merging jets, which necessitate three-dimensional fluid simulations. These were performed using the commercial computational fluid dynamics code STAR-CCM+. Conjugate heat transfer was modeled between the plates, cladding, manifold structure, and fluid. Steady-state simulations were performed but lacked good residual convergence. Unsteady simulations were then performed, which converged well and demonstrated that flow instability existed in the lower portion of the manifold. It was established that the flow instability had little effect on the peak plate temperatures, which were well below the melting point. The estimated plate surface temperatures and target region pressure were shown to provide sufficient margin to subcooled boiling for standard operating conditions. This demonstrated the safety of both potential target configurations during normal operation.

Monitoring method for neutron flux for a spallation target in an accelerator driven sub-critical system**Supported by Strategic Priority Research Program of Chinese Academy of Sciences (XDA03010000 and XDA03030000) and the National Natural Science Foundation of China(91426301).

In this paper, we study a monitoring method for neutron flux for the spallation target used in an accelerator driven sub-critical (ADS) system, where a spallation target located vertically at the centre of a sub-critical core is bombarded vertically by high-energy protons from an accelerator. First, by considering the characteristics in the spatial variation of neutron flux from the spallation target, we propose a multi-point measurement technique, i.e. the spallation neutron flux should be measured at multiple vertical locations. To explain why the flux should be measured at multiple locations, we have studied neutron production from a tungsten target bombarded by a 250 MeV-proton beam with Geant4-based Monte Carlo simulations. The simulation results indicate that the neutron flux at the central location is up to three orders of magnitude higher than the flux at lower locations. Secondly, we have developed an effective technique in order to measure the spallation neutron flux with a fission chamber (FC), by establishing the relation between the fission rate measured by FC and the spallation neutron flux. Since this relation is linear for a FC, a constant calibration factor is used to derive the neutron flux from the measured fission rate. This calibration factor can be extracted from the energy spectra of spallation neutrons. Finally, we have evaluated the proposed calibration method for a FC in the environment of an ADS system. The results indicate that the proposed method functions very well.

Study on transient beam loading compensation for China ADS proton linac injector II**Supported by National Natural Science Foundation of China (91426303, 11525523)

Significant transient beam loading effects were observed during beam commissioning tests of prototype II of the injector for the accelerator driven sub-critical (ADS) system, which took place at the Institute of Modern Physics, Chinese Academy of Sciences, between October and December 2014. During these tests experiments were performed with continuous wave (CW) operation of the cavities with pulsed beam current, and the system was configured to make use of a prototype digital low level radio frequency (LLRF) controller. The system was originally operated in pulsed mode with a simple proportional plus integral and deviation (PID) feedback control algorithm, which was not able to maintain the desired gradient regulation during pulsed 10 mA beam operations. A unique simple transient beam loading compensation method which made use of a combination of proportional and integral (PI) feedback and feedforward control algorithm was implemented in order to significantly reduce the beam induced transient effect in the cavity gradients. The superconducting cavity field variation was reduced to less than 1.7% after turning on this control algorithm. The design and experimental results of this system are presented in this paper.