Simon C Middleburgh

Simon C Middleburgh
Bangor University · Nuclear Futures Institute

Ph.D. and M.Eng from Imperial College London

About

94
Publications
15,266
Reads
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1,744
Citations
Additional affiliations
March 2018 - present
Bangor University
Position
  • Professor (Associate)
April 2015 - March 2018
Westinghouse Electric Company
Position
  • Engineer
April 2012 - April 2015
Australian Nuclear Science and Technology Organisation
Position
  • Nuclear Materials Modelling Leader

Publications

Publications (94)
Article
Improvements in fuel efficiency and economy are significantly important both for today's nuclear power reactors and for new, advanced nuclear reactor designs. Burnable absorbers (BA), which are a key component in fuel efficiency and economy, are being developed to improve fuel cycle flexibility and to reduce some of the performance drawbacks associ...
Article
Full-text available
Uranium nitride (UN) spheres embedded in uranium dioxide (UO2) matrix is considered an innovative accident tolerant fuel (ATF). However, the interaction between UN and UO2 restricts the applicability of such composite in light water reactors. A possibility to limit this interaction is to separate the two materials with a diffusion barrier that has...
Article
In this study, the thermal expansion behaviour of equiatomic alloys in the Mo-Nb-Ta-Ti-W system is studied to provide a predictive method to assess the behaviour of this and other high entropy alloy systems. The simulations used are based on first principles density functional perturbation theory and the quasi-harmonic approximation. Calculations h...
Article
The equiatomic TiZrNbHfTa high entropy alloy (HEA) and its hydrides (TiZrNbHfTaH0.4- 2.0) have been modelled at the atomic scale and the phase transformations that occur during hydrogen absorption have been simulated. The thermodynamics of vacancy formation, hydrogen accommodation and hydride decomposition have been examined using density functiona...
Article
Zirconium diboride microspheres are candidate nuclear fuel additives. Dual-scale composite architectures (DCA) were produced in spray dried and sintered zirconium diboride microspheres. These findings expand the conventionally accepted hollow (“shell”), partially hollow (“dimpled”) and shrivelled (“wrinkled”) architectures previously reported in li...
Article
Full-text available
UN-UO2 composite fuel is considered an advanced technology fuel (ATF) option to overcome the low oxidation resistance of the UN fuel. However, the interaction between UO2 and UN limits the performance of such composites. A possible way to avoid this interaction is to encapsulate the UN fuel with a material that has a high melting point, high therma...
Article
Lithium is known to accelerate the corrosion of zirconium alloys in light water reactor conditions. Identifying the mechanism by which this occurs will allow alloying additions and alternative coolant chemistries to be proposed with the aim of improved performance. Accommodation mechanisms for Li in bulk ZrO2 were investigated using density functio...
Conference Paper
Full-text available
Uranium nitride (UN)-uranium dioxide (UO2) composites have been proposed as an innovative advanced technology fuel (ATF) option for light water reactors (LWRs). However, the interdiffusion of oxygen and nitrogen during fabrication result in the formation of α-U2N3. A way to avoid this interaction is to coat the UN with a material that is impermeabl...
Article
As a burnable absorber, gadolinium oxide (Gd2O3) is widely used in light water reactors due to the high neutron absorption cross section of several gadolinium isotopes and its good solid solubility in UO2. However, some isotopes of natural Gd cause residual reactivity suppression, while some are not efficient neutron absorbers, reducing the efficie...
Article
The isotopic fractions of plutonium produced in a reactor are of significant value as nuclear forensic signatures, and the mechanisms of their production and alteration should be investigated thoroughly. A series of neutronics calculations were made on a typical UO2 PWR setup, introducing (Th, U)O2 MOX rods gradually, to investigate how the presenc...
Conference Paper
Current zirconium-based fuel claddings are susceptible to high temperature steam oxidation in accident conditions such as LOCAs. This causes a build-up of hydrogen, as well as degrades fuel element mechanical properties leading to balloon-and-burst phenomena. This presents an engineering challenge for water-cooled reactors to be improved by the int...
Article
Grain boundaries in ZrO2 may act as favourable pathways for species, such as oxygen and hydrogen, which play an important role in corrosion when compared with volume diffusion through the bulk of the crystalline material. It is known that segregation of impurity and alloying elements can lead to highly-doped grain boundaries with amorphous structur...
Article
The aim of this work is to probe the helium induced defect production and accumulation in 40 keV He+ irradiated polycrystalline W and its alternative alloy W-5wt.%Ta using transmission electron microscopy (TEM) combined with in-situ helium irradiation at 800°С. A maximum damage level of 1 dpa with a maximum He-to-dpa ratio of 5.5 at%/dpa has been r...
Article
Full-text available
Composite fuels such as UN-UO2 are being considered to address the lower oxidation resistance of the UN fuel from a safety perspective for use in light water reactors, whilst improving the in-reactor behaviour of the more ubiquitous UO2 fuel. An innovative UN-UO2 accident tolerant fuel has recently been fabricated and studied: UN microspheres embed...
Article
Full-text available
The expanded compositional freedom afforded by high-entropy alloys (HEAs) represents a unique opportunity for the design of alloys for advanced nuclear applications, in particular for applications where current engineering alloys fall short. This review assesses the work done to date in the field of HEAs for nuclear applications, provides critical...
Article
Full-text available
Uranium silicide, U3Si2, is considered as an advanced nuclear fuel for commercial light water reactors with improved accident tolerance as well as competitive economics. Nd is employed as a local burnup indicator for conventional oxide fuels due, among other reasons, to its low mobility in the UO2 fuel matrix and its high fission product yield. As...
Article
Amorphous uranium dioxide (UO2) has been modelled on the atomic scale using a combination of quantum mechanical (density functional theory) and classical forcefield methods (molecular dynamics and reverse Monte-Carlo). The atomic scale structure of the amorphous state has been predicted and is presented in the form of simulated X-ray diffraction pa...
Article
Full-text available
A UK National Thermal-Hydraulics Facility (NTHF) dedicated to supporting new reactor and other relevant business is being developed, one of the purposes being to deliver on the government’s carbon emission reduction commitments. The facility site is foreseen to be at Menai Science Park on the isle of Anglesey in North Wales, a region expected to se...
Article
Full-text available
Uranium nitride (UN)-uranium dioxide (UO2) composite fuels are being considered as an accident tolerant fuel (ATF) option for light water reactors. However, the complexity related to the chemical interactions between UN and UO2 during sintering is still an open problem. Moreover, there is a lack of knowledge regarding the influence of the sintering...
Article
The synthesis, characterization, and first-principles calculations of Ti3SiC2/Al2O3 ceramics were reported. X-ray diffraction measurements showed that the composite ceramics were highly pure. Scanning electron microscopy and transmission electron microscopy were used to characterize the interface information for Ti3SiC2 and Al2O3 crystals. Surface...
Article
The inscription of unique logo and security marking on diamonds and gemstones is in high demand by worldwide manufacturers and businesses for anti-counterfeiting purposes and traceability. Short pulsed lasers enable marking of transparent materials, challenge remains to produce digital security micro-features on thin facets of the natural diamond i...
Article
The structure of amorphous U2O7 has been examined by extended x-ray absorption near edge spectroscopy (EXAFS) and modelled using density functional theory (DFT) simulations. A hybridised metastudtite-UO3 structure is proposed, consisting of peroxide bonds (O-Operoxo), uranyl units (U=Oyl) and U-O bonding. Experimental and simulated X-ray diffractio...
Article
The synthesis of uranium diboride (UB2) from uranium dioxide (UO2) has been carried out for the first time after a coordinated experimental and theoretical investigation. The reliable conversion of UO2 to UB2 is of importance when considering commercially relevant products (e.g. as an advanced technology fuel - ATF), avoiding the use of uranium met...
Article
By combining experimental observations on Gd doped fuel with a theoretical understanding, the variation in thermal conductivity with Gd concentration and accommodation mechanism has been modelled. Four types of Gd accommodation mechanisms have been studied. In UO2−x, isolated substitutional Gd³⁺ ions are compensated by oxygen vacancies and {2GdU':V...
Article
The effects of irradiation on CaWO4, SrWO4, BaWO4, YVO4, LaVO4, YNbO4, and LaNbO4 were investigated on thin crystals using 1.0 MeV Kr ions at 50‐1000 K. All of the ABO4 compounds can be amorphized with calculated damage cross sections (σa = 1/Fc0) in the range of ~ 0.30‐1.09 × 10‐14 cm2 ion‐1 at zero Kelvin. Analysis of fluence‐temperature data ret...
Poster
Full-text available
Uranium mononitride (UN) has been considered a potential accident tolerant fuel (ATF) mainly because its high uranium density, high melting point, and high thermal conductivity. Composite fuels like UN-UO2 have been proposed so as to combine the good properties of both fuels. This study is focused on analysing the first results regarding the sinter...
Article
Full-text available
This work is a first assessment of the radiation tolerance of the nanolayered ternary carbides (MAX phases), Zr3AlC2, Nb4AlC3 and (Zr0.5,Ti0.5)3AlC2, using proton irradiation followed by post-irradiation examination based primarily on x-ray diffraction analysis. These specific MAX phase compounds are being evaluated as candidate coating materials f...
Article
UB2–U3Si2 composite fuel pellets have been manufactured and characterised. Both main phases were observed to be stable in contact with one-another up to the maximum processing temperature of 1500∘C. The solubility and behaviour of hydrogen in UB2 was predicted and compared to previous work on the gas’ behaviour in U3Si2. H2 was found to be insolubl...
Article
Full-text available
Physical properties of U3Si2 with non-magnetic, ferromagnetic, and anti-ferromagnetic structures are predicted using DFT+U with Hubbard-U values from 0 to 4 eV. The stability of U3Si2 is compared with its neighboring phases, U3Si and USi. The results emphasize the importance of magnetism. For non-magnetic U3Si2 a very large Hubbard-U value is requi...
Article
Full-text available
Yttria partially stabilized zirconia (ZrO2)x(Y2O3)½-x has been investigated to understand accommodation of excess oxygen into its structure. ZrO2 powder with 8 wt% Y2O3 additions was treated in 30 vol% H2O2 solution to promote oxidation of the material. A new Raman peak was observed after treatment at 840 cm−1, consistent with previous reports of s...
Article
Full-text available
Amorphous zirconia (a-ZrO2) has been simulated using a synergistic combination of state-of-the-art methods: employing reverse Monte-Carlo, molecular dynamics and density functional theory together. This combination has enabled the complex chemistry of the amorphous system to be efficiently investigated. Notably, the a-ZrO2 system was observed to ac...
Article
Uranium nitride-silicide composites are being considered as a high-density and high thermal conductivity fuel option for light water reactors. During development, chemical interactions were observed near the silicide melting point which resulted in formation of an unknown U–Si–N ternary phase. In the present work, U–Si–N composite samples were prod...
Article
Full-text available
High-entropy alloys (HEAs) with high melting points and low thermal neutron cross-section are promising new cladding materials for generation III+ and IV power reactors. In this study a recently developed high throughput computational screening tool Alloy Search and Predict (ASAP) has been used to identify the most likely candidate single-phase HEA...
Article
Uranium silicide, U3Si2, has been proposed as an advanced nuclear fuel to be used in light water reactors (LWRs). Development of this alternative to the predominant current fuel, UO2, is motivated by enhanced accident tolerance as a result of higher thermal conductivity as well as improved fuel cycle economics through increased uranium density. In...
Article
The stability, diffusivity and clustering behaviour of defects in uranium diboride (UB2) was investigated in light of the potential application as a burnable absorber in nuclear fuel. UB2 was found to accommodate limited deviations from stoichiometry, which should be a consideration when manufacturing and operating the material. Self-diffusivity of...
Article
Full-text available
An unexplained discrepancy exists between the experimentally measured and theoretically calculated magnetic moments of Mn in α-Fe. In this study, we use density functional theory to suggest that this discrepancy is likely due to the local strain environment of a Mn atom in the Fe structure. The ferromagnetic coupling, found by experiment, was shown...
Article
In-situ neutron diffraction patterns were collected for a sample of as-cast U3Si2 during heating to 1600 °C. Anomalous changes were observed above 1000 °C, including the formation of a new diffraction peak not belonging to P4/mbm U3Si2, unequal changes in the peak intensities and onset of anisotropic lattice expansion. The large data-set enabled de...
Article
Hydrogen uptake and accommodation into U3Si2, a candidate accident-tolerant fuel system, has been modelled on the atomic scale using the density functional theory. The solution energy of multiple H atoms is computed, reaching a stoichiometry of U3Si2H2 which has been experimentally observed in previous work (reported as U3Si2H1.8). The absorption o...
Article
Solute clustering and G-phase precipitation cause hardening phenomena observed in some low alloy and stainless steels, respectively. Density functional theory was used to investigate the energetic driving force for the formation of these precipitates, capturing temperature effects through analysis of the system's configurational and magnetic entrop...
Article
Full-text available
This work represents the first use of proton irradiation to simulate in-core radiation damage in Ti3SiC2 and Ti3AlC2 MAX phases. Irradiation experiments were performed to 0.1 dpa at 350 °C, with a damage rate of 4.57 × 10⁻⁶ dpa s⁻¹. The MAX phases displayed significant dimensional instabilities at the crystal level during irradiation leading to lar...
Article
U3Si2 has been considered as an alternative fuel for Light Water Reactors (LWRs) within the Accident Tolerant Fuels (ATF) initiative, begun after the Fukushima-Daiichi Nuclear accidents. Its main advantages are high thermal conductivity and high heavy metal density. Despite these benefits, U3Si2 presents an anisotropic crystallographic structure an...
Article
A Systematic study of defects and incorporation of xenon (Xe) and zirconium (Zr) fission products in uranium diboride (UB2) has been investigated using density functional theory (DFT) calculations as implemented in Quantum ESPRESSO code. The incorporation and solution energies show that both FPs (Xe and Zr) are most stable in U vacancies with Zr be...
Article
Full-text available
The metallic phase fission product containing Mo-Pd-Rh-Ru-Tc can be described as a hexagonal high-entropy alloy (HEA) and is thus investigated using atomic scale simulation techniques relevant to HEAs. Contrary to previous assumptions, the removal of Tc from the system to form the Mo-Pd-Rh-Ru analog is predicted to reduce the stability of the solid...
Article
The stability of a series of ABO4 minerals incorporating radioactive 99Tc during the latter’s β-decay to 99Ru was investigated theoretically using density functional theory (DFT) computations. The compounds investigated were KTcO4, RbTcO4 and CsTcO4. The stability of the latter, CsTcO4, during transmutation, when the caesium consists of the radioac...
Poster
Full-text available
UB2 is proposed as a candidate material for nuclear fuel components. The material is compared to well-known transition metal diborides, for which thermo-mechanical properties a well established. An ab-initio atomic scale investigation of the properties of UB2 reveals a mixed covalanet-metallic bonding, and that defects exhibit a highly localised el...
Article
Uranium silicides, in particular U3Si2, are being explored as an advanced nuclear fuel with increased accident tolerance as well as competitive economics compared to the baseline UO2 fuel. Here we use density functional theory calculations and thermochemical analysis to assess the stability of U3Si2 with respect to non-stoichiometry reactions in bo...
Article
Full-text available
The most energetically favourable accommodation processes for common impurities and alloying elements in Be metal and Be-Fe-Al intermetallics were investigated using atomic scale simulations. Fe additions, combined with suitable heat treatments, may scavange Al and Si through their incorporation into the FeBe5 intermetallic. In the absence of Fe, A...
Article
Density functional theory calculations have been used with spin-orbit coupling and on-site Coulomb correction (GGA + U) methods to investigate the U-Si system. Structural prediction methods were employed to identify alternate stable structures. Convex hulls of the U-Si system were constructed for each of the methods to highlight the competing energ...
Article
A method for rapidly predicting the formation and stability of undiscovered single phase high-entropy alloys (SPHEAs) is provided. Our software implementation of the algorithm uses data for 73 metallic elements and rapidly combines them - 4, 5 or 6 elements at a time - using the Miedema semi-empirical methodology to yield estimates of formation ent...
Article
Full-text available
The Mn + 1AXn phases (M = early transition metal; A = group A element and X = C and N) are materials exhibiting many important metallic and ceramic properties. In the present study powder processing experiments and density functional theory calculations are employed in parallel to examine formation of Zr2(Al1−xBix)C (0 ≤ x ≤ 1). Here we show that Z...
Article
High-entropy alloys (HEAs) have advantageous properties compared with other systems as a result of their chemistry and crystal structure. The transition between a face-centered cubic (FCC) and body-centered cubic (BCC) structure in the Alx CoCrFeNi high-entropy alloy system has been investigated on the atomic scale in this work. The Alx CoCrFeNi sy...
Article
Full-text available
The crystalline and amorphous structures of U3Si have been investigated using density functional theory techniques for the first time. The effects of disorder and the impact of fission products has been separated to understand the swelling characteristics of U3Si in both crystalline and amorphous U3Si. Initially, the stability of the three experime...
Article
Full-text available
Subject Areas: solid state physics/computational chemistry/ materials science Keywords: high-entropy alloy, fission product, nuclear fuel performance and safety, density functional theory Noble metal particles in the Mo-Pd-Rh-Ru-Tc system have been simulated on the atomic scale using density functional theory techniques for the first time. The comp...
Article
Although the equilibrium phase diagram predicts that alloys in the central part of the V–Zr system should consist of V2Zr Laves phase with partial segregation of one element, it is known that under non-equilibrium conditions these materials can form amorphous structures. Here we examine the structures and stabilities of thin film V–Zr alloys deposi...
Article
Full-text available
The slow transport of dopants through crystal lattices has hindered the development of novel devices. Typically atoms are contained within deep potential energy wells which necessitates multiple attempts to hop between minimum energy positions. This is because the bonds that constrain atoms are strongest at the minimum positions. As they hop betwee...
Article
Full-text available
Classical molecular dynamics simulations have been performed on uranium dioxide (UO2) employing a recently developed many-body potential model. Thermal conductivities are computed for a defect free UO2 lattice and a radiation-damaged, defect containing lattice at 300 K, 1000 K and 1500 K. Defects significantly degrade the thermal conductivity of UO...
Article
The title compound is synthesized in aqueous medium from a mixture of titanium(IV) bis(ammonium lactato)dihydroxide and Ce(NO3)3 (sintering between 800 and 1400 °C).