Protactinium-231 – New burnable neutron absorber

Burnable neutron absorbers such as gadolinium and erbium are used for compensating excess reactivity in nuclear reactors. Their daughter nuclides resulting from neutron absorption by erbium and gadolinium do not play important role from the viewpoint of neutronics processes occurring in the reactor core. Selection of such burnable neutron absorber, daughter nuclides of which would favorably impact fission chain reaction, is of significant interest. The aim of the present study is to investigate neutronics properties of 231Pa – the new burnable neutron absorber – and possibilities of its producing in significant quantities. The chain of isotopic transformations starting from 237Np is the analogue of the chain of isotopic transformations started from 231Pa. However, improvement of neutron-multiplication properties in the 237Np-chain can only be achieved in fast neutron spectra while in the case of 231Pa-chain positive neutron balance can be achieved both in fast and thermal neutron spectra. From this viewpoint the chain starting from 231Pa is unique. In addition, 237Np can be produced in nuclear reactors as the result of neutron radiative capture by 235U while significant amounts of 231Pa can only be produced through the threshold (n,2n) and (n,3n)-reactions on 232Th under its irradiation with super high-energy neutrons. Such neutrons with super high energies are practically absent even in fast spectrum reactors, but, however, these neutrons are available in fusion reactors. Breeding of 231Pa in fusion reactors and further use of 231Pa in nuclear power reactors can make it possible to realize potential capabilities of fusion facilities for radical increase of nuclear reactor fuel burn-up. Thus, 231Pa isotope is the new and unique burnable neutron absorber never suggested for the purpose before. Evaluated nuclear data libraries JENDL-4.0 and ENDF/B-V, as well as computer software system SCALE-4.3 were used in the implementation of the present study. The following results were obtained. (1) In contrast to conventional burnable neutron absorbers on the basis of gadolinium and erbium, the protactinium isotope suggested in this paper appears to be more attractive because it allows us not only compensating initial excess reactivity, but, also, ensuring high fuel burn-up due to good multiplication properties of its daughter nuclides. (2) Significant quantities of protactinium could be produced in hybrid fusion–fission reactors acting as sources of neutrons (not sources of energy) with parameters already achieved by the present moment by experimental facilities in USA, Japan, UK

Advanced nuclear fuel cycle for the RF using actinides breeding in thorium blankets of fusion neutron source

The possible role of existing thorium reserves in the Russian Federation on engaging thorium in being currently closed (U-Pu)—fuel cycle of nuclear power of the country is considered. The application efficiency of thermonuclear neutron sources with thorium blanket for the economical use of existing thorium reserves is demonstrated. The aim of the work is to find solutions of such major tasks as the reduction of both front-end and back-end of nuclear fuel cycle and an enhancing its protection against the uncontrolled proliferation of fissile materials by means of the smallest changes in the fuel cycle. During implementation of the work we analyzed the results obtained earlier by the authors, brought new information on the number of thorium available in the Russian Federation and made further assessments. On the basis of proposal on the inclusion of hybrid reactors with Th-blanket into the future nuclear power for the production of light uranium fraction 232 + 233+234U, and 231Pa, we obtained the following results: 1 The fuel cycle will shift from fissile 235U to 233U which is more attractive for thermal power reactors. 2 The light uranium fraction is the most "protected" in the uranium component of fuel and mixed with regenerated uranium will in addition become a low enriched uranium fuel, that will weaken the problem of uncontrolled proliferation of fissile materials. 3 231Pa doping into the fuel stabilizes its multiplying properties that will allow us to implement long-term fuel residence time and eventually to increase the export potential of all nuclear power technologies. 4 The thorium reserves being near city Krasnoufimsk are large enough for operation of large-scale nuclear power of the Russian Federation of 70 GW (e.) capacity during more than a quarter century. The general conclusion: the inclusion of a small number of hybrid reactors with Th-blanket into the future nuclear power will allow us substantially to solve its problems, as well as to increase its export potential

Biotechnology approaches to overcome biotic and abiotic stress constraints in legumes

Biotic and abiotic stresses cause significant yield losses in legumes and can significantly affect their productivity. Biotechnology tools such as marker-assisted breeding, tissue culture, in vitro mutagenesis and genetic transformation can contribute to solve or reduce some of these constraints. However, only limited success has been achieved so far. The emergence of “omic” technologies and the establishment of model legume plants such as Medicago truncatula and Lotus japonicus are promising strategies for understanding the molecular genetic basis of stress resistance, which is an important bottleneck for molecular breeding. Understanding the mechanisms that regulate the expression of stress-related genes is a fundamental issue in plant biology and will be necessary for the genetic improvement of legumes. In this review, we describe the current status of biotechnology approaches in relation to biotic and abiotic stresses in legumes and how these useful tools could be used to improve resistance to important constraints affecting legume crops.E. Prats is funded by an European Marie Curie Reintegration Grant, N. Rispail by (FP5) Eufaba project. Our work in this area is supported by Spanish CICYT project AGL-2002-03248 and European Union project FP6-2002-FOOD-1-506223. K. Singh’s work in this area is supported in part by the Grains Research and Development Corporation (GRDC) and the Department of Education, Science and Training (DEST) in Australia.Peer reviewe