05 Nuclear fuels (scientific, technical)

channel at temperatures above 700°C. The studied forest residue could form fly ash deposits in the flue gas channel at temperatures between 600 and 860°C. The Salix could cause fly ash depositions at temperatures between 840 and approximately 1000°C. If soil contami- nation was present as well, Salix could cause bed sintering at temperatures above 1030°C.

00100246 Thermal conductivity of coal ash and slags and models used Rezaei, H. R. et al. Fuel, 2000, 79, (13), 1697-1710. A one-dimensional heat transfer method was used to determine the thermal conductivity for a range of coal ash and synthetic ash samples at elevated temperatures. The effect of parameters such as tempera- ture. porosity, and sintering time were investigated. The thermal conductivity of the samples was generally observed to increase with increasing temperature. During heating of the samples, softening of minerals and sintering reactions resulted in changes in the physical structure of the ash, which then altered the observed thermal conductivity. The thermal conductivity of sintered ash samples was found to be higher than that of unsintered samples. The sintering temperature and sintering time were found to increase the observed thermal conductivity irreversibly. A decrease in sample porosity was also observed to increase the thermal conductivity. Chemical compo- sition was found to have little effect on the thermal conductivity, apart from influencing the extent of sintering. Predictions of the thermal conductivity of ash samples based on Rayleigh’s model are also presented. The thermal conductivity of slag and particulate structures was modelled by considering spherical pores distributed in a continuous slag phase. A particulate layer structure was modelled by considering solid particles dispersed in a continuous gas phase. The Brailsford and Major model of random distribution for mixed phases gives results within 20% of the measured values for a partially sintered sample.

00100247 Trace elements in microbiological desulfurization of coal from the Janina Mine Lewinska-Preis, L. ef al. Przegl. Gorn., 1999, 55, (3), 25-29. (In Polish) This paper examines changes in sulfur, zinc, ash, beryllium, chromium, gallium, cadmium, molybdenum, cobalt, lithium, manganese, copper, nickel, vanadium, and lead contents of microbiologically desulfurized coal. With decreasing the total sulfur content by 44%, the trace element contents decreased from 36 % (Ga) to 93% (Be). Chemical extraction in the presence of bacteria was the cause in the reduction in the trace element content.

00100246 Use of heat generated by exhaust gases from industrial furnaces Lipets, A.U. et al. Teploenergetika (Moscow), 1999, 4, 36-40. (In Russian) This paper describes an air and water heater that uses exhaust gases produced by industrial furnaces. Cascade tubular air heaters for furnaces fired with highly dispersed fuel, Z-tubular air heaters for furnaces fired with gas or low-sulfur coal, corrosion-resistant tubular air heaters for petroleum processing furnaces, waste heat water heaters and combined air waste-heat boilers are discussed in detail.

05 NUCLEAR FUELS

Scientific, technical

00/00249 A methodology for the quantitative evaluation of NPP fault diagnostic systems’ dynamic aspects Jong, H. K. and Poong, H. S. Annals Nucl. Energy, 2000,27, (16), 1459- 1481. A fault diagnostic system (FDS) is an operator decision support system which is implemented both to increase nuclear power plant (NPP) efficiency as well as to reduce human error and cognitive workload that may cause nuclear power plant NPP accidents. Evaluation is an indispensable activity in constructing a reliable FDS. First the dynamic aspects of FDSs for evaluation in this work is defined. The dynamic aspect is concerned with the way a FDS responds to input. Next, a hierarchical structure in the evaluation for the dynamic aspects of FDSs is presented. Dynamic aspects include both what a FDS provides and how a FDS operates. The former is defined as content and the latter as behaviour. Content and behaviour contain two elements and six elements in the lower hierarchies, respectively. Content is a

criterion for evaluating the integrity of a FDS, the problem types which a FDS deals with, along with the level of information. Behaviour contains robustness, understandability, timeliness, transparency, effec- tiveness, and communicativeness of FDSs. On the other hand, the static aspects are concerned with the hardware and the software of the system. For quantitative evaluation, the method used to gain and aggregate the priorities of the criteria in this work is the analytic hierarchy process. The criteria at the lowest level are quantified through simple numerical expressions and questionnaires developed in this work. These well describe the characteristics of the criteria and appropriately use subjective, empirical, and technical methods. Finally, in order to demonstrate the feasibility of the evaluation method used in this study, one case study was performed for the fault diagnosis module of OASYS? (On-Line Operator Aid SYStem for Nuclear Power Plant), which is an operator support system developed at the Korea Advanced Institute of Science and Technology (KAIST).

00100250 A possibility of highly efficient uranium utilization with a pebble bed fast reactor Ryu, K. and Sekimoto, H. Annals Nucl. Energy, 2000, 27, (12) 1139- 1145. In order to achieve highly efficient natural uranium utilization with a once-through fuel cycle, an idea of a pebble bed type fast reactor is investigated. The effective multiplication factor of 1.049 is obtained in the case of zero radial buckling for an optimum fuel velocity. The discharged fuel burn-up becomes 439 Gwd/& for mean power density of 50 W/cc, which is equivalent to the utilization of 457% of natural uranium.

OOlOO251 A stochastic transport theory of neutron and photon coupled fields: neutron and photon counting statistics in nuclear assemblies Mmioz-Cobo, J.L. e/ al. Annals Nucl. Energy, 2000, 27, (12) 1087- 1114. The behaviour of neutrons and gamma rays in a nuclear reactor or configuration of fissile material can be represented as a stochastic process. The observation of this stochastic process is usually achieved by measuring the fluctuations of the neutron and gamma ray population on the system. The general theory of the stochastic neutron field has been developed to a high degree. However, the theory of the stochastic nature of the gamma rays and neutrons couples the two processes. The generalized probability balances are developed from which the first and higher moments of the neutron and gamma rays fields are obtained. The paper also provides a description of the probability generating functions for both photon and neutron detectors that are the foundations for measurements of the fluctuations. The formalism developed in this paper for the representation of the statistical descriptors of the neutron-photon coupled field is applicable for many neutron noise analysis measurements.

00100252 A variational principle in probabilistic dynamics Labeau, P. E. et al. Annals Nucl. Energy, 2000, 27, (17), 1543-1575. Probabilistic dynamics offers a theoretical framework for an integrated treatment of accident sequences. But such realistic modelling in risk analysis calls for the development of efficient numerical schemes, in order to benefit from the conceptual advantages it provides. Up to now, mostly simulation techniques have been envisioned to deal with this kind of problem. However, a sufficiently exhaustive search for scenarios and the low probability of the situations of interest limit the efficiency of these methods. This work, therefore, explores an alternative approach, based on a variationally processed correction of a reliability characteristic, first estimated with an approximation of the probability field. This first estimation can result either from the solution of a simplified problem or from the output of another solution scheme. A variational principle for the evaluation of a functional of the probability distribution in this dynamic context is established. The possible achievements as well as the limitations of this new approach are discussed, starting from the results obtained for two test-cases.

00/00253 Calculational modelling of target nuclide build-up in the RBMK reactor at Leningrad nuclear power plant Artemov, V. G. et al. Progr. Nucl. Energy, 2000, 36, (2), 97-107. Software support of radiation technologies being implemented at Leningrad nuclear power plant (LNNP) is considered. The procedure of “Co build-up data and their efforts) evaluation is demonstrated through calculation of 6, Co build-up rate in an irradiation assembly situated in a core channel in the LNPP reactor No. 4 of RBNK type.

00100254 Computer simulation aids recovery Fell, N. Nucl. Eng. Inr., 2000, 45, (553), 18-19. Nuclear power plants pose great challenges for inspection and repair, this is especially true of the UK’s Magnox reactors - the world’s oldest power reactors.

Fuel and Energy Abstracts January 2001 25