No abstract available

[en] A method of solving the kinetic equation for a heterogeneous reactor is proposed. The method is a generalization of the homogenization method and yields more accurate finite-difference equations which can easily be solved on a computer. The proposed method retains the advantages of the homogenization method in the special case of heterogeneous systems. (author)

[en] In Japan Atomic Energy Agency, three critical assemblies for thermal neutron systems are now in operation: Tank-type Critical Assembly (TCA), Static Experiment Critical Facility (STACY) and Transient Experiment Critical Facility (TRACY). These critical assemblies have been used for studying the thermal neutron reactor physics and the nuclear criticality safety properties for various types of nuclear fuels. TCA has a heterogeneous core which is composed of UO₂ rod and MOX fuel rod array immersed in light water moderator. Both of STACY and TRACY have homogenous cores which compose of low enriched nitrate fuel solution. STACY has accumulated many kinds of fundamental criticality conditions by changing the core geometry, U²³⁵ enrichment, uranium concentration, and acid molarity for the uranyl nitrate solution. On the other hand, TRACY has accumulated the transient experiment data in a criticality accident condition including prompt criticality. The static experimental data of TCA and STACY were used as available benchmarks and complied in the International Handbooks of Evaluated Criticality Safety Benchmark Experiments produced by OECD/NEA. The transient data accumulated in TRACY are also complied according to the reactivity insertion mode, used as standard transient benchmarks for validation of kinetic codes for evaluating the criticality accident. Based on the future prospect of reactor physics and the critical safety experiments for the thermal neutron system, JAEA has decided to renew the program of STACY to attain higher performance with more wider experimental condition. This paper describes main experimental condition of the newly-built heterogeneous core in STACY. (authors)

[en] Nuclear core of third generation should be attractive from the nuclear fuel cycle management aspect. The main goal is to achieve a good conversion of fertile isotopes into fissile isotopes while respecting safety constraints. Preliminaries studies have shown the interest of heterogeneous core loaded with fertile and fissile assemblies. The core is composed of 33 fertile assemblies and 208 fissile assemblies with 11 cm fertile axial layers placed every 50 cm of fissile material. The purpose of this work is to find out an optimized loading pattern and axial distribution of fissile and fertile elements in regards with the following criteria: power peak and void coefficient minimization. Due to the huge number of possible combination, we have replaced the global optimization by two simplest: first optimization of the fertile / fissile distributions on an assembly in 1-dimension representation, secondly optimization of the core's loading pattern in 3-dimension representation. The evaluations of the criteria have been done using the neutron physics transport solver MINOS integrated in the new lattice-core APOLLO3 code. The research algorithms used in this study are an evolutionary algorithm, a 'Max Min ant system colony algorithm' and a particle swarm adapted to our multi criteria approach. These algorithms are distributed using heterogeneous island method. A second level of parallelism has been introduced inside each island. Therefore we could increase the number of evaluations while respecting the CPU time limitation of the batch queues available. There are several solutions that stand out from the simulations. Some of them are completely original and have proved to be relevant a posteriori. Relevant loading pattern can be obtained in less than half a day, so we can consider this method as a decision support tool for the exploitation reactors and also for the design of new reactors. (authors)

[en] A new theory of leakage in heterogeneous systems has recently been introduced in which the derivation of cell-averaged diffusion coefficients for use in whole reactor calculations is reduced to the calculation of a flux, ξ, arising from a tilted source in one lattice cell only. This report describes the manner which an existing transport theory computer programme was modified to calculate this new flux. It is concluded that the tilted flux is sensitive to boundary conditions. In particular, no generally satisfactory choice of boundary conditions in a cylindricalised cell has been found. (author)

No abstract available

[en] The breeding ratios of the 1500 MW fast power reactors with the heterogeneous cores cooled by dissociating N₂O₄ are calculated. The reactors with the heterogeneous cores of a spiked type and those with the so-called intraassembly heterogeneity when different fuel elements with pure fertile material and conventional fuel are placed within the assembly are considered. It is shown that qualitative conclusions which have arrived at numerous papers regarding the sodium-cooled reactors may be refferred to the considered fast reactors of the BRGD-1500 type with the heterogeneous cores. In this case utilization of the reactors with the heterogeneous core allows to increase the breeding ratio as compared to the reactors with a conventional (homogeneous) cores if low-alloyed and non-enriched metallic uranium is used as a fertile material. In this case the doubling time decreases not so markedly that is mainly attributed to the specific fuel load growth

[en] Improvements in cost performance of computer hardware are extending applicability of cell-heterogeneous transport calculations that are currently applied in lattice cell or assembly geometry. In this paper, a cell-heterogeneous whole-core transport calculation by the method of characteristics (MOC) is applied to calculations for analyses of pressurized water reactor (PWR) initial cores. Calculation accuracy by the MOC has been verified within the cell-heterogeneous whole core system in comparison with the measurement results obtained in the startup physics test

[en] Short communication

[en] This paper surveys the current status of the Feinberg-Galanin theory of heterogeneous assemblies. It concludes with a list of topics requiring further study. (author)