Jose Arregui-Mena

Profile Information

Name: Dr. Jose Arregui-Mena
Institution: Oak Ridge National Laboratory
Position: Dr
Affiliation: Oak Ridge National Laboratory
h-Index: 11
ORCID: 0000-0002-6131-3268
Expertise: Concrete, Irradiation Effect, Nuclear Graphite

Publications:

		"Characterisation of the spatial variability of material properties of Gilsocarbon and NBG-18 using random fields" Jose Arregui-Mena, Philip Edmondson, Lee Margetts, DV Griffiths, William Windes, Mark Carroll, Paul Mummery, Journal of Nuclear Materials Vol. 511 2018 91-108 Link Graphite is a candidate material for Generation IV concepts and is used as a moderator in Advanced Gascooled Reactors (AGR) in the UK. Spatial material variability is present within billets causing different material property values between different components. Variations in material properties and irradiation effects can produce stress concentrations and diverse mechanical responses in a nuclear reactor graphite core. In order to characterise the material variability, geostatistical techniques called variography and random field theory were adapted for studying the density and Young's modulus of a billet of Gilsocarbon and NBG-18 graphite grades. Variography is a technique for estimating the distance over which material property values have significant spatial correlation, known as the scale of fluctuation or spatial correlation length. The paper uses random field theory to create models that mimic the original spatial and statistical distributions of the original data set. This study found different values of correlation length for density and Young's modulus around the edges of a Gilsocarbon billet, while in the case of NBG-18, similar correlation lengths where found across the billet. Examples of several random fields are given to reproduce the spatial patterns and values found in the original data.
		"Development of mesopores in superfine grain graphite neutronirradiated at high fluence" Cristian Contescu, Jose Arregui-Mena, Philip Edmondson, Carbon Vol. 141 2019 663-675 Microstructural changes induced by neutron irradiation of superfine grain graphite G347A (Tokai Carbon, Japan) were examined by nitrogen adsorption at 77 K and by three microscopy techniques (SEM, TEM and FIB-SEM tomography). The specimens were irradiated at doses of up to 30 dpa, covering stages before and after the turnaround fluence at three temperatures (300, 450, 750 C) of their irradiation envelope. The initial graphite densification at low fluences did not produce any detectable effect in the pore size range (<350 nm) measured by gas adsorption. However, graphite irradiated at high fluences, after turnaround, showed severe structural changes. At all three temperatures and high irradiation fluences, gas adsorption revealed significant increase of the volume of narrow mesopores (<5e20 nm) and up to five times increase of BET surface area, both in linear relationship with the relative volume expansion. Analysis of microscopy images showed multiplication of fine macropores (>50 nm) at high irradiation fluences and more structural changes on multiple scales, from nanometers to microns. This work demonstrates the unique ability of gas adsorption techniques to analyze open pores with sizes between sub-nanometer and sub-micron in bulk nuclear graphite, with supporting microscopy results.
		"Development of mesopores in superfine grain graphite neutron-irradiated at high fluence" Cristian Contescu, Jose Arregui-Mena, Anne Campbell, Philip Edmondson, Carbon Vol. 141 2018 663-675 Link Microstructural changes induced by neutron irradiation of superfine grain graphite G347A (Tokai Carbon, Japan) were examined by nitrogen adsorption at 77 K and by three microscopy techniques (SEM, TEM and FIB-SEM tomography). The specimens were irradiated at doses of up to 30 dpa, covering stages before and after the turnaround fluence at three temperatures (300, 450, 750 °C) of their irradiation envelope. The initial graphite densification at low fluences did not produce any detectable effect in the pore size range (<350 nm) measured by gas adsorption. However, graphite irradiated at high fluences, after turnaround, showed severe structural changes. At all three temperatures and high irradiation fluences, gas adsorption revealed significant increase of the volume of narrow mesopores (<5–20 nm) and up to five times increase of BET surface area, both in linear relationship with the relative volume expansion. Analysis of microscopy images showed multiplication of fine macropores (>50 nm) at high irradiation fluences and more structural changes on multiple scales, from nanometers to microns. This work demonstrates the unique ability of gas adsorption techniques to analyze open pores with sizes between sub-nanometer and sub-micron in bulk nuclear graphite, with supporting microscopy results.
		"Electron tomography of unirradiated and irradiated nuclear graphite" Jose Arregui-Mena, Journal of Nuclear Materials Vol. [unknown] Graphite is the moderator material of several Generation IV nuclear reactor concepts, as well as the British Advanced Gas-cooled Reactors (AGR). Porosity can heavily influence the material properties, me- chanical irradiation response, and neutron induced shrinkage or swelling of nuclear-grade graphite. Due to the sub-micron size of several types of pores found in graphite, only a high-resolution imaging tech- nique such as electron tomography are capable of visualizing these features in three dimensions. In this research, we used electron tomography to characterize as-received and neutron irradiated samples of IG-110 nuclear-grade graphite to show for the first time the 3D structure of both native and irradiation- induced nano-cracks. This technique also reveals unique characteristics of graphite such as the structure that surrounds pores and could be used to inform molecular dynamic simulations of irradiated graphite and experimental techniques such as gas-absorption. This research also shows the utility of this technique for the study of other nuclear porous carbon-based materials.
		"Multiscale characterization and comparison of historical and modern nuclear graphite grades" Jose Arregui-Mena, Materials Characterization Vol. 190 [unknown] Beginning with Chicago Pile I, graphite has been used as a moderator material in nuclear power stations and is considered a potential material for use in future Generation IV advanced reactors. The microstructure of graphite is responsible for much of its mechanical and thermo-physical properties, and how it responds to irradiation. To understand graphite microstructure, it is necessary to understand its porosity at the macro- and micro-scales; and to understand its porosity, it is necessary to characterize the morphological connectivity of the void content and the two main phases of graphite: filler and binder. Here, using several microscopy and analytical techniques, a detailed examination of the heterogeneity, microstructure and pore structure of different graphite grades and their binder and filler phases is presented. Significant differences were found between coarser and finer nuclear grades. Coarse grades have a more diverse range of filler particles, pores and thermal cracks. Finer grades have a more well-defined pore size distribution, fewer variations of filler particles sizes and do not contain as many large thermal cracks. Fine grades tend to have a well-connected network of pores whereas coarser grades contain a larger content of closed porosity. The framework developed within this work can be applied and used to assess the various graphite grades that would down-select materials for specific use in graphite moderated reactor designs.
		"Nitrogen adsorption data,FIB-SEM tomography and TEM micrographs of neutron-irradiated superfine graingraphite" Jose Arregui-Mena, Cristian Contescu, Philip Edmondson, Data in brief Vol. 21 2018 2643-2650
		"Spatial variability in the mechanical properties of Gilsocarbon" Lee Margetts, Jose Arregui-Mena, William Bodel, Robert Worth, Paul Mummery, Carbon Vol. 110 2016 497-517 Link The objective of this study is to investigate whether there is significant spatial variability in the mechanical properties of Gilsocarbon nuclear graphite at different sections of the billet; specifically the dynamic Poisson's ratio, dynamic shear modulus, dynamic Young's modulus and density. Similar studies have been done, usually in the context of manufacturing, to assess the quality of graphite components for nuclear reactors. In this new study, the measurements have been carried out at a much higher spatial resolution than previously. A Torness/Heysham B billet was machined into cubes so that measurements could be made across the circumference and height of the billet. ASTM standards were followed to assess the measurements of the samples. The spatial variability of material properties is described and analysed statistically. The study shows that material variability is present at different heights and circumferential locations of the billet. This discovery will have a significant impact on the structural integrity and through life performance predictions made in industry; both in current and future nuclear reactors. The computer modelling of graphite components may predict different outcomes to standard analyses (that use mean values) if this variability is incorporated into the analysis workflow; specifically through stochastic modelling.
		"Using porous random fields to predict the elastic modulus of unoxidized and oxidized superfine graphite" Jose Arregui-Mena, Materials & Design Vol. [unknown] Nuclear graphite is a candidate material for Generation IV nuclear power plants. Porous materials such as graphite can contain complex networks of pores that influence the material’s mechanical and irradiation response. A methodology known as the random finite element method (RFEM) was adapted to create synthetic microstructures and predict the influence of porosity on the elastic properties of graphite during oxidation. RFEM combines random field theory and the finite element method in a Monte Carlo framework to estimate the mechanical response of a given grade of graphite. In this research, the random fields were verified through experimental characterization to predict the elastic response of three nuclear graphite grades, ETU-10, IG-110, and 2114. Finite element models (FEM) were generated using segmentations of x-ray computed tomography (XCT) data known as image-based models (IBMs) to validate and compare with the RFEM results and better understand the effects of uniform oxidation in these graphite

Presentations:

	"Microstructural characterization of nuclear graphite: from microscale to nanoscale" Jose Arregui-Mena, Cristian Contescu, Philip Edmondson, ORPA Research Symposium August 8-8, (2018)
	"Neutron irradiation effects on the microstructure of nuclear graphite" Jose Arregui-Mena, Benjamin Maerz, Cristian Contescu, Anne Campbell, Philip Edmondson, Yutai Katoh, NuMat 2018 October 14-18, (2018)

NSUF Articles:

DOE Awards 31 RTE Proposals, Opens FY-20 1st Call - Projects total $1.1 million; Next proposals due 10/31 Awards will go to 22 principal investigators from universities, six from national laboratories, and three from foreign universities. Tuesday, September 17, 2019 - Calls and Awards, Announcement

Accomplishments

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Authored an NSUF-supported publication

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Presented an NSUF-supported publication

Top 5% Submitter

Top 5% of all RTE Proposal submissions

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Awarded an RTE Proposal

Accomplished Collaborator

Collaborated on 3+ RTE Proposals

NSUF Supported Research

EBSD characterization of neutron irradiated mineral concrete aggregates - FY 2019 RTE 1st Call, #1693

Investigation of the irradiation induced porosity in concrete aggregates with x-ray computed tomography and helium pycnometry - FY 2019 RTE 3rd Call, #2904

NSUF Research Collaborations

BET and TEM characterization of nuclear graphite irradiated at temperatures below 230°C - FY 2019 RTE 2nd Call, #1773

Characterization of alpha irradiated and control cementitious grouts / grout components used for nuclear waste encapsulation - FY 2019 RTE 2nd Call, #1720

Electron tomography study of dislocation loops and precipitates in ion irradiated Fe-Cr alloys - FY 2023 RTE 1st Call, #4597

Investigation of the effects of neutron irradiation on minerals of concrete aggregates - FY 2020 RTE 2nd Call, #4206

Microstructural characterization of neutron irradiated C-C composites - FY 2023 RTE 1st Call, #4600

Micro-structural investigation of the pore structure of uncrept and crept irradiated PCEA graphite specimens with SEM and FIB tomography - FY 2018 RTE 3rd Call, #1596

TEM investigation of irradiation, irradiation creep and thermal annealing effects in nuclear graphite - FY 2018 RTE 2nd Call, #1495