Accelerator-driven system for transmutation of high-level waste

The accelerator-driven transmutation system has been studied at the Japan Atomic Energy Research Institute. This system is a hydrid system which consists of a high intensity accelerator, a spallation target and a subcritical core region. In the conceptual design study, two types of system concepts, sodium cooled and lead-bismuth cooled system, are being studied. In this study, we fucus on our lead-bismuth cooled accelerator-driven transmutation system to investigate basic characteristics. The fuel compositions were optimized for efficient transmutation of minor actinide. The transmutation of long-lived fission products was also considered.     

Research and development on accelerator-driven transmutation system at JAERI

Japan Atomic Energy Research Institute carries out research and development on accelerator-driven system (ADS) to transmute minor actinides and long-lived fission products in high-level radioactive waste. The system is composed of high intensity proton accelerator, lead-bismuth spallation target and lead-bismuth cooled subcritical core with nitride fuel. About 2500 kg of minor actinide is loaded into the subcritical core. Annual transmutation amount using this system is 250 kg with 800 MW of thermal output. This transmutation amount corresponds to the amount of minor actinides produced from 10 units of 1GWe power reactors annually. A superconducting linear accelerator with the beam power of 20–30 MW is connected to drive the subcritical core. To maximize the transmutation efficiency, the nitride fuel without uranium, such as (Np, Am, Pu)N, is selected. The nitride fuel irradiated in the ADS is reprocessed by pyrochemical process followed by the re-fabrication of nitride fuel. Many research and development activities are under way and planned in the fields of subcritical core design, spallation target technology, lead-bismuth handling technology, accelerator development, and minor actinide fuel development. Especially, to study and evaluate the feasibility of the ADS from physics and engineering aspects, the transmutation experimental facility (TEF) is proposed under a framework of the High-Intensity Proton Accelerator Project.     

Research activities for accelerator-driven transmutation system at JAERI

Japan Atomic Energy Research Institute (JAERI) performs Research and Development (R&D) for accelerator-driven systems (ADS) for transmutation of long-lived nuclides. To study the basic characteristics of ADS, Transmutation Experimental Facility is proposed within the framework of the J-PARC project. The facility consists of two buildings, Transmutation Physics Experimental Facility to research the neutronics and the controllability of ADS and ADS Target Test Facility for material irradiation and partial mockup of beam window. A comprehensive R&D program for future ADS plant is also underway in three technical fields, 1) accelerator, 2) lead-bismuth target/coolant and 3) subcritical core.     

Research and Development Program on Accelerator Driven Subcritical System in JAEA

For a dedicated transmutation system, Japan Atomic Energy Agency (JAEA) has been proceeding with the research and development on an accelerator-driven subcritical system (ADS). The ADS proposed by JAEA is a lead-bismuth eutectic (LBE) cooled fast subcritical core with 800 MWth. JAEA has started a comprehensive research and development (R&D) program since the fiscal year of 2002 to acquire knowledge and elemental technology that are necessary for the validation of engineering feasibility of the ADS. In this paper, the outline and the results in the first three-year stage of the program are reported. Items of R&D were concentrated on three technical areas peculiar to the ADS: (1) a superconducting linear accelerator (SC-LINAC), (2) the LBE as spallation target and core coolant, and (3) a subcritical core design and reactor physics of the ADS. For R&D on the accelerator, a prototype cryomodule was built and its good performance in electric field was examined. For R&D on the LBE, various technical data for material corrosion, thermal-hydraulics and radioactive impurity were obtained by loop tests and reactor irradiation. For R&D on the subcritical core, engineering feasibility for the LBE cooled tank-type ADS was discussed using thermal-hydraulic and structural analysis not only in normal operation but also in transient situations. Reactor physics experiments for subcritical monitoring and physics parameters of the ADS were also performed at critical assemblies.     

Physical studies of minor actinide transmutation in the accelerator-driven subcritical system

The accelerator-driven subcritical system(ADS)with a hard neutron energy spectrum was used to study transmutation of minor actinides(MAs). The aim of the study was to improve the efficiency of MA transmutation while ensuring that variations in the effective multiplication factor(k_(eff)) remained within safe margins during reactor operation. All calculations were completed using code COUPLE3.0. The subcritical reactor was operated at a thermal power level of 800 MW, and a mixture of mononitrides of MAs and plutonium(Pu) was used as fuel.Zirconium nitride(ZrN) was used as an inert matrix in the fuel elements. The initial mass composition in terms of weight percentages in the heavy metal component(IHM)was 30.6% Pu/IHM and 69.4% MA/IHM. To verify the feasibility of this MA loading scheme, variations in k_(eff), the amplification factor of the core, maximum power density and the content of MAs and Pu were calculated over six refueling cycles. Each cycle was of 600 days duration, and therefore, there were 3600 effective full power days.Results demonstrated that the effective transmutation support ratio of MAs was approximately 28, and the ADS was able to efficiently transmute MAs. The changes in other physical parameters were also within their normal ranges.It is concluded that the proposed MA transmutation scheme for an ADS core is reasonable.     

Development of conceptual design tool for liquid metal cooled-reactors

A conceptual design tool for three types of liquid metal reactors (LMRs), ultra long life, accelerator-driven subcritical transmutation and large scaled LMRs has been proposed. This tool is developed for system design with artificial intelligence, scaling of design parameters, and validation analysis. The system design consists of design synthesis and design analysis. System design decides the optimal structure and layout of a LMR using design synthesis with rule bases and databases, and design analysis with design constraints. The designed system is scaled by scale laws to be optimal with desired power level, and then a specific design basis accident is analyzed in validation part. Design synthesis contains the data about each component and general LMRs, and the rules about selection of each component and general LMRs. Design analysis contains several design constraints for formulation and solution of a design problem. In these two parts, a designer's intention can be externalized through emphasis on design requirements. For the purpose of demonstration, the conceptual design tool was applied to an ultra long life LMR with 35 MWe power level. This ultra long life LMR was designed from knowledge structure based on all the characteristics of ultra long life, accelerator-driven subcritical transmutation, and large scaled LMRs, and then optimally scaled to the 35 MWe power level.     

Safety analysis of an accelerator-driven test facility

One of the milestones in the roadmap of accelerator-driven transmutation of waste (ATW) of the U.S. Department of Energy is the design and construction of an accelerator-driven test facility (ADTF) with a thermal power of 100 MW. Analysis of the dynamic behavior of the ADTF has been carried out in the frame of a bilateral collaboration between the Forschungszentrum Karlsruhe and the Argonne National Laboratory (ANL). In the present study five different system configurations with various types of fuel and different types of coolant have been taken into consideration.In the systems with sodium as coolant, the transient behavior under the unprotected loss-of-flow scenario shows the most serious safety concern. As long as the external source is switched on, loss-of-flow will lead to an overheating of coolant, cladding and fuel. Boiling of coolant, cladding failure and molten fuel injection take place just in several seconds after the coast-down of the pump. Safety measures have to be designed for switching off the proton beam.In the system with liquid lead–bismuth eutectic (LBE) as coolant, the buoyancy effect is much stronger. Due to its high boiling point, coolant boiling and, subsequently, flow oscillation in fuel assemblies can be avoided. By a proper design of the heat removal system, the buoyancy-driven convection would provide a sufficiently high cooling capability of the reactor core, to keep the integrity of the fuel pins.     

European research on HLM thermal-hydraulics for ADS applications

The objective of the European 6th framework project EUROTRANS is to demonstrate the technical feasibility of transmutation of high level nuclear waste using accelerator driven systems. Within this objective the design of a European experimental ADS should demonstrate the technical feasibilities to transmute a sizeable amount of waste and to operate an ADS safely. This ADS will be a subcritical reactor system having liquid lead-bismuth eutectic as coolant. The liquid lead-bismuth eutectic is also intended to serve as target material for the spallation reaction which forms a crucial part to the subcritical reactor core. Since lead-bismuth eutectic is used as core coolant and spallation material, knowledge of its thermal hydraulic behaviour is essential. Within the DEMETRA domain of the EUROTRANS project, basic thermal hydraulic studies in order to support the design and safety analysis of XT-ADS components and the development of measurement techniques have been started.     

加速器驱动的10 MW次临界反应堆物理方案研究

加速器驱动的次临界系统（ADS）是未来最有可能实现工业化嬗变核废料的装置。通过设计1个10 MW的ADS物理方案,研究ADS的嬗变能力。采用MCNPX和ORIGEN的耦合程序,利用基于ENDF6.8处理所得的6个温度（300、600、900、1 200、1 500、1 800 K）下连续能量核数据库,计算得到ADS随燃耗时间变化的有效增殖因数k_eff、功率峰因子和质子束流强度。同时通过计算给出了该设计方案下ADS燃料多普勒系数、冷却剂空泡系数和有效缓发中子份额,利用这些物理量研究了该ADS方案的安全特性,并通过燃耗计算研究了ADS的嬗变能力。结果表明,在1 000 d燃耗时长内,k_eff和质子流强随时间的波动较小,燃料燃耗深度较浅,系统可提升功率运行,在假想事故下系统能保持次临界状态。系统嬗变支持比约为8。     

Development and validation of depletion code system IMPC Burnup for ADS

Depletion calculation is important for studying the transmutation efficiency of minor actinides and longlife fission products in accelerator-driven subcritical reactor system(ADS). Herein the Python language is used to develop a burnup code system called IMPC-Burnup by coupling FLUKA, OpenMC, and ORIGEN2. The program is preliminarily verified by OECD-NEA pin cell and IAEAADS benchmarking by comparison with experimental values and calculated results from other studies. Moreover,the physics design scheme of the CIADS subcritical core is utilized to test the feasibility of IMPC-Burnup program in the burnup calculation of ADS system. Reference results are given by the COUPLE3.0 program. The results of IMPC-Burnup show good agreement with those of COUPLE3.0. In addition, since the upper limit of the neutron transport energy for OpenMC is 20 MeV, neutrons with energies greater than 20 MeV in the CIADS subcritical core cannot be transported; thus, an equivalent flux method has been proposed to consider neutrons above 20 MeV in the OpenMC transport calculation. The results are compared to those that do not include neutrons greater than 20 MeV. The conclusion is that the accuracy of the actinide nuclide mass in the burnup calculation is improved when the equivalent flux method is used. Therefore, the IMPC-Burnup code is suitable for burnup analysis of the ADS system.     

启明星Ⅱ号双堆芯零功率装置

启明星Ⅱ号是针对我国新型先进核能系统基础性研发及工程化设计验证而研制的双堆芯零功率装置。启明星Ⅱ号拥有两个堆芯,水堆堆芯侧重于开展热中子能谱环境下的原理性验证实验研究,铅堆堆芯侧重于重金属冷却的快中子反应堆及加速器驱动的次临界系统（ADS）等先进核能系统的中子物理特性实验研究。启明星Ⅱ号通过一套仪控系统实现了两个堆芯的集成化控制和测量数据采集,每个堆芯均配备了多套非能动安全停堆系统,固有安全性强。在启明星Ⅱ号上获取了多种堆芯的基准性临界实验数据,可为我国轻水堆的技术创新、重金属冷却反应堆工程化设计及新型核能系统的集成研发提供支持。     

Partitioning and transmutation studies at JAERI both under OMEGA program and High-Intensity Proton Accelerator Project

At the Japan Atomic Energy Research Institute (JAERI), active and comprehensive studies on partitioning and transmutation (P&T) of long-lived nuclear waste from the reprocessing processes of spent fuel has been carried out under the OMEGA program. Studies at JAERI include a design study of dedicated transmutation systems both of an MA burner fast reactor (ABR) and an accelerator-driven subcritical system (ADS), and the development of a high intensity proton accelerator as well as the development of partitioning process, nitride fuel fabrication/dry separation process technologies and nuclear data studies.

During the course of studies, JAERI developed the concept of the double-strata fuel cycle, in which a dedicated system is used for transmutation. Comparing the various transmutation systems, such as thermal neutron spectrum or fast neutron spectrum systems, power reactors or dedicated systems, from the viewpoints of reactor physics, nuclear fuel cycle and socio-technical issues, it was concluded that the ADS is the best option for transmutation of minor actinide(MA). JAERI, therefore, decided to concentrate its R&D efforts on the development of ADS and related technologies.

One of the goals of R&D is to provide a basis for designing demonstration facilities of ADS, aqueous partitioning process and nitride fuel fabrication and dry separation technologies. As the initial step toward this purpose, the construction of an ADS experimental facility is planned under the High-Intensity Proton Accelerator Project which JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing since 1998.

The paper discusses the some of the results of P&T studies and the outline of the High-Intensity Proton Accelerator Project under which ADS experimental facility will be constructed.     

Nuclear data-induced uncertainty quantification of neutronics parameters of accelerator-driven system

Nuclear data-induced uncertainties of neutronics parameters of one accelerator-driven system concept designed by the Japan Atomic Energy Agency are quantified. The variance-covariance data provided in the JENDL-4.0 library are used. Uncertainties are quantified for effective neutron multiplication factor, subcritical neutron multiplication rate, a family of delayed neutron fractions, power peaking and coolant void reactivity at several operational states. Inter-cycle and inter-parameter correlation matrices and detailed information such as nuclide-wise and nuclear data-wise uncertainties are also provided.     

First nuclear transmutation of 237Np and 241Am by accelerator-driven system at Kyoto University Critical Assembly

This study demonstrates, for the first time, the principle of nuclear transmutation of minor actinide (MA) by the accelerator-driven system (ADS) through the injection of high-energy neutrons into the subcritical core at the Kyoto University Critical Assembly. The main objective of the experiments is to confirm fission reactions of neptunium-237 (²³⁷Np) and americium-241 (²⁴¹Am), and capture reactions of ²³⁷Np. Subcritical irradiation of ²³⁷Np and ²⁴¹Am foils is conducted in a hard spectrum core with the use of the back-to-back fission chamber that obtains simultaneously two signals from specially installed test (²³⁷Np or ²⁴¹Am) and reference (uranium-235) foils. The first nuclear transmutation of ²³⁷Np and ²⁴¹Am by ADS soundly implemented by combining the subcritical core and the 100 MeV proton accelerator, and the use of a lead-bismuth target, is conclusively demonstrated through the experimental results of fission and capture reaction events.     

Neutron cross section sensitivity for minor actinide transmutation in energy amplifier systems

The nuclear data sensitivity in 3D Monte Carlo burnup calculations of minor actinide transmutation in Energy Amplifier Systems is assessed. Ansaldo Nucleare’s 80 MW_th Energy Amplifier Demonstration Facility (EADF) design serves as a technical and geometrical platform for the analysis. The accelerator-driven EADF is a fast, subcritical system based on classical MOX-fuel technology and on molten lead–bismuth eutectic cooling. For Monte Carlo simulations, the state-of-the-art computer code package EA-MC, developed by C. Rubbia and his group at CERN, is utilised. The code offers treatment of both high-energy particle interactions and low-energy neutron transport with a sophisticated method based on a full Monte Carlo simulation, together with the option of employing different modern nuclear data libraries. In particular, the impact of nuclear data discrepancies on transmutation properties prediction with increasing exposure is examined.     

ADS熔盐散裂靶中子学性能研究

与传统加速器驱动次临界系统（ADS）采用金属靶作为散裂中子靶的设计不同,加速器驱动次临界熔盐堆（AD-MSRs）采用靶堆一体的设计,直接使用燃料熔盐作为散裂中子靶。由于熔盐靶的中子学性能直接影响AD MSRs的能量放大系数、核废物的嬗变和核燃料增殖的效率,所以本研究基于MCNPX程序,详细计算了高能质子轰击氟盐和氯盐两种熔盐靶产生的散裂中子产额、散裂中子能谱、能量沉积分布以及散裂产物等中子学性能,并与液态Pb和铅铋共熔体（LBE）两种液态金属靶进行了对比。计算结果表明,熔盐靶在散裂中子产额上与液态金属靶有一定的差距,但熔盐靶内能量沉积分布的梯度较小,更有利于靶区的热量导出。与液态Pb和LBE靶相比,熔盐靶的散裂产物中包含更多的气体以及高质量数的α发射体核素。     

HYPER (Hybrid Power Extraction Reactor): A system for clean nuclear energy

The Korea Atomic Energy Research Institute (KAERI) has been performing accelerator driven system related research and development (RID) called HYPER (HYbrid Power Extraction Reactor) for the transmutation of nuclear waste and energy production through the transmutation process. HYPER program is within the frame work of the national mid and long-term nuclear research plan. KAERI is aiming to develop the elemental technologies for the subcritical transmutation system by the year of 2001 and build a small bench scale test facility (5 MW) by the year of 2006. Some major features of HYPER have been developed and employed. On-power fueling concepts are employed to keep system power constant with a minimum variation of accelerator power. A hollow cylinder-type metal fuel is designed for the on-line refueling concept. Lead–bismuth (Pb–Bi) is adopted as a coolant and spallation target material. 1 GeV 16 mA proton beam is designed to be provided for HYPER. HYPER is to transmute about 380 kg of TRU a year and produce 1000 MW of power. The support ratio of HYPER for LWR units producing the same power is believed to be 56.     

Neutronics analysis of minor actinides transmutation in a fusion-driven subcritical system

The minor actinides (MAs) transmutation in a fusion-driven subcritical system is analyzed in this paper. The subcritical reactor is driven by a tokamak D-T fusion device with relatively easily achieved plasma parameters and tokamak technologies. The MAs discharged from the light water reactor (LWR) are loaded in transmutation zone. Sodium is used as the coolant. The mass percentage of the reprocessed plutonium (Pu) in the fuel is raised from 0 to 48% and stepped by 12% to determine its effect on the MAs transmutation. The lesser the Pu is loaded, the larger the MAs transmutation rate is, but the smaller the energy multiplication factor is. The neutronics analysis of two loading patterns is performed and compared. The loading pattern where the mass percentage of Pu in two regions is 15% and 32.9% respectively is conducive to the improvement of the transmutation fraction within the limits of burn-up. The final transmutation fraction of MAs can reach 17.8% after five years of irradiation. The multiple recycling is investigated. The transmutation fraction of MAs can reach about 61.8% after six times of recycling, and goes up to about 86.5% after 25.     

244Cm Transmutation in Accelerator-Driven System

Mixed oxide (MOX) fueled LWRs are characterized by enhanced accumulation of curium isotopes compared to uranium fueled LWRs. Toxicity of relatively short-lived isotope ²⁴⁴Cm (T ₁/2=18 yr) appears to be dominant in transuranics discharge. The present paper deals with analysis of the scientific feasibility to transmute ²⁴⁴Cm. Liquid bismuth-curium core operated in a subcritical mode with neutron support from accelerator is proposed to provide transmutation rate through fissioning that exceeds the rate of natural decay by one order of magnitude. Beam current in the range 30–40 mA is required to drive the core. One accelerator-driven transmutor could solve the problem of curium accumulation in a large-scale nuclear energy system based on MOX fueled LWRs.     

The accelerator driven system strategy in Japan

Recent status of study on accelerator driven system (ADS) in Japan is presented. The double-strata fuel cycle concept has been proposed by Japan Atomic Energy Research Institute (JAERI) under the `OMEGA' program as a system for partitioning and transmutation (P&T) of long-lived radioactive nuclides. The ADS dedicated to transmutation is the key technology of the double-strata fuel cycle concept. The proposed system is a lead-bismuth cooled, nitride fuel 800 MW ADS for transmutation of minor actinides and long-lived fission products. JAERI has carried out a conceptual design study under the joint project between JAERI and KEK (High Energy Accelerator Research Organization) on high-intensity proton accelerators. In addition to a high-intensity proton accelerator complex, two experimental facilities are planned for development and demonstration of accelerator driven transmutation technology: The major objective of an ADS physics experimental facility is to obtain reactor physics data of hybrid subcritical system. The major objective of an ADS engineering experimental facility is to accumulate material data for the design of a lead-bismuth target system.