05 Nuclear fuels (scientific, technical)

05 NUCLEAR FUELS

Scientific, technical

04/01830 A PHWR with slightly enriched uranium. About the first core Notari, C. Annals of Nuclear Energy, 2004, 31, (3), 303-309. Many different studies have been performed in Argentina regarding the use of slightly enriched uranium in pressurized heavy water reactor (PHWR) nuclear plants. These referred mainly to operating plants so that a transition had to be considered from the current natural uranium fuel cycle to the slightly enriched one. The first argentine NPP, Atucha I, commissioned in 1974 and designed to operate with natural uranium was converted to slightly enriched uranium in a process that was initiated in 1995 and culminated in 2001. In this analysis, where new PHWR plants are considered, technical and economical arguments are presented which favour the use of a natural uranium initial core. The levelized fuel costs are shown to be practically insensitive to the first core and a fast transition between the two cycles is more influential than an initial enriched core.

04/01831 AMTEC/TE static converters for high energy utilization, small nuclear power plants EI-Genk, M. S. and Tournier, J.-M. P. Energy Conversion and Management, 2004, 45, (4), 511 535. A conceptual design of static converters for small, co-generation modular nuclear power plants is developed and analysed. Each converter is comprised of an alkali metal thermal-to-electric conversion (AMTEC) top cycle and thermoelectric (TE) bottom cycle cooled by natural convection of air. In addition to electricity production at a net efficiency in the low thirties, the small nuclear power plants with AMTEC/TE converters could provide co-generation heat for space heating, seawater desalination and/or high temperature process heat or steam. For the potassium AMTEC/TE converter, the conversion efficiency is about 1% point higher, the hot side temperature >100 K lower and the co-generation heat is slightly lower than for the sodium AMTEC/TE converter when operated at the same anode vapour pressure. On the other hand, when operated at the same hot side temperature, the efficiency of electricity production of power plants with K-AMTEC/TE converters could be ~25% higher, while the co- generation thermal energy for space heating is ~25% lower than with Na-AMTEC/TE converters. The present analysis showed that K- and Na-AMTEC/TE converters could be sized to produce up to 64 and 81 kW~ each at hot side temperatures of 1030 and 1150 K, respectively, while achieving >90% total utilization of the nuclear reactor's fission energy for the plant.

04/01832 Analysis of pressure signals using a Singular System Analysis (SSA) methodology Palomo, M. J. et al. Progress in Nuclear Energy, 2003, 43, (1-4), 329- 336. Pressure signals are used for control and monitoring the safety in nuclear power plants. These pressure transmitters are tested period- ically. In particular, on;y the transmitters checked to analyse the response times are of interest. The noise analysis is a very efficient tool to obtain adequate response times, but although this method can produce accurate results if performed properly, inherent problems in the tests can produce invalid results, for example if the test signal is oscillatory. An approach to remove the oscillatory contamination contribution from the pressure transmitter signal is the Singular Spectrum Analysis (SSA). This method is based on the fact that the dynamics associated with the signal can be described statistically in a linear way by its principal axes. Many or most directions in the embedding space can be associated with noise and typically a small number of these principal directions can explain the main dynamic characteristics of the signal; these principal directions are related with the singular values of the correlation matrix signal. This methodology has been applied successfully to several pressure signals of a typical Pressurized Water Reactor, which show an oscillatory contribution of 0.6 Hz. The SSA method removes this oscillatory contamination very efficiently.

04/01833 Assessment of linear and non-linear autoregressive methods for BWR stability monitoring Manera, A. et al. Progress in Nuclear Energy, 2003, 43, (1-4), 321-327. A benchmark has been performed to compare the performances of exponential autoregressive (ExpAR) models against linear autoregres- sive (AR) models with respect to boiling water reactor stability monitoring. The well-known March-Leuba reduced-order model is used to generate the time-series to be analysed, since this model is able

256 Fuel and Energy Abstracts July 2004

to reproduce the most significant non-linear behaviour of boiling water reactors (i.e. converging, diverging and limit-cycle oscillations). In this way the stability characteristics of the signals to be analysed are known a priori. An application to experimental time-traces measured on a thermalhydraulic natural circulation loop is reported as well. All methods perform equally well in determining the stability character- istics of the analysed signals.

04•01834 Data reconciliation and fault detection by means of plant-wide mass and energy balances Sunde, S. and Berg, 0 . Progress in Nuclear Energy, 2003, 43, (1-4), 97- 104. A plant-wide mass and heat balance model was fitted to 39 values of temperature, pressure and flow for a turbine cycle supplied by steam from a BWR. The calculated results were in good agreement with the measurements. For example, deviations between calculated and measured feedwater flow were usually in the order of 2 kg/s. The quality of the fitted results may be expressed as an overall assesment index Q stating directly the probability that the process is free of faults. The results are discussed with respect to the inclusion versus exclusion of the turbines' flow passing characteristics in the plant model.

04/01835 Development of a BWR control rod pattern design system based on fuzzy logic and knowledge Francois, J.-L. et al. Annals of Nuclear Energy, 2004, 31, (4), 343-356. The development of a system for the control rod pattern design of boiling water reactors based on fuzzy logic and knowledge is presented in this paper. The fuzzy logic module makes use of membership functions and fuzzy rules to control the neutron multiplication factor and the maximum relative nodal power by acting over the control rods' relative movement and the in-core water flow. The Mamdani implication process is used to evaluate the membership functions. The multiplication factor is controlled in order to bring the reactor to the critical state, and the maximum relative nodal power is controlled to maintain the main thermal limits in the core under their design values. Knowledge rules are implemented to govern the control rods' movement and the coolant flow in the core. The fuzzy logic control system is linked to the three-dimensional neutronic and thermal- hydraulic steady state simulator CM-PRESTO. The system was tested with the cycle 10 of Laguna Verde Nuclear Power Plant, Unit 1. The results obtained show that a very reasonable control rod programming can be achieved with a quite simple methodology. The obtained cycle length is comparable with that achieved with a Haling based simulation.

04/01836 Development of microphone leak detection technology on Fugen NPP Shimanskiy, S. et al. Progress in Nuclear Energy, 2003, 43, (1 4), 357 364. A method of leak detection, based on high-temperature resistant microphones, was originally developed in JNC to detect leakages with flow rates from 1 m3/h to 500 m3/h. The development performed on Fugen is focused on detection of a small leakage at an early stage. Specifically, for the inlet feeder pipes the leak rate of 0.2 gpm (0.046

s m / h ) has been chosen as a target detection capability. Evaluation of detection sensitivity was carried out in order to check the capability of the method to satisfy this requirement. The possibility of detecting and locating a small leakage has been demonstrated through the research.

04/01837 Dynamics modeling and stability analysis of a fluidized bed nuclear reactor Lathouwers, D. et al. Progress in Nuclear Energy, 2003, 43, (1-4), 437- 443. A theoretical model describing the coupling of neutronics, thermo- hydraulics and fluidization in a fluidized bed nuclear reactor is presented. The stability of the system is investigated by linearizing and perturbing the system around its equilibrium points and identifying the root loci of the system. It is found that within the operational range, the eigenvalues are located in the negative part of the phase plane, implying linear stability. Simulations of transient conditions are performed, viz. a hypothetical start-up transient and a quasi-static transient related to noise resulting from stochastic movements of the fuel particles. These simulations show that although the total power of the reactor may reach high values, the fuel temperature is well below safety limits at all times.

04/01838 Genetic algorithms and artificial neural networks for loading pattern optimisation of advanced gas-cooled reactors Ziver, A. K. et al. Annals of Nuclear Energy, 2004, 31, (4), 431-457. A non-generational genetic algorithm (GA) has been developed for fuel management optimization of Advanced Gas-Cooled Reactors, which are operated by British Energy and produce around 20% of the UK's electricity requirements. An evolutionary search is coded using the genetic operators; namely selection by tournament, two-point