氚增殖剂Li4SiO4 陶瓷小球的制备工艺

欧洲和中国聚变堆固态产氚包层（TBM）的氚增殖剂倾向于采用直径0.5～2mm的Li₄SiO₄陶瓷小球填充床。本工作探讨锂陶瓷小球的性能指标设计,研究挤压-滚圆、烧结法制备Li₄SiO₄小球的工艺可行性,测试分析小球的密度、直径、球形度、晶粒尺寸、压碎载荷等性能。研究表明：挤压-滚圆成型、1050℃无压烧结的Li₄SiO₄陶瓷小球密度为90.4%TD,堆积密度为52.9%TD;平均直径为0.95mm,标准偏差为0.15mm;球形度为1.10;平均压碎载荷为18.50N,标准偏差为2.76N;平均晶粒尺寸为14μm;相结构由Li₄SiO₄主晶相、少量Li₂SiO₃和Li₂Si₂O₅等组成。采用优化的挤压 滚圆、烧结工艺可制备出合格的Li₄SiO₄陶瓷小球产品。     

Li4SiO4陶瓷球的研制

产氚包层是聚变堆的关键系统，其设计与研发是我国参与ITER计划的重要研究领域。氦冷／固态氚增殖剂产氚包层采用锂陶瓷材料，目前，国际上最为关注的是具有较为优异和全面氚增殖特性的LinSiO4和Li2TiO3等。     

产氚锂陶瓷的研究现状

本文概述了几类典型的锂陶瓷粉体制备、成型方法和释氚性能,分析了影响锂陶瓷释氚性能的因素,比较了锂陶瓷的成型方法及国内外锂陶瓷释氚性能研究的差距,提出了国内锂陶瓷发展方向。     

单斜相偏锆酸锂陶瓷氚增殖材料研究

单斜相偏锆酸锂是聚变堆中最有前途的氚增殖材料之一。该材料具有较高的锂原子密度和优异的氚释放行为，成为近年来最受重视的陶瓷氚增殖材料。在Ｌｉ２Ｏ－ＺｒＯ２二元系中，存在九种不同的锆酸锂相，因此制备单一相的锆锂陶瓷十分困难。本文作者以干法制备工艺为基础，从热扩散的角度分析了Ｌｉ２ＺｒＯ３的形成机理，改进了制备工艺，成功地制备出了单斜相Ｌｉ２ＺｒＯ２陶瓷材料粉末样品。     

Li_4SiO_4陶瓷微球的间接湿法制备工艺与表征

以碳酸锂、二氧化硅为原料,用间接湿法工艺制备Li4SiO4(正硅酸锂)陶瓷微球,主要过程为将反应原料混合物的悬浊液经冷冻成型工艺一步成球,再经反应烧结获得Li4SiO4陶瓷微球。通过调节体系固相含量和烧结温度等关键工艺条件,制备出粒径为0.5～1.0mm的Li4SiO4陶瓷微球。Li4SiO4陶瓷微球表面和断面具有丰富的孔道结构,微球的表观密度为85%T.D.(理论密度);Li4SiO4的晶相为α相,相纯达99%,Li含量为21.7%,球形度优于1.04,目标微球的平均抗压强度为45N。     

基于蒙特卡罗方法的固态氚增殖剂聚变中子辐照损伤行为分析

实验包层模块(TBM)是聚变反应堆最重要的组件之一,作用是产氚和能量提取。锂陶瓷具有良好的化学稳定性、热机械性能、产氚性能以及可在更高温度下使用等特点,被认为是聚变堆包层最具吸引力的氚增殖剂材料。中国ITER-TBM设计方案采用了氦冷固态氚增殖剂(HCCB)TBM结构,其聚变环境下的辐照损伤行为可为中国HCCB TBM结构设计提供支持。针对固态氚增殖剂聚变中子辐照损伤问题,利用蒙特卡罗模拟,对比分析了Li_4SiO_4和Li_2TiO_3的中子辐照离位损伤和嬗变气体损伤。结果表明:在相同的服役时间下,Li_4SiO_4比Li_2TiO_3将产生更多的嬗变气体,且在高6 Li丰度情况下,其中子辐照损伤也更严重,会产生更高的损伤剂量和更大的损伤截面。但是,嬗变气体所造成的空位损伤Li_2TiO_3要比Li_4SiO_4严重;对两种陶瓷材料来讲,氦损伤效应均强于氚损伤效应。     

D+注入Li4SiO4的表面化学状态及其热解吸行为

锂陶瓷氚增殖剂的氢同位素行为是聚变堆固态产氚包层关心的重要课题。本文将3 keV D⁺注入Li₄SiO₄,采用X射线光电子能谱在线分析注氘前后材料表面的化学状态,同时采用热解吸谱（TDS）实验技术,研究注氘后Li₄SiO₄中氢同位素的热解吸行为。实验结果表明：D⁺注入会改变Li₄SiO₄表面的化学环境,产生多种辐照缺陷和化学键合状态;氘滞留量和热解行为受注氘时样品的温度影响较大,可在一定程度上预测产氚包层中氚的滞留行为。     

固态陶瓷氚增殖剂释氚实验研究综述

氚自持是氘氚聚变能实现工程应用和稳态运行必须解决的关键问题之一,氚增殖剂是实现氚自持的关键功能材料.锂基陶瓷固有的热稳定性和化学惰性使其在安全性能方面具有独特的优势,被视为非常具有发展前景的氚增殖剂材料.氚增殖剂不仅要求产氚率高,还要将氚尽可能多地从陶瓷增殖剂中释放出来.本文初步梳理了国内外关于固态氚增殖剂主要释氚实验...     

聚变堆液态金属锂铅包层多功能涂层研发

液态金属锂铅包层是目前国际上聚变堆包层设计研究的主要方案之一,结构材料表面制备涂层是降低锂铅包层中的氚渗透率、液态锂铅腐蚀及磁流体动力学(MHD)效应的重要技术之一.本文主要从涂层材料及其制备工艺两个方面重点介绍了国内外在液态锂铅包层涂层材料研发方面的进展概况,并对涂层技术发展进行了展望,最后提出了中国发展液态锂铅包层涂层的规划建议.     

氚在真空贮存容器材料中的吸附和渗透行为

研究了贮存氚靶约4 a和20 a的两个316 L不锈钢真空贮存容器(以下简称贮存容器)及其垫片材料对氚的吸附行为,并对氚在贮存容器材料中的渗透速率进行了测量和分析。结果表明,贮存容器外表面氚污染为几十Bq/cm2,不锈钢与陶瓷中吸附的氚活度均为106Bq/g;热解吸至1 273 K过程中,材料中99%的氚释放出来;在解吸出的氚中,陶瓷中的HTO比例高于不锈钢;贮存温度对氚靶贮存容器的渗氚速率有较大影响,夏季约为冬季的4倍。上述结果提示,氚在贮存容器材料内表面吸附后,一部分会向晶格扩散并滞留下来;另一部分则透过材料向外环境渗透,其中温度是影响氚向外环境渗透的主要因素之一。     

超临界水冷固态实验包层中子学与热工水力特性研究

基于国际热核聚变实验堆(ITER)实验包层方案,提出了一个超临界水冷固态实验包层概念设计方案。设计采用Be作为中子倍增剂,Li4SiO4作为氚增殖剂,CLAM钢作为结构材料。包层第一壁采用多层盘道设计以提高第一壁出口温度,内部采用增殖剂与中子倍增剂分层布置以提高热沉积与氚增殖率。为验证包层设计的可行性,分析计算了三维包层氚增殖率与热沉积的分布,然后根据中子学计算得到的结果对超临界水冷固态实验包层进行了数值模拟研究。结果表明:包层功率密度分布较合理;氚增殖率满足运行中氚自持的要求;在冷却剂出口温度达到500℃条件下材料温度不超过限值。该设计方案能满足中子学设计与热工水力的要求。     

Li4SiO4 pebbles reduction in He + 0.1% H2 purge gas and effects on tritium release properties

Lithium orthosilicate reduction was examined by Temperature Programmed Reaction (TPR) and Temperature Programmed Desorption (TPD) methods performed in He (or Ar) + H₂ purge gas flowing through pebble bed specimens. The parameters governing the kinetics and the steady-state of the reduction process to Li₄SiO_4−x were determined at 800°C. The level x of the O-vacancy concentration at steady-state (of the order of 1.5×10⁻³ mole fraction) was found to be compatible with the impurities content in the specimens. Pebble pre-annealing treatments were found to affect the microstructure and the reduction mechanism. Post-irradiation tritium release by TPD tests were performed on both stoichiometric and reduced pebbles with similar results. Tritium release properties of this breeder system seem to be independent from the material reduction state (x).     

Low-temperature irradiation effects in lithium orthosilicates

The emission spectra of lithium orthosilicates (Li₄SiO₄₎ ceramics have been measured in the range of 1.8–5.8 eV under irradiation by 6–30 eV photons or 1–30 keV electrons at 6–300 K. The tunnel recombination phosphorescence, as well as luminescence, stimulated by 1.5–2.5 eV photons has been detected in the sample preliminarily irradiated at 6 or 80 K. The main peaks of thermally stimulated luminescence (TSL) in the irradiated ceramics have been observed at 72, 118 and 265 K. The creation spectra of the 118 K TSL peak, as well as the excitation spectrum of photostimulated luminescence (PSL) span the region of the intrinsic absorption of a lithium orthosilicate (9–30 eV). The intensity of PSL and the TSL peaks in Li₄SiO₄ ceramics prepared in hydrogen/argon atmosphere is several times lower than that in the mainly investigated Li₄SiO₄ ceramics prepared in the atmosphere of dry argon. The optical characteristics of Li₄SiO₄ are compared with the ones known for Li₂O and SiO₂. Low-temperature luminescent methods are promising for the investigation of electron–hole processes and radiation defects serving as the traps for tritium released in D–T fusion reactor blanket systems.     

Tritium diffusivity in crystal grain of Li2TiO3 and tritium release behavior under several purge gas conditions

It has been reported by the present authors that behavior of tritium release from solid breeder grain is consisted of diffusion in grain, tritium transfer at surface layer and surface reactions on grain surface such as adsorption or isotope exchange reactions. Tritium release curves estimated using the tritium release model gave good agreement with observed tritium release curves from Li₄SiO₄, Li₂ZrO₃ or LiAlO₂.

Tritium release behavior from Li₂TiO₃ under humid purge gas, dry purge gas and dry purge gas with hydrogen conditions is discussed in this study, tritium release curves using the release model that we proposed previously give a good agreements with experimental tritium release curves. Tritium effective diffusivity in the crystal grain of Li₂TiO₃ is also estimated in this study using a curve-fitting method applied to the release curves obtained under the humid purge gas condition. It is discussed that change of color of Li₂TiO₃ surface under hydrogen purge gas condition is observed and this phenomenon might affect tritium release behavior from Li₂TiO₃.     

氚增殖剂球床组件堆内辐照物理热工计算分析

为验证在中国先进研究堆(CARR)内进行国际热核聚变实验堆(ITER)氚增殖包层模块(TBM)辐照实验的可行性和安全性,进行了氚增殖剂球床组件堆内辐照物理及热工计算分析。氚增殖剂包层模块主要是固态氚增殖剂陶瓷球床。本文采用Monte Carlo粒子输运模拟程序对氚增殖剂球床进行堆内建模,计算球床的中子注量率、能量沉积和产额,得到不同功率下球床的中子注量率、发热功率和产氚速率以及球床组件引入反应堆的反应性。根据物理计算得到的组件各部件发热情况建立热工计算一维模型,通过更改反应堆功率得到满足实验要求的工况并采用三维程序进行验证。物理与热工计算分析的结果表明,在反应堆运行功率为20 MW的工况下球床组件各部件的温度均不超过限值。     

Fabrication and characterization of Li4SiO4 pebbles by melt spraying method

The solid breeder blanket concept proposed by the China features the tritium breeding ceramic as pebble beds in several submodules. The lithium orthosilicate (Li₄SiO₄) is considered as first candidate ceramic breeder materials fabricated by the melt spraying method, which is favorable to other processes in terms of density and recycling. The production process involves rapid quenching of the liquid droplets from the melt to room temperature which cause internal stresses and leads in some cases to formation of microcracks and the dispersion of mechanical properties. Molar ratio (Li/Si) of the pebbles was evaluated by ICP–OES. It is shown that the Li/Si ratio of the pebbles is slightly varying from batch to batch because of evaporation of lithium at high temperatures. The crush tests on single pebbles show that a mean value of 7.0 N was obtained in crush load experiments of 40 pebbles with a diameter of 1.0 mm. It results that heat treatment of pebbles improves the density and mechanical stability. The activation characteristics for the current composition of Li₄SiO₄ pebbles were assessed. The calculations were used to identify critical amounts of impurities and were compared to the results of pure material without impurities.     

高氚增殖比包层的设计及热工水力分析

本文设计了一种高氚增殖比包层(HBRB),该包层采用多孔U-10Zr合金作为中子倍增剂,Li4SiO4球床作为增殖剂,低活化马氏体(RAFM)钢作为结构材料。在详细研究包层加工工艺、流量分配、中子性能等问题的基础上,完成了包层内部详细结构设计。利用中子学软件分析计算了包层的氚增殖比(TBR)和热沉积分布,并根据计算结果对包层进行热力耦合分析。结果表明:包层TBR较高,且核性能稳定;冷却剂的流量分配情况和压降合理;包层内各组件冷却充分,温度和结构材料热应力不超过限值。     

Preliminary performance analysis and optimization based on 1D neutronics model for Indian DEMO HCCB blanket

India, under its breeding blanket R&D program for DEMO, is focusing on the development of two tritium breeding blanket concepts; namely the lead-lithium-cooled ceramic breeder and the helium-cooled ceramic breeder (HCCB). The study presented in this paper focuses on the neutronic design analysis and optimization from the tritium breeding perspective of the HCCB blanket. The Indian concept has an edge-on configuration and is one of the variants of the helium-cooled solid breeder blanket concepts proposed by several partner countries in ITER. The Indian HCCB blanket having lithium titanate (Li₂TiO₃) as the tritium breeder and beryllium (Be) as the neutron multiplier with reduced-activation ferritic/martensitic steel structure aims at utilizing the low-energy neutrons at the rear part of the blanket. The aim of the optimization study is to minimize the radial blanket thickness while ensuring tritium self-sufficiency and provide data for further neutronic design and thermal-hydraulic layout of the HCCB blanket. It is found that inboard and outboard blanket thicknesses of 40 cm and 60 cm, respectively, can give a tritium breeding ratio (TBR) >1.3, with 60% ⁶Li enrichment, which is assumed to be sufficient to cover potential tritium losses and associated uncertainties. The results also demonstrated that the Be packing fraction (PF) has a more profound impact on the TBR as compared to 6Li enrichment and the PF of Li₂TiO₃.