[en] The main parameter characterizing the neutron economy of an accelerator driven subcritical fission device, like the Energy Amplifier (EA), is the factor M by which the source spallation neutrons are multiplied by the fission dominated cascade. A related quantity is the multiplication coefficient K_src=(M-1)/M, that is the average ratio of the neutron population in two subsequent generations of the source-initiated cascade. Such a factor k_src, depending on both the properties of the source and of the medium, is in general conceptual and numerically different from the effective criticality factor k_eff, commonly used in reactor theory, which is in fact only relevant to the fundamental mode of the neutron flux distribution, and is independent on the source. The effective criticality factor k_eff is however a meaningful measure of the actual safety characteristics of the device, that is 1-k_eff is a proper gauge of the distance from criticality. In this paper the difference between k_eff is addressed numerically in the case of an externally driven Thorium fuelled and Lead cooled subcritical device representing a simplified version of the Energy Amplifier. It is found that codes or calculations implementing the critical reactor formalism (neutrons are distributed according to a cos-type imposed distribution together with a fission spectrum energy distribution and non-fission multiplication, i. e. n,X_n reactions, is not considered explicitly) in order to describe a subcritical device, systematically underestimate the reactivity on the system by about 0.028 in k (∼ 2800 pcm) which implies an error in the estimation of the necessary concentration of ''233U close to 5% which in turn induces an adverse effect on the stability of k during burnup. Finally, the discrepancies arising from the use of different nuclear data libraries are as significant as the effects of using different neutron source approximations and hence also deserve attention. We think that a reevaluation of the nuclear libraries related to the Thorium cycle is necessary, particularly as far as the JEF-2.2 data are concerned. (Author) 11 refs

[en] The Monte Carlo method (MC) is currently used to simulate the real time behaviour of a sub-critical system like for instance the energy amplifier demonstration facility (EADF). The advantage of this method is that it can be made intrinsically free of unwanted approximations, provided that (i) the relevant cross sections are well known - a necessity of any method of computation - and (ii) the actual geometry is sufficiently well modeled. For instance a variety of processes with many different particles in the final state as well as detailed angular distributions can be taken correctly into account and there is no real limit to the complexity of the geometry and the number of separate components. This technique also ensures continuity between the simulation of the high energy, proton induced initial cascade, for which MC is the only formalism, and the subsequent sub-critical, fission dominated nuclear cascade. Therefore MC constitutes a superb tool to simulate realistically both the ordinary operation and a variety of transients in sub-critical or critical systems. (orig.)

[en] Progress in particle accelerator technology makes it possible to use a proton accelerator to eliminate nuclear waste efficiently. The Energy Amplifier (EA) proposed by Carlo Rubbia and his group is a subcritical system driven by a proton accelerator. It is particularly attractive for destroying, through fission, transuranic elements produced by present nuclear reactors. The EA could also transform efficiently and at minimal cost long-lived fission fragments using the concept of Adiabatic Resonance Crossing (ARC) recently tested at CERN with the TARC experiment. The ARC concept can be extended to several other domains of application (production of radioactive isotopes for medicine and industry, neutron research applications, etc.). Author is convinced that fundamental research is a strong driving force in innovation and that it can lead to potential solutions of some of the most difficult problems facing our society at the beginning of the third millennium. In particular, nuclear energy may represent an acceptable solution of the energy problem and it would be a mistake to exclude it, a priori, from fundamental research and development. The Energy Amplifier, based on the physics principle well established by dedicated experiments at CERN, is the result of an optimization made possible by the use of an innovative simulation code validated in those experiments (FEAT and TARC). This experimental programme has generated new applications in various fields: medical applications for which CERN has filed a patent, research with the approved TOF facility at CERN and other surprising ideas such as the nuclear space engine. All of these are extremely rewarding for those who have been involved in this project, and I can only hope that it will also help Governments to recognise the importance of continuing to support strongly fundamental research

[en] A general method for investigating the effectiveness of actinide transmutation systems is proposed. The method allows to assess the impact of different long term transmutation strategies on the actinide inventories of the systems, the composition of the actinide waste, and the radiological risk associated with the disposal of this waste. In a comparative study, the method is applied to systems with a wide range of characteristics including a PWR, a fast reactor, a high lux superthermal system, and two accelerator based systems with fast neutron spectra. The results of the study emphasize the importance of a good overall neutron balance for completely burning the actinides. As to the radiological risk of the waste, it is found that most transuranic actinides can be recycled in fast reactors and PWRs with similar risks, and that high lux superthermal systems bum actinides generally with a somewhat smaller risk than other systems. Interestingly, it appears that, in the long range, the radiological risk of the waste cannot be reduced by changing from the uranium-plutonium to the thorium-uranium fuel cycle. (authors)

[en] This lecture describes the basic process of Accelerator-Driven Systems (ADS) is Nuclear Transmutation. One way to obtain intense neutron sources is to use a hybrid sub-critical reactor-accelerator system called just Accelerator-Driven System. The idea of producing neutrons by spallation with an accelerator has been around for a long time, since 1950. In November 1993, Carlo Rubbia proposed, in an exploratory phase, a first Thermal neutron Energy Amplifier system based on the thorium cycle, with a view to energy production. The Existing ADS Concepts are reviewed. The spallation process is explained in detail including: Spallation Neutron Yield, Spallation Neutron Spectrum, Spallation Product Distribution, Energy Deposition, Models and Codes for High-Energy Nuclear Reactions. Physics of Sub-Critical Systems is explained including: Multiplication Factor, Source Importance, Spatial flux Distribution, Source Amplification. A Review of Sub-Critical Core Experiments is presented. The second part of this paper deals Nuclear Data, and Methods for ADS Design. It includes description of the EA-MC Monte Carlo code package (Structure of the program, Neutron transport and time evolution, Nuclear Data, Geometry Modelling, Validation); Limitations in the high energy particle transport (Neutron Yield, spallation product distribution, spallation source distribution, energy deposition); Limitations in the low energy neutron transport (Methodology, Modeling of the spallation source, nuclear data below 20 MeV, statistics in the case of Monte Carlo codes); Experimental validation of neutron transport and nuclear data

[en] For transmutation systems based on externally driven subcritical assemblies with a fast neutron spectrum, there is an incentive to expose the actinides directly to the source neutrons, since these neutrons have higher energies than the fission neutrons. To clarify the influence of the high-energy models on the transmutation effectiveness of such systems, a sensitivity study based on the Phoenix concept, i.e. a sodium-cooled system with a minor actinide oxide fuelled target, was performed. The calculations show that the difference arising from the use of different basic data sets are quite as significant as the effects of using different source approximations and hence also deserve attention. (authors). 10 refs., 4 figs., 7 tabs

[en] At the Paul Scherrer Institute (PSI), hybrid systems with a fast neutron spectrum are extensively investigated. The high-energy particle interaction is treated using the Monte Carlo method. For the transport of neutrons at low energies a deterministic approach is adopted, together with modern nuclear data libraries. (authors). 14 refs., 1 figs

[en] The international Thorium Energy Committee (iThEC) in Geneva has been established to investigate the ADS (accelerator-driven subcritical reactor) fuelled by thorium. The committee, formed by prominent members of the scientific community of CERN also comprises business leaders and members acquainted with public relations in an effort aimed at broadening the appeal of the ADS concept. The use of thorium in a subcritical fast reactor configuration driven by an accelerator and cooled by natural convection of liquid metal offers significant advantages in terms of resource abundance, security, non-proliferation and drastic reduction of existing and future waste. Switzerland has unique strengths in a number of areas directly related to the basic elements of an ADS system for the destruction of nuclear waste. First, the Paul Scherrer Institute (PSI) in Villigen has developed a cyclotron with a proton beam whose characteristics and power have the capacity to drive a nuclear waste incinerator. Secondly, the presence of CERN in Switzerland is also an important asset because it is at CERN that the founding experiments of an ADS were performed. iThEC proposes that Switzerland undertakes, along with other interested parties, a programme on the elimination of nuclear waste through the thorium-ADS concept

[en] Progress in particle accelerator technology makes it possible to use a proton accelerator to produce energy and to destroy nuclear waste efficiently. The energy amplifier (EA) proposed by Carlo Rubbia and his group is a sub-critical fast neutron system driven by a proton accelerator. It is particularly attractive for destroying, through fission, transuranic elements produced by present nuclear reactors. The EA could also transform efficiently and at minimal cost long-lived fission fragments using the concept of adiabatic resonance crossing (ARC) recently tested at CERN with the TARC experiment. (author)

[en] A detailed neutronic analysis has been performed of the 80 MW(th) Energy Amplifier Demonstration Facility, fuelled with uranium and plutonium mixed oxides and cooled by lead-bismuth eutectic. The neutronic calculations presented in this paper are a result of a state-of-the-art computer code package developed by the EET group at CERN. Both high-energy particle interactions and low-energy neutron transport are treated with a sophisticated method based on a full Monte Carlo simulation, together with modern nuclear data libraries. The code is designed to run both on parallel and scalar computers. A series of experiments carried out at the CERN-PS (i) confirmed that the spallation process is correctly predicted and (ii) validated the reliability of the predictions of the integral neutronic parameters of the Energy Amplifier Demonstration Facility. (author)