Results 1 - 10 of 9675
Results 1 - 10 of 9675. Search took: 0.033 seconds
|Sort by: date | relevance|
[en] Design and construction of a high power CW (Continuous Wave) electron linac for studying feasibility of nuclear waste transmutation was started in 1989 at PNC. The PNC linac is the 10 MeV, 20 mA (average current, 20% duty) accelerator with eight normal conducting TWRR (Traveling Wave Resonant Ring) disk loaded accelerating tubes. Various methods have been proposed to transmute long-lived fission products using accelerators. The transmutation by photonuclear reaction using a electron accelerator has advantages of the small production for secondary radioactive waste and broad base of accelerator technology. The PNC high power CW electron accelerator has been pre-commissioned with the injector and the first accelerating tube. By December 1995, the accelerator was partially built and the injector pre-commissioning began. Then 3.1 MeV beam had coasted though the beam dump. We have been very successful to produce 1 ms pulse width electron beam with 100 mA peak and energy about 3.1 MeV at present. The whole facility will be completed in March 1997. (authors)
[en] A historical overview of transmutation ideas and praxis from antiquity to latest developments in advanced nuclear reactor systems is given. The transmutation of elements has long been a great puzzle in science from antiquity to Middle Ages, many alchemist’s unfulfilled dream, until Rutherford’s discovery of the artificial nuclear transformation of nitrogen into oxygen. Nuclear reactions, since then, lead to production of numerous new elements and isotopes, to the discovery of the nuclear fission, the nuclear chain reaction, and as a consequence, to the construction of nuclear reactors. Nowadays, new subcritical reactor systems, based on particle accelerators, the so called Accelerator Driven Systems or (ADS) are investigated and designed to produce safely and more effectively a clean nuclear energy.
[en] The efficient and safe management of spent fuel produced during the operation of commercial nuclear power plants is an important issue. In this context, partitioning and transmutation (P and T) of minor actinides and long-lived fission products can play an important role, significantly reducing the burden on geological repositories of nuclear waste and allowing their more effective use. Various systems, including existing reactors, fast reactors and advanced systems have been considered to optimise the transmutation scheme. Recently, many countries have shown interest in accelerator-driven systems (ADS) due to their potential for transmutation of minor actinides. Much R and D work is still required in order to demonstrate their desired capability as a whole system, and the current analysis methods and nuclear data for minor actinide burners are not as well established as those for conventionally-fuelled systems. Recognizing a need for code and data validation in this area, the Nuclear Science Committee of the OECD/NEA has organised various theoretical benchmarks on ADS burners. Many improvements and clarifications concerning nuclear data and calculation methods have been achieved. However, some significant discrepancies for important parameters are not fully understood and still require clarification. Therefore, this international benchmark based on MASURCA experiments, which were carried out under the auspices of the EC 5. Framework Programme, was launched in December 2001 in co-operation with the CEA (France) and CIEMAT (Spain). The benchmark model was oriented to compare simulation predictions based on available codes and nuclear data libraries with experimental data related to TRU transmutation, criticality constants and time evolution of the neutronic flux following source variation, within liquid metal fast subcritical systems. A total of 16 different institutions participated in this first experiment based benchmark, providing 34 solutions. The large number of solutions provided has allowed to analyse the calculation results with many different combinations of simulation methods, including deterministic and Monte Carlo methods, and nuclear databases. The intercomparisons of these results and their direct comparison against experimental results (when available), were helpful to identify the sources of discrepancies observed among different solutions. Nevertheless, this MUSE-4 benchmark could not answer all the questions raised. A follow-up exercise may be useful for a more thorough investigation on external fast neutron source propagation within the multiplier media and thermal neutron transport in large and nearly transparent reflectors. (author)
[en] The article discusses the development of a linear proton accelerator for the MYRRHA Accelerator Driven System (ADS). The linear proton accelerator provides a high energy and high intensity proton beam that is directed to a spallation target, which will deliver neutrons to a subcritical nuclear reactor core. The article describes the MYRRHA linear accelerator, which mainly consists of a sequence of superconducting accelerating radiofrequent cavities that are positioned in a linear configuration. The beam requirements for MYRRHA are discussed involving, amongst others, a continuous wave beam delivery mode with a high reliability goal. The key concepts to increase the reliability of the accelerator are described.
[en] The EUROTRANS (European Research Programme for the Transmutation of High-level Nuclear Waste in an Accelerator-driven System) Integrated Project within the ongoing EURATOM 6. European Commission Framework Programme (FP6) is devoted to the study of transmutation of high-level waste from nuclear power plants. The work is focused on transmutation in an accelerator-driven system (ADS). The objective of EUROTRANS is the assessment of the design and the feasibility of an industrial ADS prototype dedicated to transmutation. The necessary R and D results in the areas of fuel development, structural materials, thermal-hydraulics, heavy liquid metal technology and nuclear data will be made available, together with the experimental demonstration of the ADS component coupling. The outcome of this work will allow to provide a reasonably reliable assessment of technological feasibility and a cost estimate for ADS-based transmutation, and to possibly decide on the detailed design of an experimental ADS and its construction in the future. EUROTRANS is integrating critical masses of resources (23 M euros contribution, 43 M euros total eligible costs) and activities of 29 partners from 14 countries, within industry (10 partners), national research centres (18 partners) and 17 universities in Europe. The universities are collectively represented by one partner, the European Nuclear Engineering Network (ENEN). EUROTRANS is the logical continuation of the three FP5 Clusters FUETRA, BASTRA and TESTRA together with the PDS-XADS Project. It takes credit from the Road-map on ADS of the Technical Working Group. EUROTRANS strengthens and consolidates the European research and development activities with regard to transmutation. The involvement of universities strengthens education and training in nuclear technologies. The involvement of industry assures a market-oriented and economic design development and an effective dissemination of the results. The four-year project started in April 2005. (authors)
[en] Full text of publication follows: After use, PWR fuel contains approximately 95% uranium, 1% plutonium, and 4% fission products and a wide variety of minor actinides. Uranium and plutonium are recycled after reprocessing in reactors, but the remaining 4% of fission products and minor actinides, will be vitrified in ultimate waste and must be stored in a geological formation. The purpose of separation and transmutation procedures is to isolate certain products that come from the irradiated fuel and that have a very long half-life and high radioactivity (minor actinides) or that are likely to be mobile in geological formations (fission products, FP), and to treat them in a reactor in order to durably reduce their radiotoxicity and the volume of ultimate waste. In practice, most fission products are not easy to separate or transmute in an industrial reactor; only technetium is relatively easy to process (ANTICORP experiment at Phenix). Other FPs (iodine, caesium), for which this procedure would be advantageous, are either difficult to separate (Cs 137) or difficult to process (iodine because of its high volatility). This leaves the minor actinides as the only remaining candidate. Although they constitute only 0.1% of the fuel, their very long half-life and high activity mean that they will represent the majority of the potential radiotoxicity after a few centuries (considering the plutonium that is recycled in reactors). The transmutation of these actinides can take place only in a fast reactor where the neutrons are sufficiently available and have the energy required to cause their fission. In a water reactor the preference for captures over fissions leads to the formation of superior actinides. These are equally inconvenient because of their long half-life and high radioactivity. In a scenario where the minor actinides to be transmuted (neptunium, americium, curium) were diluted in the feed fuel (homogeneous mode), their abundance would probably be limited to 4-5% in critical reactors (FNRNa) for safety purposes and reactor operation. At Phenix, the homogeneous transmutation experiments are mainly METAPHIX and, of course, the 2 kg of americium distributed in the fuel in the core and caused by plutonium ageing. The SUPERFACT experiment in the 80's and 90's was also an early demonstration of the feasibility of this type of recycling. The minor actinide contents could reach significantly higher values in subcritical systems (ADS); the FUTURIX-FTA experiments aim to study the behaviour under irradiation of such fuels. Note, however, that assemblies of this type containing non-negligible quantities of minor actinides can cause radiological protection and thermal power problems, making their manufacture, handling, and transport rather complicated. Research at Phenix therefore focused more on the possibility of heterogeneous transmutation (ECRIX, CAMIX, COCHIX experiments, etc.). This involves needles loaded only with minor actinides incorporated in an inert matrix. The neutrons used are leakage neutrons at the edge of the core, which allows special moderator mechanisms to be installed to optimise fission reactions without disturbing core operation. In conclusion, this paper reports on the current status of all transmutation tests in progress at the Phenix power plant, presenting them in their context and considering their objectives. (authors)
[en] 1. PURPOSE The reduction of long-lived fission products (LLFP) and minor actinides (MA) is a key point for the public acceptability and economy of nuclear energy. In principle, any nuclear fast reactor is able to burn and transmute MA, but the amount of MA content has to be limited a few percent, having unfavourable consequences on the coolant void reactivity, Doppler effect, and delayed neutron fraction, and therefore on the dynamic behaviour and control. Accelerator Driven Systems (ADS) are instead able to safely burn and/or transmute a large quantity of actinides and LLFP, as they do not rely on delayed neutrons for control or power change and the reactivity feedbacks have very little importance during accidents. Such systems are very innovative being based on the coupling of an accelerator with a subcritical system by means of a target system, where the neutronic source needed to maintain the neutron reaction chain is produced by spallation reactions. To this end the PDS-XADS (Preliminary Design Studies on an experimental Accelerator Driven System) project was funded by the European Community in the 5th Framework Program in order both to demonstrate the feasibility of the coupling between an accelerator and a sub-critical core loaded with standard MOX fuel and to investigate the transmutation capability in order to achieve values suitable for an Industrial Scale Transmuter. This paper summarizes and compares the results of neutronic calculations aimed at evaluating the transmutation capability of cores cooled by Lead-Bismuth Eutectic alloy and loaded with assemblies based on (Pu, Am, Cm) oxide dispersed in a molybdenum metal (CERMET) or magnesia (CERCER) matrices. It also describes the constraints considered in the design of such cores and describes the thermo-mechanical behaviour of these innovative fuels along the cycle. 2. DESCRIPTION OF THE WORK: The U-free composite fuels (CERMET and CERCER) were selected for this study, being considered at European level the most promising among the various technologies foreseen for designing ADS core with enhanced waste transmutation. The neutronic calculations were performed with a special ERANOS Procedure (MECONG) that utilizes a RZ core models for the description of the core geometry and represents the various regions in homogeneous manner. A multi-recycling scenario was hypothesized and a proper amount of plutonium and minor actinides was supplied at the beginning of each cycle in order to ensure the same operating reactivity (keff=0.97). Moreover some core design parameters were changed in order to investigate the capability of such cores to burn/transmute MA with acceptable safety features. The behaviour of fuels pin during the cycle in terms of fuel temperature, internal pressure, stresses and strains was investigated by using TRANSURANUS code. 3. RESULTS AND CONCLUSIONS: The preliminary analysis shows that a good compromise between transmutation and core performance can be achieved for both fuels increasing the core power. Of course the increase of the core size has a significant implication on the overall plant architecture, in particular on accelerator and spallation module
[en] The EUROTRANS project is an integrated project in the 6. European Framework Programme in the context of partitioning and transmutation (P and T). The objective of this project is the step-wise approach of a European Transmutation Demonstration. This project aims to deliver an advanced design of a small-scale accelerator-driven system (ADS), XT-ADS, as well as the conceptual design of a European Facility for Industrial Transmutation, EFIT. The design of both machines is co-ordinated in Domain 1 (DM1) ''Design'' of the project. The main objectives of the XT-ADS are: demonstration of the ADS concept, providing a test facility for transmutation and providing irradiation possibilities in conditions representative of EFIT operating conditions. The latter allows the use of the XT-ADS as a materials testing facility as well as an aid for the fuel qualification of EFIT and for the qualification of candidate structural materials. The XT-ADS core is based on MOX fuel relatively high in Pu content and is cooled using a lead-bismuth eutectic (LBE). The combination of these two components results in a fast spectrum core. During the first 18 months of the project, the core of the XT-ADS has been developed starting from the MYRRHA DRAFT2 file. The XT-ADS core has only been fixed at the end of last June, so the calculations relating to this reference core are ongoing. There have been some scoping studies in the MYRRHA project on the capabilities as an irradiation facility (in-pile sections). As with the modified fuel pin and fuel assembly design, we started from the work done in the MYRRHA project to define the respective capabilities for the XT-ADS. (authors)
[en] In the framework of the seventh Information Exchange Meeting on Actinide and fission product partitioning and transmutation, this document presents the summaries of the papers presented during the technical session 5 on ''Progress in Physics and nuclear data''. (A.L.B.)