Available online at ScienceDirect. Physics Procedia 69 (2015 ) 79 86

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1 Available online at ScienceDirect Phyic Procedia 69 (015 ) World Conference on Neutron Radiography 5-10 October 014 Characterization of a real-time neutron imaging tet tation at China Advanced Reearch Reactor Linfeng He, Songbai Han*, Hongli Wang, Guohai Wei, Yu Wang, Meimei Wu, Yuntao Liu, Dongfeng Chen Neutron Scattering Laboratory, China Intitute of Atomic Energy, P.O.BOX 75(30), Beijing 10413, China Abtract A real-time neutron imaging tet tation wa recently intalled at the China Advanced Reearch Reactor. The objective of thi work wa to determine it operational characteritic, including neutron beam profile, the patial reolution and time reolution. The performance of the equipment wa demontrated by a real time neutron imaging tet of the water dynamic in a fuel cell. 015 The Author. Publihed by by Elevier Elevier B.V. B.V. Thi i an open acce article under the CC BY-NC-ND licene ( Selection and peer-review under reponibility of Paul Scherrer Intitut. Selection and peer-review under reponibility of Paul Scherrer Intitut Keyword: Real-time neutron imaging, CMOS, CARR 1. Introduction Analyi technique baed on dynamic neutron imaging are a powerful tool to invetigate fat procee in variou field, uch a water flow management of fuel cell (D. Kramer et al., 005; T.A. Trabold et al., 006), twophae flow(n. Takenaka et al., 1999; J.E. Cha et al., 005), etc. China Advanced Reearch Reactor (CARR) i a 60-MW tank-in-pool type reactor (D.F. Chen et al., 006), with an expected maximal unditurbed thermal neutron flux of cm A a multi-purpoe reearch reactor, CARR i devoted to neutron cattering, neutron imaging, radioiotope production, neutron tranmutation doping of ilicon, neutron activation analyi, and o on. Recently, a real-time neutron imaging tet tation wa intalled at the end of the CNGA neutron guide for tudying the methodology of high-peed imaging. The objective of thi work i to fully characterize it key pecification involving neutron beam profile, the time reolution and patial reolution. Moreover, it performance had been teted through the experiment of oberving water dynamic in a fuel cell. * Correponding author addre: hanb@ciae.ac.cn The Author. Publihed by Elevier B.V. Thi i an open acce article under the CC BY-NC-ND licene ( Selection and peer-review under reponibility of Paul Scherrer Intitut doi: /j.phpro

2 80 Linfeng He et al. / Phyic Procedia 69 ( 015 ) Experimental et-up The real-time neutron imaging tet tation wa intalled at the end of the curve cold neutron guide CNGA (the cold ource will be available in 016), which i located at the neutron guide hall of CARR. It conit of 3.75m inpile guide, 17m curve guide and 8m traight guide. Thi guide ha 30*150 mm cro ection, 1.88Å characteritic wavelength, and m= upper-mirror coating. The imaging tet tation i located at.6m away from the end of CNGA. Between the guide and imaging equipment a hutter i intalled, made of 15cm thick boron polyethylene and 5cm thick lead. Figure 1 how a implified view of the CNGA guide with it horizontal accee. Fig. 1 Layout of CNGA guide with it horizontal accee. Fig. The preent tatu of the real-time neutron imaging tet tation at CARR. Figure how the preent tatu of the intalled etup. It detection ytem (Linfeng He et al., 013) conit of a cintillator converter creen, a mirror and a commercial CMOS camera (Colin Coate et al., 009). The cintillator creen i 0.5-mm thick and 0cm*0cm field of view baed on 6 LiF/ZnS co-doped with Ag. The camera i a PCO-Edge type (PCO optic, USA), equipped with a CMOS enor, with,560,160 pixel ( m ize) and peak efficiency of 45 % at 450nm. A 50 mm/f=0.9 len i ued and an adapter enure a len-tocamera ditance. In order to minimize gamma expoure of the camera it i hielded in a cm thick lead box. 3. Reult 3.1 Beam profile: The neutron flux wa meaured to be 4.5*10 7 cm - -1 at the beam center at 10MW reactor power uing the gold foil activation method. Neutron beam ditribution had been invetigated by uing MC Simulation and neutron imaging (ee figure 3). The beam ditribution of the imulated reult agree very well with the meaured, except the defect at the bottom which i caued by the limited ize of cintillator. The effective beam ize (down to 50% peak flux) i around 3.cm*16cm meaured from the flat field image.

3 Linfeng He et al. / Phyic Procedia 69 ( 015 ) Fig. 3 The neutron beam ditribution at the cintillator creen. (Left: Calculated by MC imulation with Vite, Right: meaured by neutron radiography) unit: cm Fig. 4 Neutron image of the flat field uing pinhole Fig. 5 Ditribution of beam intenity horizontal and vertical direction repectively

4 8 Linfeng He et al. / Phyic Procedia 69 ( 015 ) A mm pinhole aperture made by 1mm think Cd heet wa located at 0.8m away from the end of the CNGA guide. According to the pinhole image ize (figure 5) and Eq (1), the L/D value could be etimated to 90 and 145 at vertical and horizontal repectively. r L / D = l (1) i FWHM of image ize(figure 5), r i pinhole dimenion, and l i ditance between pinhole and image. 3. Spatial reolution: The patial reolution of the radiographic ytem wa evaluated by analyzing the image of a high contrat harp edge, baed on the Edge Spread Function (ESF) and the Modular Tranfer Function (MTF) (Yu Wang et al., 01). A gadolinium lab with the thickne of 00 m wa irradiated in cloe contact to the cintillator creen. Figure 6 how the edge pread function fitted to the gray-level intenity ditribution (M.A. Stanojev Pereira et al., 008; A.A. Harm et al., 197): ESF = p1 + p a tan( p ( x p4)) () Where p1, p, p3, and p4 are free parameter and x i the canning coordinate. The correponding MTF (ee figure 7) wa obtained from the ESF derivated by Fourier tranform. The patial frequency correponding to the MTF value of 0.1 wa conidered a the patial reolution of the imaging ytem in lp/mm. The evaluated reolution wa 0.34 mm (1.46 lp/mm), calculated from an average of ten ditinct value determined in ten ditinct region of the edge object, among which five were performed in each in horizontal and vertical direction, repectively. It wa the ideal reolution value, a the ditance between the object and the cintillator creen wa approximated to zero. Fig. 6 Typical gray-level intenity ditribution and the fitted edge pread function According to our previou work (Linfeng He, et al., 014), the overall patial reolution of the ytem i affected by the ditance d between ample and cintillator, collimation ratio L/D, cintillator pread pot eigenvalue, and effective pixel ize at cintillator Δ / MCCD, a decribed in Eq (3).

5 Linfeng He et al. / Phyic Procedia 69 ( 015 ) Fig. 7 Modular Tranfer Function of the fitted edge pread function (3) When d=0, Δ / MCCD =0.138mm, u=1.46 lp/mm and MTF( u ) = 0.1, the cintillator pread pot eigenvalue wa calculated to be =0.8mm. Conidering that normal object cintillator creen ditance i le than 4cm (the collimation L/D ratio=90), according to Eq(3), the ytem patial reolution hould be between 0.34mm and 0.5mm. 3.3 Time reolution Time reolution depend on the camera can peed, the neutron flux and the ignal-to-noie level. Table1 how the maximum camera peed at variou expoure area. For low reolution and mall effective enor ize the camera reache cloe to 1000fp can peed. Table 1 Maximum can peed of CMOS with variou expoure area Senor area Max frame rate of CMOS fp fp fp fp The camera could achieve grey level in the beam center at 1 ec expoure time at a neutron flux of 4.5*10 7 /cm / at 10MW. It wa etimated that around 90 grey level will be reached at 1000 fp can peed when the reactor i operated at full power (60MW, without the cold ource). The ignal to noie ratio i N N / n = = (4) σ + σ + σ N + σ + σ r r N i grey level, σ i tatitic noie which i N, σ r i readout noie, and σ i dark current which i neglected here. Conidering that it read-out noie i.e-, correponding to grey level 4.9, the ignal to noie ratio i 8.4. Thi

6 84 Linfeng He et al. / Phyic Procedia 69 ( 015 ) value would be improved ignificantly if the cold ource i available or binning the pixel. A real-time imaging experiment of a rotating computer cooling fan wa carried out at a reactor power of 10MW to tet the ytem performance in an extreme condition. A hown in figure 8, the left picture wa a tatic neutron image of the fan when the expoure time wa 1 ec and the right one i a ingle frame of a high peed movie of the neutron irradiated fan with a frame rate of 1000fp (per frame the expoure time wa 0.9 mec). The outline of the fan can be recognized in the image though the maximum grey level i only 14. Fig. 8 The neutron image of a cooling fan of a GPU, meaured at 10MW. Left: tatic image (expoure time i 1 ec), Right: one frame of the dynamic image at 1000fp. 3.4 Real time neutron imaging tet of fuel cell Fuel cell repreent a promiing alternative to internal combution engine in car ince it can be integrated in an energy converion chain uing renewable ource and reducing polluting emiion. However, water management i till one of the key iue limiting the widepread ue of fuel cell. Operating parameter, material propertie and flow field geometry have a determinitic role on the water torage and ditribution within the flow channel and porou media in a fuel cell. Neutron imaging ha played a ignificant role in decribing the correlation between current denity and meaured total water content and it ditribution in operating fuel cell. Real time neutron imaging of the water flow (or dynamic) in fuel cell wa performed and demontrated the potential of the preented etup for uch invetigation. For the firt meaurement et, the fuel cell wa dried at room temperature for everal day and a et of 10 individual image obtained in 0 ec (the maximum expoure time of thi camera i ec) have been captured at 10MW. For the econd et of meaurement the flow channel of the fuel cell were fully immered in water at firt, then heated up to fuel cell working temperature of 70 C, and air wa blown into the channel at 50 ml/ peed. During thi procedure, 900 individual image were captured at the ame condition a in the firt et. Figure 9 howed the photograph and the neutron radiograph of the fuel cell which had been calibrated by the flat field and the dark field image. Left: Photography of fuel cell; Right: One frame of neutron image of fuel cell after normalization. Fig. 9: Real-time neutron imaging tet for the water proce of fuel cell.

7 Linfeng He et al. / Phyic Procedia 69 ( 015 ) The water ditribution can hardly be ditinguihed in the normalized neutron image. In order to how only the water ditribution the image of the dry fuel cell wa ubtracted from the wet cell, uing Eq (5). (5) I wa the neutron path length of water in the neutron image of the fuel cell, I wa the neutron image of the dry fuel cell, and are the neutron attenuation coefficient of the fuel cell body and water repectively, and x n and x w are the geometric thicknee of fuel cell and water. Fig. 10 The water ditribution at flow channel of fuel cell. The red circle area in figure 10 i the water ditribution at the flow channel of the fuel cell and it grey level repreent the tranmiion coefficient of water. Conidering that the total cro ection of water i 0.36/mm, the average water thickne wa etimated to 1.4mm. Furthermore, figure 11 how that the water ditribution vanihed gradually in 30min. Fig. 11 The water ditribution changed by time. (a)-(d) correponded to frame 1, frame 300, frame 600, frame 900, repectively. Summary and concluion The obtained reult have demontrated the viability of the preent neutron real-time imaging tation. Even at low reactor power and abence of a cold ource, the preent image quality wa ufficient to how important feature of the water dynamic in a fuel cell. The image quality will be improved dramatically after the intallation

8 86 Linfeng He et al. / Phyic Procedia 69 ( 015 ) of the advanced thermal and cold neutron imaging facilitie (Songbai Han et al., 013) in the future. Acknowledgement Thi work wa upported by the National Science Foundation of China (grant No and ). Reference J.E. Cha, I.C. Lim, C.M. Sim, I.C. Chu, Y.S. Choi, Y. Saito, B.J. Jun, 005. Obervation of the two-phae flow pattern for a finned aembly uing neutron radiography. Nuclear Intrument and Method in Phyic Reearch A 54: D.F. Chen, Y.T. Liu, C. Gou, and C.T. Ye, 006. Development of neutron cattering on 60 MW reearch reactor in CIAE. Phyical B : Colin Coate, Boyd Fowler, Gerhard Holt, 009. White paper from A.A. Harm, B.K. Garide, P.S.W. Chan, J, 197. Appl. Phy. 43, Songbai Han, Meimei Wu, Hongli Wang, Lijie Hao, Guohai Wei, Linfeng He, Yu Wang, Yuntao Liu, Dongfeng Chen, 013. Deign of cold neutron imaging facility at china advanced reearch reactor Phyic Procedia 43, Linfeng He, Songbai Han, Hongli Wang, Lijie Hao, Meimei Wu, Guohai Wei, Yu Wang, Yuntao Liu, Kai Sun, Dongfeng Chen, 013. Deign of real time neutron radiography at china advanced reearch reactor. Phyic Procedia Linfeng He, Songbai Han, Yu Wang, Guohai Wei, Meimei Wu, Hongli Wang, Yuntao Liu, Dongfeng Chen, 014. Calculation and Analyi of the Neutron Radiography Spatial Reolution. Nuclear Technique, Vol.37 (4), D. Kramer, E. Lehmann, G. Frei, P. Vontobel, A. Wokaun, G.G. Scherer, 005. An on-line tudy of fuel cell behaviour by thermal neutron. Nuclear Intrument and Method in Phyic Reearch A 54:5-60. D. Kramer, Jianbo Zhang, Ryoichi Shimoi, Eberhard Lehmann, Alexander Wokaun, Kazuhiko Shinohara, Gunther, G. Scherer, 005. In itu diagnotic of two-phae flow phenomena in polymer electrolyte fuel cell by neutron imaging. Experimental, data treatment, and quantification. Electrochimica Acta Part A 50: ; M.A. Stanojev Pereira, R. Pugliei, F. Pugliei, Radiat, 008. Mea 43, N. Takenaka, H. Aano, T. Fujii, M. Mizubata, K. Yohii, Application of fat neutron radiography to three-dimenional viualization of teady two-phae flow in a rod bundle.nuclear Intrument and Method in Phyic Reearch A 44: T.A. Trabold, J.P. Owejan, D.L. Jacobon, M. Arif, P.R. Huffman, 006. In itu invetigation of water tranport in an operating PEM fuel cell uing neutron radiography: Part 1-Experimental method and erpentine flow field reult. International Journal of Heat and Ma Tranfer 49: Yu Wang, Songbai Han, Linfeng He, Guohai Wei, Lijie Hao, Meimei Wu, Hongli Wang, Yuntao Liu, Dongfeng Chen, 01. Calculation method for neutron radiography patial reolution Nuclear Technique Vol.4 (4),