Design of an experimental setup for the coefficient of friction measurement of high-temperature graphite in high-temperature gas-cooled reactors
[Objective]High-temperature gas-cooled reactors(HTGRs),a key component of fourth-generation nuclear reactors,are attracting considerable global interest.Graphite materials,serving as crucial structural materials and moderators in HTGRs,play a substantial role in reactor design,operation,and maintenance.A particular area of focus is the tribological properties of graphite.[Methods]In response to the limitations of existing methods used for measuring the friction coefficient of graphite at high temperatures,pressures,and load conditions,a new method has been proposed in this article.This method relies on a self-designed graphite-based device,which simulates the environmental parameters within the core of an HTGR,thereby allowing the measurement of the coefficient of friction of graphite materials.The graphite material used in this study is BG80,which fulfills the requirements of HTGRs well.Gas atmospheres of the measurement tests comprised helium and nitrogen.The gases were used separately to achieve different atmospheric conditions.The temperature range of the device can be changed from 25℃to 1 300℃,which includes normal and ultrahigh temperatures as well as those reached during accidents in HTGR power plants.The load range of the device is 0～30 kg,which is close to the load experienced by graphite materials in the reactors.The device can be internally heated by a self-designed graphite heater powered by direct current.Further,the temperature of the device can be well controlled using an auxiliary system.The device shell is made of stainless steel,with a cavity constructed from insulating bricks and filled with insulation cotton to maintain the temperature.Graphite rods are used for heating,and force sensors are used to collect data on pushing and pulling forces,which are used to accurately calculate the friction force and coefficient of friction.Data processing involves measuring frictional forces via a sensing device when pushing forces are applied at a fixed rate under a given temperature and atmospheric condition as well as under a given load in the normal direction.To mitigate measurement errors,differences between pushing,pulling,and normal loading forces are used for data analysis.Then,linear regression is employed to determine the coefficient of friction from the measured forces.[Results and Conclusions]The results demonstrate that the measurement method can stably and accurately obtain data on the coefficient of friction of graphite materials.In addition,generally,when the displacement is greater than 5 mm,the coefficient of friction begins to stabilize during subsequent displacement processes.Concurrently,when the temperature is>500℃,the coefficient of friction in helium significantly decreases compared to that below 500℃.The results of this study provide support for the numerical simulations and design improvements of HTGRs.
high-temperature gas-cooled reactorgraphite coefficient of frictionfourth-generation reactormeasuring device
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