Solid Breeder Test Blanket Module Research Articles

Measurements of the effective thermal conductivity of a non-compressed Li4SiO4 pebble bed

Li4SiO4 is a tritium breeder material for helium cooled solid breeder blanket concept. The thermal properties of ceramic pebble beds provide important support for designing the solid breeder test blanket module (TBM). A new apparatus was developed to measure the effective thermal conductivity of a packed ceramic pebble bed by steady state method. Accordingly, the effective thermal conductivity of a non-compressed Li4SiO4 pebble bed at temperatures ranging from 300°C to 640°C was measured as well in this study. The packing factor was about 59.7% for the single size pebble bed and helium at atmospheric pressure was used as a filling gas. The experimental results show that the effective thermal conductivity increased with increasing the average bed temperature.

Characterisation and radiolysis of modified lithium orthosilicate pebbles with noble metal impurities

Modified lithium orthosilicate (Li4SiO4) pebbles with additions of titanium dioxide (TiO2) are suggested as an alternative tritium breeding ceramic for the European solid breeder test blanket module. The noble metals – platinum (Pt), gold (Au) and rhodium (Rh), can be introduced into the modified Li4SiO4 pebbles during the melt-based process, due to the corrosion of Pt-Rh and Pt-Au alloy crucible components. In this study, the surface microstructure, chemical and phase composition of the modified Li4SiO4 pebbles with different contents of the noble metals was analysed. The influence of the noble metals on the radiolysis was evaluated after irradiation with accelerated electrons (E=5MeV), up to 12MGy absorbed dose at 300–345K in a dry argon atmosphere. Using electron spin resonance (ESR) spectroscopy, it was determined that the noble metals (up to 300ppm) do not significantly influence the formation and accumulation of radiation-induced defects (RD) in the modified Li4SiO4 pebbles.

Neutronics and thermo-hydraulic design of supercritical-water cooled solid breeder TBM

In this paper, the supercritical-water cooled solid breeder test blanket module (SWCB TBM), using the supercritical water as the coolant, Li4SiO4 lithium ceramic pebbles as a breeder, and beryllium pebbles as a neutron multiplier, was designed and analyzed for ITER.The results of neutronics, thermo-hydraulic and thermo-mechanical analysis are presented for the SWCB TBM. Neutronics calculations show that the proposed TBM has high tritium breeding ratio and power density. The tritium breeding ratio (TBR) of the proposed design is 1.17, which is greater than that of 1.15 required for tritium self-sufficiency. The thermo-hydraulic calculation proved that the TBM components can be effectively cooled to the allowable temperature with the temperature of outlet reaching 500°C. According to thermo-mechanics calculation results, the first wall with the width of 17mm is safe and the deformation of first wall is far below the limited value. All the results showed that the current TBM design was reasonable under the ITER normal condition.

Flow Distribution Analysis of Water-Cooled Solid Breeder Test Blanket Module

Blanket system is one of the most important systems in a fusion reactor, which plays an important role in heat removing, radiation shielding and tritium breeding. Water-cooled ceramic breeder (WCCB) blanket module (BM) is one of tritium breeding blanket module concepts for Chinese Fusion Engineering Testing Reactor. According to the preliminary design of WCCB BM, there are complicated cascade and parallel cooling channels, in which maybe exists the nonuniform distribution of flow rate, and resulting adverse effect on heat transfer and safety. In this paper, the whole model of one BM is built by thermal hydraulic analytical code named Relap 5 and the flow distribution issue of water-cooled solid breeder (WCSB) test blanket module (TBM) is analyzed. The systematic analysis results show that the flow rate differences of most parts of the WCSB TBM are less than 4 % in a steady state. Start-up, operational transient and loss of flow accident are also studied, and flow instability in these transient cases is found and needs for further analysis. Three dimensional local model of First Wall is also built by CFX, to investigate flow characteristics at partial WCSB TBM, which shows that flow distribution calculated by CFX is consistent with the results from the thermal hydraulic analytical code. Both of the results of the steady state and transient analysis show that the thermal hydraulic analytical code is appropriate in analyzing the flow distribution and transient issue from the systematic view.

Influence of chemisorption products of carbon dioxide and water vapour on radiolysis of tritium breeder

Lithium orthosilicate pebbles with 2.5wt% excess of silica are the reference tritium breeding material for the European solid breeder test blanket modules. On the surface of the pebbles chemisorption products of carbon dioxide and water vapour (lithium carbonate and hydroxide) may accumulate during the fabrication process. In this study the influence of the chemisorption products on radiolysis of the pebbles was investigated. Using nanosized lithium orthosilicate powders, factors, which can influence the formation and radiolysis of the chemisorption products, were determined and described as well. The formation of radiation-induced defects and radiolysis products was studied with electron spin resonance and the method of chemical scavengers. It was found that the radiolysis of the chemisorption products on the surface of the pebbles can increase the concentration of radiation-induced defects and so could affect the tritium diffusion, retention and the released species.

Fabrication of modified lithium orthosilicate pebbles by addition of titania

Lithium orthosilicate pebbles are one of the ceramic tritium breeder materials destined for the European solid breeder test blanket modules of ITER, the large-scale scientific experiment intended to prove the viability of fusion as an energy source, presently under construction in Cadarache, France. While the current reference material is fabricated by melt-spraying with 2.5wt.% excess of silica, resulting in a two-phase material of lithium orthosilicate and metasilicate, a modified melt-based process was used to fabricate breeder pebbles with additions of titania in order to obtain pebbles with lithium metatitanate as a secondary phase. The fabricated two-phase pebbles exhibit a fine-grained microstructure and increased crush loads. The optimum titanate content has yet to be evaluated, nonetheless the pebbles may have the potential to combine the advantages of both lithium orthosilicate and metatitanate breeder ceramics.

Thermal–hydraulic and safety analysis for Chinese helium-cooled solid breeder TBM cooling system

The thermal–hydraulic behavior and safety performance of the Chinese helium-cooled solid breeder (CH HCSB) test blanket module (TBM) with helium cooling system (HCS) has been studied using RELAP5/Mod3.4 code. According to accident analysis specification for TBM, two design basis accidents including loss of off-site power and TBM first wall (FW) ex-vessel coolant pipe break are investigated. The influences of different break locations and plasma termination behaviors are analyzed comprehensively. The results show that natural circulation is established in helium cooling circuit and the TBM can be cooled effectively after loss of off-site power. It is much more critical when the pipe break occurs at the downstream side of the circulator compared with that of upstream side of the circulator. In case of a more serious accident that the ex-vessel break extends to the TBM FW, the results reveal that TBM could be cooled down by natural circulation and radiation. In addition, at the beginning of ex-vessel loss of coolant accident (LOCA), large temperature difference between break and intact TBM FW pipes is found. The accidental results finally show that the integrity of the FW can be guaranteed if the plasma is terminated with a 3s delay time by fusion power shutdown system (FPSS) in the case of ex-vessel LOCA.

Fabrication of Li4SiO4 Pebbles Using Slurry Droplet Wetting Method for Solid Breeding Material

Lithium orthosilicate (Li4SiO4) pebbles are the primary candidate breeder for the Korean Helium-Cooled Solid Breeder test blanket module because of their superior overall performance qualities such as reasonable lithium atom density, favorable tritium release behavior, low activation property, and chemical stability. The aim of this study is to develop a fabrication method for Li4SiO4 pebbles with high sphericity and stable micro-crystalline structure. Li4SiO4 slurry was prepared by mixing Li4SiO4 powder and polyvinyl alcohol (PVA) solution. The Li4SiO4 gel-spheres were made by dropping slurry mixture into hydrogen peroxide (H2O2) solution. The gel-spheres were floated up to the surface of the H2O2 solution after staying at the bottom for a while and then aged on the surface of the H2O2 solution. The gel-spheres were dried at room temperature and sintered at several temperatures for 4 hours in air atmosphere. The sintered pebbles kept the shape of spheres during the sintering process in spite of shrinkage. Furthermore, the pebbles had relatively high sphericity. Also, the effects of PVA content and sintering temperature on the properties of the Li4SiO4 pebbles were investigated.

Improvement of hydrogen isotope exchange reactions on Li4SiO4 ceramic pebble by catalytic metals

Abstract Li4SiO4 ceramic pebble is considered as a candidate tritium breeding material of Chinese Helium Cooled Solid Breeder Test Blanket Module (CH HCSB TBM) for the International Thermonuclear Experimental Reactor (ITER). In this paper, Li4SiO4 ceramic pebbles deposited with catalytic metals, including Pt, Pd, Ru and Ir, were prepared by wet impregnation method. The metal particles on Li4SiO4 pebble exhibit a good promotion of hydrogen isotope exchange reactions in H2–D2O gas system, with conversion equilibrium temperature reduction of 200–300 °C. The out-of-pile tritium release experiments were performed using 1.0 wt% Pt/Li4SiO4 and Li4SiO4 pebbles irradiated in a thermal neutron reactor. The thermal desorption spectroscopy shows that Pt was effective to increase the tritium release rate at lower temperatures, and the ratio of tritium molecule (HT) to tritiated water (HTO) of 1.0 wt% Pt/Li4SiO4 was much more than that of Li4SiO4, which released mainly as HTO. Thus, catalytic metals deposited on Li4SiO4 pebble may help to accelerate the recovery of bred tritium particularly in low temperature region, and increase the tritium molecule form released from the tritium breeding materials.

Experimental investigation on cryogenic hydrogen adsorption of molecular sieves

Tritium extraction system (TES) is one of the most important components in the helium cooled solid breeder test blanket modules (TBMs) of ITER. TES will extract various isotopic species of hydrogen by the liquid nitrogen cooled molecular sieve adsorber beds (MSB). The cryogenic hydrogen adsorption properties of several kinds of molecular sieves have been investigated at the pressure of hydrogen of 100Pa, 200Pa, and 0.2MPa in order to offer the suitable molecular sieve for the MSB in TES. The saturated hydrogen adsorption capacities of the MS5A-2 and MS13X-2 have been measured at 100Pa hydrogen pressure. To demonstrate the hydrogen extraction from continuous He–H2 purge gases, the MS5A-2 has been tested in circulating 99.79% He–0.21% H2 mixture with a flow rate of 16.8L/min. The results show that the globular MS5A-2 with a diameter of 3–5mm can adsorb/desorb hydrogen quickly. The saturated hydrogen adsorption capacity of MS5A-2 is 7.55mlg−1 (NTP) and MS5A-2 could effectively extract trace hydrogen from mixture gases. As a result, this type of molecular sieve can be the candidate of the one in the MSB in ITER TBM.

Sensitivity of the homogenized model in the neutronics analysis for the Korea Helium Cooled Solid Breeder Test Blanket Module

Abstract The Korea Helium Cooled Solid Breeder Test Blanket Module (Korea HCSB TBM) uses a pebble material in the tritium breeder, neutron multiplier and neutron reflector. A simplified multi-layer model homogenized in the pebble regions is used in the neutronics analysis to increase the efficiency of modeling calculations. Modeling results show that the homogenized model underestimated the TBR by approximately 2% compared to more traditional model. Differences in total mass and packing fractions are the major factors affecting this underestimate. Future uses of the homogenized model should take these factors into account.

R&D progress of Korean HCSB TBM

Several R&Ds are being performed for Korean helium cooled solid breeder (HCSB) test blanket module (TBM) in the field of hydrogen isotopes permeation characteristics measurement in the helium purge line, joining technologies of structural materials, breeder pebble materials development, and the measurement of pebble bed characteristics. Electron beam welding for reduced activated ferritic–martensitic (RAFM) steel is evaluated to find optimal welding conditions. Also, a hydrogen permeation measurement apparatus is newly installed for the evaluation of the permeation barrier characteristics of stainless steel and RAFM steels. Two fabrication methods of lithium orthosilicate pebbles are investigated using slurry droplet methods. As methods of silicon carbide coating on the graphite pebble, microwave coating and chemical vapor deposition coating are evaluated. Two apparatuses are established to assess the thermo-mechanical properties of graphite and breeder pebble beds. The current status of R&D activities on these areas is introduced and the main progresses are addressed in this paper.

R&D status of key technologies for the development of KO TBM

R&D activities currently being undertaken for Korean Helium Cooled Solid Breeder (HCSB) Test Blanket Module (TBM) include joining technologies of structural materials, breeder pebble material development, and measurement of pebble bed characteristics. The joining performance of ferritic–martensitic steel is evaluated. TIG welding for ferritic–martensitic steel is evaluated to find welding conditions with two different current modes. The fabrication methods of lithium silicate powder and lithium titanate pebble are under development using special process. The Li 2TiO 3 pebbles showing an average diameter of 1.8 mm was fabricated by water-based sol–gel method. The Li 4SiO 4 powder with the particle size of about 200 nm was synthesized by PVA polymer solution method. The method of silicon carbide coating on the graphite pebble is investigated, and its possibility is verified based on the coating results on the graphite plate. Sputtered SiC coating layer was crystallized by high temperature heat treatment. The measurement method and database of the thermal properties of the pebble and pebble bed are important for the design of TBM as well as breeding blanket. The initial characteristics of the pebbles are assessed measuring the effective thermal diffusivity of graphite pebble by laser flash method.

Thermo-hydraulic analysis on Korean helium cooled solid breeder TBM with updated back manifolds design

Thermo-hydraulic design of test blanket module (TBM) is challenging in that each component of TBM should be properly controlled within narrow temperature margins in the extreme conditions such as high heat flux from plasma and volumetric heat generation due to neutron irradiation. This paper presents thermo-hydraulic analysis results on the Korean helium cooled solid breeder (HCSB) TBM with the updated design. In the previous study, computation was performed on the TBM model with assumption that the coolant is uniformly distributed at back manifolds, without including the back manifolds in the computational model. In the present study, the updated configuration of the back manifolds is introduced. Flow distribution in each manifold is investigated as well as flow characteristics. Then, thermo-hydraulic analysis on the TBM model is carried out with flow distributions calculated from the flow analysis results on the back manifolds. It is found that the current manifolds are reasonably designed so that the TBM components are effectively cooled against associated thermal loads.

TIG and HIP joining of Reduced Activation Ferrite/Martensitic steel for the Korean ITER–TBM

Korea is developing a Helium Cooled Solid Breeder Test Blanket Module for ITER. The primary candidate structural material is a Reduced Activation Ferritic/Martensitic steel. The complex TBM structure requires developing joining technologies for successful fabrication. The characteristics of Tungsten Inert Gas welding and Hot Isostatic Pressing joining of RAFM steel were investigated. Metallurgical examinations showed that the steel grain size was increased after HIP joining and recovered by post joining heat treatment. Both TIG welding and HIP joining are found to be acceptable for ITER TBM based on mechanical tests and microstructure examination.

Overview of Fusion Nuclear Technology Activities at SWIP

The fusion nuclear technology (FNT) activities at SWIP are overviewed, which are including the design and R&D of the helium-cooled solid breeder test blanket module (TBM), development of Liquid metal blanket technology, structure and function materials research for ITER shielding and test blanket, ITER shielding blanket material development and the joining technologies and the R&D for ITER gravity support.

Non-axisymmetric magnetic field due to ferromagnetic inserts and helium cooled solid breeder test blanket modules in ITER

An analysis is carried out on the three-dimensional modeling and computation of the magnetic field in ITER. The commercial finite element code ANSYS-EM is employed for this study. In particular, an emphasis is put on the analysis of the characteristics of non-axisymmetric magnetic fields produced by ferromagnetic materials, including ferromagnetic inserts (FIs) and helium cooled solid breeder test blanket modules (TBMs). It is found that the ITER design requirement for toroidal field ripple is violated by the presence of TBMs, even in the presence of FIs. Calculations of TBM-produced error fields also show that TBM produces a significant error field at q = 2 surface exceeding the ITER design requirement. Discussions are made of the potential implication of the TBM-produced non-axisymmetric fields on plasma performance and the design of a TBM emulation system.

Global depletion analysis of Korean helium cooled solid breeder TBM model for demo fusion reactor

The Korean HCSB (helium cooled solid breeder) TBM (test blanket module) is proposed with its specific compositions of lithium ceramic, beryllium and graphite in pebble form. In the Korean HCSB TBM, the amount of beryllium is reduced and the reduction is replaced by graphite for a neutron reflector, while tritium breeding ratio (TBR) remains almost unchanged with relatively low Li 6 enrichment of ∼40%. However, the previous Korean HCSB was designed based on the LOCAL assumption, in which the surroundings are assumed by the reflective boundary condition. In this research, we establish a simple GLOBAL neutronics model based on demo fusion reactor and perform neutronics analyses including depletion (transmutation) calculation during 100 EFPDs (effective full power days) using the modified MONTEBURNS code.

Conceptual design on interface between ITER and tritium extraction system of Chinese helium-cooled solid breeder test blanket module

Tritium extraction system is essential for CN HCSB TBM for safety and technical reasons. Based on the assessments of system functions, integration issues and safety considerations, two main modifications of the system from previous design (Feng et al., 2007 [1]; Chen et al., 2008 [2]) are adopted: a) the TES has been split to 2 parts with one in port cell and another in tritium building. Q 2O in the purge gas is reduced to Q 2 in a hot metal bed located in port cell; Q 2 is separated from the stream by a pair of cryogenic molecular sieve beds and a Pd/Ag diffuser located in tritium building. b) isotope separation process has been excluded. TES components sizes are estimated and space allocations are estimated. Required services and where and when they are needed are preliminary defined. Fluids delivered towards ITER tritium system are analyzed.

Preliminary evaluations of electromagnetic impacts between CN HCSB-TBM and ITER

The general design of China Helium-Cooled Solid Breeder Test Blanket Module (CN HCSBTBM) needs to withstand the related electromagnetic loads such as mechanical force and torques during plasma transients in ITER. The preliminary electromagnetic safety analyses for the electromagnetic loads during two plasma disruption scenarios have been performed with ANSYS Finite Element Module (FEM) code. At the same time the ways to reduce the perturbation of the toroidal field (TF) ripple have been valuated by taking fully account of the TBM and the ferromagnetic inserts. The maximum Tresca stress occurs at exponential decay of plasma current and its value is 33.2 MPa, which is within the allowable limits. The TF ripple will be effectively reduced to a desirable scope with the integrated considerations of the design and look for balance among the ferromagnetic inserts, the TBM and ITER frame.