Accelerator-driven systems (ADS), i.e. a subcritical system driven by an accelerator in order to sustain a chain reaction, are being considered for their potential use in the transmutation of nuclear waste. The performance of such hybrid nuclear systems depends to a large extent on the specification and reliability of high-power accelerators, as well as on the integration of the accelerator with spallation targets and subcritical systems. Much R&D is still required in order to demonstrate the desired capability as a whole system...

Approximately two decades ago, H. Takahashi revived the concept of accelerator-driven systems to propose it for the transmutation of radioactive nuclear wastes. In parallel, partitioning and transmutation (P/T) strategies have also been revisited, so as to enlarge the options as concerns waste management. At present, after numerous studies and some experimental demonstrations, it is possible to characterise the different options and strategies, in order to put them into perspective and to offer some practical paths towards implementation...

The construction of the J-PARC accelerator complex is proceeding rapidly at the JAERI Tokai site. The key concepts related to this accelerator complex are high power, low beam loss and high availability. A brief description of the project and the status of the construction are presented...

Under the OMEGA programme, the Japan Atomic Energy Research Institute (JAERI) continues to carry out the development of partitioning processes, nitride fuel technology, and a basic study to support the development of accelerator-driven systems (ADS). The current status of the technical issues to realiseADS are summarised: high-intensity proton accelerator, lead-bismuth technology, subcritical level, power control for the core, beam window and spallation target, and the Transmutation Experimental Facility proposed in the framework of the High-intensity Proton Accelerator Project: J-PARC. Further, the roles of P&T on high-level waste disposal including cost estimate are summarised. Kyoto University and KEK are moving forward with the experimental project Accelerator-driven Subcritical Reactor (ADSR), in which a small proton accelerator called Fixed-field Alternating Gradient (FFAG) will be coupled with a critical assembly, KUCA...

Los Alamos has been an active participant in the development of high-intensity accelerators, including the RFQ, LAMPF with the innovation of a CCL structure, and more recently, LEDA with a 100-mA CW beam. Participation in technology development related to high-intensity applications such as transmutation of waste, and others, remains a strong interest at Los Alamos. Past efforts leading up to present programmes are discussed. These programmes include development of novel normal and superconducting structures, RF power systems, beam dynamics, beam diagnostics and general system considerations...

Teams from the CEA and CNRS French research agencies are working on high-intensity high-duty factor proton, H– and deuteron linear accelerators for several applications (waste transmutation, nuclear and high-energy physics, spallation neutron sources, tritium production, materials irradiation facilities...). The R&D programmes undertaken to progress on the different components of such linacs and the simulation tools developed to optimise their design will be described.

The KAERI ADS system is known as the HYbrid Power Extraction Reactor (HYPER) project. Research on this project began as a 10-year nuclear research programme in 1997. The conceptual design of the HYPER core is almost complete. HYPER is designed to transmute TRU and some fission products such as 129I and 99Tc. HYPER is a 1 000 MWth system and its keff is 0.98. The required current is 10.6 mA at BOC and 16.4 mA at EOC. The inventory of TRU is 6 510 kg at BOC, and 282 kg of TRU is transmuted per year. In the case of fission products, 129I and 99Tc are transmuted at the rates of 7 and 27 kg/yr, respectively. Pb-Bi is used as the coolant and target material. The average outlet temperature is 490°C when the inlet temperature of coolant is 340°C. The maximum cladding temperature turned out to be 570°C. It was found that a 2.5-mm thick beam window is needed to sustain the mechanical load. When the inlet velocity of Pb-Bi is 0.95 m/s, the maximum allowable current is 24.1 mA, which is greater than the required current of HYPER. U surrogate fuel was fabricated and tested. KAERI joined the MEGAPIE project in 2001 for Pb-Bi research. KAERI also installed the static Pb-Bi corrosion test device in 2003 and began experiments. KAERI will complete the construction of a Pb-Bi corrosion loop in 2004.

A fast subcritical reactor coupled to a particle accelerator is a concept of transmutation system that would allow large quantities of minor actinides to be burned efficiently. The research on transmutation encompassing accelerator-driven systems (ADS) is a part of the EURATOM research and development programme that lies within the area of partitioning and transmutation (P&T) of long-lived radionuclides in nuclear waste. P&T is one of the most notable research areas of the EURATOM Fifth (1998-2002) as well as the Sixth (2002-2006) Framework Programmes (FP). The objective of the research work in this area is to determine practical ways of reducing the amount and/or hazard of the waste to be disposed of. In FP5, there are 13 projects in this area with a total budget of about 69 M€ EU contribution is about 28 M€ In FP6, the research in this area, with a EU contribution of about 30 M€, strengthens the work that has been carried out in FP5 with a view to building a European Research Area (ERA) in this field. This has lead to integrating all EU activities on partitioning into one integrated project, and the same is planned for the transmutation activities. Moreover, a targeted project concerning the impact of P&T on waste management has also been initiated. International co-operation in the area of P&T with non-EU countries (such as Canada, USA and Japan), including the Commonwealth of Independent States (CIS) is also outlined.

The paper describes the status and the main technical achievements in view of the preparation of the TRADE experiment to be performed in the TRIGA reactor of the ENEA Casaccia Centre in Italy. The first beam operation is foreseen for early 2007 and the first operation of the full experiment in TRIGA by early 2008. Substantial improvements have recently been introduced with respect to the original design developed in 2002-2003, both in the functionality of the components and in the general layout of the experiment, within the main target goals already described in previous papers [1,2]. The main additional elements of TRADE with respect to the already-existing TRIGA-1 MWatt reactor are: (1) a high-energy accelerator with a suitable current and conservative, well-proven technologies, (2) a beam transport line to bring the beam in the TRIGA reactor operated as a subcritical system, (3) a solid target inserted in the core of TRIGA with the purpose of producing an adequate neutron source by the spallation reaction, and (4) additional shielding due to the production and injection of a particle beam in order to conservatively ensure an adequate radiation protection of the above new components. The accelerator chosen is a compact negative ion (H–) accelerator with an energy of approximately 140 MeV and a variable current with a maximum of about 300 mA. The beam transport has been drastically simplified with respect to previous designs, reducing the integrated bending power to the minimal 90 required by the difference in orientation of the horizontal accelerator and the vertical access tube to the spallation target. The presence of an extracted proton beam introduces significant contributions in terms of beam losses and additional radioactivity in the immediate vicinities of the accelerator, beam transport and target. To this effect additional shields have been introduced both in the regions immediately adjacent to the active elements and some additional conservative shielding in the form of a full “box” around the full reactor building, but physically well separated from the reactor structure. The present schedule of TRADE foresees the first accelerator operation by early 2007. A period of one year is foreseen for the operation of the beam transport and the spallation target in the so-called “test station” realised in the accelerator building. When all possible certifications of the operability of the target system have been successfully completed the coupling between the accelerator and TRIGA will become operational.

During the 1990s, in different European countries, the idea of using accelerator-driven systems as efficient tools for transmutation of radioactive wastes came to the forefront. At the national level, various concepts of accelerator-driven system have also been suggested. In 1998, a Technical Working Group was mandated by the Research Ministers of France, Italy and Spain, to identify the critical technical issues and to prepare a “Roadmap” for a demonstration programme. The Roadmap, issued in April 2001, defines the main requirements of an experimental accelerator-driven system commonly accepted by the European countries. Subsequently, certain European research centres, universities and nuclear industry companies decided to merge their efforts on this topic so as to propose a common European experimental accelerator-driven system. One of the first steps towards attaining this objective is to evaluate the different candidates previously developed in Europe in order to select the most appropriate concept. This led to the creation of the Preliminary Design Studies of an EXperimental Accelerator-Driven System (PDS-XADS) project performed within the Fifth Framework Programme and supported by the European Commission.

The MEGAPIE project was started to design, build and operate a liquid metal spallation neutron target as a key experiment on the road to an experimental accelerator-driven system and to improve the neutron flux at the PSI spallation source. The design of the target system has now been completed and manufacturing has started. The target is designed for a beam power of 1 MW and 6 Ah of accumulated current. It will contain about 88 l of LBE serving as target material and primary heat removal fluid. The heat will be removed by forced convection using an in-line electromagnetic pump with a 4 l/sec capacity. The heat will be evacuated from the target through 12 mono-wall cooling pins via an intermediate oil and a water cooling loop. The beam window made of the martensitic steel T91 will be cooled by a jet of cold LBE extracted at the heat exchanger exit by a second EM pump from the LBE main stream. A preliminary safety analysis has been performed considering normal, off-normal and accident conditions and a corresponding report has been submitted to authorities for licensing. The experience gained up to now shows that MEGAPIE may well be the first liquid metal target to be irradiated under high-power beam conditions.

In this work we report the activities performed in Europe to assess the reliability characteristics for an ADS-class accelerator system. These activities are mainly carried in the context of Working Package 3 (“Accelerator”) of the EC programme PDS-XADS (funded by the Fifth Framework Programme, under contract FIKW-CT-2001-00179) aimed at the design of a highly reliable accelerator for an experimental ADS. We review the reliability-oriented guidelines followed to select the reference accelerator design, and present the methodologies used for highlighting the critical areas needing further work and R&D activities in future programmes. Furthermore, we describe the synergies with ongoing high-energy physics programmes aimed at the availability assessment of complex accelerator systems, which may facilitate the compilation of a much-needed reliability database of accelerator components. A rough exploratory “parts count” reliability analysis is then presented and briefly discussed to assess the needed work on the path to obtain more accurate reliability/availability predictions of the ADS accelerator operation.

It is a generally accepted fact that construction of a high-power proton accelerator (HPPA) capable of driving a system of nuclear subcritical assembly for nuclear transmutation or energy amplification is feasible theoretically and conceptually. However, there are a number of technological challenges in several areas that need to be solved so ADS can become feasible. In this paper, we discuss the key requirements of ADS, available technologies and extension and/or extrapolation of today’s technology to render the ADS practical. ADS technology would necessarily be an extension of the accelerator of the Spallation Neutron Source (SNS), which is under construction at Oak Ridge National Laboratory. A discussion on how to extend SNS technology to ADS technology is also provided. As both accelerator and target/reactor would operate in uncharted regions of performances, extending and integrating today’s technology to the ADS realm would require many performance/requirements trade-offs between accelerator and reactor designers. The uncharted regime of performance includes two to three orders of magnitude higher beam power, improving the reliability of the accelerator to that of a similar range of reactor, and improving and controlling accelerator beam loss fraction to the 10–6 range in order to facilitate hands-on maintenance of the accelerator system. An opinion on a possible road map to achieve the ADS goals is also provided.

Accelerator-driven systems place very stringent availability requirements on the proton beam led into the subcritical reactor core. This paper describes the technical options chosen by a European collaboration supported by the European Commission in the framework of a Preliminary Design Study of an eXperimental ADS (PDS-XADS). These options are considered a sound basis for the development of an ADS-compatible accelerator. It mainly consists of a superconducting linac fed by an ECR ion source and a four-vane RFQ. The modularity of such an accelerator is a strong advantage, and high availability may be obtained by the proper combination of maximum reliability and of a powerful fault tolerance scheme. The methods to obtain fault tolerance are described, and the upcoming R&D programme is presented. The importance of an adapted construction methods is stressed.

ADS require a high-intensity proton accelerator of which energy and beam power are about 1 GeV and 20-30 MW, respectively. JAERI, KEK, MHI and MELCO have conducted a programme for the development of a superconducting proton linac for the ADS since 2002. This programme, which is based on the achievement of the J-PARC design work, consists of two parts, development of a 972-MHz cryomodule and system design of a superconducting proton linac in the energy range between 0.1 and 1.5 GeV. In the development work of the 972-MHz cryomodule, a prototype cryomodule which includes two nine-cell cavities of b = 0.725, will be developed and the goal is stable operation in the horizontal tests at the surface peak field at 30 MV/m. In the system design work, a preliminary beam dynamics design has been determined with the configuration of a cryomodule with two 972-MHz, nine-cell elliptical cavities, and a room-temperature focusing magnet. This paper provides the present status of the cryomodule development and the system design.

Taking into account the PDS-XADS requirements concerning accelerating field, quality factor and reliability, two spoke-type cavities have been designed at IPN Orsay. One of them has been successfully tested and the second one is currently being fabricated. This paper reports on the excellent performance of the first cavity, substantially exceeding the requirements, which make spoke cavities an attractive solution for a reliable PDS-XADS proton driver.

A 3.5-MeV RFQ accelerator for a Chinese accelerator-driven subcritical reactor system (ADS) has been under construction in China over the past two years. It is is a 75-keV/3.5-MeV, 352.2-Hz, 50-mA four-vane type RFQ. In this paper the characteristics of the machine are described, including its physical parameters, RF characteristics, thermal and structural analyses, cold model measurements, RF power system and its fabrication test of technology model. The microwave ion source and the LEBT also are described.

In order to meet the high availability/reliability required by the PDS-XADS design, the accelerator needs to implement, to the maximum possible extent, a fault tolerance strategy that would allow beam operation in the presence of most of the envisaged faults that could occur in its beam line components. In this work we report the results of beam dynamics simulations performed to characterise the effects of the faults of the main linac components (cavities, focusing magnets...) on the beam parameters. The outcome of this activity is the definition of the possible corrective and preventive actions that could be conceived (and implemented in the system) in order to guarantee the fault tolerance characteristics of the accelerator. The PDS-XADS programme is funded by the EC 5 th Framework Programme, under contract FIKW-CT-2001-00179

The Kumatori Accelerator-driven Reactor Test project (KART) was undertaken at Kyoto University Research Reactor Institute (KURRI) as of fiscal year 2002, with the aim to demonstrate the basic feasibility of ADS and to develop a 150-MeV proton Fixed-field Alternating Gradient (FFAG) accelerator complex as a neutron production driver. This FFAG complex will be connected with the Kyoto University Critical Assembly (KUCA) for basic ADS experiments by the end of March 2006.

Over the past two years, INFN-LNS has undertaken to improve the source reliability for high-power proton accelerators. A full set of magnetic field measurements has been carried out to define a different design of the TRIPS magnetic system, based on permanent magnets, in order to increase the reliability of the source devoted to the ADS. The OPERA-3D package was used to design the new magnetic system as a combination of three rings of NdFeB magnets and soft iron in between. The description of the magnetic measurements and the comparison with the simulations are presented, along with the design of a new version of the source, called PM-TRIPS. Finally the new low-energy beam transfer line (LEBT) will be described, with particular regard to the improvement of accelerator availability, which can be obtained with the installation of two PM-TRIPS sources or more on a switching magnet.

In this paper we discuss recent work to further improve our superconducting (SC) ADS driver linac design. Our design assumes use of the 6.7-MeV LEDA RFQ as an injector to the SC driver linac. We have examined the feasibility of accelerating a 20-mA CW beam to 600 MeV using only 350-MHz SC multi-spoke resonator cavities operating at 4 K. Replacing the 2 K, 700-MHz SC elliptical cavity sections with spoke resonators has several advantages, including reduced cryo-plant operating cost and an improved real-estate accelerating gradient due to the longer active lengths of the 350-MHz cavities. We discuss the details of the new design layout and beam dynamics simulations, including effects due to operational and alignment errors. Preliminary cavity modelling results for the proposed five-gap spoke resonators are also discussed. This accelerator design would be appropriate as a driver linac for applications such as waste transmutation, fusion materials testing, etc.

Successful development of a reliable and normal hands-on maintainable high-power linac requires minimisation of beam losses along the accelerator. The high sensitivity of the high-power linac focusing channel to random perturbation encourages designers to concentrate their attention on the tolerance estimation problem. The degradation of beam parameters, including transverse size and emittance growth, is caused by channel and beam parameter perturbations. The calculation of channel sensitivity permits to estimate the influence of each perturbing factor on the beam parameters and to determine the main source of perturbation, to find perturbing factors compensation possibilities and to determine the factors required to guarantee beam passage throughout the real channel without losses. Methods for the estimation of tolerance in high-power linac accelerating-focusing channels are considered in the present paper. The realisation of these methods in the LIDOS code package is presented. Monte Carlo simulation results for various types of accelerating channels are discussed.

The Spallation Neutron Source accelerator system will provide a 1-GeV, 1.44-MW proton beam to a liquid mercury target for neutron production. The accelerator complex consists of an H– injector capable of producing a 38-mA peak current, a 1-GeV linear accelerator, an accumulator ring and associated transport lines. The linear accelerator consists of a drift-tube linac, a coupled-cavity linac and a superconducting linac which provide a 1.5-mA average current to the accumulator ring. The design of the accelerator systems is complete; installation of the accelerator components is in progress; and staged beam commissioning is proceeding as installation progresses. The installation and final commissioning of the project is on schedule for completion in early 2006. The status of the project design, installation and commissioning will be presented.

TRASCO ADS is a programme aiming at the design of an accelerator-driven subcritical system in which INFN, ENEA and Italian firms work on the preliminary study and design of the high-intensity proton linac accelerator and on the windowless interface between the accelerator and the reactor. The accelerator UHV and the spallation target vacuum are divided only by a suitable pumping and trapping system for the gases and the vapours emerging from the molten LBE. In order to design a pumping system for the accelerator-reactor interface region, vacuum gas dynamics theoretical considerations and experimental evaluations are needed to understand the behaviour of the vapours and gases in the target region. For the same purpose the literature data and experimental results on the radioactive gases and vapours, produced by the spallation process, must be investigated. From the vacuum gas dynamics point of view, a numerical method based on angular coefficients has been validated to estimate the net flux of the LBE vapours and the gases coming from the spallation process, the oxidation control and the tube outgassing. From the safety point of view, preliminary experiments are under way for an estimation of the net flux of high-activity gases such as mercury and polonium (using tellurium as a polonium simulator) with the purpose to evaluate the radioactivity in the beam tube. All these data, compared with those from literature and the experimental results, give an improvement towards a suitable design of the pumping system for an  DS windowless interface according to technological and nuclear safety constrains.

Lead-bismuth eutectic (LBE) corrosion has been considered as an important design factor to limit the temperature and velocity of the accelerator-driven transmutation system. For the corrosion study, KAERI finished the set-up of the LBE static corrosion facility and also finished the preliminary design of a dynamic corrosion loop and started a set-up process to construct the loop by the fall of 2004. In this paper, we describe the results of the preliminary static test during 500 hrs under a reduced condition to check the performance of the static facility. We also describe a design concept of corrosion loop and the state of the art for its installation at KAERI, as well as the results of EM pump preliminary testing.

The MYRRHA accelerator-driven system (ADS) is being developed in Mol, Belgium incorporating a windowless spallation target, as this is the only option within the constraints of the envisaged neutron source performance. In this paper the research programme and experimental set-up required for the R&D effort towards the conditioning of Pb-Bi eutectic for use in a windowless liquid-metal spallation target are presented. The experiences acquired commissioning the set-up, the current status of the experiment and first results are discussed.

A spallation target system is a key component in the development of an accelerator-driven system (ADS). It is known that a 15-25 MW spallation target is required for a practical 1 000 MWth ADS. The design of a 20 MW spallation target is very challenging because more than 60% of the beam power is deposited as heat in a small volume of the target system. In the present work, a numerical design study was performed to obtain the optimal design parameters of a 20 MW spallation target for a 1 000 MWth ADS. A dual injection tube was proposed for the reduction of the LBE flow rate at the target channel. The results of the present study show that a 30-cm wide proton beam with a uniform beam distribution should be adopted for the spallation target of a 20 MW power. When the dual LBE injection tube is employed, the LBE flow rate is reduced by a factor of four without reducing the maximum allowable beam current.

The Japan Atomic Energy Research Institute (JAERI) is conducting the research and development (R&D) on the accelerator-driven subcritical system (ADS) for the effective transmutation of minor actinides (MAs). The ADS proposed by JAERI is an 800 MWth, Pb-Bi cooled, tank-type subcritical reactor loaded with nitride fuel (MA+Pu). Pb-Bi is also used as the spallation target. In this study, the feasibility of the ADS was discussed by focusing on the design around the beam window. The partition wall was placed between the target region and the ductless-type fuel assemblies to keep the good cooling performance for the hot-spot fuel pin. The flow control nozzle was installed to cool the beam window effectively. The thermal-hydraulic analysis showed that the maximum temperature at the outer surface of the beam window could be repressed below 500 C even in the case of maximum beam power (30 MW). The stress caused by the external pressure and the temperature distribution of the beam window was below the allowable limit.

Spallation reactions have recently attracted considerable attention due to their importance in technical applications and fundamental physics. For example, they can act as intense neutron sources for accelerator-driven radiologically clean nuclear systems (ADS) [1,2] for energy generation and nuclear waste transmutation. In this system, lead constitutes an ideal spallation target since its neutron yield is high and it is very transparent to neutrons of energies below 1 MeV. Isotopic production data from proton-induced reactions with energies up to 5 GeV are of great importance for understanding the reaction mechanisms of intermediate nuclear reactions. Recently, precise and numerous measurements of elements produced from proton-induced spallation reactions with energy ranges from 10 MeV to 5 GeV using several target materials were carried out [3-5] due to the interest in a spallation neutron source and ADS. More than 15 000 experimental data points have been obtained. R. Michel [3-5], et al., systematically investigated the data in order to provide a database for model calculations while Yu. E. Titarenko [6] measured the yields of residual product for proton energies from 100 to 2 600 MeV to compare theoretical codes. The target elements were chosen according to their relevance in cosmo chemistry and cosmo physics applications in which the production of cosmogenic nuclides in extraterrestrial matter, the target elements with atomic numbers < 29 and a few high-Z, such as Rb, Sr, Y, Zr, Te, Ba, Nb, etc. are needed. Heavy elements such as Ta, W, Hg, Pb, Bi, Tu and U are under discussion as spallation target materials for spallation neutron source and ADS applications.

The window target unit for an LBE-cooled primary core is one of the basic options considered in the framework of the preliminary design study of an experimental accelerator-driven system (PDS-XADS). In the present work, a numerical design study using the computational fluid dynamics (CFD) code CFX 5.6 was performed for the active part of this option with special attention to the coolability of the window. Steady-state as well as beam trip behaviours under normal operating conditions were investigated with the advanced turbulence model combined with the advanced wall treatment available in the new CFX 5 version. Based on the results of CFX 5.6 calculations, the window thickness was reduced to 2 mm in the centre from the initial proposal of 3 mm in order to satisfy the thermal design limit. The maximum temperature change rate of the window under beam trips is predicted to be as high as 412 C/s at 0.1 s after the beam interrupt. It is clear that beam trips with a beam interrupt duration less than 1 s could also be crucial to the integrity of the window.

In an accelerator-driven system (ADS), a target system is incorporated. The main purpose of the target system is to produce excess neutrons, which brings the subcritical reactor core in an ADS to critical condition. Critical condition allows for operation as a reactor system specifically to fulfil transmutation capability as well as electricity generation. From a safety point of view, the target system is quite a new component and potentially provides a novel radiotoxic burden to the environment and to humans. It is generally understood that there is still unknown physics involved in the operation of a target system, in particular, regarding nuclear spallation. Moreover, we have not yet developed the related engineering to cope with so-called “spallation products.” As a primary step towards better comprehension, this paper describes how we can have a better computational tool to predict the yields of spallation products in a proposed target system.

At the Kyoto University Research Reactor Institute (KURRI), a new project for research on the accelerator-driven subcritical reactor (ADS) was started in 2002. For this project, a new ring-type accelerator based on the up-to-date FFAG (fixed field alternating gradient) technology will be under construction through 2005. With this new accelerator, a proton beam having arbitrary energy from 2.5 to 150 MeV will be generated and the proton beam from this accelerator will be introduced into a core at the Kyoto University Critical Assembly (KUCA) in order to generate high-energy neutrons via collision with heavy metal (e.g. tungsten). Before starting this new experiment, basic research on ADS was performed at KUCA, combining a KUCA core with an accelerator to generate 14 MeV neutrons via a D-T reaction and to investigate the nuclear characteristics of a subcritical reactor with an external neutron source.

The TRADE (TRIGA accelerator-driven experiment) experiment, which is to be performed in the TRIGA reactor of the ENEA/Casaccia centre, involves the coupling of a 140 MeV, 0.3 mA beam that is produced by a cyclotron to a target hosted in the central thimble of the reactor scrammed to subcriticality. A 25-m  long beam line was designed to transfer the beam by injecting it from the pool top, taking special care to have very low losses in the TRIGA reactor building where limited shielding of the beam line is possible. The beam transfer line is composed of a matching section (MS), which matches the beam to the following section, and a final bending section (FB), which shapes and directs the beam onto the target. Attention was paid to reduce the number and size of elements of the FB that were immersed in the pool water. Shielding calculations show that a sustainable radiation level is possible with the foreseen beam losses. The paper presents a description of the beam line at the present stage of the project.

Characteristics of an ADS burner of minor actinides (MA) were estimated, taking into account the following initial assumptions: 10 MW proton accelerator-driver  1 GeV, 10 mA), two-zone cascade subcritical reactor with Äkeff = 0.05, central zone of neutron multiplication and transmutation zone on the basis of NaF-ZrF4 molten salt. Such a scheme reduced by three times the power of the accelerator-driver at the same blanket power. Reactor power was obtained equal to 800 MWth; its burning effectiveness was ~50 kg MA per year or the MA production of five thermal rectors of equal power. The main neutron physics characteristics of the reactor were calculated, including power distribution, reactivity effects, actinides burn-up, thermo-hydraulics of zones, etc.

SCK•CEN, the Belgian Nuclear Research Centre, is designing an accelerator-driven system (ADS), MYRRHA, which aims to serve as a basis for the European experimental ADS and to provide protons and neutrons for various R&D applications. It consists of a proton accelerator that delivers a 350 MeV, 5 mA proton beam to a liquid lead-bismuth eutectic (LBE) spallation target, which in turn couples to an LBE-cooled, subcritical fast-spectrum core in a pool-type configuration. The liquid metal flow pattern in the lower part of the MYRRHA pool vessel needs to be investigated in order to assess the details of recirculation and stagnant zones for adequate coolant flow and sufficient physico-chemical mixing as well as to judge the scaling of flow down to a model that can be handled experimentally. To this end, three-dimensional (3-D) computational fluid dynamics calculations were performed by NRG in collaboration with the MYRRHA team.

Temperature transients induced by beam interruptions of different durations in MOX-fuelled and lead-bismuth cooled experimental ADS are investigated as a WPPT benchmark computational problem. The final report of the second phase of calculations will be published shortly by the NEA. This second phase of calculations aimed to investigate the impact of different fuel power density conditions on the transient results and uncertainties. Temperature variations are investigated assuming fresh fuel conditions, four different fuel power densities and two interruption durations. The main results obtained by the nine participants are presented and compared in this paper. Moreover, their uncertainty component due to the assumptions on models and data recommended in the benchmark specifications is evaluated by means of sensitivity studies carried out by some participants as a further contribution.

Within the Fifth Framework Programme of the European Union (EU), the PDS-XADS project is focused on Preliminary Design Studies of an Experimental Accelerator-driven Reactor System (ADS). Three basic designs are being studied in detail – two ADS design options, one with a lead-bismuth eutectic (LBE) cooled core (an 80 MWth unit and a smaller unit) and another (80 MWth) with a gas (helium) cooled core. One part of the PDS-XADS project involves the assessment of the safety of the two 80 MWth designs. The main objectives are as follows: develop an integrated safety approach common to both the LBE and the gas-cooled concepts; identify the main safety issues in an XADS with their phenomenology and develop an evaluation methodology for both alternatives; and perform transient analyses with the aim of producing safety analysis reports on the design features required to meet XADS safety objectives.

Comparative safety analyses and investigations were performed for a small-scale ADS with conventional MOX fuel and an 800 MWth power class ADT with advanced fertile-free fuels, both cooled by Pb/Bi. The analyses covered perturbations of the source [e.g. unprotected transient overcurrent (UTOC) and beam interruptions] as well as perturbations on the core side, protected/unprotected transient overpower (P/UTOP) induced by reactivity additions and unprotected loss of flow (ULOF) accidents. These showed that the small-scale ADS had a very good safety performance, while for the 800 MWth ADT with ZrO2 and MgO matrix based fuels some safety problems were identified, mainly related to the large positive void feedback and high linear power rate. Further design and safety optimisations are under consideration.

In the field of waste management incorporating a transmutation option, accelerator-driven systems (ADS) represent an important alternative to conventional reactors due to their higher safety level when minor actinides (such as neptunium and americium) are loaded into the core. The Preliminary Design Study of an Experimental Accelerator-driven System (PDS-XADS) is being performed within the European Union’s Fifth Framework Programme. The main goal of PDS-XADS is to demonstrate the feasibility of an ADS and to compare different coolant (Pb/Bi and gas) and power (50-80 MWth) options. At this stage, all options use MOX fuel. Comparative safety analyses were performed using the TRAC/AAA code for the 80 MWth Pb/Bi and gas-cooled designs. The analyses covered reactivity increase (as an example of perturbations of the core), transient overcurrent (as an example of perturbations of the source) and loss of coolant (as an example of transients coming from faults in the primary and secondary coolant systems).

In order to support ADS-related technologies, the thermal-hydraulic ADS lead-bismuth loop (TALL) was designed and constructed at KTH to investigate the heat transfer performance of different heat exchangers, and the thermal-hydraulic characteristics of natural and forced circulation flow under steady and transient conditions. The LBE loop is of full height and was scaled such that the prototypic (power/volume) ratio would represent the main components. So far, the forced convection and heat transfer of LBE through a straight tube heat exchanger and a U-tube heat exchanger have been accomplished and documented [1]. Transient experiments in the test facility are being conducted with reference to safety issues of ADS under the following conditions: a) startup and shutdown, b) loss of heat sink, c) loss of external driving head, d) heater trips, e) sudden change in power, and f) blockage in pipe. Preliminary tests were encouraging given the agreement of experimental data with RELAP5 analysis. More transient experiments and RELAP5 analysis will be performed in the future.

Beam window breakage is one of the accidents under consideration for the operation of an accelerator-driven subcritical system (ADS). After the beam window breaks, the target material [lead-bismuth eutectic (LBE)] flows into the beam duct in liquid and gaseous phases. The inlet velocity of the liquid LBE and the pressure of gaseous LBE in the duct were analysed.

In this work a new approach to the realisation of an accelerator-coupled hybrid system (ACS) is proposed. A significant improvement of the feedback effect due to the particularities of the neutron production in a spallation target is expected. In the present study, we explain the principles of system functioning as well as the advantages and disadvantages of the proposed concept. The quantitative analysis of the innovative ACS operation is based on a generalised point kinetics approach. In the framework of this simplified model, we show that the particular dependence of the spallation neutron yield allows for the creation of a supplementary negative feedback effect (Doppler-like). Implementation of this concept should compensate, to some extent, the eventual feedback degradation in the cores dedicated to the transmutation of nuclear waste.

Burn-up for the reference core of MYRRHA over a single cycle of 90 days was estimated with MCNPX and SPECTRUM (an MCNPX postprocessor developed at SCK•CEN). Over this cycle, the source multiplication factor ks dropped from 0.952 to 0.941 (Drs = 1 263 pcm) while the effective multiplication factor keff dropped from 0.946 to 0.933 (Dr = 1 484 pcm). A number of possible techniques have already been proposed and studied to minimise this burn-up swing such as proton current variation, use of burnable poisons, use of negative void coefficients and multi-batch core operation. We propose the concept of a realistic operational cycle in which voided boxes and/or burnable absorbers (with different levels of enrichment) are used to minimise the burn-up swing in the MYRRHA case. In this paper, we also make an initial assessment of the applicability of these operational cycles to the MYRRHA case.

Under the framework of the High-intensity Proton Accelerator Project called J-PARC (Japan Proton Accelerator Research Complex), the Japan Atomic Energy Research Institute (JAERI) plans to construct the Transmutation Experimental Facility (TEF). The TEF consists of two facilities: the Transmutation Physics Experimental Facility (TEF-P) and the ADS Target Test Facility (TEF-T). The TEF-P is a critical facility that can accept a 600 MeV, 10 W proton beam. The TEF-T is a material irradiation facility using a 600 MeV, 200 kW proton beam and a Pb-Bi target; however, neutron multiplication by nuclear fuel will not be attempted. This report describes the purpose of the facility, the present status of the conceptual design and the expected experiments to be performed.

Development of the project SPHINX (spent hot fuel incinerator by neutron flux) is based on the utilisation of a subcritical nuclear reactor system with liquid fuel based on molten fluorides. Existing experimental facilities have been used for experimental testing of the system, individual technological components and newly developed materials that should be resistant in the environment of molten fluorides at operational temperatures. Examples of facilities include the experimental reactors LR-0 and VR-1 with inserted zones for the investigation of neutronic characteristics of transmuter blanket cores, research reactor LVR-15 with instrumented probes for transmuter blanket sample testing in high neutron flux conditions, and experimental loops with molten fluoride salts for an investigation of transmuter system operational conditions. This paper describes some of the experiments performed and results obtained thus far.

This paper is concerned with the transmutation of TRUs in DUPIC (direct use of spent PWR fuel in CANDU) spent fuel in the HYPER system, which is an LBE-cooled ADS. The DUPIC concept is a synergistic combination of PWR and CANDU, in which PWR spent fuels are directly re-utilised in CANDU reactors after a very simple refabrication process. The objective of this study is to investigate the TRU transmutation potential of the HYPER core for the DUPIC-HYPER fuel cycle. All the previously developed HYPER core design concepts were retained except those which involve fuel composed of TRUs from DUPIC spent fuel. The HYPER core characteristics were analysed using the REBUS-3/DIF3D code system.

The effect of heat treatment on fuel rods at 630°C and 700°C and the interfacial reaction between fuel and lead were investigated. The U-Zr metallic fuel was fabricated by mixing, pressing, sintering and extrusion. There were two kinds of phases – á-Zr precipitates and a ä-UZr2 matrix in the U-Zr metallic fuel. After heat treatment of the extruded rod at 630°C and 700°C, the volume changes of the samples increased slightly and the density variation was negligible. Therefore, it is evident that U-Zr fuels have good thermal stability. The interface between U-55Zr fuel and Pb according to annealing time at 650°C consisted of two distinctive regions – a reaction zone in the vicinity of the surface and an initial zone in the inner area. It should be noted that the thickness of the reaction zone was 26 µm, 36 µm and 46 µm at 100 hrs, 200 hrs and 1 000 hrs, respectively. Also, the reaction zone consisted of an á-Zr layer and a Zr-depleted area.