- Email: [email protected]
Infrastructure development for radioactive materials at the NSLS-II
Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Infrastructure development for radioactive materials at the NSLS-II D.J. Sprouster a, *, R. Weidner a , S.K. Ghose b , E. Dooryhee b , T.J. Novakowski c , T. Stan d , P. Wells d , N. Almirall d , G.R. Odette d , L.E. Ecker a a b c d
Nuclear Science and Technology Department, Brookhaven National Laboratory, PO Box 5000, Upton, NY 11973, USA National Synchrotron Light Source-II, Brookhaven National Laboratory, PO Box 5000, Upton, NY 11973, USA Center for Materials Under eXtreme Environment (CMUXE), School of Nuclear Engineering, Purdue University, West Lafayette, IN 47907, USA Materials Department, University of California, Santa Barbara, CA 93106, USA
a b s t r a c t The X-ray Powder Diffraction (XPD) Beamline at the National Synchrotron Light Source-II is a multipurpose instrument designed for high-resolution, high-energy X-ray scattering techniques. In this article, the capabilities, opportunities and recent developments in the characterization of radioactive materials at XPD are described. The overarching goal of this work is to provide researchers access to advanced synchrotron techniques suited to the structural characterization of materials for advanced nuclear energy systems. XPD is a new beamline providing high photon flux for X-ray Diffraction, Pair Distribution Function analysis and Small Angle X-ray Scattering. The infrastructure and software described here extend the existing capabilities at XPD to accommodate radioactive materials. Such techniques will contribute crucial information to the characterization and quantification of advanced materials for nuclear energy applications. We describe the automated radioactive sample collection capabilities and recent X-ray Diffraction and Small Angle X-ray Scattering results from neutron irradiated reactor pressure vessel steels and oxide dispersion strengthened steels. Published by Elsevier B.V.
1. Introduction There is a critical need to apply advanced characterization techniques to radioactive materials to inform life extension for current nuclear reactors and to promote understanding and development of radiation resistant alloys and nuclear fuels for advanced reactors [1–6]. In addition, data is required for validation and verification of computational simulations of material performance including embrittlement, swelling and creep of materials exposed to high neutron flux [1,7,8]. High-energy X-ray Powder Diffraction (XRD), Pair Distribution Function analysis (PDF) and Small Angle X-ray Scattering (SAXS) offer bulk, nondestructive characterization that is complementary to electron microscopy and atom probe tomography for characterizing nuclear fuels and structural materials [9,10]. Fully exploiting synchrotron techniques for radioactive materials is difficult due to shielding and radiation controls required at the synchrotron beamline. In addition, there are time-consuming barriers to synchrotron access for new users, including a safety review process that, despite efforts at standardization, is frequently performed on an ad hoc basis for radioactive materials. In addition, the choice of advanced techniques is material and application specific, further complicating the experience and increasing the risk of obtaining insufficient or unusable data for new users. Employing advanced techniques can require new collection and analysis methods tailored specifically for these samples.
Our unique approach is to enable researchers with radioactive materials to more fully exploit the high-throughput experimental capabilities at the X-ray Powder Diffraction Beamline (XPD) at the National Synchrotron Light Source-II (NSLS-II) by developing equipment, experimental protocols, data collection and data analysis strategies specifically tailored for radioactive samples. The baseline equipment of XPD includes a robotic sample manipulator and sample magazines for handling large batches of samples with minimum time overhead. Its scope of operation has been extended to manipulate samples thereby reducing radiation exposure to users and promoting more efficient use of beamtime. The small plastic holder inserts (see Fig. 1) allow users to load radioactive materials into containment at their home institutions. Scripts for accelerating data reduction and analysis were developed for the applications shown here and will be integrated into the software available for use at XPD. A high-energy SAXS experimental set-up was designed and implemented to be used with the robot. Together these hardware and software developments improve access for characterizing radioactive materials at XPD and are available to all users of the National Synchrotron Light Source-II (NSLS-II). The data generated by improved user access for performing synchrotron experiments are ultimately expected to provide new insight into the microstructure of radioactive materials. In this article, we describe the recently installed experimental infrastructure and data analysis software located at the XPD beamline
* Corresponding author.
E-mail address: [email protected] (D.J. Sprouster). https://doi.org/10.1016/j.nima.2017.10.053 Received 14 September 2017; Received in revised form 14 October 2017; Accepted 18 October 2017 Available online 4 November 2017 0168-9002/Published by Elsevier B.V.
D.J. Sprouster et al.
Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45
3. Infrastructure for nuclear materials
of the NSLS-II, specifically to accommodate radioactive materials. We outline the capabilities, operation and performance (with representative examples) of XPD. We also describe how to access the experimental equipment and software specialized for radioactive samples through the Nuclear Science User Facilities (NSUF) or the NSLS-II General User Program.
All radioactive samples, regardless of form, must have at least a single layer of containment at the NSLS-II. This requirement is typically satisfied by a single layer of Kapton tape for solid samples (140 μm). For dispersible or powdered radioactive samples, three layers (or three nested Kapton capillary tubes) of containment are required. Additional limits are placed on the amount of transuranics allowed at XPD. General Use equipment, including sample holders (which also serve as containment) and sample magazine, was installed at XPD and has been recently customized for use with radioactive samples. The sample holders designed for transmission geometry are shown in Fig. 1(c). The holder consists of a metallic base, plastic insert for mounting the sample, and magnetic ring to fasten the plastic insert onto the sample base. Each base is bar coded, so that it can be read by a camera at the base of the robot at XPD. The plastic inserts were produced by machining ABS plastic and the magnets were purchased from Amazing Magnets (Anaheim, CA). Solid samples can be wrapped in Kapton tape, and then loaded into the sample holder insert between two additional pieces of Kapton at the user’s home institution. The inserts are mounted on the sample holders and placed in the magazine at XPD. The entire procedure can take less than one minute, minimizing personnel exposure to the samples. With the robot (Stäubli) and sample containment equipment, XPD can be declared and posted as a ‘‘Radioactive Materials Area’’ during a scheduled beamtime and can accommodate a total dose rate of 0.1 rem/h at 30 cm. The magazines are designed to hold 20 samples. If the sample activity is relatively low (∼5 mrem/h at 30 cm), 20 samples can be loaded into each magazine for high-throughput measurements. Alternatively, one more highly active sample may be close to the limit. In this case, each magazine will hold one sample and the robot will be used primarily to reduce personnel exposure during data collection. The limits on activity at the beamline are based on limiting exposure to workers. The activated steel samples described below have a large 𝛽-radiation component to which the Kapton containment provides partial shielding. Single samples up to the activity limits have been characterized.
2. Beamline description The X-ray Powder Diffraction (XPD) beamline is designed to be a multi-instrument facility with the ability to collect diffraction data at high monochromatic X-ray energies (40–70 keV), offering rapid acquisition (sub-second) as well as high angular resolution capabilities [11]. The X-ray source is a 7 m long 1.8 T damping wiggler (DW100) which feeds two independent branchlines. One branchline serves two endstations and constitutes XPD. The endstation shown in Fig. 1 can operate in two different modes: high flux mode and high resolution mode. In the high flux mode (with 500 mA current in the stored electron ring), X-ray fluxes at the sample position exceed 1013 photons s−1 with modest energy resolution (𝛥𝐸∕𝐸 ∼ 0.5–1 × 10−3 ). The high flux results in the rapid collection of diffraction (and scattering) data with common collection times of ∼0.1 s. In the high resolution mode, an additional double crystal monochromator increases the energy resolution to ∼1 × 10−4 with a decrease in the incident flux (∼1 × 1012 photons s−1 ). The nominal beam size can be adjusted from mm down to 0.6 (Ho) × 0.2 (Ve) mm2 to match the graininess and heterogeneity scales of the samples under investigation. High-speed data collection is built upon the Bluesky software developed by the NSLS-II Data Acquisition Management and Analysis Group [http://nsls-ii.github.io/bluesky/]. The core characterization techniques available at XPD include XRD data, Pair Distribution Function analysis (PDF), and Small Angle X-ray Scattering (SAXS). The SAXS addition is shown specifically in Fig. 1(b). All techniques are optimized for transmission geometry, and reflectionmode XRD can be configured with a reduced vertical beam size. The combination of high-energy and high-flux capabilities available at XPD is advantageous for the structural characterization of high-Z materials, thick engineering-scale samples and samples in containments, all of which are intrinsic to nuclear materials. A robotic sample manipulator is also installed at XPD to promote rapid data collection and highthroughput operation on large batches of samples. In this work, we show how the robot operations can be tailored for unmanned sample manipulation of radioactive (and hazardous) samples. The SAXS technique and sample holders to provide containment for use with the robot were specifically developed for the high-throughput analysis of neutron irradiated reactor pressure vessel steels, to quantify radiation-induced precipitate phases [12]. For quantitative SAXS measurements, several pieces of equipment were implemented to improve the signal-to-noise ratio and accessible 𝑄-range, including an evacuated flight tube and small beamstop (2-mm diameter) and photodiode. The primary goal of the flight tube was to reduce the parasitic air-scatter. The flight tube used was 2.75-m long, with a diameter of 0.15 m and was sourced from the NSLS. The flight tube dimensions put a physical restriction on the usable 𝑄-range (∼0.8 Å−1 at 52 keV). The air gap between the sample and the flight tube could be minimized to improve the reduction in air scatter. For this to be achieved, the photodiode could potentially be placed within the flight tube or within the beamstop at the distal end on the flight tube in front of the detector [13,14]. A larger diameter flight tube will give access to higher Q, and an overall larger 𝑄-range. Alternatively, the incident X-rays could be increased to higher energy, although this will negatively affect the low 𝑄-range. The effect of the beamstop size is to increase/decrease the 𝑄-min and, therefore, the obtainable feature size. A smaller beamstop results in a lower 𝑄-min and an increase in the obtainable feature size. The energy, sample-to-detector distance, beamstop diameter and 𝑄-range are given in Table 1 for XPD.
4. Software capabilities Python scripts were developed to enable the batch processing of XRD data using TOPAS (Bruker). The data flow for the XRD analysis is shown in Fig. 2. For quantitative line profile analysis, the user needs to measure an XRD standard (such as LaB6 or CeO2 ) and to identify the phases present in each sample. Fitting the data is then completed automatically for any number of similar samples, or evolution of phases as a function of stimulus (time, temperature, field, etc.). The python scripts also perform limited error checking and flag samples that do not meet the userspecified parameters (e.g., lattice parameters, phase fraction, grain size, microstrain). The scripts assist with data visualization and can be used to plot any refined parameter (such as lattice parameter, phase volume fraction, lattice strain or domain size) versus sample index/number. In SAXS, variations in the scattered intensity come from the electron density fluctuations between the scattering objects and the host matrix [15]. The SAXS scattered intensity, as a function of 2𝜃 or scattering vector 𝑄 (𝑄 = 4𝜋 sin 𝜃∕𝜆), is inversely proportional to a characteristic distance 𝐷, in the sample: 𝑄 = 2𝜋∕𝐷 where the size 𝐷 of the scattering features is large compared to the inter-atomic distances. SAXS data can thus be used to obtain information on the size, shape, volume, and total surface area of the scattering centers, as well as the characteristic distances between ordered or partially ordered scattering centers [15–17]. Uncalibrated SAXS intensities are typically reported in arbitrary units and are a function of sample thickness, scattering geometry, and measurement time. Meaningful analyses, such as Guinier fits or size distributions, can be performed on uncalibrated intensity data 41
D.J. Sprouster et al.
Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45
Fig. 1. XPD beamline endstation with components labeled. The flight tube for SAXS mode of operation is shown for reference in (b). Sample holders for solid radioactive samples are shown in (c) and (d).
Fig. 2. Data analysis flow for XRD batch processing of multiple patterns at XPD. The multiple patterns are generated using either the robot or during time-resolved experiments.
42
D.J. Sprouster et al.
Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45 Table 1 Operational SAXS Parameters at XPD. Beamline
Energy (keV)
Sample to detector distance (mm)
Beamstop diameter (mm)
𝑄-min (Å)
𝑄-max (Å)
XPD
52.5 42.6
2893.2 2893.2
2 2
0.0090 0.0065
0.8 0.6
Fig. 3. (a) Absolute scattering intensity for a glassy carbon standard measured at XPD and 15-ID at the Advanced Photon Source. (b) XRD patterns collected at X17A (NSLS) and XPD (NSLS-II) for the same sample of reactor pressure vessel steel. The inset in (b) shows a region around the (110) Fe matrix peak with minor phases labeled for reference.
Fig. 4. Representative XRD patterns around the BCC (110) diffraction peak for a series of irradiated RPV reactor pressure vessel steel samples measured at XPD. The phases identified in these samples (BCC Fe, FCC Fe, Fe3 C and Mo2 C) are included for reference.
Fig. 5. SAXS patterns for an unirradiated, irradiated and baseline (unirradiated) corrected reactor pressure vessel steel sample.
refinement to determine particle size and volume fraction, provided the scattering length density of the matrix and precipitate are known.
to determine the size distribution of scattering centers. Quantitative determinations of the volume fraction of the scattering centers, however, require the scattering intensity to be calibrated on an absolute scale. The absolute intensity is expressed as the ratio of the measured scattering intensity to the incident beam intensity and necessitates the measurement of the incident and transmitted beam intensity [15–18]. The absolute scattering intensity for high-energy X-ray beamlines and neutron scattering beamlines is routinely measured using a calibrated sample (glassy carbon) [18]. This method is employed at XPD to calibrate the scattering intensity. The incident and transmitted intensities are directly monitored with a photodiode and empty-field images are collected to correct for Kapton containment and air scatter. A software package in Python that performs the necessary pre-processing steps on images collected for the SAXS setup specific to XPD was developed. The stand-alone software has a graphical user interface (GUI) for easier access for new users. The software is capable of averaging multiple 2D images and correcting the intensity with the aid of a text file that lists the incident and transmitted intensities, sample thickness and associated empty-field files and correction factor (from analysis of the glassy carbon standard). The resulting calibrated 2D images can then be imported and integrated/converted to 1D scattering patterns for
5. SAXS and XRD performance of XPD Fig. 3(a) shows the SAXS patterns collected for a glassy carbon standard collected at XPD and at the Advanced Photon Source used to calibrate the scattering intensity [18]. The ability to calibrate the scattering intensity allows the quantitative determination of volume fractions at XPD. Fig. 3(b) shows a comparison between the XRD patterns collected at X17A (NSLS) and XPD for the same sample of reactor pressure vessel steel. The patterns are from a single 0.05 s (XPD) and 5 s (X17A) collection time with 100 accumulations. The patterns collected at XPD have better signal-to-noise ratio, sharper peaks, and better resolution between peaks, due to the smaller energy band-pass of the incident X-ray beam and thus better resolving power (𝛥𝐸 = 9 × 10−4 at 52 keV) [11]. The enhanced resolving power can be used to identify minor impurity phases within radioactive materials. The count times at XPD required to achieve a high-quality pattern were also orders of magnitude lower (0.05 s) compared to X17A (5 s and higher), the result of a much higher photon flux. 43
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Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45
Fig. 6. (a) XRD and (b) SAXS patterns for a series of MA957 samples annealed at different temperatures. The patterns in (a) are offset for clarity. The peak in (b) for the 1200 ◦ C SAXS pattern (∼0.37 Å−1 ) is due to multiple scattering effects and an intense diffraction spot in the 2D detector image.
6. First-light science at XPD: reactor pressure vessel steels and oxide dispersion strengthened steels
XPD is dedicated to NSUF proposals [https://nsuf.inl.gov/]. The second access route is through the general user proposal system at the NSLS-II [https://www.bnl.gov/ps/].
Fig. 4 shows a comparison of the XRD patterns collected for a series of neutron irradiated reactor pressure vessel steels (an unirradiated pattern is also included for reference). Qualitatively, all samples show that irradiation induces a decrease in the FCC domain size; an increase in the strain of the BCC matrix (slight broadening of the BCC peaks); and subtle changes in the peak positions associated with the iron and molybdenum carbide phases (Fe3 C, Mo2 C). The slight increase in the structured background is potentially due to the formation of small nmscale precipitates. Fig. 5(a) shows a representative example of the background corrected SAXS intensity, as a function of scattering vector Q, for an unirradiated and irradiated high-Cu, high-Ni reactor pressure vessel steel sample [12]. The scattering intensity at low-Q is attributed to carbide particles (with sizes of ∼40–70 nm). The scattering changes significantly in the irradiated pattern, with increased scattering amplitude at intermediate and high-Q. This increase in scattering amplitude is directly attributable to the formation of new nm-scale Mn–Ni–Si late blooming phases. Fig. 6 shows the (a) XRD and (b) SAXS patterns for a series of oxide dispersion strengthened steels (MA957) annealed at different temperatures. Fig. 6(a) shows that in addition to the main BCC matrix phase, small peaks associated with the oxide particles1 [19] are visible in all samples (phases are labeled for reference). These oxide peaks increase in intensity with increasing annealing temperature due to particle growth. The pronounced contribution to the scattering intensity shown in Fig. 6(b) for all samples clearly reflects the low electron density of the 𝑌2 Ti2 O7 oxide particles compared to the matrix. The SAXS patterns in Fig. 6(b) also show that the annealing leads to particle growth, with an increase in annealing temperature leading to a shift to lower-𝑄. The largest particle growth is observable in the 1200 ◦ C pattern, with shift to lower-𝑄 and decrease in intensity from scattering features in the intermediate 𝑄-range of 0.03 ∼0.55 Å−1 .
8. Summary/conclusions 1. Custom sample holders and a sample magazine for radioactive materials are available for use with the robot at the XPD beamline. A set of commands to control the robot work with the existing software that coordinates the diffractometer motions and data collection at the beamline. Therefore, the hardware and software were tested and are operational for the robot. The robot is available during beamtime in future cycles. 2. The SAXS capability has been successfully implemented at the XPD beamline. SAXS data is essential to determine the size and volume fraction of irradiation-induced precipitates in reactor pressure vessel steels. The work included determining the available 𝑄-range, based on the beam size and physical restraints at XPD, including the maximum allowable distance the detector could be placed away from the sample position (2.9 m). Installation of equipment for SAXS at XPD includes a ∼2.7 m long flight tube, a photodiode on the diffractometer to measure the initial and transmitted beam intensity, and a rail system to position the detector. 3. Benchmark XRD experiments were performed on a series of reactor pressure vessel steel samples and compared to previously measured XRD patterns at the NSLS. First-light XRD and SAXS measurements performed on reactor pressure vessel and oxide dispersion strengthened steel samples exemplify XPD’s capabilities in characterizing nm-scale features in nuclear materials. The enhanced performance creates opportunities to characterize minor phases in radioactive materials. 4. The XPD, the hardware for radioactive samples, and analysis software can be accessed directly through the general user proposal system and through the NSUF proposal system.
7. Access to XPD
Acknowledgments
The equipment, characterization techniques and software described here are available to the nuclear community through multiple routes. The first access route is available through a partner agreement between the Nuclear Science User Facilities (NSUF) and the Nuclear Science and Technology Department (BNL), where 6% of user beamtime available at
We wish to extend thanks to J. Trunk, K. Wehunt, H. Wang and W. Lewis of the NSLS-II for their support of the experiments and infrastructure described here. This work was carried out as a part of a Nuclear Energy Enabling Technology project at BNL and supported by the US Department of Energy, Office of Nuclear Energy (DOE-NE). This research used the X-ray Powder Diffraction beamline at the National Synchrotron Light Source-II, a U.S. Department of Energy, Office of Science User Facility operated for the Department of Energy Office of Science by Brookhaven National Laboratory under Contract No. DESC0012704.
1 Markers for the 𝑌 TiO phase have not been included in the figure due to the 2 5 significant number of hkl’s associated with this phase. We note that this phase is, however, present as previously discussed [19]. The markers shown are for the BCC Fe, TiO and 𝑌2 Ti2 O7 phase.
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Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45
References
[9] P. Willmott, An Introduction to Synchrotron Radiation, John Wiley and Sons, Ltd, 2011. [10] J. Als-Nielsen, D. McMorrow, Elements of Modern X-Ray Physics, John Wiley and Sons, Inc., 2011. [11] X. Shi, S. Ghose, E. Dooryhee, Performance calculations of the X-ray powder diffraction beamline at NSLS-II, J. Synchrotron Radiat. 20 (2013) 234. [12] D.J. Sprouster, J. Sinsheimer, E. Dooryhee, P. Ghose, S.K. Wells, T. Stan, N. Almirall, G.R. Odette, L.E. Ecker, Structural characterization of nanoscale intermetallic precipitates in highly neutron irradiated reactor pressure vessel steels, Scr. Mater. 113 (2016) 18. [13] P.J. Ellis, A.E. Cohen, S.M. Soltis, Beamstop with integrated X-ray sensor, J. Synchrotron Radiat. 10 (2003) 287. [14] C.E. Blanchet, C. Hermes, D.I. Svergun, S. Fiedler, A small and robust active beamstop for scattering experiments on high-brilliance undulator beamlines, J. Synchrotron Radiat. 22 (2015) 461. [15] A. Guinier, G. Fournet, Small-Angle Scattering of X-Rays, Wiley, New York, 1955. [16] C.G. Shull, L.C. Roess, X-ray scattering at small angles by finely-divided solids. I. general approximate theory and applications, J. Appl. Phys. 18 (1947) 295. [17] O. Glatter, O. Kratky, Small Angle X-Ray Scattering, Academic Press, New York, 1982. [18] F. Zhang, J. Ilavsky, G.G. Long, J.P.G. Quintana, A.J. Allen, P.R. Jemian, Glassy carbon as an absolute intensity calibration standard for small-angle scattering, Metall. Mater. Trans. A 41 (2010) 1151. [19] T. Stan, D.J. Sprouster, A. Ofan, G.R. Odette, L.E. Ecker, I. Charit, X-ray absorption spectroscopy characterization of embedded and extracted nano-oxides, J. Alloys Compd. 699 (2017) 1030.
[1] G.R. Odette, M.J. Alinger, B.D. Wirth, Recent developments in irradiation resistant steels, Annu. Rev. Mater. Res. 38 (2008) 471. [2] T. Allen, J. Busby, M. Meyer, D. Petti, Materials challenges for nuclear systems, Mater. Today 13 (2010) 14. [3] Y. Katoh, L.L. Snead, I. Szlufarska, W.J. Weber, Radiation effects in SiC for nuclear structural applications, Curr. Opin. Solid State Mater. Sci. 16 (2012) 143. [4] S. Zinkle, G. Was, Materials challenges in nuclear energy, Acta Mater. 61 (2013) 735. [5] I.M. Robertson, C.A. Schuh, J.S. Vetrano, N.D. Browning, D.P. Field, D.J. Jensen, M.K. Miller, I. Baker, D.C. Dunand, R. Dunin-Borkowski, B. Kabius, T. Kelly, S. LozanoPerez, A. Misra, G.S. Rohrer, A.D. Rollett, M.L. Taheri, G.B. Thompson, M. Uchic, X.L. Wang, G. Was, Towards an integrated materials characterization toolbox, J. Mater. Res. 26 (2011) 1341. [6] Y. Zhang, A. Debelle, A. Boulle, P. Kluth, F. Tuomisto, Advanced techniques for characterization of ion beam modified materials, Curr. Opin. Solid State Mater. Sci. 19 (2015) 19. [7] G.R. Odette, B.D. Wirth, D.J. Bacon, N.M. Ghoniem, Multiscale-multiphysics modeling of radiation-damaged materials: Ebrittlement of pressure-vessel steels, MRS Bull. 26 (2001) 176. [8] I. Beyerlein, A. Caro, M.J. Demkowicz, N.A. Mara, A. Misra, B.P. Uberuaga, Radiation damage tolerant nanomaterials, Mater. Today 16 (2013) 443.
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Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Infrastructure development for radioactive materials at the NSLS-II D.J. Sprouster a, *, R. Weidner a , S.K. Ghose b , E. Dooryhee b , T.J. Novakowski c , T. Stan d , P. Wells d , N. Almirall d , G.R. Odette d , L.E. Ecker a a b c d
Nuclear Science and Technology Department, Brookhaven National Laboratory, PO Box 5000, Upton, NY 11973, USA National Synchrotron Light Source-II, Brookhaven National Laboratory, PO Box 5000, Upton, NY 11973, USA Center for Materials Under eXtreme Environment (CMUXE), School of Nuclear Engineering, Purdue University, West Lafayette, IN 47907, USA Materials Department, University of California, Santa Barbara, CA 93106, USA
a b s t r a c t The X-ray Powder Diffraction (XPD) Beamline at the National Synchrotron Light Source-II is a multipurpose instrument designed for high-resolution, high-energy X-ray scattering techniques. In this article, the capabilities, opportunities and recent developments in the characterization of radioactive materials at XPD are described. The overarching goal of this work is to provide researchers access to advanced synchrotron techniques suited to the structural characterization of materials for advanced nuclear energy systems. XPD is a new beamline providing high photon flux for X-ray Diffraction, Pair Distribution Function analysis and Small Angle X-ray Scattering. The infrastructure and software described here extend the existing capabilities at XPD to accommodate radioactive materials. Such techniques will contribute crucial information to the characterization and quantification of advanced materials for nuclear energy applications. We describe the automated radioactive sample collection capabilities and recent X-ray Diffraction and Small Angle X-ray Scattering results from neutron irradiated reactor pressure vessel steels and oxide dispersion strengthened steels. Published by Elsevier B.V.
1. Introduction There is a critical need to apply advanced characterization techniques to radioactive materials to inform life extension for current nuclear reactors and to promote understanding and development of radiation resistant alloys and nuclear fuels for advanced reactors [1–6]. In addition, data is required for validation and verification of computational simulations of material performance including embrittlement, swelling and creep of materials exposed to high neutron flux [1,7,8]. High-energy X-ray Powder Diffraction (XRD), Pair Distribution Function analysis (PDF) and Small Angle X-ray Scattering (SAXS) offer bulk, nondestructive characterization that is complementary to electron microscopy and atom probe tomography for characterizing nuclear fuels and structural materials [9,10]. Fully exploiting synchrotron techniques for radioactive materials is difficult due to shielding and radiation controls required at the synchrotron beamline. In addition, there are time-consuming barriers to synchrotron access for new users, including a safety review process that, despite efforts at standardization, is frequently performed on an ad hoc basis for radioactive materials. In addition, the choice of advanced techniques is material and application specific, further complicating the experience and increasing the risk of obtaining insufficient or unusable data for new users. Employing advanced techniques can require new collection and analysis methods tailored specifically for these samples.
Our unique approach is to enable researchers with radioactive materials to more fully exploit the high-throughput experimental capabilities at the X-ray Powder Diffraction Beamline (XPD) at the National Synchrotron Light Source-II (NSLS-II) by developing equipment, experimental protocols, data collection and data analysis strategies specifically tailored for radioactive samples. The baseline equipment of XPD includes a robotic sample manipulator and sample magazines for handling large batches of samples with minimum time overhead. Its scope of operation has been extended to manipulate samples thereby reducing radiation exposure to users and promoting more efficient use of beamtime. The small plastic holder inserts (see Fig. 1) allow users to load radioactive materials into containment at their home institutions. Scripts for accelerating data reduction and analysis were developed for the applications shown here and will be integrated into the software available for use at XPD. A high-energy SAXS experimental set-up was designed and implemented to be used with the robot. Together these hardware and software developments improve access for characterizing radioactive materials at XPD and are available to all users of the National Synchrotron Light Source-II (NSLS-II). The data generated by improved user access for performing synchrotron experiments are ultimately expected to provide new insight into the microstructure of radioactive materials. In this article, we describe the recently installed experimental infrastructure and data analysis software located at the XPD beamline
* Corresponding author.
E-mail address: [email protected] (D.J. Sprouster). https://doi.org/10.1016/j.nima.2017.10.053 Received 14 September 2017; Received in revised form 14 October 2017; Accepted 18 October 2017 Available online 4 November 2017 0168-9002/Published by Elsevier B.V.
D.J. Sprouster et al.
Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45
3. Infrastructure for nuclear materials
of the NSLS-II, specifically to accommodate radioactive materials. We outline the capabilities, operation and performance (with representative examples) of XPD. We also describe how to access the experimental equipment and software specialized for radioactive samples through the Nuclear Science User Facilities (NSUF) or the NSLS-II General User Program.
All radioactive samples, regardless of form, must have at least a single layer of containment at the NSLS-II. This requirement is typically satisfied by a single layer of Kapton tape for solid samples (140 μm). For dispersible or powdered radioactive samples, three layers (or three nested Kapton capillary tubes) of containment are required. Additional limits are placed on the amount of transuranics allowed at XPD. General Use equipment, including sample holders (which also serve as containment) and sample magazine, was installed at XPD and has been recently customized for use with radioactive samples. The sample holders designed for transmission geometry are shown in Fig. 1(c). The holder consists of a metallic base, plastic insert for mounting the sample, and magnetic ring to fasten the plastic insert onto the sample base. Each base is bar coded, so that it can be read by a camera at the base of the robot at XPD. The plastic inserts were produced by machining ABS plastic and the magnets were purchased from Amazing Magnets (Anaheim, CA). Solid samples can be wrapped in Kapton tape, and then loaded into the sample holder insert between two additional pieces of Kapton at the user’s home institution. The inserts are mounted on the sample holders and placed in the magazine at XPD. The entire procedure can take less than one minute, minimizing personnel exposure to the samples. With the robot (Stäubli) and sample containment equipment, XPD can be declared and posted as a ‘‘Radioactive Materials Area’’ during a scheduled beamtime and can accommodate a total dose rate of 0.1 rem/h at 30 cm. The magazines are designed to hold 20 samples. If the sample activity is relatively low (∼5 mrem/h at 30 cm), 20 samples can be loaded into each magazine for high-throughput measurements. Alternatively, one more highly active sample may be close to the limit. In this case, each magazine will hold one sample and the robot will be used primarily to reduce personnel exposure during data collection. The limits on activity at the beamline are based on limiting exposure to workers. The activated steel samples described below have a large 𝛽-radiation component to which the Kapton containment provides partial shielding. Single samples up to the activity limits have been characterized.
2. Beamline description The X-ray Powder Diffraction (XPD) beamline is designed to be a multi-instrument facility with the ability to collect diffraction data at high monochromatic X-ray energies (40–70 keV), offering rapid acquisition (sub-second) as well as high angular resolution capabilities [11]. The X-ray source is a 7 m long 1.8 T damping wiggler (DW100) which feeds two independent branchlines. One branchline serves two endstations and constitutes XPD. The endstation shown in Fig. 1 can operate in two different modes: high flux mode and high resolution mode. In the high flux mode (with 500 mA current in the stored electron ring), X-ray fluxes at the sample position exceed 1013 photons s−1 with modest energy resolution (𝛥𝐸∕𝐸 ∼ 0.5–1 × 10−3 ). The high flux results in the rapid collection of diffraction (and scattering) data with common collection times of ∼0.1 s. In the high resolution mode, an additional double crystal monochromator increases the energy resolution to ∼1 × 10−4 with a decrease in the incident flux (∼1 × 1012 photons s−1 ). The nominal beam size can be adjusted from mm down to 0.6 (Ho) × 0.2 (Ve) mm2 to match the graininess and heterogeneity scales of the samples under investigation. High-speed data collection is built upon the Bluesky software developed by the NSLS-II Data Acquisition Management and Analysis Group [http://nsls-ii.github.io/bluesky/]. The core characterization techniques available at XPD include XRD data, Pair Distribution Function analysis (PDF), and Small Angle X-ray Scattering (SAXS). The SAXS addition is shown specifically in Fig. 1(b). All techniques are optimized for transmission geometry, and reflectionmode XRD can be configured with a reduced vertical beam size. The combination of high-energy and high-flux capabilities available at XPD is advantageous for the structural characterization of high-Z materials, thick engineering-scale samples and samples in containments, all of which are intrinsic to nuclear materials. A robotic sample manipulator is also installed at XPD to promote rapid data collection and highthroughput operation on large batches of samples. In this work, we show how the robot operations can be tailored for unmanned sample manipulation of radioactive (and hazardous) samples. The SAXS technique and sample holders to provide containment for use with the robot were specifically developed for the high-throughput analysis of neutron irradiated reactor pressure vessel steels, to quantify radiation-induced precipitate phases [12]. For quantitative SAXS measurements, several pieces of equipment were implemented to improve the signal-to-noise ratio and accessible 𝑄-range, including an evacuated flight tube and small beamstop (2-mm diameter) and photodiode. The primary goal of the flight tube was to reduce the parasitic air-scatter. The flight tube used was 2.75-m long, with a diameter of 0.15 m and was sourced from the NSLS. The flight tube dimensions put a physical restriction on the usable 𝑄-range (∼0.8 Å−1 at 52 keV). The air gap between the sample and the flight tube could be minimized to improve the reduction in air scatter. For this to be achieved, the photodiode could potentially be placed within the flight tube or within the beamstop at the distal end on the flight tube in front of the detector [13,14]. A larger diameter flight tube will give access to higher Q, and an overall larger 𝑄-range. Alternatively, the incident X-rays could be increased to higher energy, although this will negatively affect the low 𝑄-range. The effect of the beamstop size is to increase/decrease the 𝑄-min and, therefore, the obtainable feature size. A smaller beamstop results in a lower 𝑄-min and an increase in the obtainable feature size. The energy, sample-to-detector distance, beamstop diameter and 𝑄-range are given in Table 1 for XPD.
4. Software capabilities Python scripts were developed to enable the batch processing of XRD data using TOPAS (Bruker). The data flow for the XRD analysis is shown in Fig. 2. For quantitative line profile analysis, the user needs to measure an XRD standard (such as LaB6 or CeO2 ) and to identify the phases present in each sample. Fitting the data is then completed automatically for any number of similar samples, or evolution of phases as a function of stimulus (time, temperature, field, etc.). The python scripts also perform limited error checking and flag samples that do not meet the userspecified parameters (e.g., lattice parameters, phase fraction, grain size, microstrain). The scripts assist with data visualization and can be used to plot any refined parameter (such as lattice parameter, phase volume fraction, lattice strain or domain size) versus sample index/number. In SAXS, variations in the scattered intensity come from the electron density fluctuations between the scattering objects and the host matrix [15]. The SAXS scattered intensity, as a function of 2𝜃 or scattering vector 𝑄 (𝑄 = 4𝜋 sin 𝜃∕𝜆), is inversely proportional to a characteristic distance 𝐷, in the sample: 𝑄 = 2𝜋∕𝐷 where the size 𝐷 of the scattering features is large compared to the inter-atomic distances. SAXS data can thus be used to obtain information on the size, shape, volume, and total surface area of the scattering centers, as well as the characteristic distances between ordered or partially ordered scattering centers [15–17]. Uncalibrated SAXS intensities are typically reported in arbitrary units and are a function of sample thickness, scattering geometry, and measurement time. Meaningful analyses, such as Guinier fits or size distributions, can be performed on uncalibrated intensity data 41
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Fig. 1. XPD beamline endstation with components labeled. The flight tube for SAXS mode of operation is shown for reference in (b). Sample holders for solid radioactive samples are shown in (c) and (d).
Fig. 2. Data analysis flow for XRD batch processing of multiple patterns at XPD. The multiple patterns are generated using either the robot or during time-resolved experiments.
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Nuclear Inst. and Methods in Physics Research, A 880 (2018) 40–45 Table 1 Operational SAXS Parameters at XPD. Beamline
Energy (keV)
Sample to detector distance (mm)
Beamstop diameter (mm)
𝑄-min (Å)
𝑄-max (Å)
XPD
52.5 42.6
2893.2 2893.2
2 2
0.0090 0.0065
0.8 0.6
Fig. 3. (a) Absolute scattering intensity for a glassy carbon standard measured at XPD and 15-ID at the Advanced Photon Source. (b) XRD patterns collected at X17A (NSLS) and XPD (NSLS-II) for the same sample of reactor pressure vessel steel. The inset in (b) shows a region around the (110) Fe matrix peak with minor phases labeled for reference.
Fig. 4. Representative XRD patterns around the BCC (110) diffraction peak for a series of irradiated RPV reactor pressure vessel steel samples measured at XPD. The phases identified in these samples (BCC Fe, FCC Fe, Fe3 C and Mo2 C) are included for reference.
Fig. 5. SAXS patterns for an unirradiated, irradiated and baseline (unirradiated) corrected reactor pressure vessel steel sample.
refinement to determine particle size and volume fraction, provided the scattering length density of the matrix and precipitate are known.
to determine the size distribution of scattering centers. Quantitative determinations of the volume fraction of the scattering centers, however, require the scattering intensity to be calibrated on an absolute scale. The absolute intensity is expressed as the ratio of the measured scattering intensity to the incident beam intensity and necessitates the measurement of the incident and transmitted beam intensity [15–18]. The absolute scattering intensity for high-energy X-ray beamlines and neutron scattering beamlines is routinely measured using a calibrated sample (glassy carbon) [18]. This method is employed at XPD to calibrate the scattering intensity. The incident and transmitted intensities are directly monitored with a photodiode and empty-field images are collected to correct for Kapton containment and air scatter. A software package in Python that performs the necessary pre-processing steps on images collected for the SAXS setup specific to XPD was developed. The stand-alone software has a graphical user interface (GUI) for easier access for new users. The software is capable of averaging multiple 2D images and correcting the intensity with the aid of a text file that lists the incident and transmitted intensities, sample thickness and associated empty-field files and correction factor (from analysis of the glassy carbon standard). The resulting calibrated 2D images can then be imported and integrated/converted to 1D scattering patterns for
5. SAXS and XRD performance of XPD Fig. 3(a) shows the SAXS patterns collected for a glassy carbon standard collected at XPD and at the Advanced Photon Source used to calibrate the scattering intensity [18]. The ability to calibrate the scattering intensity allows the quantitative determination of volume fractions at XPD. Fig. 3(b) shows a comparison between the XRD patterns collected at X17A (NSLS) and XPD for the same sample of reactor pressure vessel steel. The patterns are from a single 0.05 s (XPD) and 5 s (X17A) collection time with 100 accumulations. The patterns collected at XPD have better signal-to-noise ratio, sharper peaks, and better resolution between peaks, due to the smaller energy band-pass of the incident X-ray beam and thus better resolving power (𝛥𝐸 = 9 × 10−4 at 52 keV) [11]. The enhanced resolving power can be used to identify minor impurity phases within radioactive materials. The count times at XPD required to achieve a high-quality pattern were also orders of magnitude lower (0.05 s) compared to X17A (5 s and higher), the result of a much higher photon flux. 43
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Fig. 6. (a) XRD and (b) SAXS patterns for a series of MA957 samples annealed at different temperatures. The patterns in (a) are offset for clarity. The peak in (b) for the 1200 ◦ C SAXS pattern (∼0.37 Å−1 ) is due to multiple scattering effects and an intense diffraction spot in the 2D detector image.
6. First-light science at XPD: reactor pressure vessel steels and oxide dispersion strengthened steels
XPD is dedicated to NSUF proposals [https://nsuf.inl.gov/]. The second access route is through the general user proposal system at the NSLS-II [https://www.bnl.gov/ps/].
Fig. 4 shows a comparison of the XRD patterns collected for a series of neutron irradiated reactor pressure vessel steels (an unirradiated pattern is also included for reference). Qualitatively, all samples show that irradiation induces a decrease in the FCC domain size; an increase in the strain of the BCC matrix (slight broadening of the BCC peaks); and subtle changes in the peak positions associated with the iron and molybdenum carbide phases (Fe3 C, Mo2 C). The slight increase in the structured background is potentially due to the formation of small nmscale precipitates. Fig. 5(a) shows a representative example of the background corrected SAXS intensity, as a function of scattering vector Q, for an unirradiated and irradiated high-Cu, high-Ni reactor pressure vessel steel sample [12]. The scattering intensity at low-Q is attributed to carbide particles (with sizes of ∼40–70 nm). The scattering changes significantly in the irradiated pattern, with increased scattering amplitude at intermediate and high-Q. This increase in scattering amplitude is directly attributable to the formation of new nm-scale Mn–Ni–Si late blooming phases. Fig. 6 shows the (a) XRD and (b) SAXS patterns for a series of oxide dispersion strengthened steels (MA957) annealed at different temperatures. Fig. 6(a) shows that in addition to the main BCC matrix phase, small peaks associated with the oxide particles1 [19] are visible in all samples (phases are labeled for reference). These oxide peaks increase in intensity with increasing annealing temperature due to particle growth. The pronounced contribution to the scattering intensity shown in Fig. 6(b) for all samples clearly reflects the low electron density of the 𝑌2 Ti2 O7 oxide particles compared to the matrix. The SAXS patterns in Fig. 6(b) also show that the annealing leads to particle growth, with an increase in annealing temperature leading to a shift to lower-𝑄. The largest particle growth is observable in the 1200 ◦ C pattern, with shift to lower-𝑄 and decrease in intensity from scattering features in the intermediate 𝑄-range of 0.03 ∼0.55 Å−1 .
8. Summary/conclusions 1. Custom sample holders and a sample magazine for radioactive materials are available for use with the robot at the XPD beamline. A set of commands to control the robot work with the existing software that coordinates the diffractometer motions and data collection at the beamline. Therefore, the hardware and software were tested and are operational for the robot. The robot is available during beamtime in future cycles. 2. The SAXS capability has been successfully implemented at the XPD beamline. SAXS data is essential to determine the size and volume fraction of irradiation-induced precipitates in reactor pressure vessel steels. The work included determining the available 𝑄-range, based on the beam size and physical restraints at XPD, including the maximum allowable distance the detector could be placed away from the sample position (2.9 m). Installation of equipment for SAXS at XPD includes a ∼2.7 m long flight tube, a photodiode on the diffractometer to measure the initial and transmitted beam intensity, and a rail system to position the detector. 3. Benchmark XRD experiments were performed on a series of reactor pressure vessel steel samples and compared to previously measured XRD patterns at the NSLS. First-light XRD and SAXS measurements performed on reactor pressure vessel and oxide dispersion strengthened steel samples exemplify XPD’s capabilities in characterizing nm-scale features in nuclear materials. The enhanced performance creates opportunities to characterize minor phases in radioactive materials. 4. The XPD, the hardware for radioactive samples, and analysis software can be accessed directly through the general user proposal system and through the NSUF proposal system.
7. Access to XPD
Acknowledgments
The equipment, characterization techniques and software described here are available to the nuclear community through multiple routes. The first access route is available through a partner agreement between the Nuclear Science User Facilities (NSUF) and the Nuclear Science and Technology Department (BNL), where 6% of user beamtime available at
We wish to extend thanks to J. Trunk, K. Wehunt, H. Wang and W. Lewis of the NSLS-II for their support of the experiments and infrastructure described here. This work was carried out as a part of a Nuclear Energy Enabling Technology project at BNL and supported by the US Department of Energy, Office of Nuclear Energy (DOE-NE). This research used the X-ray Powder Diffraction beamline at the National Synchrotron Light Source-II, a U.S. Department of Energy, Office of Science User Facility operated for the Department of Energy Office of Science by Brookhaven National Laboratory under Contract No. DESC0012704.
1 Markers for the 𝑌 TiO phase have not been included in the figure due to the 2 5 significant number of hkl’s associated with this phase. We note that this phase is, however, present as previously discussed [19]. The markers shown are for the BCC Fe, TiO and 𝑌2 Ti2 O7 phase.
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