Layout and structural solutions for the reloading system of an advanced fast reactor

Abstract

The particulars of fuel reloading in fast reactors are described. General data on a BN-1200 powergenerating unit, the principles of the construction of its reloading system, the purpose and construction of individual types of reloading equipment, and required experimental work are presented. The comparative characteristics of the BN-800 and BN-1200 reloading equipment are presented.Reloaded fuel assemblies of fast reactors, in contrast to thermal reactors, have a high specific energy release. Inside the reactor they are moved beneath the sodium level at high temperature (to 250°C). In-reactor reloading equipment is an integral part of the first loop and ensures that the loop is hermetic. For this reason, when reloading has been completed it is not removed from the reactor and when the reactor operates at power it is subject to irradiation. Such stringent operating conditions and the impossibility of monitoring the reloading visually require that the equipment be highly reliable and the reloading process fully automated.To obtain a high capacity utilization factor, the number of reactor shutdowns for reloading and the shutdown time must be decreased. The number of reactor shutdowns for reloading is determined by the nominal fuel burnup and the energy density of the core. BN-600 and -800 require two fuel reloadings per year [1]. For BN-1200, where fuel burnup is deeper and a lower energy density is used, one reloading per year is planned. The reloading time is shortened by decreasing the time required to prepare the reloading equipment and to bring the reactor up to power. The operations include decoupling and coupling of the actuating mechanisms of the safety and control system with their rods, preparation and checking of the serviceability of the reloading equipment and its control system.The BN-600 and -800 reloading systems perform reloading of the following types of assemblies -fuel assemblies, rods and bushings of the safety and control system, and assemblies of the steel and boron protection. They are characterized by the presence of a large number of pieces of equipment and associated systems. Specifically, these systems include the storage drums for fresh and spent assemblies. Sodium is used to cool a drum of spent assemblies. For this reason, the material content of the system is high and heightened safety measures must be taken because of the presence of a radioactive sodium loop.The development of a reloading system for the advanced BN-1200 fast reactor is based on the following principles: 1) maximum possible use of scientifically tested and engineered technical solutions, implemented in and 2) application of new technical solutions, which increase safety and ensure high cost-effectiveness of the facility and efficient fuel utilization.One of the principal avenues for improving the characteristics of the power-generating unit is to increase the fuel burnup as compared with BN-600 and -800 as well as to increase the diameter of the fuel elements in order to shorten their utilization. Increasing the d...