Content B₄C/Al Neutron Absorber Preparation And Properties Of HighContent B₄C/Al Neutron Absorber

Boron carbide reinforced aluminum matrix (B4C/Al) neutron absorber in nuclear power plants is used to absorb neutrons ray released by fuel rods. The neutron absorbing material will suffer from neutron ray, weak acid corrosion and dynamic stress for a long time, so the material should exhibit better neutron absorbing properties, higher mechanical properties and stronger acid resistance with the upgrade of nuclear power plants. This paper designs and prepares high content B4C/Al neutron absorbing material and studies its absorbing properties, mechanical properties and corrosion resistance behavior, which has important scientific significance for the safe operation of nuclear power plant.The paper studied the action mechanism between neutrons and B4C/Al materials by MCNP, designed the ingredient ratio of the absorbing material used in spent fuel storage grid, prepared B4C/Al neutron absorbing material by cryogenic vacuum hot pressing technology, explored the intrinsic link among density, microstructure and neutron absorbing properties, verified the feasibility of the theoretical simulations through experiments. The paper researched the coordination mechanism of plastic deformation during the forming process of high content B4C/Al neutron absorbing sheet, analyzed the microstructure and interface for B4C/Al neutron absorber reinforced with different B4C contents and particle sizes, researched systematically the physical and mechanical properties and wear behavior, further revealed the intrinsic link between the microstructure evolution and macroscopic properties, studied the corrosion behavior of the B4C/Al composite and the matrix alloy in boric acid and sulfuric acid solution by the electrochemical method, explored the effect of B4C/Al high-density interfaces on the mechanism of electrochemical corrosion.The results of simulation show that the neutron transmittance of B4C/Al materials increases with neutron energy linearly. In the thermal neutron energy region, the neutron transmission decreases with the increase of B4C content exponentially, and the macroscopic cross section increases with the increase of B4C content linearly as y= 0.14h+0.03. The neutron transmission decreases with the increasing thickness of B4C/Al material exponentially. The quantitative relationship among B4C conten、material thickness and neutron transmittance of B4C/Al is obtainedBy analyzing the density and density difference of B4C/Al neutron absorbing material, the optimum temperature for the hot pressing process is determined as 60℃, the microstructure of the B4C/Al material prepared at this temperature shows that B4C particles uniformly distribute in the B4C/Al composite. The experiment results are agreed with the simulation results, which all confirm that the neutron shielding performance of 3.5mm thick 30wt.% B4C/Al can achieve that of 0.5mmCd plate.In order to study the plastic deformation capacity of high content B4C/AI materials, the hot rolling temperature is determined as 450 ℃. The number of rolling cycles is determined as 7, with 10～15% decreasing rate of the plate thickness during each rolling initially, and later with the 20-25% decreasing rate until the deformation rate of the plate exceeding 70%. At this time, the sheet density can reach 98% of the theoretical density. By analyzing the microscopic particle distribution and orientation characteristics of the rolled sheet surface and interior, the forming mechanisms of B4C/Al plate are mainly the plastic rheological mechanics of the matrix and the team rheological mechanics of the hard particles, B4C particles on the plate surface occur assimilation along the rolling direction. The high content B4C particles will block the flow of Al matrix during the plate deformation process.B4C particles are uniformly distributed in the B4C/Al neutron absorber. The interpenetration of elements results in good combination between the particle and matrix. The density of the fabricated B4C/Al composites decreases with the increase of the B4C content, and also the density difference of different parts in each sheet is less than 0.01 g/cm2. The hardness of the composites is improved and the toughness deteriorates compared with the matrix. The micro Vickers hardness of 30%B4C/Al neutron absorber is 123.6HV (2.05 times larger than Al alloy), and the fracture toughness is 11.35MPa· m1/2 (5.16 times larger than B4C). the mode considering the cooperative effects including loading strengthenings dislocation strengthening and matrix ligament size strengthening was used to predict the yield strength of high content B4C/Al. There is a good agreement between the calculated yield strength and experimental value for the higher B4C content. B4C content has a significant effect on the wear resistance of B4C/Al composites. The increase of B4C content leads to the change of wear mechanisms, from adhesive wear as the main wear to a mix wear mechanism including adhesive wear, abrasive wear as well as oxide wear.The corrosion rate of B4C/Al neutron absorber increases with the increase of B4C content in both boric acid solution and sulfuric acid solution. The corrosion rate of the composite is higher than the matrix alloy. The corrosion rates of both the composite and matrix alloy increase with the increase of the solution concentration in sulfuric acid solution. However, the composite and matrix alloy have better corrosion resistance in 2500 ppm boric acid concentration than in the other concentrations. The corrosion rates of both the composite and matrix alloy increase with the increase of solution temperature. The corrosion of B4C/Al neutron absorbing material is mainly the interface corrosion and the galvanic corrosion between the particles and matrix.