Study On Nondestructive Coating Thickness Measurement Methods Of Coated Particles

The coating thickness of coated nuclear fuel particles is one of the most importantperformance indexes of coated nuclear fuel particles, and section microscopic methodin used in measuring the coating thickness at present. Because section microscopicmethod is a destructive method and nuclear fuel particles are radioactivity, so it makesagainst nuclear fuel particles'recovering, safe keeping and protection. Furthermore,section microscopic method is largely affected by human factors; it's not easy tomeasure the coating thickness accurately and also can't be measured quick and usedon-line. So, it's necessary to study new, quickly and safe methods to measure thecoating thickness of coated nuclear fuel particles.In this paper, section microscopic method, substrate X-ray diffraction (XRD)method, substrate X-ray fluorescence (XRF) method and coating XRF method are usedin measuring the plating thickness of flat samples with Ni-P alloy and Cu electrolessdeposit, finding the influence factors of measurement. Moreover, the mathematicsmodel of measuring coating thickness of particles by substrate XRD method, substrateXRF method and coating XRF method are built, theoretical derivated and simulated bycomputer. The particles coating thickness formulate and the thickness andcompensation thickness are given. The X-ray nondestructive methods for measuringcoating thickness of coated particle are doable.Experiments of the plating thickness of flat samples with Ni-P alloy and Cuelectroless deposit measured by substrate XRD method shows that, substrate XRDmethod measurement accord with the section microscopic method measurement, andthe error of substrate XRD method less than that of section microscopic method; Mostof the error of substrate XRD method measurement come form the measurement of thedensity of coating, we should measure the density of coating accurately; For thincoating and thick coating, the coating thickness may be deviate from the real thicknesswhen low diffraction angle peak are used in substrate XRD method, we should use thehigh diffraction angle peak in substrate XRD method; High stabilization of X-raysource and high intensity of diffraction X-ray are propitious to reducing measurementerror, we should increase the intensity of diffraction X-ray; It get the minimum errorswhen the intensity ratio of diffraction intensity of no coating samples and coatedsamples is 3.591, we should control the ratio, in other words, control the thickness rangof coating. Substrate XRD method can be used in measuring crystal and noncrystalcoating because it hardly is affected by the crystal state of coating. Experiments of the plating thickness of flat samples with Ni-P alloy and Cuelectroless deposit measured by substrate XRF method and coating XRF methodshows that, the measurement may be deviate from the real thickness when theformulate of the first order X-ray fluorescence intensity of monochromatic light is usedin calculating the thickness since the X-Ray source used in the experience is chromaticand existing multiple fluorescent; Though the X-Ray source used in the experience ischromatic and existing multiple fluorescent, the formulate from the monochromaticlight and the first order X-ray fluorescence intensity can be used in measuring thethickness yet, we should use a batch of samples with thickness known, standardizationthe proportionality coefficient, after this , it can be used in measuring the unknowncoating thickness samples. XRF method with standard samples can be shielded fromthe density measurement's error, it also affected hardly by the monochromatic light andmultiple fluorescent, its errors most come from the difference of standard samples andsamples to be measured, and it should be standardized before measuring. The calculation formulate of XRD and the first order of XRF of particles, and thecalculation formulate of thickness measurement for substrate X-ray diffraction (XRD)method, substrate X-ray fluorescence (XRF) method and coating XRF method are alsogiven through mathematics modeling of measuring coating thickness of particles bysubstrate XRD method, substrate XRF method and coating XRF method, theoreticalderivating and simulating by computer, they are all based on the flat sample formulateand add compensation thickness, the compensation thickness are given by computersimulation. The results, intensity of XRD and first order XRF come form the top half of theparticles, given by computer simulation, shows that the particles'semidiameter seldomaffect the intensity of XRD and first order XRF when particles'semidiameter reach aspecific value, the compensation thickness of substrate XRD method, thecompensation thickness of substrate XRF method and the compensation thickness ofcoating XRF method are also seldom affected by semidiameter. So, theses threemethod all can be used in measuring particles with a specific range semidiameter, itneedn't using the same semidiameter in same experience. In conclusion, it is doable to measure coating thickness of coated particles byX-ray nondestructive method. These methods would be proofed and perfected in thesubsequent experience, and get practical application.