3D optoelectronic inspection of fuel assembly components

Transcription

1 3D optoelectronic inspection of fuel assembly components Alexey V. Beloborodov 1, Alexander V. Chinov 2, Yuri V. Chugui 1, Leonid V. Finogenov 1, Anna A. Gushchina 1, Yuri K. Karlov 2, Peter I. Lavrenyuk 3, Yuri A. Lemeshko 1, Yuri V. Pimenov 3, Vladimir M. Troyanov 3, Mikhail G. Zarubin 2, Peter S. Zav yalov 1 1 Technological Design Institute of Scientific Instrument Engineering (TDI SIE) Siberian Brunch of the Russian Academy of Sciences (SB RAS) 41, Russkaya str., Novosibirsk, , Russia Tel.: + 7 [383] Fax: + 7 [383] chugui@tdisie.nsc.ru 2 JSC Novosibirsk Chemical Concentrates Plant 94, Bogdan Khmelnitsky str., , Novosibirsk, Russia 3 JSC TVEL, 49 Kashirskoe shosse, Moscow, , Russia Abstract Safely increasing of nuclear reactors is urgent problem for atomic industry. It takes 100% noncontact dimensional inspection of nuclear reactor components. Optoelectronic methods and systems for 3D inspection of fuel assembly elements, including grid spacers and fuel elements, are presented. The universal structured light method for 3D inspection of Russian and western grid spacers using diffraction elements is developed. For fuel elements inspection one considers the shadow method which allows one to implement full inspection of articles under transported along the automatic production line. TDI SIE has developed the commercial version of systems for integral inspection of grid spacers and fuel elements. The experimental results of industrial testing are given. Keywords: 3D inspection, structured light method, measurement, grid spacer, fuel element 1. Introduction High reliability of nuclear power stations takes for manufacturers to meet strict quality standards for nuclear reactors. The key component of a nuclear reactor is a fuel assembly (FA), which includes grid spacers (GS), few hundreds of fuel elements (FE) and a load bearing skeleton. Using the GSs allows us to have proper positioning of the FE assembly in cross and longitudinal sections throughout the height of the fuel element. The spacers themselves, as well as the fuel elements, are subject to full 3D inspection of their geometry. Today many manufacturers rely upon the dimensional inspection that is carried out with contact calibers. But the procedure does not provide full information on the product s geometry and depends on the human factor. An alternative solution is to use coordinate measuring machine (CMM) for selective inspection [1] which takes a lot of time - up to few hours for one fuel element cross-section. In 2002 year TDI SIE has developed laser measuring machine to inspect the geometrical parameters of Russian hexagonal grid [2], based on multipoint structured illumination method and digital information processing. Due to international contracts, Russian manufactures also have mastered production of western FAs with square grid spacers. For GS inspection we have developed a universal structured light method using diffractive optical elements for formation of multiple circular illumination [3]. The method allows measuring hexagonal grids, as well as square grids. For FE inspection one considers a shadow method [4], which provides full inspection of FAs under their transportation along the automatic production line

2 Below the optoelectronic methods and the systems applied to 3D inspection of fuel assembly components are presented. Results of systems testing are given. 2. Grid spacer inspection problem A photo of the grid spacer and the drawing of its fragment are shown in Fig. 1a, b. The following parameters are subject to dimensional inspection (Fig. 1b): D c (n) diameters of cells, formed by three bulges-protrusions (nominal diameter D c,nom = 8,9 mm); D ch (m) diameters of the inscribed circles for the guide channels (nominal diameter D ch,nom = 12,9 mm); L (k) distance between the centers of the neighboring cells (nominal value L nom = 12,75 mm); the shifts of the centers of the inscribed circles for the cells relative to their positioning on the drawing; the for spanner sizes that characterize the overall dimensions of the grid. Measurement error for some parts of grid spacer must not exceed from some micron to tens of microns. Fig. 1. Configuration of grid spacer: its photo (а), object cross-section (b) with the basic geometrical parameters, including cell diameter D c, channel diameter D ch, distance between neighboring cells L. 3. Universal DOE - based method for grid spacer inspection For GS size inspection one has proposed the structured light method. The principle of the method is illumination of the surface of an article fragment under inspection with predetermined 3D light distribution to obtain the fragment s image recorded by a photodetector array for further processing. So there are a lot of GSs of different configurations, the main problem is how to arrange universal light illumination which allows one to inspect the above mentioned GSs. One of the methods to form the predetermined light distribution is using the diffractive optical elements (DOE) [5]. Using such components in measuring systems unlike such wellknown traditional elements as diaphragms, homogenisers and properly arranged sources of radiation, allow us to obtain light distribution with any configuration. The optical arrangement for GS inspection based on the structured illumination method is presented in Fig. 2. The DOE here is used as a part of the illuminator and focuses the laser radiation into a set of rings. As a result one has the rings of light of equal diameter formed along the cell s axis with mm interval. It is important that such illumination is affected neither by the amount nor placement of the protrusions that hold FE in the cell. The structure of the illumination allows full measuring of the cell s inner surface without replacing the article under test that significantly increases the inspection performance

3 Fig. 2. The grid spacer cell inspection method using diffractive optical element. Figure 3a represents the structure of the DOE in use. The DOEs have nontransparent areas in the center and adjusting components at the periphery. The nontransparent area serves some functions. First, it protects the projection lens from direct laser radiation. Second, it decreases the angular aperture of the work field that results in no grazing rays from the surface is being illuminated by laser. The illuminated surface is projected on the camera s photomatrix by the special lens with high curvature and distortion. While being measured a spacer is being transported on a 2-axis positioning platform until all the spacer s surface has been recorded. Figures 3b, c demonstrates the images obtained by the camera in white light and coherent light. c) Fig. 3. Real images from the camera: diffractive optical element: structure (a), white light cell image (b), cell image in coherent light (c). The white light cell image (Fig. 3b) has been made for demonstration purposes by changing the laser with DOE by a white light source. Figure 3c presents the image used to process and calculate the cell parameters. The prominences of the cell allow one to see the projections of the light rings. a) Fig. 4. Experimental rings intensity for DOEs with ring spacing of 1 mm. Figure 4 shows intensity distributions formed by the manufactured DOEs recorded by a CCD-line array (pixel size is 14 μm). Experimental rings intensity profile for DOE with a ring spacing of 1 mm is presented in Fig. 4. DOE was fabricated by TDI SIE laser image generator [6]. The proposed method has become a basis for the semi-industrial system developed for GS inspection (Fig. 5a). Its experimental testing has confirmed its significant measuring precision. The error for the diameter of the inscribed circle (the cell hole) has been less than 4 micron, the error for a cell s center positioning (the cell hole) is less than 12 micron. Productivity is 5 articles per hour that 300 times more than CMM one

4 User interface of measuring system control program with measuring results for a grid spacer is presented in Fig. 5b. 4. Fuel elements inspection As known, thermal neutron fuel elements for Russian pressurized water reactors VVER and VVER -440 are shaped as tubes 9mm in diameter and from 2.5 to 4 m in length (Fig. 6). Each FE is filled with fuel pellets. The edges of a FE have plugs welded. The following parameters of a FE are to be inspected: the tube s external diameter, the external diameters of the top and bottom plugs, misalignment of the tube and the plugs. The diameters must be measured in different cross-sections along its axis with 2 mm discreteness. For dimensional inspection of geometrical parameters of a FE we have developed measuring system using a shadow method. The key position of the system is its optical measuring unit. Its optical layout is shown in Fig. 7. Here, the inspected fuel element with diameter (D) is illuminated with a quasi-parallel light beam. Projecting objective forms a shadow image of the object taken by the multielement photodetector. Fig. 5. Laser measuring system for grid spacers inspection (a), user interface with results (b). Fig. 6. Configuration of fuel element. Fig. 7. Layout of diameter measuring unit. Due to the pulse illumination of the object (one eliminates image blurring along X-axis) and due to the increased focus depth along the Y-axis (by choosing proper value of the aperture angular size) the effect of FE vibration along the X and Y- axes on measurement accuracy is radically reduced. As a photoreceiver one has used a CCD line array (2048 pixels, a pixel size is 14 micron). The output signal was processed by the signal processor. The unit carries out measurements in one cross-section of a FE. Measuring the whole FE are carried out by transported the FE through the unit s measuring zone. One can also utilize the unit to measure a FE s length. In this case one needs a pair of the units, each measuring its edge of a FE. Inspection of tube misalignment relative to the plugs measurement of this parameter takes some cross-sections measurement simultaneously. This can be done by using a CCD matrix instead of CCD line array

5 For inspection of FE geometry when being manufactured TDI SIE has developed the measuring system (Fig. 8) based on shadow method. Testing of this system has shown that errors do not exceed the maximum permissible values. Thus, the errors have constituted 3 micron for the extended diameters, 9 micron for the deviation from straightness, 72 micron - for the length (for total length of 4.5 m) and 7 micron for misalignment of the tube relative to the plugs. The productivity of the inspection system is 3 articles per minute. Fig. 8. Measuring system for FE inspection (a), user interface with measuring results (b). 5. Conclusion The universal method for 3D dimensional inspection for grid spacers is presented. The method allows inspection of the majority of a grid spacer s structural elements with micron resolution. The number of the elements inspected can be easily increased by utilizing changeable DOEs. For industrial application the commercial measuring system was developed. Productivity is 5 articles per hour. For integral inspection of fuel element geometry the commercial measuring system based on shadow method has been developed by TDI SIE. The testing carried out has shown that errors do not exceed the maximum permissible values. For instance, for the extended diameters the errors have contributed 3 micron, and for deviation from straightness is about 9 µm. Now these systems for 3D optoelectronic inspection of fuel assembly components are used by Novosibirsk atomic plant (NCCP). They can be applied for 3D dimensional inspection in many industrial branches. References 1. B. Acko. Calibration of measuring instruments on a coordinate measuring machine. Advances in production engineering & management. 2007, vol. 2, No. 3, pp O.I. Bityutskii et al. Three-dimensional noncontact inspection of geometric parameters of grid spacers in nuclear reactors. Optoelectronics, Instrumentation and Data Processing. 2003, vol. 39, No. 5, pp L.V. Finogenov, et al. 3D laser inspection of fuel assembly grid spacers for nuclear reactors based on diffraction optical elements. Measurement Science and Technology. 2007, vol. 18, No. 6, pp V.A. Beloglazova, et al. An optoelectronic device for noncontact inspection of geometrical parameters of fuel elements. Optoelectronics, Instrumentation and Data Processing. 2004, vol. 40, No. 2, pp V.A. Soifer (Ed.). Metodi komp yuternoi optiki. 2000, Moskva: Fizmatlit (in Russian). 6. V.P. Kiryanov. Laser setup for flat optical components fabrication with submicron resolution. Proc. SPIE. 1997, vol. 3091, pp