bluuebunny/crossref_metadata_2025 huggingface dataset:
High transition temperature shape memory polymer composites based on bismaleimide resin
Authors: Biju R. , Nair C. P. Reghunadhan
Published: January 2013

Bismaleimide–allyl phenol polymer system exhibiting shape memory characteristics and possessing transition temperature of up to 220°C ( Ttrans) was synthesized by coreacting 2,2-bis 4[(4-maleimidophenoxy)phenyl]propane (BMIP) and o,o′-diallylbisphenol A (DABA) with a bismaleimide-end-capped poly(tetramethyleneoxide) (BMI-PTMO). BMI-PTMO that served as shape memory polymer was synthesized and characterized using Fourier-transform infrared (FTIR), nuclear magnetic resonance, chemical analysis and size exclusion chromatography. The cured network containing varying proportions of poly(tetramethyleneoxide) was synthesized by varying the concentration of BMI-PTMO in the ternary blend. Cure characteristics were investigated by FTIR, differential scanning calorimetry and rheometry. Elastic memory composites were processed using carbon fabric from varying blend composition at fixed resin to reinforcement ratio. PTMO enhanced the flexibility of the network. The system as a whole possessing high transition temperature, its storage modulus decreased with increase in PTMO content. The polymer possessed good shape recovery characteristics and the recovery time decreased with increasing concentration of the shape memory component. The system showed shape recovery of 88–98% in about a minute at Ttrans. The extent of shape recovery was a direct function of PTMO concentration. The recovery time showed an inverse relationship to the modulus ratio.
Synthesis, proton conductivity and chemical stability of novel sulfonated copolyimides-containing benzimidazole groups for fuel cell applications
Authors: Gu Xingzhong , Xu Nan , Guo Xiaoxia , Fang Jianhua
Published: January 2013

A new diamine monomer, 2,2′-bis(4-aminophenyl)-5,5′-bibenzimidazole (BAPBI), has been simply synthesized via a one-step reaction procedure of 4-aminobenzoic acid and 3,3′-diaminobenzidine in polyphosphoric acid (PPA) at 190°C. A series of sulfonated copolyimides (SPIs)-containing benzimidazole groups have been prepared by random copolymerization of 1,4,5,8-naphthalenetetracarboxylic dianhydride, BAPBI, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid and nonsulfonated diamines in m-cresol at 180°C. Transparent and tough SPI membranes are obtained by solution cast method. The SPIs show high decomposition temperatures (∼300°C) of sulfonic acid groups, indicating good thermal stability. Covalent cross-linking was successfully achieved by treating the SPI membranes in PPA at 170°C for 10 h. The covalently cross-linked SPI membranes show much improved radical oxidative stability due to the synergic action of the covalent cross-linking and the incorporation of benzimidazole groups into the polymer structure. The covalent cross-linking is also favorable for improving the hydrolytic stability of the SPI membranes. However, the proton conductivity decreased to some extent because the sulfonic acid groups had been partially consumed during the process of covalent cross-linking.
Synthesis and properties of novel random copolymers of poly(ether ketone ether ketone ketone)–poly(ether ketone sulfone imide)
Authors: Zhou Minghong , Sun Yongfeng , Yu Yikai , Cai Mingzhong
Published: January 2013

The monomer containing sulfone and imide linkages, namely bis[4-( p-phenoxybenzoyl)-1,2-benzenedioyl]- N, N, N′, N′-4,4′-diaminodiphenyl sulfone (BPBDADPS), was prepared by the Friedel–Crafts reaction of bis(4-chloroformyl-1,2-benzenedioyl)- N, N, N′, N′-4,4′-diaminodiphenyl sulfone with diphenyl ether. Novel random copolymers of poly(ether ketone ether ketone ketone)–poly(ether ketone sulfone imide) were synthesized by the electrophilic Friedel–Crafts acylation polycondensation of terephthaloyl chloride with a mixture of 4,4′-diphenoxybenzophenone and BPBDADPS in the presence of anhydrous aluminum chloride and N-methylpyrrolidone in 1,2-dichloroethane. The random copolymers with 10–35 mol% BPBDADPS are semicrystalline and had remarkably increased glass transition temperatures ( Tgs) over the conventional poly(ether ether ketone) and poly(ether ketone ketone) due to the incorporation of polar sulfone and imide linkages in the main chains. The copolymers IV and V with 30–35 mol% BPBDADPS had not only high Tgs of 184–186°C but also moderate melting temperatures ( Tms) of 336–340°C, having good potential for melt processing. The copolymers IV and V had tensile strengths of 100.8–103.6 MPa, Young’s moduli of 2.31–2.48 GPa, and elongations at break of 10.9–12.4% and exhibited high thermal stability and good resistance to organic solvents.
Degradation kinetics of polytetrafluoroethylene and poly(ethylene-alt-tetrafluoroethylene)
Authors: Hondred Peter R. , Yoon Sungho , Bowler Nicola , Kessler Michael R.
Published: January 2013

This article studies the degradation kinetics of two fluorocarbon-based polymers, polytetrafluoroethylene (PTFE) and poly(ethylene-alt-tetrafluoroethylene) (ETFE), that are commonly used in coatings, solid lubricants and wiring insulation. During the onset of degradation, these polymers may fail in their desired function, with associated monetary or human cost. This work examines the degradation kinetics of PTFE and ETFE by applying thermogravimetric analysis. Results from an isoconversional method, where activation energy is represented as a function of the extent of degradation, are used to develop kinetic models describing their degradation. A statistical analysis to evaluate the accuracy and validity of the implemented kinetic models is presented and it is found that an nth-order, single-step autocatalytic reaction model best describes the degradation of PTFE, whereas a consecutive three-step autocatalytic reaction model best describes the degradation of ETFE.
High-performance nanostructure chiral poly(amide–imide)s containing benzamide and amino acid linkages: Preparation, characterization and ultrasonic effect on the morphology
Authors: Mallakpour Shadpour , Ayatollahi Hesan
Published: January 2013

In this research work, several novel optically active nanostructure poly(amide–imide)s (PAIs) were synthesized from the direct polycondensation reaction of 3,5-diamino- N-(pyridin-3-yl) benzamide with chiral diacids based on trimellitic anhydride-derived dicarboxylic acids containing different natural amino acids such as l-methionine, S-valine, l-alanine and l-isoleucine in green medium consisting of molten tetrabutylammonium bromide. The diamine was synthesized by a two-step reaction. At first, 3,5-dinitro- N-(pyridin-3-yl)benzamide was prepared from the reaction of one equimolar of 3-amino pyridine and one mole of 3,5-dinitrobenzoyl chloride. In the next step, the obtained dinitro was reduced by Pd/C and hydrazine hydrate. The new thermally stable optically active PAIs with inherent viscosity ranging from 0.31 to 0.46 dL g−1 were obtained with high yield. The synthesized polymers were characterized with Fourier transform infrared, proton-nuclear magnetic resonance spectroscopy, specific rotation measurements, thermogravimetric analysis, x-ray diffraction, field emission scanning electron microscopy (FE-SEM) and elemental analysis techniques. Morphological study by FE-SEM showed that these new PAIs were noncrystalline and nanostructure polymers with particle size between 50 and 70 nm. The effect of ultrasonic radiation on the obtained nanostructured polymers showed that the size of polymeric nanoparticles was reduced to about 30–45 nm.
Optimal forming principle and grinding experiment of the ultra-precision involute profile
Authors: Ling Siying , Lou Zhifeng , Wang Liding , Ma Yong
Published: January 2013

The accuracy requirement of ultra-precision involute artefacts and master gears, which are used to calibrate the gear measuring machines, is increasing as power density increases; however, the complexities and specificities in the involute processing and measuring have been the bottleneck of manufacturing technique for high-grade involute artefacts and ultra-precision master gears. In order to develop the ultra-precision involute gear profile, related researches were conducted in this study. First, the manufacturing level of high-grade involute artefacts was introduced. Then, the forming principle of the involute was discussed, and the roller–rail type and cam–baffle type of mechanical generating mechanism with little effects of driving accuracy on generating accuracy and less error sources were pointed out. Finally, the double roller–rail type of grinding and measuring devices for high-grade involute artefacts were designed according to the optimal forming principle of the involute, and a precision grinding experiment on an involute cam (a kind of high-grade involute artefacts) was conducted. The measured results show that the total profile deviation is not more than 0.6 µm and the profile form deviation is less than 0.4 µm in 105 mm generating length of the specimen. By using the refined involute cam and gear grinder with cam–baffle type of mechanical generating mechanism, a precision grinding experiment on the specimen of a master gear was conducted. The experimental results verify that the roller–rail type of mechanical generating mechanism has the processing capacity of high-grade involute artefacts with submicron-level profile accuracy and the refined gear grinder with cam–baffle type of mechanical generating mechanism has the processing capacity of ultra-precision master gear with grade-1 profile accuracy.
Creating Masterpieces
Authors: Dean Kathy Lund , Fornaciari Charles J.
Published: January 2013

Over a five-year period, we made a persistent observation: Course structures and routines, such as assignment parameters, student group process rules, and grading schemes were being consistently ignored. As a result, we got distracted by correcting these structural issues and were spending less time on student assignment performance. In this article, we detail possible causes of our students’ inattention to course structures and the resultant negative impact on their performance. We found evidence that excellent student performance, and thus desired learning outcomes, may be fostered by offering certain kinds of structure to our students, in certain ways. In our discussion, we apply four distinct analytic frames—cognition and information processing, student engagement, age cohort, and technology use—to examine the relationship between structure and performance. Armed with these insights, we explore four levels of structures that could enhance student performance: precourse foundations, course/classroom, assignment, and instructor. We provide an integrative performance-enhancement model and evidence of structures that we have found facilitate excellent student work.
Choice Theory and Family Counseling
Authors: Graham Mary Amanda , Sauerheber Jill Duba , Britzman Mark J.
Published: January 2013

Choice theory and its delivery mechanism, reality therapy, has long been utilized in therapeutic work with individuals, groups, families, and couples. Ironically, this theory is often omitted from family counseling and professional journals. Although choice theory is not perceived as a systemic approach, the effective implementation of the reality therapy can lead to second-order change for couples and families by creating systemic changes in a pragmatic manner. The focus of this article is the examination and integration of choice theory in family counseling.
Effect of a Single High Loading Dose of Rosuvastatin on Percutaneous Coronary Intervention for Acute Coronary Syndromes
Authors: Wang Zhengzhong , Dai Hongyan , Xing Mingqing , Yu Zhongxiang , Lin Xianru , Wang Shoudong , Zhang Junyi , Hou Fangjie , Ma Ying , Ren Yongqiang , Tan Kai , Wang Yanping , Ge Zhiming
Published: January 2013

Objectives:

A high loading dose of atorvastatin has been confirmed to reduce postprocedural events in patients undergoing percutaneous coronary intervention (PCI). In this study, we sought to investigate the protective effects of rosuvastatin in patients with acute coronary syndromes (ACS) undergoing PCI and to determine the effect of rosuvastatin pretreatment on the postprocedural levels of high-sensitivity C-reactive protein (hs-CRP), interleukin 6 (IL-6), and monocyte chemotactic protein 1 (MCP-1).

Methods:

A total of 125 patients with non-ST-segment elevation ACS were randomized to pretreatment with rosuvastatin (20 mg 2-4 hours before PCI [n = 62]) or placebo (n = 63). All the patients received subsequent long-term rosuvastatin treatment (10 mg/d). The main end point of the trial was the 30-day incidence of major adverse cardiac events (death, myocardial infarction, or unplanned revascularization). Plasma levels of hs-CRP, IL-6, and MCP-1 were detected before PCI and 6 hours, 24 hours, and 3 days after PCI.

Results:

The primary end point occurred in 8.1% of the patients in the rosuvastatin arm and 22.2% in the placebo arm ( P < .01); this difference was entirely attributed to a reduced incidence of myocardial infarction (8.1% vs 22.2%; P < .01). The postprocedural elevation in creatine kinase-MB and troponin I was also significantly lower in the rosuvastatin group at 6 hours, 24 hours, and 3 days. Plasma levels of hs-CRP, IL-6, and MCP-1 increased significantly after PCI in both the rosuvastatin and control groups; however, the postprocedural elevations in hs-CRP and IL-6 levels were significantly lower in the rosuvastatin group than the control group.

Conclusions:

A single, high dose (20 mg) of rosuvastatin prior to PCI reduces postprocedural myocardial injury in patients with ACS, with a concomitant attenuation of the postprocedural increase in hs-CRP and IL-6 levels.
Birthplace, Culture, Self-Esteem, and Intimate Partner Violence Among Community-Dwelling Hispanic Women
Authors: Gonzalez-Guarda Rosa M. , Vermeesch Amber L. , Florom-Smith Aubrey L. , McCabe Brian E. , Peragallo Nilda P.
Published: January 2013

The purpose of this study was to explore variations in demographics, culture, self-esteem, and intimate partner violence among Hispanic women according to birthplace, and to identify factors associated with these differences in intimate partner violence (IPV). Baseline data from a randomized control trial testing the efficacy of an HIV prevention program were used. Path analyses identified differences in IPV between Colombian women and women from other Central/South American countries. Self-esteem was the only factor associated with these differences. Interventions addressing the unique needs of Hispanic women from different subgroups are needed.
Intimate Partner Violence and Mental Health Among Italian Adolescents
Authors: Romito Patrizia , Beltramini Lucia , Escribà-Agüir Vicenta
Published: January 2013

Only a few studies have analyzed the health impact of intimate partner violence (IPV) on male and female adolescents, taking into account other kinds of violence that can affect their health. In this study, 43.7% of female adolescents and 34.8% of males reported IPV; females reported more psychological and sexual IPV, with no differences for physical IPV. Controlling for family and sexual violence and other confounding factors, female adolescents exposed to IPV had significantly higher adjusted odds ratios (AORs) for depression, panic attacks, eating problems, and suicidal ideation. For male adolescents, only the OR of eating problems almost reached statistical significance.
Electoral systems and the Sheriff of Nottingham
Authors: Riera Pedro
Published: January 2013

Abundant research provides evidence that electoral systems have an impact on party system fragmentation. Taking up these findings, and adopting a dynamic approach, this article explores the effect of electoral refoms on electoral disproportionality. Specifically, it demonstrates that permissive changes in the electoral system improve the overall correspondence between vote-shares and seat-shares of parties. The explanation is that underrepresented parties in the parliament obtain more seats the more inclusive the electoral rules become. Likewise, disproportionality is higher after a restrictive electoral reform. The article employs my own data on electoral reforms from 59 established and new democracies between 1945 and 2010. Evidence is found not only that electoral reform has an effect on electoral disproportionality as measured with the Gallagher’s least squares index, but also that this impact is in turn conditioned by the size of the change in the rules and the level of democratic experience.
Influences on forms of national identity and feeling ‘at home’ among Muslim groups in Britain, Germany and Spain
Authors: Karlsen Saffron , Nazroo James Y.
Published: January 2013

Muslims in Europe are increasingly constructed as problematic and insular. This article examines whether this construction may be justified and the impact this has had on the attitudes of Muslims living in different countries in Europe. Over 70 percent of Bangladeshi, Turkish and Moroccan Muslims living in Britain, Germany and Spain, respectively, felt ‘at home’ in their country of residence. This sense of being at home, and whether the events of 11 September 2001 or 11 March 2004 affected this was associated with citizenship of or birth in Europe, experiences of victimization and perceived local social support. Citizenship, experiences of discrimination and strength of religious identities were associated with reporting British, German or Spanish identities. Rather than providing evidence of self-segregation, these findings emphasize the impact of the political and social marginalization faced by Muslim groups in Europe, which significantly affects their ability to feel themselves at home there.
Relationships between the timing of social interactions and preschoolers’ engagement in preschool classrooms
Authors: Test Joan E , Cornelius-White Jeffrey H D
Published: January 2013

Social factors in the classroom (such as interactions with peers and teachers, talk, observation of others, and presence of peers and teachers) influence engagement, but little is known about the sequence or timing of these social factors with engagement. In this observational study of 12 preschoolers, ages 2–5 years, the influence of the timing of social factors on engagement was examined in depth, using sequential analysis techniques. Children’s talk to teachers and teacher presence encouraged initial engagement in activities. Teacher and peer presence, talk to and from peers, and self-talk encouraged continuing, sustained engagement, while teacher talk to children led to disengagement. Children’s observations of peers in a new activity led both into and out of engagement. Teacher interactions with children function as a bridge into and out of engagements but did little to sustain engagement, whereas peer interactions and self-talk sustained ongoing engagements. Implications for encouraging engagement in preschool classrooms are considered.
Sample Composition Discrepancies in Different Stages of a Probability-based Online Panel
Authors: Bosnjak Michael , Haas Iris , Galesic Mirta , Kaczmirek Lars , Bandilla Wolfgang , Couper Mick P.
Published: January 2013

We report sample composition discrepancies related to demographic and personality variables occurring in different stages of development of a probability-based online panel. The first stage—selecting eligible participants—produces differences between Internet users and nonusers in age, education, and gender distribution as well as in the personality traits of openness to experience, conscientiousness, and extraversion. The second and third stages of panel development—asking about willingness to participate in the panel and actual participation in online surveys—result in fewer and smaller discrepancies. The results suggest that among the three potential sources of sample composition bias considered, the largest impact comes from coverage differences with regard to Internet access.
Sound science in geological disposal in the United Kingdom
Authors: Tweed C. J.
Published: January 2013

The safe implementation of geological disposal must be underpinned by sound science. This paper describes the approaches taken by the Nuclear Decommissioning Authority Radioactive Waste Management Directorate, the implementing body for geological disposal in the UK, to build an evidence
base of scientific data and understanding which is robust to scrutiny and so provides confidence in the safety of geological disposal.
Waste container durability: monitoring of a stainless steel 4 metre box over 12 years
Authors: Smart N. R. , Winsley R. J. , Fennell P. A. H. , Reddy B. , Rance A. P. , Padovani C.
Published: January 2013

In the UK, most intermediate level radioactive waste is packaged in stainless steel containers. It is important that containers should maintain their integrity for extended periods of storage prior to final disposal. A prototype 4 metre box fabricated from 304S11 stainless steel was monitored at an inland rural building for over twelve years to gain experience in monitoring environmental conditions and corrosion during storage. A wide range of different types of aerosol particles were observed on the surfaces and in the air. They contained corrosive ions such as chloride, as well as other anions such as sulfate and nitrate. The chloride deposition rate was between 0.1 and 4 μg cm−2 yr−1 depending on the orientation and location of the surface, with a chloride/sulfate ratio ranging from ∼0.3–2. The temperature and relative humidity typically ranged from 0–30°C and 40–90%, respectively. The greatest degree of corrosion developed on the base of the box, which had elevated chloride concentrations (10–140 μg cm−2). However, there was little evidence of corrosion propagation on the surface of the box and no evidence of stress corrosion cracking. The average pit propagation rates on a 316L coupon mounted next to the 4 m box were <1 μm yr−1.
Corrosion and expansion of grouted Magnox
Authors: Cronin J. , Collier N.
Published: January 2013

With potential storage of several hundred years underground in a geological disposal facility (GDF) before closure, there is a requirement for radioactive waste packages to perform adequately. Over the past 25 years, cementitous grouts based on blast furnace slag (BFS) and ordinary Portland cement (OPC), have been used in the UK to immobilize intermediate-level waste (ILW), Magnox swarf, and currently such wasteforms are in surface storage awaiting geological disposal. Magnox fuel cladding will slowly corrode when encapsulated in alkaline cementitious grouts to produce hydrogen gas and an expansive corrosion product. Expansive corrosion products may lead to degradation of the wasteform and, if extensive, could affect the container. This study investigated the acute and chronic rates of corrosion of unirradiated Magnox swarf encapsulated in a BFS/OPC grout over a range of temperatures (25, 40, 60, 75 and 90°C) for curing times of up to 2½ years. Structural product degradation starts to develop as the tensile strength of the grout is approached by the expansive forces generated. Deformation of some experimental containers was also noted. An estimate of the time taken for a grouted product to fracture from this study due to the corrosion solely of Magnox is 350 years for storage at 25°C. Although not fully described in this paper, the main cement phases were calcium silicate hydrate, portlandite and gehlenite; the main product of Magnox corrosion was brucite. The curing temperature did not affect the compositions of the Magnox metal, corrosion product or grout.
Release of uranium from candidate wasteforms
Authors: Collier N. , Harrison M. , Brogden M. , Hanson B.
Published: January 2013

Large volumes of depleted natural and low-enriched uranium exist in the UK waste inventory. This work reports on initial investigations of the leaching performance of candidate glass and cement encapsulation matrices containing UO3 powder as well as that of uranium oxide powders. The surface areas of UO3 powder and the monolith samples of UO3 conditioned in the glass and cement matrices were very different making leaching comparisons difficult. The results showed that for both types of monolith conditioned samples a steady increase of uranium concentration in solution with time was generally not observed. The wt.% of uranium leached from UO3 conditioned in the lead borosilicate glass wasteform was approximately five orders of magnitude less than that leached from UO3 powder. Similarly, the quantities of uranium leached from UO3 conditioned in composite cement made with ordinary Portland cement, and from magnesium phosphate cement, were approximately four and three orders of magnitude, respectively, less than that leached from UO3 powder. The performance of a mixed oxide borosilicate glass wasteform was only slightly better than that of UO3 powder. This work shows that wasteforms based on encapsulation in lead borosilicate glass and cement matrices have the greatest potential for further development.
Site-bond modelling of porous quasi-brittle media
Authors: Jivkov A. P. , Gunther M. , Travis K. P.
Published: January 2013

Geological repository designs employ a multi-barrier approach. The materials, which include wasteforms, backfill and host rock, are typically porous quasi-brittle. Mechanical damage (e.g. nucleation and growth of microcracks) can result in significant changes in permeability. A knowledge of how the permeability is affected is critical to accurate modelling of radionuclide transport. This work proposes a novel 3D lattice-type model for the damage evolution in such materials, referred to as the site-bond model. Its advantages over previous models are that the shape of the lattice cell is physically realistic and that any macroscopic elastic response can be represented, including those of cementitious and geological materials. Damage accumulates as bonds fail upon reaching prescribed failure strengths. These are dictated by a predefined pore size distribution. Concrete is used as a study material. It is demonstrated that the model can predict the macroscopic stress–strain response under unconfined tension and compression with emergent non-linearity due to damage evolution. Ongoing work on the prediction of permeability changes with damage is discussed. This is based on the interaction between the model proposed here and a lattice model of the pore space.
Break-up testing of waste-form materials
Authors: Metcalfe M. P. , Koch W. , Turner G.
Published: January 2013

The Nuclear Decommissioning Authority (NDA) is developing a safety case for the long-term management of higher activity wastes. This includes safety assessments of transport to and operations at the repository. One of the main faults and hazards to be considered is waste package response to impact accidents.

The criteria of impact performance for waste packages are based upon activity release of particulates generated from the break up of the waste form during impact. The NDA approach to impact performance is based upon waste package response from finite element modelling in combination with break-up tests.

Previous break up research commissioned by the NDA has concentrated on commercial graphite and glass samples. These extended studies, undertaken by the National Nuclear Laboratory in collaboration with the Department of Aerosol Technology of the Fraunhofer Institute of Toxicology and Experimental Medicine, provide break-up data specific to nuclear facilities and waste materials. These include archived unirrradiated graphite used to construct Magnox reactor cores and reflectors, simulant high level waste glass, selected grout formulations and selected metal-in-grout formulations.
An overview of near-field evolution research in support of the UK geological disposal programme
Authors: Beattie T. M. , Williams S. J.
Published: January 2013

The near field, together with the containment and isolation provided by the geosphere, contributes to the long-term safety provided by a geological disposal facility (GDF) after closure. The different engineered barriers can prevent or limit the release of radionuclides and their migration to the undisturbed host rock or geosphere and are expected to fulfil their post-closure safety functions for many thousands to hundreds of thousands of years. They will continue to contribute to containment after their eventual degradation when there would no longer be confidence that they would continue to fulfil all of their safety functions in their totality. By that time, significant radioactive decay will have occurred, substantially reducing the hazard associated with the wastes. Therefore, demonstration of long-term safety requires an understanding of the evolution of the engineered barriers and the consequences for the generic safety functions that the different barriers provide. This paper provides an overview of the research of the Nuclear Decommissioning Authority Radioactive Waste Management Directorate into the evolution of the near field of a GDF.
Long term leachate evolution during flow-through leaching of a vault backfill (NRVB)
Authors: Butcher E. J. , Borwick J. , Collier N. , Williams S. J.
Published: January 2013

Some of the illustrative concepts for the disposal of intermediate-level waste in a geological disposal facility in the UK employ a cementitious backfill around the waste packages. The concept for higher strength rocks would use a highly alkaline backfill composed of Portland cement (now known as CEM I), hydrated lime and limestone flour, referred to as Nirex reference vault backfill (NRVB).

This paper reports a study of the extensive leaching of cured NRVB in a range of generic leachant compositions (deionized water, 0.1 M and 1 M NaCl solutions) under flow-through conditions using a flexible wall permeameter. The experiments were designed to run for up to two years and to pass at least 1000 volumes of leachant (defined as the cumulative leachate volume produced/NRVB solid specimen volume) through the NRVB samples. Results for the pH evolution profiles of the leachates and the microstructural analysis of the unleached and leached samples are presented.
Modelling coupled processes in bentonite: recent results from the UK's contribution to the Äspö EBS Task Force
Authors: Holton D. , Baxter S. , Hoch A. R.
Published: January 2013

A range of potential concepts for the geological disposal of high level wastes and spent fuel are being studied and considered in the UK. These include concepts that use bentonite as a buffer material around the waste containers. The bentonite will be required to fulfil certain safety functions, the most important being (1) to protect the waste containers from detrimental thermal, hydraulic, mechanical and chemical processes; and (2) to retard the release of radionuclides from any waste container that fails. The bentonite should have a low permeability and a high sorption capacity.

These safety functions could be challenged by certain features, events and processes (FEPs) that may occur during the evolution of the disposal system. A consideration of how these FEPs may affect the safety functions can be used to identify and to prioritize the important areas for research on bentonite. We identify these important areas (which include hydration of compacted bentonite, illitization and erosion of bentonite), and describe how they are being investigated in current international research on bentonite.

The Äspö EBS Task Force is a collaborative international project designed to carry out research on bentonite. In 2011, the Nuclear Decommissioning Authority Radioactive Waste Management Directorate joined the EBS Task Force partly to benefit from its collective experience. The work of the EBS Task Force is split into two research subareas: (1) the THM subarea, which includes tasks to understand homogenization of bentonite as it resaturates, to investigate the hydraulic interaction between bentonite and fractured rock, and to model in situ experiments; and (2) the THC subarea, which includes tasks to investigate the issue of understanding transport through bentonite, and to model in situ experiments. In particular, the bentonite rock interaction experiment is a large-scale in situ experiment concerned with understanding groundwater exchange across bentonite rock interfaces, with the objective of establishing better understanding of bentonite wetting. In this paper, we describe our work to model the spatial and temporal resaturation of bentonite buffer in a fractured host rock.
Calcium silicate hydrate (C-S-H) gel dissolution and pH buffering in a cementitious near field
Authors: Baston G. M. N. , Clacher A. P. , Heath T. G. , Hunter F. M. I. , Smith V. , Swanton S. W.
Published: January 2013

A cementitious backfill has been proposed in many geological disposal concepts for intermediate-level waste and low-level waste in the UK and elsewhere. In this paper, the main features of the chemical evolution of backfill and the associated changes in the near-field pH are illustrated with results from recent work. For example, interaction of the groundwater with calcium silicate hydrate (C-S-H) phases in a backfill is expected to play an important role in the long-term pH-buffering behaviour. Existing experimental data for the dissolution of C-S-H gels are compared with recent experimental results from leach tests on gels of a lower calcium to silicon ratio (C/S) to provide a consistent set of data across the full C/S range. The results confirm that a congruent dissolution point around C/S = 0.8 is approached by leaching from below (i.e. for gels with 0.29 < C/S < 0.8), as well as from above, as reported elsewhere. In addition, a spreadsheet model has been developed to calculate the volume of backfill required at the vault scale to meet specified pH performance criteria. This model includes the major reactions of the backfill with the groundwater, waste encapsulants and waste components. It can also consider the effects of specific waste packages on local pH performance to allow comparison with the vault-scale calculations.
Cracking in a cementitious backfill and its implications for flow and chemistry
Authors: Swift B. T. , Bamforth P. B. , Baston G. M. N.
Published: January 2013

In the UK, disposal of packaged intermediate-level radioactive waste may involve waste packages being placed in a geological disposal facility (GDF) and surrounded by a cementitious backfill. Cracking of the backfill could occur due to a number of mechanisms, and this could affect the post-closure performance of the GDF.

This work has assessed potential cracking in the backfill during the backfilling and early post-closure period of GDF vaults with an open crown space in a higher strength rock. From the comprehensive range of processes considered, three were identified as potentially causing cracking: (1) during backfilling, plastic settlement under solid horizontal surfaces could result in horizontal gaps beneath waste packages; (2) within days of backfilling, early-age thermal contraction of the backfill could result in primarily vertical cracks; (3) over a number of years, expansion of waste packages could result in large horizontal cracks.

A groundwater flow model incorporating a representation of the cracks was used to calculate flows through a backfilled GDF vault, and through the cracks themselves. Including cracks increased the flow rate significantly. A reactive transport model was used to estimate the evolution of the pore water chemistry as groundwater flows through the cracked backfill. Calcite and brucite were predicted to precipitate, with brucite subsequently dissolving. Calcite build-up could seal some cracks.
An introduction to geosphere research studies for the UK geological disposal programme
Authors: Norris S.
Published: January 2013

This paper gives an overview of the geosphere research studies being undertaken by the Radioactive Waste Management Directorate (RWMD) of the Nuclear Decommissioning Authority. The approach of the RWMD in the current generic phase of the UK managing radioactive waste safely (MRWS) programme is to maintain an understanding of key processes and to carry out research and development into techniques so capability can be built. Although RWMD can demonstrate a general understanding of geosphere processes at this stage in the UK project, it is recognized that this will need to be made site-specific as the MRWS programme progresses. An understanding of the geosphere at the selected site(s) will be an important part of the future programme. Where possible, the RWMD will participate in international studies so that relevant site-based information can be accessed. In this way, the RWMD will be prepared for site-specific work in stage 5 of the MRWS process.
Comparison of a post-closure transient criticality model with the Oklo natural reactors
Authors: Mason R. M. , Martin J. K. , Smith P. N. , Turland B. D.
Published: January 2013

In support of the disposal system safety case for a geological disposal facility (GDF) there is a requirement to consider 'what-if' hypothetical scenarios for post-closure nuclear criticality. Although all such scenarios are considered very unlikely, one 'what-if' scenario is the mobilization of fissile material from a number of waste packages and its slow accumulation within the GDF or the immediate surroundings. Should sufficient fissile material accumulate a quasi-steady-state (QSS) transient criticality event could result. A computer model has been developed to understand the evolution and consequences of such an event.

Since a postulated QSS criticality could persist for many millennia, building confidence in the modelling approach is difficult. However, the Oklo natural reactors in Africa operated for similar durations around two billion years ago, providing a natural analogue for comparison. This paper describes the modelling approach, its application to hypothetical criticality events for a GDF, and how the model can be compared to Oklo. The model results are found to be in agreement with the observational evidence from Oklo, building confidence in the use of the QSS model to simulate postulated post-closure criticality events in GDFs.
The consequences of hypothetical post-closure criticality
Authors: Mason R. M. , Smith P. N. , Turland B. D. , Jackson C. P.
Published: January 2013

The Environment Agency Guidance on Requirements for Authorisation (GRA) of a geological disposal facility (GDF) requires a demonstration that "the possibility of a local accumulation of fissile material such as to produce a neutron chain reaction is not a significant concern." A neutron chain reaction that is just self-sustaining is also known as critical.

Waste packages can be designed to ensure that criticality is impossible during the transport and operational phases of a GDF, and for a significant period post-closure. Over longer times, however, packages may degrade, and groundwater flows could lead to a localized accumulation of fissile material. Hence, even though the initial distribution of materials would need to change substantially, criticality cannot be ruled out completely.

This paper describes how an accumulation of fissile material could, hypothetically, lead to a critical configuration; how such a system could evolve; what the local consequences could be; and how the engineered and geological barriers could be affected. The conclusion from studies to date is that, even for large (and very unlikely) fissile accumulations, the consequences of a post-closure criticality event are not a significant concern.
Comparison of discrete fracture network and equivalent continuum simulations of fluid flow through two-dimensional fracture networks for the DECOVALEX–2011 project
Authors: Leung C. T. O. , Hoch A. R. , Zimmerman R. W.
Published: January 2013

Fluid flow through a two-dimensional fracture network has been simulated using a discrete fracture model. The computed field-scale permeabilities were then compared to those obtained using an equivalent continuum approach in which the permeability of each grid block is first obtained by performing fine-scale simulations of flow through the fracture network within that region. In the equivalent continuum simulations, different grid-sizes were used, corresponding to N by N grids with N = 10, 40, 100 and 400. The field-scale permeabilities found from the equivalent continuum simulations were generally within 10% of the values found from the discrete fracture simulations. The discrepancies between the two approaches seemed to be randomly related to the grid size, as no convergence was observed as N increased. An interesting finding was that the equivalent continuum approach gave accurate results in cases where the grid block size was clearly smaller than the 'representative elementary volume'.
Radionuclide diffusion into undisturbed and altered crystalline rocks
Authors: Havlová V. , Večerník P. , Najser J. , Sosna K. , Breiter K.
Published: January 2013

An extensive set of porosity, ε, effective diffusion coefficient, De, and hydraulic conductivity, K, data were obtained from 45 granitic samples from the Bohemian Massif, Czech Republic. The measured dataset can be used to define parameter ranges for data to be used in safety assessment calculations for a deep (>400 m) radioactive waste repository, even though the samples originated from shallower depths (<108 m). The dataset can also be used for other purposes, such as evaluating the migration of contaminants in granitic rock (e.g. from shallow intermediate-level radioactive waste repositories and chemical waste repositories).

Sample relaxation and ageing processes should be taken into account in research otherwise migration parameters might be overestimated in comparisons between lab results and those determined in situ.
BIOPROTA: international collaboration in biosphere research for radioactive waste disposal
Authors: Smith K. , Smith G. M. , Norris S.
Published: January 2013

Consideration of the biosphere is important in the post-closure safety assessment of a geological disposal facility (GDF) as the biosphere acts as the receptor for any contaminants that may be released from the geosphere. Considerable uncertainty exists in the characteristics of the biosphere at times in the far future when any contaminant releases from a GDF would reach the accessible environment. These uncertainties include human behaviour, affecting environmental change as well as exposure modes.

A number of critical scientific issues have been identified through the practical application of the International Atomic Energy Agency reference biosphere approach within both site generic and site specific repository assessment projects. These issues are being addressed through an international collaboration programme, BIOPROTA. The purpose of this paper is to describe the BIOPROTA programme, its objectives and typical working method. The approach is illustrated with examples from the recent work programme including model intercomparison studies for the radionuclides 36Cl and 79Se.
Comparison of modelled uptake to cereal crops of 14C from gaseous or groundwater mediated pathways
Authors: Smith K. , Jackson D. , Smith G. , Norris S.
Published: January 2013

Carbon-14 has been identified as one of the more significant radionuclides in solid radioactive wastes in a repository, due to the potential radiological impact arising if 14C were to be released and enter the biosphere. However, the assessment of radiation doses is complicated by the major role of carbon in biological processes, and this has tended to lead to the adoption of a cautious assessment approach.

An international comparison of five models used to predict uptake of 14C to agricultural crops has been undertaken, within the BIOPROTA framework. Processes investigated include conversion of 14C-labelled CH4 into CO2 in soils, carbon accumulation in and release from soil carbon pools, gaseous emanation to, and dispersion from, the plant canopy atmosphere and, incorporation into plants by photosynthesis.

For a unit rate of entry of 14C to soil, modelled activity concentrations in cereal crops differ by three to five orders of magnitude. This reflects, in part, differing assumptions for mixing and dispersion of air above the soil surface and within the crop canopy layer. For a unit activity concentration of 14C in air, the modelled uptake to cereal crops converges significantly. Following an assumed irrigation of crops with groundwater containing unit activity of 14C, the predicted uptake to crops varied by two to four orders of magnitude, again largely dominated by assumptions regarding the canopy atmosphere. In all cases, there is some convergence in model predictions as field size increases.

A continuing programme of field research is being undertaken in parallel with the assessment work.
Gas migration experiments in bentonite: implications for numerical modelling
Authors: Graham C. C. , Harrington J. F. , Cuss R. J. , Sellin P.
Published: January 2013

In the Swedish KBS-3 repository concept, there is potential for gas to be generated from corrosion of ferrous materials under anoxic conditions, combined with the radioactive decay of the waste and radiolysis of water. A full understanding of the probable behaviour of this gas phase within the engineered barrier system (EBS) is therefore required for performance assessment. We demonstrate key features from gas transport experiments on pre-compacted Mx80 bentonite, under laboratory and field conditions, and discuss their implications in terms of a conceptual model for gas migration behaviour. On both scales, major gas entry is seen to occur close to the sum of the porewater and swelling pressures of the bentonite. In addition, gas pressure at breakthrough is profoundly sensitive to the number and location of available sinks for gas escape. Observations of breakthrough can be explained by the creation of dilatational pathways, resulting in localized changes in the monitored porewater pressures and total stresses. These pathways are highly unstable, evolving spatially and temporally, and must consequently influence the gas permeability as their distribution/geometry develops.

Such observations are poorly embodied by conventional concepts of two-phase flow, which do not fully represent the key processes involved. Although dilatancy based models provide a better description of these processes, the paucity of data limits further development and validation of these models at present.
Rate and speciation of volatile carbon-14 and tritium releases from irradiated graphite
Authors: Baston G. M. N. , Marshall T. A. , Otlet R. L. , Walker A. J. , Mather I. D. , Williams S. J.
Published: January 2013

The release and migration of gaseous carbon-14 has been identified as a key issue for geological disposal of intermediate-level radioactive wastes in the UK. A significant fraction of carbon-14 in the UK inventory is in irradiated graphite. This paper describes measurements of gaseous carbon-14 releases from irradiated graphite on immersion in alkaline solution. Apparatus has been developed to discriminate organic and inorganic (14CO/14CO2) species in the gas phase by means of selective oxidation and capture. In the initial experiment, small amounts of gaseous carbon-14 (∼4 Bq) were released from 9 g of crushed graphite within a two-week period. In a long-term experiment, cumulative releases were measured periodically from an intact specimen of graphite over a 14 month period. A small fraction of the graphite carbon-14 inventory was released to the gas phase (∼0.004% as CO/CO2 and ∼0.001% associated with organic compounds). A larger quantity of carbon-14, about 0.1%, was released to the solution phase and was thought to be mainly 14CO2, with some possible organic component. In general, the rate of gaseous carbon-14 release decreased with time. The results suggest a small initial release of relatively labile, accessible carbon-14, with longer term release occurring at a much slower rate. Tritium (T) releases were also measured.