Accelerator-driven Subcritical System Research Articles

Design and Numerical Analysis of Oil-Cooled Cooler of Liquid Lead-Bismuth Loop

Since heat exchanger is an important device that can control temperature distribution of the liquid Lead-Bismuth Eutectic (LBE) loop, its proper design makes sure investigations on key technologies of Accelerator Driven Sub-critical System (ADS) can be carried out smoothly. Based on heat transfer theory, a design proposal was presented for the cooler of the multi-functional forced convection LBE loop KYLIN-II that is being developed by FDS team. The cooler is a double-pipe countercurrent heat exchanger cooled by heat transfer oil YD-350L. Numerical analysis based on the commercial software ANSYS FLUENT 14.5 was also performed to validate that design proposal in design case and two different operation cases. Theoretical design parameters agreed well with those of the numerical simulation. Deviations of some important parameters (i.e. temperatures of fluids and overall heat transfer coefficient of the cooler) between theoretical values and numerical simulation results were under 2%. The bulk temperature and film temperature of the oil were lower than 305 °C and 360 °C respectively, which were acceptable for heat transfer oil. All these results indicated that the design proposal in the paper was reasonable and could be applied to the design of KYLIN-II LBE loop.

Physics design of an accelerator for an accelerator-driven subcritical system

An accelerator-driven subcritical system (ADS) program was launched in China in 2011, which aims to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power in multiple phases lasting about 20 years. The driver linac is defined to be 1.5 GeV in energy, 10 mA in current and in cw operation mode. To meet the extremely high reliability and availability, the linac is designed with much installed margin and fault tolerance, including hot-spare injectors and local compensation method for key element failures. The accelerator complex consists of two parallel 10-MeV injectors, a joint medium-energy beam transport line, a main linac, and a high-energy beam transport line. The superconducting acceleration structures are employed except for the radio frequency quadrupole accelerators (RFQs) which are at room temperature. The general design considerations and the beam dynamics design of the driver linac complex are presented here.

A Fully Digital Beam Position and Phase Measurement Electronics for the Proton LINAC in ADS

The beam measurement is essential for an accelerator. In the proton LINAC in China Accelerator Driven Sub-critical system (ADS), a high resolution measurement of beam position and phase is required within one single system. To meet the requirement, this beam position and phase measurement (BPPM) electronics is designed based on a direct RF under-sampling technique, which simplifies both the analog and digital processing circuits. The signals received from the LINAC are narrow pulses with a repetition frequency of 162.5 MHz and a dynamic range more than 40 dB. After analog manipulation, the input RF signals are directly converted to In-phase and Quadrature-phase (IQ) streams through under-sampling based on the high-speed high-resolution Analog-to-Digital conversion technique. All signal processing is integrated in one single FPGA, in which real-time beam position, phase and current can be obtained. A series of simulations and tests have been conducted to evaluate the performance. Initial test results indicate that this system achieves a position resolution better than 20 um and a phase resolution better than 0.1 degree over a 40 dB dynamic range with the bandwidth of 780 kHz, which is well beyond the application requirements.

Tritium supply assessment for ITER and DEMOnstration power plant

The International Thermonuclear Experimental Reactor (ITER) and next generation DEMOnstration fusion reactor need amounts of tritium for test/initial startup and will consume kilograms tritium for operation per year. The available supply of tritium for fusion reactor is man-made sources. Now most of commercial tritium resource is extracted from moderator and coolant of CANada Deuterium Uranium (CANDU) type Heavy Water Reactor (HWR), in the Ontario Hydro Darlington facility of Canada and Wolsong facility of Korea. In this study, the tritium production rate in CANDU reactor was simulated and estimated. And other possible routes, including Accelerator Production of Tritium (APT), tritium production in Commercial Light Water Reactor (CLWR) and Accelerator Driven Subcritical system (ADS), were also evaluated in feasibility and economy. Based on the tritium requirement investigated according to ITER test schedule and startup inventory required for a FDS-II-scale DEMO calculated by TAS1.0, the assessment results showed that after ITER retired in 2038, the tritium inventory of CANDU reactor could not afford DEMO reactor startup without extra resource.

Investigation on the applicability of turbulent-Prandtl-number models for liquid lead-bismuth eutectic

With the proposal of Accelerator Driven Sub-critical System (ADS) together with liquid lead-bismuth eutectic (LBE) as coolant for both reactor and spallation target, the use of accurate heat transfer correlation and reliable turbulent-Prandtl-number model of LBE in turbulent flows is essential when designing ADS components of primary loop and heat exchanger of secondary loop. Unlike conventional fluids, there is not an acknowledged turbulent-Prandtl-number model for LBE flows. This paper reviews and assesses the existing turbulent-Pandtl-number models and various heat transfer correlations in circular tubes. Computational fluid dynamics (CFD) analysis is employed to evaluate the applicability of various turbulent-Prandtl-number models for LBE in the circular tube under boundary conditions of constant heat flux and constant wall temperature. Based on the assessment of turbulent-Prandtl-number models, the reliable turbulent-Prandtl-number models are recommended for CFD applications to LBE flows under boundary conditions of constant heat flux and constant wall temperature. The present study indicates that turbulent Prandtl number has a significant difference in turbulent LBE flow between constant-heat-flux and constant-wall-temperature boundary conditions.

Thermal-hydraulic analysis of LBE spallation target for accelerator-driven systems

In an accelerator-driven subcritical system (ADS), a high-performance spallation neutron source is used to feed the subcritical reactor. Neutron generation depends on the proton beam intensity. If the beam intensity is increased by a given factor, the number of generated neutrons will increase. The mechanism yielding a high rate of neutron production per energy is the spallation process, and this mechanism produces a very high-energy deposition in the spallation target material. Producing a high rate of neutrons is accompanied by creation of problems of decay heat cooling and radiological protection. As a first step in designing a full-scale industrial ADS, a small-scale experimental ADS, which is similar to the European experimental ADS (XADS) is analysed. The analysis presented in this paper is based on lead–bismuth eutectic (LBE) cooled XADS-type experimental reactors, designed during the European experimental (PDS-XADS) project. Computational fluid dynamics analysis has been carried out for the spallation target. Steady state behaviour and shear stress transport turbulence model with the automatic wall treatment were applied in the present analysis.

An ADS 650 MHz medium beta cavity study and design

The Accelerator Driven Sub-critical System (ADS) is under development and aims at the safe disposal of nuclear waste and providing electric power in China. The main accelerator of the ADS is composed of two injector sections and one main linear acceleration section. The 650 MHz β=0.82 superconducting cavities will be adopted to accelerate the proton bunches from 360 MeV to 1.5 GeV in the medium energy section. This paper presents the study and design results of this kind of superconducting cavity.

Fabrication of niobium superconducting accelerator cavity by electron beam welded joints

Fabrication of superconducting cavities has been taken up as a part of the development of accelerator driven sub critical system (ADSS) by Bhabha Atomic Research Centre. Large grain (RRR>99) pure niobium was chosen as the material for the cavity. Niobium,for its application as superconductor requires extremely high quality joints, feasible only by electron beam welding at high vacuum environment. An indigenously developed 100kV, 4kW high vacuum electron beam welding machine has been utilized to carry out the welding operations. Planning of the weld sequences was chalked out. Holding fixtures for the cavity, consists of seven numbers of joints have been fabricated beforehand. A few coupons were welded for optimization of the weld parameters and for inspection of the weld purity by indigenously developed secondary ion mass spectroscopy. The report describes the welding equipment and the stage wise joining operations of the cavity in details and also discusses the qualification testing of the welded cavity.

Design, fabrication, room temperature RF test of 1050 MHz, β = 0.49 single cell large grain niobium cavity

BARC is developing a technology for the accelerator driven subcritical system (ADSS) that will be mainly utilized for the transmutation of nuclear waste and enrichment of U233. Design and prototyping of a superconducting medium velocity cavity has been taken up as a part of the ADSS project. The cavity design for β = 0.49, f = 1050 MHz has been optimized to minimize the peak electric and magnetic fields, with a goal of 5 MV/m of accelerating gradient at a Q > 5×109 at 2 K. After the design optimization one single cell cavity was fabricated from large grain (RRR>99) Niobium material. This report presents the design, fabrication, electron beam welding and RF measurements at room temperature before and after electron beam welding.

Une curieuse carcinose péritonéale

Nitrides have been proposed to be a suitable material for fast neutronic systems from beginning of the development of nuclear fuel. Starting with the production of uranium nitride and sesquinitrides up to mixed plutonium uranium nitrides, today's developments are inert nitride matrix materials to burn plutonium or to transmute long-lived actinides in accelerator-driven sub-critical systems (ADS) or fast reactors (FR). Several authors proposed zirconium nitride as possible inert matrix material for this reason. Mixed zirconium nitrides can be fabricated by carbothermal nitridation of the oxides in a narrow temperature window. Obtaining high quality material with low carbon and oxygen content is still the major challenge. Producing mixed nitride fuels by special shaping methods, as for example direct coagulation casting or freeze drying, in comparison to conventional powder compaction enables to use this material in special shapes to optimize burn up.The history of nitride fuels at PSI will be shown up to today's CONFIRM project, dealing with plutonium zirconium nitride fuels.

Detector Dead Time Determination and Optimal Counting Rate for a Detector Near a Spallation Source or a Subcritical Multiplying System

The operation of accelerator-driven systems or spallation sources requires the monitoring of intense neutron fluxes, which may be billions-fold more intense than the fluxes obtained with usual radioactive sources. If a neutron detector is placed near a very intense source, it can become saturated because of detector dead time. On the contrary, if it is placed far away from the source, it will lose counting statistics. For this reason, there must exist an optimal position for placing the detector. The optimal position is defined as the one with the minimal relative uncertainty in the counting rate. In this work, we review the techniques to determine the detector dead time that can be applied with an accelerator-driven subcritical system or a spallation source. For the case of a spallation source, counting rates do not follow Poisson's statistics because of the multiplicity of the number of neutrons emitted by incident proton. It has been found a simple expression that relates the optimal counting rate with the source multiplicity and the uncertainty in the determination of the dead time.

A Fast Numerical Method for the Calculation of the Equilibrium Isotopic Composition of a Transmutation System in an Advanced Fuel Cycle

A fast numerical method for the calculation in a zero-dimensional approach of the equilibrium isotopic composition of an iteratively used transmutation system in an advanced fuel cycle, based on the Banach fixed point theorem, is described in this paper. The method divides the fuel cycle in successive stages: fuel fabrication, storage, irradiation inside the transmutation system, cooling, reprocessing, and incorporation of the external material into the new fresh fuel. The change of the fuel isotopic composition, represented by an isotope vector, is described in a matrix formulation. The resulting matrix equations are solved using direct methods with arbitrary precision arithmetic. The method has been successfully applied to a double-strata fuel cycle with light water reactors and accelerator-driven subcritical systems. After comparison to the results of the EVOLCODE 2.0 burn-up code, the observed differences are about a few percents in the mass estimations of the main actinides.

Nuclear Level Density Parameters ofPb203-209andBi206-210Deformed Target Isotopes Used on Accelerator-Driven Systems in Collective Excitation Modes

The nuclear level density parameters of some deformed isotopes of target nuclei (Pb, Bi) used on the accelerator-driven subcritical systems (ADSs) have been calculated taking into consideration different collective excitation modes of observed nuclear spectra near the neutron binding energy. The method used in the present work assumes equidistant spacing of the collective coupled state bands of the considered isotopes. The present calculated results for different collective excitation bands have been compared with the compiled values from the literature for s-wave neutron resonance data, and good agreement was found.

A study of non-elastic reaction rates for the ADS materials in the environment of spallation neutrons produced by 1.6 GeV d-beam

For the design and modeling of Accelerator Driven sub-critical System (ADS) a detailed study of response of ADS materials to the spallation neutrons is required. For this purpose reaction rates of different reactions like (n, xn) and (n, xnyp) in 209Bi, natMo, 56Fe, natNi, 55Mn, natTi and natCo materials are determined in an experiment conducted at Nuclotron of JINR, Dubna, using 1.6GeV d-beam in the ‘Energy+Transmutation’ set-up. Reaction rates of various (n, xn) and (n, xnyp) reactions are studied in these samples. Results of reaction rates deduced from all the gamma peaks observed in case of 209Bi (n, xn) reactions with x=3−9, natMo (n, γ), (n, 3n), (n, 6n), 56Fe (n, p), (n, p2n), (n, p4n), natNi (n, 2n), (n, 3n), (n, p), (n, d), (n, t), 55Mn (n, γ), (n, 2n), (n, 4n), natTi (n, p), (n, d), (n, t) and natCo (n, γ), (n, xn) reactions with x=2–5 along with (n, p), (n, 2p2n), (n, 2p4n) and (n, 2p6n) are presented. The measured reaction rates for all the elements show good consistency for all the reaction channels and all observed Eγ's of the product nucleus. For all the above mentioned reactions, both experimental as well as theoretical spectrum average cross-sections (σsp.av.cs) are deduced and compared. A close agreement is found between the experimental σsp.av.cs and theoretical σsp.av.cs values.

Design, fabrication, RF test at 2 K of 1050MHz, β=0.49 single cell large and fine grain niobium cavity

BARC is developing a technology for the accelerator driven subcritical system (ADSS) that will be mainly utilized for the transmutation of nuclear waste and enrichment of U233. Design and prototyping of a superconducting medium velocity cavity has been taken up as a part of the ADSS project. The cavity design for β = 0.49, f = 1050 MHz has been optimized to minimize the peak electric and magnetic fields, with a goal of 5 MV/m of accelerating gradient at a Q > 5 × 109 at 2 K. After the design optimization, two single cell cavities were fabricated from polycrystalline (RRR > 200) and large grain (RRR > 96) Niobium material. The cavities have been tested at 2 K in a vertical cryostat at Jefferson Lab and both achieved the performance specifications.

Yields of Fission Products in the Gamma Induced Fission of Preactinides and Actinides

Nuclear data such as fission cross-sections and yields of fission products in neutronand gammainduced fission of pre-actinides and actinides are important for the Accelerator-Driven Subcritical systems (ADSs). Particularly yields of fission products in high energy neutronand gamma-induced fission of long lived minor actinides (Np, Pu, Am and Cm) and pre-actinides (e.g., Pb and Bi) are needed for decay heat calculation. This is because in ADSs high energy (GeV) proton beam from accelerator are bombarded on Pb and Bi to produce high energy neutron by spallation process, which can incinerate minor actinides and transmute long-lived fission products to solve the problem of radioactive hazard. In this process high energy γ-ray also produce, which can cause reaction and fission of the spallation source and minor actinides. We present the yields of fission products from the bremsstrahlung induced fission of Bi and Pb by using 50, 60, 70 MeV and 2.5 GeV electron beam of the Pohang Accelerator Laboratory, Korea. The yields of fission products obtained in the 8 – 10 MeV bremsstrahlung induced fission of Th, U and Pu using Microtron at Mangalore University and electron LINAC at EBC centre, Kharghar, New-Mumbai, India are also discussed.

233Pa(2nth, f ) cross-section determination using a fission track technique

The 233Pa(2nth, f) cross-section has been experimentally determined for the first time using a fission track technique. It was found to be 4834 ± 57 b, which is significantly high and thus is very important for 232Th-233U-based fuel in advanced heavy-water reactors (AHWR) and accelerator-driven sub-critical systems (ADSs). This is because the 233Pa is an important intermediary in the thorium-based fuel cycle and thus its fission cross-section is a key parameter in the modeling of AHWR and ADSs. The 233Pa(2nth, f) cross-section was calculated theoretically using the TALYS computer code and found to be in good agreement with the experimental value after normalization with respect to 241Am(2nth, f).

A study of reaction rates of (n, f ) , (n, $ \gamma$ ) and (n, 2n) reactions in natU and 232Th by the neutron fluence produced in the graphite set-up (GAMMA-3) irradiated by 2.33 GeV deuteron beam

Spallation neutrons produced in the collision of a 2.33GeV deuteron beam with a large lead target are moderated by a thick graphite block surrounding the target and used to activate the radioactive samples of natU and Th put at three different positions, identified as holes “a”, “b” and “c” in the graphite block. Rates of the (n, f), (n, \( \gamma\) and (n, 2n) reactions in the two samples are determined using the gamma spectrometry. The ratios of the experimental reaction rates, R (n, 2n)/R (n, f), for 232Th and natU are estimated in order to understand the role of the (n, x n) kind of reactions in Accelerator-Driven Sub-critical Systems. For the Th-sample, the ratio is ∼ 54 (10)% in the case of hole “a” and ∼ 95 (57)% in the case of hole “b” compared to 1.73(20)% for hole “a” and 0.710(9)% for hole “b” in the case of the natU sample. Also the ratio of fission rates in uranium to thorium, natU (n, f)/ 232Th (n, f), is ∼ 11.2 (17) in the case of hole “a” and 26.8(85) in hole “b”. Similarly, the ratio 238U (n, 2n)/ 232Th (n, 2n) is 0.36(4) for hole “a” and 0.20(10) for hole “b” showing that 232Th is more prone to the (n, x n) reaction than 238U . All the experimental reaction rates are compared with the simulated ones by generating neutron fluxes at the three holes from MCNPX 2.6c and making use of the LA150 library of cross-sections. The experimental and calculated reaction rates of all the three reactions are in reasonably good agreement. The transmutation power, Pnorm as well as Pnorm/Pbeam of the set-up is estimated using the reaction rates of the (n, \( \gamma\) and (n, 2n) reactions for both the samples in the three holes and compared with some of the results of the “Energy plus Transmutation” set-up and TARC experiment.

Design and experiment results of the LEBT pre-chopper for CSNS

In a high intensity proton accelerator complex comprising a linac and a ring, a beam chopper is often necessary in order to reduce the beam loss during injection from the linac to the ring. The China Spallation Neutron Source (CSNS) front end incorporates a pre-chopper in the Low Energy Beam Transport line (LEBT) that will remove a 530 ns section of beam at approximately 1 MHz rate. Physical design of the pre-chopper is presented in this paper. The distinguished feature of this electrostatic beam chopper is the novel design of deflecting structure, and the theoretic fast beam rise/fall time, which is an essential requirement for CSNS accelerator to avoid radioactivity induced by the lost particles due to insufficient chopping during the transient time; Taking advantage of the existing LEBT of the Accelerator Driven Subcritical System (ADS), the beam study of a similar chopper system was successfully performed and the achieved rise/fall time was less than 20 ns, which is the fastest one compared to other similar pre-choppers. This type of pre-chopper will be used in the CSNS LEBT, which is under construction.

Compact superferric FFAG accelerators for medium energy hadron applications

Medium energy hadron beams are desirable in various applications such as accelerator-driven subcritical systems (ADSR), high intensity neutron sources and carbon therapy. Compactness and easy operation characters are important for this energy region, especially in the case of medical use purposes. This paper introduces a novel superferric scheme with scaling fixed-field alternating gradient (FFAG) accelerators, which can provide 400MeV/u carbon ions for cancer therapy. By employing a maximum field of 5T with a high field index, 8.5m diameter with 85cm radius excursion is achieved in a single FFAG ring. The lattice configuration and design of superferric magnet sectors with high permeability materials were described in detail. This scheme can also be extended to other hadron applications.