05 Nuclear fuels (scientific, technical)

various nuclear technology issues that will be of importance for future DT fuelled machines. The Active Gas Handling System (AGHS) built for the supply and reprocessing of tritium is still in operation to detritiate the exhaust gases and to provide the necessary ventilation during vessel openings because >l g of tritium remain in the machine even 4 years after the DTEl campaign. The tritium is bound in co- deposited layers and flakes formed mainly on the shadowed inner part of the divertor, and in the bulk of tiles. Areas of erosion and deposition arc being identified and preliminary models for the material movement developed. Characterization of the properties of tiles and flakes is very important to develop the best handling techniques. Due to the activation of the machine and the use of Be and T entry to the torus is limited by the need to minimize worker doses and is currently only possible in full pressurized suite. Work inside it is, therefore, performed with remote handling tools where practicable, e.g. the removal of the divertor septum and the collection of dust and flakes from areas below the divertor to achieve a more accurate tritium balance. Techniques need to be developed to reduce the tritium content in waste to permit disposal as low level waste (~12 kBq/g) and to recover tritium for re-use. Validation of activation models, under- standing of the risks due to inhalation of tritiated particles and the local environmental impact of tritium are further important aspects. The paper presents various nuclear issues studied at JET due to activation and tritium.

03/02247 Hybrid RO MSF: a practical option for nuclear desalination Al-Mutaz, I. S. International Journul of Nuclear Desalination, 2003, 1, (1) 47-57. Hybrid RO MSF desalination combines the advantages of the high desalting performance of distillation processes and lower energy requirement of membrane processes. It allows a better match between power and water requirements and enables better utilization of the power generated from MSF into the RO. Hybrid RO MSF can lead to an optimized feedwater temperature of the RO plant since is possible to use cooling seawater from the reject stage of the MSF plant as feed to the RO plant. Higher feed temperature is advantages for the RO plant since water flux of the membrane is about 2.5% higher per degree temperature rise at a fixed pressure. Various RO MSF combinations coupled with a nuclear power plant were studied. The optimum hybrid RO MSF scheme will be reviewed in order to illustrate the considerable gain of this option. The potential advantages of RO MSF hybrid desalination systems with nuclear plant will be discussed. The appropriate combinations depend on the local conditions and power/water requirements. The required power to water ratio and product water quality is among the important factors determining the particular RO MSF schemes to be used.

03102248 Influence of gases on direct-drive cryogenic targets in laser fusion reactor with wet wall Norimatsu, T. et al. Fusion Engineering and Design, 2003, 65, (3), 393- 397. A design space of the injection velocity of a cryogenic target for the vapour pressure in a future laser fusion reactor with a wet wall is discussed. The discussion includes gain reduction due to X-ray preheat, spheric@ degradation, and melting of the cryogenic layer due to adsorption of the metal vapour in the reactor. The preliminary estimation indicates that the injection velocity of a cryogenic target insulated with a 200~urn-thick, 250 mg/cc foam layer should be >130 m/ s and the vapour pressure in the reactor must be <0.07 Torr.

03102249 Liquid lithium target under steady state ultra high heat load of 1 GW/m* range for International Fusion Materials Irradiation Facihty (IFMIF) Nakamura, H. et al. Fusion Engineering and Design, 2003, 65, (3), 467- 474. International Fusion Materials Irradiation Facility is an accelerator- based neutron source using the D-Li stripping reaction to provide high intensity neutron field with energy of 14 MeV and damage dose rate of around 20 dpaiyear for fusion materials development. To handle the intense deuterium beam power up to 10 M W which corresponds to ultra high heat flux of 1 GW/m’, the liquid Li jet flow with a maximum velocity of 20 m/s and a concave flow configuration is necessary. According to thermal-hydraulic analysis, an induced centrifugal force with a radius of concave hack wall (25 cm) realized that the Li temperature is lower than the Li boiling point. To confirm the hydraulic characteristics of Li flow, water jet simulation experiment has been done. Moreover, validation experiment in Li loop is under way in Osaka University. In addition, a permissible heat load of the Li flow under a surface heat deposition has been discussed.

03tO2250 Measurement of neutron total cross-section of Dy at Pohang Neutron Facility Rim, G. el al. Annals qf Nuclear Energy, 2003, 30, (1 I), 1123-l 134.

The neutron total cross-section of natural Dy has been measured in the energy region from 0.025 eV to 100 eV by the neutron time-of-flight method at Pohang Neutron Facility, which consists of an electron linear accelerator, a water-cooled Ta target with a water moderator, and a time-of-flight path with an 11 m length. A 6Li-ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.5 cm has been used as a neutron detector and a metallic plate of Dy sample have been used for the neutron transmission measurement. The background level has been determined by using notch-filters of Co, Ta, and Cd sheets. In order to reduce the gamma rays from a Bremsstrahlung and that from a neutron capture, a neutron-gamma separation system was employed based on their different pulse shape. The present measurements are in general agreement with the previous ones and the evaluated data in ENDF/B- VI. The resonance parameters of Dy isotopes (l61,162,163Dy) have been extracted from the transmission data by using the S A M M Y code and compared with the previous ones.

03/02251 Model-free fuzzy tracking control of a nuclear reactor Marseguerra, M. and Zio, E. Annals of Nuclear Enrrg~, 2003, 30. (9), 953-981. This study presents an approach, based on fuzzy logic and Lyapunov stability theory, to the tracking control of a nuclear reactor system. The control is carried out adaptively on the basis of a fuzzy rule base in which the so-called Consequents of the IF-THEN rules are modified through a proper adaptive law which enables tracking the desired reference trajectory. The power of the method is demonstrated first on a simplified model, taken from the literature, and then on a full nuclear reactor simulation code available from the Nuclear Energy Agency (NEA).

03/02252 Neutronic optimization of PHWR fuel Notari, C. Annals of Nuclear Energy, 2003, 30, (lo), 1065-1074. The pressurized heavy water reactors (PHWR) fuel element optimiz- ation in Argentine nuclear power plants (NPPs) is considered from a neutronic perspective. The requirements related to the use of slightly enriched uranium in reactors originally designed to operate in the natural uranium fuel cycle, with increased exit burnups and increased residence time in the core, are better faced with thinner rods in a rod- dense bundle. A 52-rod bundle, currently under development, is analysed and an improvement of a 48-rod bundle is proposed. Cell and complete core calculations are performed in order to establish the achievable exit burnup and to determine how far the fuel management strategy used in the natural uranium case has to be modified in order to satisfy the restrictions imposed by the thermal hydraulic l imits in Atucha I reactor. The improvement in the void coefficient, which is always an important topic in these reactors, is examined in order to show that all the fuel elements considered give place to a negative void coefficient with an adequate combination of enrichment and absorbers in the bundle.

03/02253 Nuclear and fuel cycle analysis for a fusion transmutation of waste reactor Hoffman, E. A. and Stacey, W. M. Fusion Engineering and Design, 2003, 63-64, 87-9 1. Two metal fuel sub-critical fast reactor concepts, cooled by PbLi and PbBi, respectively, for a fusion transmutation of waste reactor are introduced. Analyses of the nuclear-thermal stability and potential for a criticality event in these reactors are discussed. The results of equilibrium nuclear fuel cycle analyses of these reactors and the impact of transmutation on the characteristics of radioactive waste in repositories are discussed.

03/02254 Optimal power control system of a research nuclear reactor Zhao, F. et al. Nuclear Engineering and Design, 2003, 219. (3), 241-252. The power control system is a key control system for a nuclear reactor, which directly concerns the safe operation of a nuclear reactor. Much attention is paid to the power control system performance of nuclear reactor in engineering. The designers put a high value upon design of an optimal power control system. In this paper, a design method is applied to the design of power control system. According to the optimal control theory, an objective function, quadratic performance index with weight factors is proposed. Then, the objective function is transformed into frequency domain form by use of Paserval’s theorem. In frequency domain, an optimal transfer function can be obtained at the lowest value of objective function. The system with optimal transfer function has an optimal performance. The transfer function of the power control system is derived from a typical research nuclear reactor. Using the state feedback theory, the transfer function is synthesized to the optimal transfer function. The simulative results with the optimal controller and with a conventional controller show that the perform- ance of the optimal power control system is largely improved on

Fuel and Energy Abstracts November 2003 371