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The characteristics of structurally different fuel element simulators are presented. It is shown that an indirectly heated fuel element simulator with an auxiliary cladding has advantages over existing simulators and makes it possible to achieve heat flux densities comparable to or higher than the normal loads for VVÉR.One of the important problems in studying accident regimes on the large-scale stands [1] is to determine the temperature regime of fuel assemblies in various situations. A model fuel assembly is built on the basis of electrically heated fuel element simulators. The simulators used in research can be divided conventionally into two groups -directly and indirectly heated. Heating is accomplished in the directly heated simulators by passing current through the cladding. In this case, the seal and housing units must be electrically insulated in the experimental setups. The directly heated simulators are hollow or filled with inert gas, and they are successfully used for studying the crisis of heat emission and various heat and mass transfer processes [2][3][4]. Filling with gas under pressure (gas unloading) makes it possible to avoid any instability of a thin-wall cladding when coolant flows past the simulators under high pressure. In some cases, pressure unloading is accomplished by pouring Al 2 O 3 or SiO 2 powder into the simulator (cladding).The most important requirement for investigating thermohydraulic processes in loss-of-coolant accidents is to maintain a correspondence between the volume heat capacity of the simulator and the fuel [5]. This requirement can be most fully met by using indirectly heated simulators. In such simulators, heat is released by passing current through an electric heating element. Electrically insulating material is placed between the electric heating element and the cladding.At the present time, various designs of indirectly heated simulators of fuel elements are used to solve particular problems [5][6][7][8][9]. A universal design of a simulator suitable for solving all problems does not exist.The simulators which have been developed in our country have made it possible to obtain experimental data on the temperature regimes of fuel assemblies in the course of an accident with a pipeline rupture, the dynamics of flooding and cooldown, deformation of fuel-element cladding at high temperature and internal pressure, the states of the zirconium cladding during a short-time crisis of heat transfer, and other problems [9]. Since the design of the simulators is complicated, the materials are expensive, and the operating lifetime is short, simulators which are made using the technology of tubular electric-heating elements (tehes) are primarily used for making the fuel assemblies.Periclase -fused magnesium oxide -is used as the electric insulator and heat conducting material in most tubular electric heating elements. Periclase is used because of its low cost, it is readily available, and it has the required properties:

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