Combustion And Explosion Characteristics Of Zr-4 Alloy Powder And Its Suppression Technology

Zirconium alloy has the advantages of high temperature resistance to water vapor corrosion,high thermal conductivity,and small thermal neutron absorption cross section,so it is widely used in nuclear fuel rod cladding.The head-end cutting process of spent fuel reprocessing will generate zirconium alloy dust,which may cause dust explosion.This paper takes Zr-4 alloy powder as the research object to study the sample’s micro morphology,element composition,combustion characteristics,explosion characteristics and combustion and explosion suppression methods,and provides experiments for the safety assessment of the head-end cutting process of zirconium alloy cladding.According to the data,the specific research content and conclusions of this article are as follows:（1）A variety of instruments were used to characterize the zirconium alloy powder samples.The laser particle size analyzer showed that the median diameter of the samples was in the range of 2.4μm to 209.9μm.The sample under the electron microscope showed a variety of irregular shapes,and there were delamination marks on the surface.Using EDS analysis,it is found that Zr accounts for most of the samples,and the samples meet the standards of nuclear-grade Zr-4 alloy.XRD and XPS tests found that the two samples were the same substance,and the main phase was metallic zirconium.（2）The lowest ignition temperature measuring device of the dust layer was used to study the combustion characteristics of zirconium alloy powder.It was found that the smaller the particle size of the zirconium alloy powder,the higher the ignition sensitivity.The minimum ignition temperature of the zirconium alloy powder with a median diameter of 2.4μm is 200℃.Using infrared thermal imaging camera,it is found that the combustion flame temperature of the four particle size samples is relatively close.The zirconium alloy powder with a median diameter of 71.7μm has a transition from ignition to complete combustion,and the zirconium alloy powder with a larger particle size burns less vigorously.（3）Using a dust cloud minimum ignition energy test device to study the explosion characteristics of zirconium alloy dust cloud,it is found that the delay time increases,and the minimum ignition energy of zirconium alloy dust cloud shows a trend of first decreasing and then increasing.The dust concentration increases,the air humidity decreases,the dust particle size decreases,and the minimum ignition energy increases.The minimum ignition energy measured when the dust median diameter is 2.4μm and the concentration is 400 g/m³ is 13 m J.As the particle size of zirconium alloy powder increases,the low explosion limit of dust is on the rise,and the low explosion limit of zirconium alloy powder with a median diameter of 2.4μm is 60 g/m³.（4）A horizontal steel pipeline test device was used to study the explosive characteristics of zirconium alloy powder in the pipeline.It was found that as the distance from the flameproof diaphragm increases,the maximum explosion pressure of zirconium alloy dust tends to first decrease and then increase,and the flame speed There is a tendency to first decrease,then increase,and finally decrease.Increasing the dust concentration or reducing the dust particle size,the maximum explosion pressure and flame velocity will continue to increase.The maximum explosion pressure of zirconium alloy powder with a median diameter of 2.4μm and a concentration of 400 g/m³ reached 0.491 MPa,and the maximum flame velocity was 860 m/s.Fluent simulation shows that after the methane mixture is ignited,the flame propagates to the driven side to ignite the zirconium alloy dust cloud in 1.3 ms,and deflagration occurs.The maximum temperature in the pipeline exceeds 3200℃.（5）The lowest ignition temperature test device of the dust layer that can control the atmosphere and the minimum ignition energy test device of the dust cloud that can control the atmosphere are used to study the inertia suppression technology,and it is found that high concentrations of N₂,Ar,CO₂ have an inhibitory effect on the combustion of zirconium alloy powder,And the higher the concentration or the smaller the dust particle size,the stronger the inhibitory effect.Ar has a stronger inhibitory effect than N₂,which is much stronger than CO₂.When the concentration of the inerting atmosphere introduced increases from 30%to 60%-80%,the minimum ignition energy of the zirconium alloy dust cloud will increase until it exceeds 1000 m J.A higher concentration of inerting atmosphere can inhibit the zirconium alloy dust from being caused by electric sparks.The flame propagation speed analysis obtained by the high-speed camera confirmed the inerting effect of the three inerting atmospheres.