Monoblock Concept Research Articles

Resin-Build-Up as A Direct Monoblock Concept for Root Canal Dentin, Core, and Crown Restoration on Anterior Endodontically Treated Tooth

Resin-Build-Up as A Direct Monoblock Concept for Root Canal Dentin, Core, and Crown Restoration on Anterior Endodontically Treated Tooth

Electromagnetic load evaluation of K-DEMO divertor for MD and VDE plasma disruption scenarios

Electromagnetic (EM) force caused by the instability of plasma operation is one of the most significant external loads in the DEMO, as well as the extremely high heat flux (more than 10 MW/m2). Abrupt disruption of plasma current of several MA causes thermal quench and current quench sequentially. This paper presents the EM force on the divertor calculated by considering the Poloidal field variation (PFV), halo current (HC), and toroidal field variation (TFV) generated during the quenching process for the K-DEMO. The K-DEMO with the fusion power of 2,200 MW has a major radius of 6.8 m and a plasma current of 12 MA in steady-state operation. The K-DEMO divertor basically employs a water-cooled tungsten monoblock concept with a reduced activation ferritic martensitic RAFM steel heat sink. EM force was calculated using ANSYS Mechanical/Emag solver. For the convenience of calculation, the existing inconvenient GUI environment based on MAPDL was changed to ANSYS Workbench and improved. To evaluate the EM forces generated in the K-DEMO divertor when various disruption scenarios occur, three scenarios were selected for major disruption (MD) and vertical displacement event (VDE), respectively. The variation of PFV, HC, and TFV in the disruption are significant input data for EM analysis. The major disruption data were converted from ITER disruption scenarios by using the in-house code since the plasma data for the disruption scenarios has not been developed for the K-DEMO. This study presents the preliminary evaluation of EM force for the K-DEMO and improved calculation platform although the disruption data derived from ITER are used. The EM forces generated by the selected six scenarios were calculated and compared. In the MD_DW_slow_fast and VDE_DW_slow_fast scenarios, the maximum EM force was 4.8 MN on the K-DEMO divertor module along the vertical direction, and the HC influence was dominant.

Power exhaust concepts and divertor designs for Japanese and European DEMO fusion reactors

Concepts of the power exhaust and divertor design have been developed, with a high priority in the pre-conceptual design phase of the Japan–Europe broader approach DEMO design activity (BA DDA). Common critical issues are the large power exhaust and its fraction in the main plasma and divertor by the radiative cooling (P rad tot/P heat ⩾ 0.8). Different exhaust concepts in the main plasma and divertor have been developed for Japanese (JA) and European (EU) DEMOs. JA proposed a conventional closed divertor geometry to challenge large P sep/R p handling of 30–35 MW m−1 in order to maintain the radiation fraction in the main plasma at the ITER-level (f rad main = P rad main/P heat ∼ 0.4) and higher plasma performance. EU challenged both increasing f rad main to ∼0.65 and handling the ITER-level P sep/R p in the open divertor geometry. Power exhaust simulations have been performed by SONIC (JA) and SOLPS5.1 (EU) with corresponding P sep = 250–300 MW and 150–200 MW, respectively. Both results showed that large divertor radiation fraction (P rad div/P sep ⩾ 0.8) was required to reduce both peak q target (⩽10 MW m−2) and T e,i div. In addition, the JA divertor performance with EU-reference P sep of 150 MW showed benefit of the closed geometry to reduce the peak q target and T e,i div near the separatrix, and to produce the partial detachment. Integrated designs of the water cooled divertor target, cassette and coolant pipe routing have been developed in both EU and JA, based on the tungsten (W) monoblock concept with Cu-alloy pipe. For year-long operation, DEMO-specific risks such as radiation embrittlement of Cu-interlayers and Cu-alloy cooling pipe were recognized, and both foresee higher water temperature (130 °C–200 °C) compared to that for ITER. At the same time, several improved technologies of high heat flux components have been developed in EU, and different heat sink design, i.e. Cu-alloy cooling pipes for targets and RAFM steel ones for the baffle, dome and cassette, was proposed in JA. The two approaches provide important case-studies of the DEMO divertor, and will significantly contribute to both DEMO designs.

Conceptual design of a liquid-metal divertor for the European DEMO

Liquid metal (LM) divertors are considered for the European DEMO reactor, because they may offer improved performance compared to the tungsten monoblock concept. The goal of this work is to provide a concept design, and explore the limitations of liquid metal divertors. To this end, a set of design requirements was formulated in close collaboration with the EUROfusion Power Plant Physics and Technology team (responsible for the design of the EU-DEMO). Tin was chosen as the preferred liquid metal, because unacceptable Tritium retention issues arise when lithium is used in DEMO. A concept design was then chosen that consists of water cooled pipes that are square on the outside and round on the inside, a corrosion barrier, and a 3D-printed porous tungsten armor layer filled with liquid tin. The porous armor layer acts as a Capillary Porous System (CPS). The design was analyzed using thermo-mechanical FEM simulations for various armor thicknesses and heat sink materials: Densimet, W/Cu composites, and CuCrZr. The highest heat loading capability achieved is 26.5 MW/m2 in steady state (18.9 MW/m2 when taking into account a safety margin of 1.4). This is achieved using a CuCrZr pipe, with a 1.9 mm thick armor. When increasing the armor layer to 3 mm thick, more than 80 MW/m2 can be withstood during slow transients thanks to vapor shielding, but at the same time the steady-state capability is reduced to 18 MW/m2. Resilience against disruptions cannot yet be proven, but is deemed within the realm of possibility based on estimates regarding the behavior of vapor shielding. This should be further investigated. Overall, the concept is considered a significant improvement compared to the original specifications (which are also the specifications to the tungsten monoblocks: 10 MW/m2 in steady state, and ∼20 MW/m2 during slow transients). Moreover, the possibility of withstanding disruptions is regarded as a potentially major improvement.

FUNDAMENTAL CONCEPT OF MONOBLOCK IN ENDODONTICS

The advent of dentin adhesive technology in endodontics has made monoblock a well known concept in endodontics. However it has created many controversies on whether monoblock would reinforce the roots and provide a superior coronal seal.In this review, attempts have been made to understand monoblock in a broader aspect and understand how the monoblock concept can be applied to the materials used till date which rehabilitates the root canal space. The potential of currently available bondable materials to achieve mechanically homogeneous units with root dentin is then discussed in relation to the classical concept in which the term monoblock was first employed in restorative dentistry and subsequently in endodontics.

The monoblock concept in endodontics

The ultimate challenge for successful endodontic therapy is to establish a homogenous unit of the root canals which requires a hermetic seal. Adhesion of root canal sealers to dentin is important to seal the root canal system thoroughly and to prevent microleakage. Bonding of root filling materials to the radicular dentin is known as ‘monoblocks’ which has become more popular after introduction of bonding concept in the root canal system. The aim of this review highlights on newer materials and different concepts in rehabilitation of root canal space. Thus the potential of these monoblocks is discussed with the possibility of their application in endodontics in future. Keywords: Monoblocks, MTA, Fibre posts, Bonding to root canal.

A comparative finite element study of stress and deformation on three commonly used all ceramic fixed denture prosthesis under the influence of different bite forces

Aim: To simplify the complexity in design, modeling and analysis of Fixed Partial Dentures (FPD) and to evaluate the maximum stress and deformation developed using Finite-Element Method.Materials and Methods: The specimen was created based on monoblock concept. The monoblock concept assumes that the total FPD unit, i.e., Abutment, pontic, connector and retainer together will act as a single unit. Monoblock castings do not differ from those made in segments and later welded as regard to the distribution of stresses. The Specimen of dimension 30 X 5 X 5mm were made of the three commonly used FPD materials such as feldspathic ceramics, Lithium di silicate and Zirconia. Rectangle shape was considered with notches at 1 X 450 as a close approximation of actual FPDs. The modeling was done using Solid Works 2012, and analysis was carried out using ANSYS Mechanical APDL R14.5. The maximum stress and deformations corresponding to various masticatory loads (100 N, 500 N, 600N, 800 N & 1000 N) were found out, and the results were compared with previous studies in FPD.Results: The results revealed that the maximum principal stress and deformation are found at the centre of the pontic. Furthermore, it was found that for all masticatory loads, the maximum stress and deformation were encountered in Feldspathic ceramic and least for Zirconia.Conclusion: A less complex model using the monoblock concept was developed to design and analyze FPD, so that the meshing complexities, computational time and cost can be reduced drastically. The results could well be considered as a benchmark in FPD-related studies.

A fatigue lifetime assessment of WEST ITER Like Plasma Facing Unit

Based on a monoblock concept (e.g. a tube-in-tile concept), each elementary tungsten plasma facing component (called Plasma-Facing Unit PFU) of the WEST lower divertor follows as closely as possible the same monoblock geometry, materials and bonding technology that is envisaged for ITER. A fatigue simulation of W PFU was used to validate its specific integration into WEST. The complex design, the material heterogeneities and the usage outside operational load design envelope are all possible causes of fatigue failure. This paper shows how the ITER like monoblocks and its U-shaped attachments technology are integrated into the WEST divertor by performing finite element analysis. The WEST lower divertor is designed to withstand 15MW steady-state of injected power, with peaked heat fluxes up to 20MW/m2. The integration and the design choices of a WEST ITER Like Plasma Facing Unit inside the WEST vacuum chamber is valid for an “expected life time” of repeated inter ELMs thermal steady state (>10s) cycles and for 300 off-normal vertical displacement events.

Fractured tooth rebonding: A ultra-conservative approach

Majority of the traumatic dental injuries involves the anterior teeth specially the maxillary incisors. Rebonding of the fractured fragment to the tooth retrieved in a fairly intact condition provides an ultra-conservative treatment option. Rebonding techniques provide good esthetics, restores immediate function and provides positive psychological support to the patient. With the introduction of resin based material and the mono block concept, rebonding is a feasible treatment procedure. These case reports discuss the techniques for rebonding fractured fragment to the tooth in a very conservative and cost-effective manner.Clinical Relevance to Interdisciplinary DentistryManagement of traumatic injuries requires a multidisciplinary approach.Fractured fragment rebonding where the fracture line violates the biological width will require periodontal procedures such as osteotomy, crown lengthening and gingivectomy to be carried out.With the advancement in materials and techniques fractured fragment rebonding offers a viable restorative option for the clinician which restores immediate esthetics using an ultra-conservative approach.

Thermal fatigue characterization of CFC divertor modules using a one step brazing process

From the European side, three directional carbon fiber composites (CFCs) are foreseen to be used as plasma facing material for the strike point region of the initial ITER divertor installed for the non-tritium operational phase. For such divertor components two designs, the flat tile and the monoblock concept, are feasible, comprising a joint of the CFC with a Cu/Cu-alloy heat sink.This paper deals with the qualification of a reliable and cheap joining technology for such components, i.e. the simultaneous joining of the CuCrZr heat sink to a compliant Cu layer for the accommodation of thermal stresses and of the Cu layer and the CFC using a non-active Cu–Ge brazing material. For this purpose flat tile and monoblock mock-ups were manufactured, microstructurally analyzed, and subsequently exposed to cyclic high heat flux tests in the electron beam facility JUDITH. Applying hundreds of cycles at up to 20MW/m2 the tested mock-ups underwent partial damaging, which was characterized in post-mortem microstructural investigations to analyze occurring degradation mechanisms, e.g. partial delamination at the CFC/Cu-interface.

Restoration of endodontically treated teeth: The monoblock concept

Restoration of endodontically treated teeth: The monoblock concept

Microleakage of various root filling systems by glucose filtration analysis

The aim of this study was to evaluate the microleakage of Resilon + Epiphany, EndoRez, Activ GP, and conventional AH Plus + gutta-percha technique using the glucose filtration model. One hundred twenty maxillary incisors were divided into 5 experimental and 2 control groups. After root canal shaping, the experimental groups were filled with AH Plus + gutta-percha (lateral compaction), Resilon + Epiphany (lateral compaction), AH Plus + Protaper's proprietory cone, EndoRez + sealer, or Activ GP + sealer). The specimens were mounted on a glucose model and samples were taken for 3 weeks for leakage measurement. No statistically significant difference was observed between the leakage of all groups at the 3 testing periods (P > .05). The filling materials with the monoblock concept do not seem to be superior to the conventional AH Plus + gutta-percha system regarding microleakage.

The Recent Progress of FGM on Nuclear Materials - Design and Fabrication of W/Cu Functionally Graded Material High Heat Flux Components for Fusion Reactor

Two kinds of W/Cu functionally graded material based high heat flux components, including monoblock concept and flat tile concept, are designed and fabricated. Thermally induced stresses and strains under operation conditions in these components are analyzed using finite element analysis. The effect on stress and strain of using different graded structures to join Cu to W is examined and compared. There has no obvious difference on operation thermal stress mitigating between monoblock design and flat tile design. The component with monoblock concept was fabricated by a one step fast resistance sintering, and the component with flat tile concept was fabricated by infiltration-welding method successfully.

CFC/Cu bond damage in actively cooled plasma facing components

Carbon fibre composite (CFC) armours have been successfully used for actively cooled plasma facing components (PFCs) of the Tore Supra (TS) tokamak. They were also selected for the divertor of the stellarator W7-X under construction and for the vertical target of the ITER divertor. In TS and W7-X a flat tile design for heat fluxes of 10 MW m−2 has been chosen. To predict the lifetime of such PFCs, it is necessary to analyse the damage mechanisms and to model the damage propagation when the component is exposed to thermal cycling loads. Work has been performed to identify a constitutive law for the CFC and parameters to model crack propagation from the edge singularity. The aim is to predict damage rates and to propose geometric or material improvements to increase the strength and the lifetime of the interfacial bond. For ITER a tube-in-tile concept (monoblock), designed to sustain heat fluxes up to 20 MW m−2, has been developed. The optimization of the CFC/Cu bond, proposed for flat tiles, could be adopted for the monoblock concept.

High heat flux actively cooled plasma facing components development, realisation and first results in Tore Supra

The development, design, manufacture and testing of actively cooled high heat flux (HHF) plasma facing components (PFCs) has been an essential part of the Tore Supra programme towards long powerful tokamak operation. The Tore Supra PFC programme has culminated in the installation and operation of a toroidal pump limiter, since 2002, which already allowed to reach new world records in steady state operation (1 GJ injected in a 6 min discharge). The HHF PFCs development and manufacturing was achieved through a long lead development and industrialisation programme (about 10 years) marked out with a number of challenges. The major technical topics cope with bonding technology analysis involving an adequate material selection and procurement, repair processes development and implementation, development of destructive and non-destructive testing methods, and more generally industrialisation assessment. All these lessons are relevant to the ITER divertor PFCs manufacturing, although the technical solution adopted for Tore Supra (flat tiles concept) is different from the one proposed for the ITER divertor (monoblock concept). The routine operation of the actively cooled toroidal pumped limiter (TPL), capable to sustain up to 10 MW m −2 of nominal convected heat flux, is described. Up to now, the limiter fulfills its objectives in terms of heat exhaust. However, the thermographic monitoring exhibits unexpected behavior of the surface temperature. Particle exhaust control displays a complex pattern, due to the high fraction of the injected deuterium, which remains in the wall. The first experimental results with a full actively cooled wall gives access to ITER relevant information on wall conditioning, hydrogen plasma density and vacuum vessel inventory control, carbon erosion and redeposition and capability of in situ monitoring in a completely actively cooled environment.

Manufacturing of small scale W monoblock mockups by hot radial pressing

In the frame of the European Technology R&D programme for International thermonuclear experimental reactor (ITER) and in the area of high heat flux plasma facing components (HHFC), representative small-scale mock-ups were manufactured and tested to compare different concepts and joining technologies (i.e. active brazing, hot isostatic pressing (HIPping), diffusion bonding, etc.). On the basis of the results obtained by thermal fatigue tests, the monoblock concept resulted to be the most robust one, particularly when the HIPping manufacturing technology is used. Within this programme, ENEA developed an alternative technique for manufacturing plasma-facing components with a monoblock geometry of the ITER machine. The basic idea of this technique, named hot radial pressing (HRP), is to perform a radial diffusion bonding between the cooling tube and the armour tile by pressurising the internal tube only and by keeping the process parameters within the range in which the thermo-mechanical properties of the copper alloys are not yet degraded. The HRP is performed by a standard furnace, in which only a section of the canister is heated. The manufacturing procedure and the results of the screening and fatigue thermal tests performed on the ENEA mock-ups are reported in this paper.

Manufacturing and testing of monoblock tungsten small-scale mock-ups

In the frame of the European Technology R&D program for ITER, and in the area of High Heat Flux plasma facing Components (HHFC), representative small-scale mock-ups were manufactured and tested to compare different concepts and joining technologies (i.e. active brazing, Hot Isostatic Pressing (HIPping), diffusion bonding, etc.). On the basis of the results obtained by thermal fatigue tests, the monoblock concept resulted to be the most promising one, particularly when the HIPping manufacturing technology is used. Within this program, ENEA manufactured tungsten monoblock mock-ups by using the HIPping technology. The mock-ups were tested with respect to thermal fatigue and, upon screening tests, the best performance obtained was 15 MW/m 2 for 200 cycles. One of these mock-ups was enclosed in the ‘Paride’ neutron irradiation campaign. This campaign has the scope of enlarging the available database on the performance degradation of prototypical basic solutions of the ITER plasma facing components due to neutron irradiation. The manufacturing procedure and the results of the screening and fatigue thermal tests performed on the ENEA mock-ups are reported in this paper.

Fabrication of monoblock high heat flux components for ITER divertor upper vertical target using hot isostatic pressing diffusion welding

The monoblock concept is one of the most promising design concepts for high heat flux (HHF) components to be used in international thermonuclear reactor (ITER) divertor area. The fabrication of monoblocks is difficult due to the thermal expansion mismatch between copper alloy and tungsten. To overcome this problem, a Cu-OFHC compliant layer is used. A hot isostatic pressing diffusion welding (HIP-DW) technique is proposed. Diffusion welding experiments using flat samples were performed to determine suitable metallurgical conditions and HIP parameters for diffusion welding of W to Cu and Cu to CuCrZr alloy. A thin nickel interlayer providing metallurgical compatibility between W and Cu was tested. Diffusion welding of Cu to CuCrZr is limited by the Cu alloy ageing temperature, however a HIP diffusion brazing (HIP-DB) technique was successfully tested. Simultaneously, finite element modelling was used to improve the joint design: it was shown that the use of chamfered tiles allows reducing the high stress concentration on cooling.

Thermo-mechanical tests of a CFC divertor mock-up

Thermo-mechanical tests have been performed on a divertor mock-up consisting of a metallic tube armoured with five carbon fibre composite tiles. The tube is inserted inside the tiles and brazed with TiCuSil braze (monoblock concept). The tube material is TZM, a molybdenum alloy, and the armour material is SEP CARB N112, a high conductivity carbon-carbon composite. Using special surface preparation consisting of laser drilling, small (∼- 500 μm) holes in the composite have been made to increase the surface wetted by the braze and the resistance. The mock-up has been tested at the JAERI 400 kW electron beam test facility JEBIS. The aim of the test was to assess the performance of the mock-up in screening and thermal fatigue tests with particular attention to the behaviour of the armour to heat sink joint.

The time lag in diffusion IV.

Liquid metal (LM) divertors are considered for the European DEMO reactor, because they may offer improved performance compared to the tungsten monoblock concept. The goal of this work is to provide a concept design, and explore the limitations of liquid metal divertors. To this end, a set of design requirements was formulated in close collaboration with the EUROfusion Power Plant Physics and Technology team (responsible for the design of the EU-DEMO). Tin was chosen as the preferred liquid metal, because unacceptable Tritium retention issues arise when lithium is used in DEMO. A concept design was then chosen that consists of water cooled pipes that are square on the outside and round on the inside, a corrosion barrier, and a 3D-printed porous tungsten armor layer filled with liquid tin. The porous armor layer acts as a Capillary Porous System (CPS). The design was analyzed using thermo-mechanical FEM simulations for various armor thicknesses and heat sink materials: Densimet, W/Cu composites, and CuCrZr. The highest heat loading capability achieved is 26.5 MW/m2 in steady state (18.9 MW/m2 when taking into account a safety margin of 1.4). This is achieved using a CuCrZr pipe, with a 1.9 mm thick armor. When increasing the armor layer to 3 mm thick, more than 80 MW/m2 can be withstood during slow transients thanks to vapor shielding, but at the same time the steady-state capability is reduced to 18 MW/m2. Resilience against disruptions cannot yet be proven, but is deemed within the realm of possibility based on estimates regarding the behavior of vapor shielding. This should be further investigated. Overall, the concept is considered a significant improvement compared to the original specifications (which are also the specifications to the tungsten monoblocks: 10 MW/m2 in steady state, and ∼20 MW/m2 during slow transients). Moreover, the possibility of withstanding disruptions is regarded as a potentially major improvement.