Preparation And Properties Of Boron Carbide Based Neutron Absorption Composites

With the construction of Chinese Spallation Neutron Source(CSNS),the resumption of nuclear power projects in China during the 13th Five-Year Plan and the progress and development of nuclear industry technology and other industries,the high-energy radiation ray or equipment has been widely used in many fields such as scientific research,industry,military,medical care.Meanwhile,radiation shielding and protection problems brought about by this issue have also drawn increasing attention.Boron carbide(B4C)has been widely used in nuclear industries such as neutron absorption and shielding because of their stable physical and chemical properties,excellent slow neutron absorption ability and relatively low price.However,the preparation of traditional sintered boron carbide usually requires a complicated preparation process,high sintering temperature,and the price of sintered B4C is also very expensive.Based on energy saving,environmental protection,simple equipment technology and good neutron absorption effect,B4C was selected as a neutron absorber.Two kinds of B4C-based new hydrogen-free neutron absorption composites were prepared by introducing a second phase,and the neutron absorption properties were studied.The preparation process and mechanical properties of these two materials were studied systematically.The neutron absorption properties of these two materials were carried out by theoretical simulation and neutron beam current experiments,respectively.A series of B4C/SG neutron absorption composites were prepared by adding different amounts of silicate glass(SG),and sintering at 765? in vacuum and nitrogen atmosphere.The effects of binder content,pressure,holding time,sintering atmosphere and particle distribution grading on the properties of B4C/SG composites were investigated.The performance of composite contain 10 wt.%?40 wt.%SG were tested.And results show that the density,bending strength and impact toughness of B4C/SG composites are increasing gradually with the increase of SG content.When the SG content is 40 wt.%,the bending strength and the impact toughness of the B4C/SG composites after vacuum sintering are 36.28 MPa and 2.84 kJ/m2,respectively.B4C/polytetrafluoroethylene(PTFE)neutron absorption composite materials with high density were successfully prepared by compression molding and heat treated at 380?.The effects of different B4C content on the phase structure,micro structure,mechanical properties and neutron absorption properties were investigated.The performance of composite containing 30 wt.%?60 wt.%PTFE were tested.Results show that the density,relative density and impact toughness of B4C/PTFE composites are increasing gradually and the hardness are decreasing gradually with the increase of PTFE content.The relative density and impact toughness of B4C/PTFE composites are 94.24%and 19.1 J/cm2,respectively,when the PTFE content is 50 wt.%.Meanwhile,mechanical properties experiments tested and verified above-mentioned two composites' applicability for neutron beamline applications.The neutron absorption properties of these two composites were calculated by MCNPX theory and measured by neutron beam current experiment.Based on the Monte Carlo principle,the transmissivity of B4C/SG and B4C/PTFE composites was simulated.The experimental results show that the neutron transmissivity decreases with the increase of the sample thickness,B4C content,and neutron wavelength.The neutron reflectivity decreases with the increase of B4C and neutron wavelength.The results of neutron transmissivity test on small angle neutron scattering spectrometer(SANS)of CSNS show:The neutron transmissivity decreases with the increase of B4C content and neutron wavelength,and decreases much faster with the increase of B4C content.The results of theoretical simulation are in good agreement with the measured results.Both theoretical simulation and experimental tests show that these two composites have excellent neutron absorption properties.Due to the simple preparation process and excellent mechanical properties,it is expected to be applied to neutron source shielding and neutron collimating parts in neutron source and related nuclear industry.