Ultra-high gamma irradiation of calcium silicate hydrates: Impact on mechanical properties, nanostructure, and atomic environments
Introduction
Nuclear powerplants all over the world are aging, about 67% of all existing nuclear reactors are more than 30 years old [1]. Currently, the US Nuclear Regulatory Commission is evaluating the license extension of some light water reactors (LWRs) from 60 to 80 years. Extending the safe operation of these reactors over 80 years will require ensuring the durability of different nuclear reactor components—including the nuclear fuel rod cladding [2], [3], cables [4], reactor pressure vessel (RPV) [5], [6], and concrete [7]—under increasing neutron and gamma irradiation dosages. One important component of an LWR is the concrete wall that surrounds the RPV, known as the biological or primary shield, that absorbs radiation created in the fuel rods and provides structural support in some specific designs. This concrete wall is irreplaceable over the lifetime of a nuclear plant, making it necessary to ensure its structural integrity over an extended period before granting a renewal for the LWR. Over 80 years, the concrete in the biological shield wall can be exposed to about 100–200 MGy gamma irradiation [8], and neutron fluxes up to 6 × 1019 n/cm2 (E > 0.1 MeV) [9]. High-energy neutrons can cause radiation-induced volumetric expansion (RIVE) through the amorphization of the different minerals present in the aggregates [9], [10], whereas gamma irradiation can cause drying, accelerated carbonation, and radiolysis in the cement paste [11], [12].
Radiolysis of water generates H2 gas and H2O2, which can accelerate the carbonation of cement paste [11], [13]. Gamma irradiation has been reported to induce carbonation, which favored vaterite and aragonite formation rather than calcite formation in the natural carbonation of pristine cement paste [11]. Specifically, vaterite formed inside the small pores around Calcium Silicate Hydrate (C-S-H), the major binding phase of cement paste, reducing the porosity and increasing the strength of the irradiated samples. An increase in calcite content due to accelerated carbonation under gamma irradiation has also been reported [13], indicating some unresolved questions regarding gamma irradiation effects on different CaCO3 polymorph formations. Gamma irradiation up to 200 MGy at different levels of drying of cement paste had a hydrogen generation rate proportional to the gamma irradiation dosage rate, even at different irradiation temperatures [8], [14]. Moreover, the G-value (i.e., number of hydrogen molecules produced per 100 eV of energy absorbed) decreased with the irradiation period and increased with the free-water content of paste. Previously, Tajuelo Rodriguez et al. studied pure synthetic C-S-H by using gamma irradiation up to 1.39 MGy and reported no significant changes in morphology, mean silicate chain length, basal spacing, and viscous and elastic response in C-S-H [15], [16]. Likewise, C-A-S-H (Calcium AluminoSilicate Hydrate) present in slag-blended cement was not affected by 4.77 MGy of gamma radiation [17]. The majority of studies available in the literature employ a relatively low gamma irradiation dose (Fig. 1) compared with the expected dosage level in the 80-year proposed design life of an LWR. Therefore, an irradiation study over a range of irradiation dosage is required. Additionally, although past literature mostly focuses on the irradiation effects on the nano- and microstructure of cementitious materials, the nature of irradiation-induced damage on the local atomic environments of C-S-H is largely unexplored.
In this study, we examine the effects of gamma irradiation on the mechanical properties, microstructure, nanostructure, and 1H and 29Si atomic environments of pure C-S-H samples at a range of ultralow to ultrahigh dosages (0.1–189 MGy) for three different Ca/Si ratios: 0.75, 1.0, and 1.33. Solid-state Nuclear Magnetic Resonance (NMR) is a state-of-the-art characterization tool that can resolve crucial atomic structure details in cementitious materials [29]. Thus, to understand the effect of radiolysis and find the source of hydrogen generation due to gamma irradiation, 1H NMR was used to evaluate the change in chemical environments of hydrogen species with increasing radiation dosage. Potential changes in local silica environments were investigated by using 29Si NMR. X-Ray Diffraction (XRD) and Thermal Gravimetric Analysis (TGA) were used to record the reduction in basal spacing and the removal of interlayer water due to the drying effect of gamma irradiation. X-ray Computed Tomography (XCT) and Ultra Small and Small Angle X-ray Scattering [(U)SAXS] were used to evaluate the change in porosity. Finally, nanoindentation and Ultrasonic Pulse Velocity (UPV) were used to evaluate the change in static Young's modulus, and dynamic Young's modulus, shear modulus, and Poisson's ratio after irradiation. Briefly, 29Si NMR showed the depolymerization of the minor Q3 silicate structure, and 1H NMR indicated disorder in select C-S-H proton environments. XRD showed a decrease in Basal spacing. The mechanical properties of the C-S-H samples increased after irradiation and the porosity of C-S-H both in micro and nanoscale was mostly unchanged after irradiation.
Section snippets
C-S-H sample synthesis and gamma irradiation
C-S-H of three Ca/Si ratios of 0.75, 1, and 1.33 were synthesized by mixing SiO2 and CaO via a mechanochemical synthesis procedure, were dried at 11% Relative Humidity (RH), and were then pressed into pellets before exposure to gamma irradiation. The full detailed C-S-H synthesis and pellet formation procedure are presented elsewhere [15]. Energy Dispersive X-ray spectroscopy (EDX) was used to verify the Ca/Si ratio of the synthesized samples (Table S1 of the Supporting Information).
The C-S-H
Change in basal spacing
C-S-H has a layered structure, and the distance between two consecutive calcium layers is denoted as the basal spacing. The basal spacing can be measured from the 002 Bragg reflection peak (7–10° 2θ) in XRD data. The XRD patterns of both pristine and irradiated C-S-H samples are shown in Figs. 3a–3b. The XRD patterns are in good agreement with the XRD patterns reported for the C-S-H synthesized through the mechanochemical method [15], [42], as well as the hydrothermal method [43], [44] used in
Conclusion
The mechanical properties, nanostructure, and 1H and 29Si atomic environments of C-S-H, the primary binding phase of concrete, is altered when exposed from a low to ultrahigh range of gamma irradiation dosage (0.1–189 MGy). By using a combination of XRD, TGA, nanoindentation, UPV, 29Si NMR, and 1H NMR, the C-S-H structure was evaluated, and two major changes in the overall C-S-H nanostructure and indication of two potential changes in the 1H and 29Si atomic environments of minor CaO-H and Q3
CRediT authorship contribution statement
E.T.R. supervised the synthesis of the C-S-H samples and coordinated the irradiation with Y.L.P. and T.M.R. E.T.R. performed TEM and nanoindentation. W.A.H. performed a statistical analysis of the nanoindentation data. A.B. and E.T.R. performed and analyzed the XRD and TGA data. E. C. performed XCT measurements and data analysis. H. S. performed UPV measurements and analysis. J. I. and E. T. R. ran (U)SAXS experiments and data analysis. A.B. and N.G. conducted the NMR experiments and prepared
Notice of copyright
This manuscript has been co-authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The publisher acknowledges the US government license to provide public access under the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
Declaration of competing interest
There are no conflicts of interest to declare.
Acknowledgments
This work was supported by the US Department of Energy's (DOE's) Office of Nuclear Energy, Light Water Reactor Sustainability Program, by an appointment to the ORNL Advanced Short-Term Research Opportunity program, which is sponsored by DOE and administered by the Oak Ridge Institute for Science and Education, and by DOE's Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051D14517 as part of a Nuclear Science User Facilities experiment. This research used resources of
References (94)
- et al.
Effect of irradiation dose rates on ethylene-propylene rubber for nuclear cables
Appl. Surf. Sci.
(2019) - et al.
Radiation effects in concrete for nuclear power plants – part I : quantification of radiation exposure and radiation effects
Nucl. Eng. Des.
(2015) - et al.
Radiation effects in concrete for nuclear power plants, part II: perspective from micromechanical modeling
Nucl. Eng. Des.
(2015) - et al.
Impact of gamma-ray irradiation on hardened white Portland cement pastes exposed to atmosphere
Cem. Concr. Res.
(2018) - et al.
Experimental evidence of the influence of iron on pore water radiolysis in cement-based materials
J. Nucl. Mater.
(2013) - et al.
Solid-state nuclear magnetic resonance spectroscopy of cements
Mater. Today Adv.
(2019) - et al.
Thermal stability of C-S-H phases and applicability of Richardson and Groves’ and Richardson C-(A)-S-H(I) models to synthetic C-S-H
Cem. Concr. Res.
(2017) - et al.
29Si MAS NMR study of the structure of calcium silicate hydrate
Adv. Cem. Based Mater.
(1996) - et al.
Pomonti, An X-ray powder diffraction study of damage produced in Ca(OH)2 and Mg(OH)2 by electron irradiation using the 2.5 MeV SIRIUS accelerator
J. Nucl. Mater.
(2018) - et al.
Elastic properties of the main species present in Portland cement pastes
Acta Mater.
(2009)
Reply to zhou et al’.S “A discussion of the paper ‘Dynamic microstructural evaluation of hardened cement paste during first drying monitored by 1H NMR relaxometry’”
Cem. Concr. Res.
Creep behavior of C-S-H under different drying relative humidities: interpretation of microindentation tests and sorption measurements by multi-scale analysis
Cem. Concr. Res.
Influence of calcium to silica ratio on H2 gas production in calcium silicate hydrate
Radiat. Phys. Chem.
Proton high resolution solid state NMR study of C3S hydration
Cem. Concr. Res.
Calcium silicate hydrates investigated by solid - state high resolution 1H and 29Si nuclear magnetic resonance
Cem. Concr. Res.
Effects of the temperature and relative humidity on the structure of C-S-H gel
Cem. Concr. Res.
Models for the composition and structure of calcium silicate hydrate (C-S-H) gel in hardened tricalcium silicate pastes
Cem. Concr. Res.
Carbonation of C-S-H and C-A-S-H samples studied by 13C, 27Al and 29Si MAS NMR spectroscopy
Cem. Concr. Res.
Testing of models of the dissolution of cements - leaching of synthetic CSH gels
Cem. Concr. Res.
Influence of calcium to silica ratio on aluminium uptake in calcium silicate hydrate
Cem. Concr. Res.
Chemical structure of cement aged at normal and elevated temperatures and pressures: part I. Class G oilwell cement
Cem. Concr. Res.
Chemical structure of cement aged at normal and elevated temperatures and pressures, part II: low permeability class G oilwell cement
Cem. Concr. Res.
New insights into creep characteristics of calcium silicate hydrates at molecular level
Cem. Concr. Res.
Young’s modulus and creep of calcium-silicate-hydrate compacts measured by microindentation
Cem. Concr. Res.
Effect of relative humidity and porosity on the logarithmic creep of the layered C-S–H minerals tobermorite and jennite
Cem. Concr. Compos.
Microstructural and bulk property changes in hardened cement paste during the first drying process
Cem. Concr. Res.
A new straightforward approach to generate si-H groups on silica
J. Colloid Interface Sci.
Operational reactors by age
Voids in irradiated stainless steel
Nature
Distribution of metallic fission-product particles in the cladding liner of spent nuclear fuel
Npj Mater. Degrad.
Irradiation-induced cu aggregations in fe: an origin of embrittlement of reactor pressure vessel steels
Phys. Rev. B
Predictive reactor pressure vessel steel irradiation embrittlement models: issues and opportunities
JOM
The effects of nuclear radiation on the mechanical properties of concrete
Am. Concr. Inst.
Evaluation of irradiation effects on concrete structure - gamma ray irradaition tests on cement paste
3.18 - Radiation effects in concrete for nuclear systems
Effect of gamma irradiation on properties of hardened cement paste
Mater. Struct.
Hydrogen production and the stability of hardened cement paste under gamma irradiation
J. Adv. Concr. Technol.
Examination of gamma - irradiated calcium silicate hydrates. Part I : chemical - structural properties
J. Am. Ceram. Soc.
Examination of gamma-irradiated calcium silicate hydrates. Part II : mechanical properties
J. Adv. Concr. Technol.
Gamma irradiation resistance of an early age slag-blended cement matrix for nuclear waste encapsulation
J. Mater. Res.
Effect of gamma irradiation on cement composites observed with XRD and SEM methods in the range of radiation dose 0-1409 MGy
Acta Phys. Pol. A
Development of soundness assessment procedure for concrete members affected by neutron and gamma-ray irradiation
J. Adv. Concr. Technol.
Sulfate-Attack Resistance and Gamma-Irradiation Resistance of Some Portland Cement Based Mortars, Upton, NY
Influence of \gamma irradiation on concrete strength
Acta Polytech.
The effects of gamma radiation on the creep properties of concrete
Radiolytic gas production from concrete containing Savannah River Plant waste, Aiken, South Carolina
The effect of gamma radiation on the fracture properties of concrete
Cited by (7)
Characterisation of iron-rich cementitious materials
2024, Cement and Concrete ResearchImpact of C–S–H seeds on cementitious hydration kinetics: New insights on porosity and microstructure
2024, Materials Today CommunicationsA mesoscale 3D model of irradiated concrete informed via a 2.5 U-Net semantic segmentation
2024, Construction and Building MaterialsNanomechanical analysis of Gamma-irradiated cement paste exposed to different humidities
2023, Construction and Building MaterialsA structural model of the long-term degradation of the concrete biological shield
2023, Nuclear Engineering and DesignInfluence of electromagnetic radiation on the degradation of reinforced concrete structures – Review
2022, Case Studies in Construction MaterialsCitation Excerpt :It has been established that neutron and gamma irradiation can change the characteristics of the cement paste nanostructure, i.e. CSH gels [58]. It is noted that irradiation reduces the basal CSH distance (∼0,6 ± 0,1 Å for 189 MGy) and increases its Young's modulus [59]. The authors of [60] found that the size of CSH globules increased after irradiation.