[en] Some basic elements on the generation of cross section libraries for nuclear reactors are exposed. Sections 2 to 6 deal with the theory and formalism of the cell codes. In sections 7 to 10 some peculiar aspects of cell calculations for thermal reactors are presented. (author)

[en] The transient part in the dynamical behaviour of electron oscillations in a partially ionized plasma is analysed. The influence of electron-neutral collisions on time evolution is pointed out

[en] The influence of external fields on plasma dynamics can produce additional instabilities and dampings through the interaction of waves that otherwise would propagate freely. The aim of this paper is to analyze into the framework of kinetic theory, the change of the dispersion characteristics caused by a monochromatic external wave having phase velocity →∞, and to show how the coupling between electron plasma oscillations arises when an external field is present. When the Laplace transform is inverted in order to obtain the time behavior of the electric field, an integral equation is obtained so that the poles of the integrals do not give directly the dispersion relation, but the characteristics of the wave propagation are determined by the coupling of waves as follows from the integral equation

[en] The burn-up of nuclear fuel is defined as the energy produced per mass of fuel and, hence, is related to the inventory of fission products formed in the matrix of the fuel. It affects both neutron-physical and material properties. Therefore, it is essential to have methods available that allow a reliable determination of this important parameter. The burn-up is usually determined by measuring the content of an element that results from the fission process. The isotope 148Nd has proven to be an ideal monitor due to its chemical and neutron physical properties. On the other hand, 148Nd can only be determined by wet-chemistry methods, which means a rather costly and time consuming chemistry process. Another method using the sum of 145Nd and 146Nd is proposed. In case of very high burn-ups of U02 fuel and, especially, MOX fuel this method needs weighed yields for U and Pu to obtain a sufficient accuracy. Among the non-destructive spectrometric methods, the burn-up determination with 137Cs provides adequate results provided the gamma radiation detector is calibrated and self-attenuation effects of Cs together with measurement geometries are considered. (Author)

[en] This paper deals with some aspects of quantistic effects in a partially ionized plasma. A simplified Boltzmann-Vlasov equation is obtained, by taking into account the Pauli exclusion principle. Then two problems are analysed: the dispersion of electrostatic waves and the electrical conductivity

[en] In this paper we consider some key issues associated with nuclear waste incineration and how these issues can be addressed with the euse of accelerator driven systems (ADS). The first issue is related to the safety and control of reactor systems. The control of critical reactor systems is determined mainly by delayed neutrons (which do not appear immediately in the fission process) and their associated reactivity. When critical reactor systems are used to burn nuclear waste, this delayed neutron fraction decreases making the control of the system significantly more difficult. For sub-critical accelerator driven systems, it is shown that the spallation neutrons (which are independent of the sub-critical assembly), can be considered as a very much enhanced delayed neutron fraction. As a result, accelerator driven sub-critical systems will react more benignly and can cope with greater reactivity excursions than critical reactor systems. This is especially true for fast neutron systems. The second issue we address is how much waste we may have to deal with and whether ADSs can cope. At the present level of global nuclear power production, about 10''4 tons of spent fuel are being produced each year containing approximately 90 tons Pu, 6 tons Np, 2 tons Am, and 0.5 tons Cm. Since fissioning 1 to Pu will result in an energy release of approximately 1 GW_ey (i. e. the energy produced by one large reactor in one year), a large number of ADSs will be required to burn all the plutonium and minor actinides. The scale of this problem can be significantly reduced by recycling the Pu back into MOX or TMOX fueled PWRs. A detailed analysis of this problem is presented. Finally, we consider some conceptual designs for an accelerator driven waste incinerator with a view to starting relatively small scale experiments. In principle, one should be able to design a system in which at any time less than one critical mass (e. g. of Pu) is present thereby avoiding the possibility of criticality accident. The effective neutron multiplication factor should, however, be as close to 1 as possible to give as high a multiplication factor of the spallation neutrons as possible. We consider the neutronics of some simple geometrical core arrangements. (Author) 6 refs

[en] The so called innovative options, within the field of nuclear fission systems, promise radical improvements in the fuel cycle with regard to waste disposal, non-proliferation and the possibility of severe accidents. In particular, new systems based on the use of accelerators and thorium have been proposed for nuclear power production and waste incineration. In this paper we consider potential proliferation problems associated with these innovative options - in particular the choice of nuclear materials (e.g. thorium vs. uranium), the technology using these materials (e.g. accelerator driven sub-critical systems), and the reprocessing scheme. In particular, a metric for the assessment of the proliferation potential of nuclear material inventories at any stage in the fuel cycle is developed. In addition, considerations on the use of the accelerator beam current for clandestine fissile material production are presented. (orig.)

[en] On the basis of reactivity considerations, it is shown that thoria hosted weapon and reactor grade Plutonium can be used to fuel thermal and fast nuclear reactors. Disposition and incineration rates have been calculated for normal and extended lifetimes of the fuel. Excess weapon plutonium (W-Pu) arising from warhead dismantling can be disposed of in this manner without the production of new plutonium and bring the W-Pu to the Spent Fuel Standard. To go beyond the Spent Fuel Standard, and tackle the proliferation problem associated with the global Pu stock build-up from Pu in spent fuel, requires a more radical approach. On the basis of the present calculations, extended irradiation in both the thermal and fast thoria fuelled systems appears possible but will not lead to complete elimination without repeated reprocessing and recycling. The constantly deteriorating isotopic quality of the rest Pu will, however, severely limit the number of times such material can be recycled. For this purpose therefore, it appears that dedicated accelerator driven actinide burners will provide a more flexible and faster approach to rest Pu and minor actinide burning. 7 refs., 4 figs., 1 tab

[en] We investigate a novel scheme for burning weapons grade plutonium (W-Pu) in conventional light water reactors with a view to optimizing the destruction rate of plutonium and increasing the proliferation resistance of the resulting spent fuel. The main feature of this scheme is the use of a fuel based on W-Pu and weapons grade uranium (W-U) in an inert matrix. The extended irradiation (k2000 days) of this fuel leads to a high destruction rate (95%) of the Pu. Proliferation resistance of the spent matrix fuel is guaranteed by the very high levels of ²³⁸Pu in the total plutonium (k30%). The technicalities of how such inert matrix based fuel pins, with lifetime approximately 2000 days, may be used together with standard pins, with lifetime approximately 900 days in a PWR is described together with the criticality changes which may be expected through the use of fuel pins based on the inert matrix. On a timescale of a few hundred years the levels of ²³⁸Pu, with half-life of 88.75 years, will decrease to around 5%. High proliferation resistance of the spent matrix based fuel can be recovered by re-irradiating the matrix for a further period of 1000 days. The process of re-irradiation and decay can be repeated, without reprocessing, for as long as the spent matrix is considered a proliferation risk. (author). 12 refs, 10 figs, 5 tabs

[en] We consider fuelling the core of a LWR with assemblies of standard and inert matrix based Pu fuels such that there is no net rate of Pu production. The Pu in the inert matrix fuel is obtained by recycling that from spent UO₂ fuel. The Pu produced in the standard UO₂ assemblies during reactor operation is then balanced by the Pu burnt in the inert matrix assemblies. This can be achieved by replacing approximately one fifth of the standard assemblies with inert matrix based Pu assemblies. Extended irradiation of the inert matrix assemblies is also considered. Calculations are presented for a homogeneous core containing standard and inert matrix assemblies at various stages of irradiation. On this basis, it is suggested that the large variations in k_∞ associated with individual assemblies of inert matrix based Pu in a LWR neutron spectrum can be considerably reduced by a suitable choice of the cycle loading pattern for the assemblies. (author). 6 refs, 5 figs, 2 tabs