聚变堆金属材料中子辐照多尺度计算模拟

中子辐照条件下材料结构与性能是中国聚变工程实验堆(CFETR)以及未来聚变反应堆工程设计的重要依据。钨材料是CFETR拟全面使用的壁材料,但中子辐照导致钨硬度升高和韧性大幅下降,严重影响材料的服役性能,进而影响CFETR运行的安全性和稳定性。在目前缺乏聚变中子源进行辐照实验的情况下,开展聚变堆材料中子辐照模拟研究显得愈发重要和紧迫。在国家磁约束核聚变能发展研究专项的支持下,本文以钨为模型材料,构建金属材料聚变中子辐照模拟平台,解决中子辐照模拟的共性关键技术问题,实现中子级联损伤→辐照微结构→力热性能的多尺度模拟,籍此预测聚变中子辐照条件下材料的行为。     

聚变堆金属材料中子辐照多尺度计算模拟

中子辐照条件下材料结构与性能是中国聚变工程实验堆(CFETR)以及未来聚变反应堆工程设计的重要依据.钨材料是CFETR拟全面使用的壁材料,但中子辐照导致钨硬度升高和韧性大幅下降,严重影响材料的服役性能,进而影响CFETR运行的安全性和稳定性.在目前缺乏聚变中子源进行辐照实验的情况下,开展聚变堆材料中子辐照模拟研究显得愈...     

中国低活化马氏体钢在电子辐照下产生位错环的原位观察

高流强的中子辐照在结构材料内部产生严重的级联离位损伤,使得材料性能下降,而辐照缺陷是聚变堆材料性能下降的根本原因.为了研究结构材料在高辐照剂量下的损伤机理,针对中国低活化马氏体钢(CLAM钢),通过使用高能电子辐照来模拟中子对材料造成的高剂量辐照损伤,并对微观结构进行原位观察.进行了辐照下产生的位错环随辐照剂量的演化过程的观察,并分析了位错环浓度和尺寸随辐照剂量和温度的变化规律.     

国产反应堆压力容器材料辐照效应研究

反应堆压力容器(RPV)材料经受中子辐照后,发生脆化效应导致韧性降低是影响反应堆安全运行的重大因素。为准确评估国产RPV的安全性,采用国产RPV材料在试验堆内加速模拟辐照的试验方法,研究国产RPV材料的辐照脆化性能。结果表明,国产RPV材料在寿期运行工况下,存在一定程度的辐照强化效应和辐照脆化效应。     

中国抗中子辐照钢的抗辐照设计与验证

聚变堆等未来先进核能系统要求材料在强流高能中子辐照下长期保持良好的结构稳定性和机械性能。为适应未来先进核能技术发展的需要,中国科学院核能安全技术研究所·凤麟团队牵头研发了具有我国自主知识产权的中国抗中子辐照钢——CLAM钢。CLAM钢的设计考虑了未来核能清洁性的要求,以及苛刻服役环境中材料抗辐照、耐高温、耐腐蚀等性能要求。通过中子学计算分析设计了低活化成分范围,基于选择性纳米相析出进行了抗辐照、耐高温性能优化设计。针对材料的抗辐照性能,利用国内外中子、离子、电子及等离子体辐照设施开展了系列辐照考验研究,通过多角度表征辐照前后材料的微观结构和宏观性能,综合评估了材料的辐照性能,并与国际上同类材料在相近或相同条件下的辐照性能进行了对比分析,结果表明CLAM钢具有良好的抗辐照性能。     

中国抗中子辐照钢的抗辐照设计与验证

聚变堆等未来先进核能系统要求材料在强流高能中子辐照下长期保持良好的结构稳定性和机械性能。为适应未来先进核能技术发展的需要,中国科学院核能安全技术研究所•凤麟团队牵头研发了具有我国自主知识产权的中国抗中子辐照钢--CLAM钢。CLAM钢的设计考虑了未来核能清洁性的要求,以及苛刻服役环境中材料抗辐照、耐高温、耐腐蚀等性能要求。通过中子学计算分析设计了低活化成分范围,基于选择性纳米相析出进行了抗辐照、耐高温性能优化设计。针对材料的抗辐照性能,利用国内外中子、离子、电子及等离子体辐照设施开展了系列辐照考验研究,通过多角度表征辐照前后材料的微观结构和宏观性能,综合评估了材料的辐照性能,并与国际上同类材料在相近或相同条件下的辐照性能进行了对比分析,结果表明CLAM钢具有良好的抗辐照性能。     

采用高能重离子辐照研究铁素体/马氏体钢脆化效应

正铁素体/马氏体钢作为快堆组件的候选结构材料,辐照脆化是降低其堆内应用性能的关键问题,采用离子模拟辐照方法可大幅降低材料研究成本。对应于快堆服役环境的要求,采用高能重离子模拟辐照结合小冲杆测试技术对一种9Cr铁素体/马氏体钢的抗辐照性能进行了评价。     

600℃下氦离子辐照316L不锈钢氦泡形成的研究

在聚变堆与快堆中，高能中子通过（ｎα）反应在结构材料中产生大量的氦。氦聚集形成氦泡，引起材料各种性能的下降；特别是高温下氦流到晶界形成氦泡，使材料发生脆性断裂。对材料中氦泡的形核及长大规律的研究是研究材料中氦脆的基本机制及堆辐照环境中材料微观结构变化...     

基于CAD的内耦合严格两步法停堆剂量率计算方法研究

核装置尤其是聚变装置中结构材料的辐照活化问题,对核装置的辐射安全具有重要影响。停堆剂量率是材料辐照活化计算中的重要参数,也是聚变堆设计的重要参考依据。本文基于超级蒙卡核模拟软件系统SuperMC的中子/光子输运计算功能和中子活化计算功能,开展了严格两步法停堆剂量率计算方法研究。与传统的输运-活化程序外耦合方法相比,本文发展了一种基于CAD的内耦合严格两步法停堆剂量率计算方法,直接基于CAD模型进行网格材料映射,并支持扇形圆柱源抽样,在提高易用性和灵活性的同时,消除了传统方法在圆柱坐标系活化区计算的不足和处理复杂几何时的局限性。最后利用国际热核聚变实验堆ITER发布的停堆剂量率计算基准例题进行了校核计算,计算结果表明了该方法的正确性和可靠性。     

铝基碳化硼材料堆内辐照方案设计

铝基碳化硼是一种新型的乏燃料贮存格架用材料,为检验其辐照性能,需进行堆内辐照实验。本文从样品成分及形状、辐照罐结构、辐照位置等方面,对铝基碳化硼材料堆内辐照方案进行设计。经初步中子物理学和热工计算表明：在所选择的两个辐照孔道内进行辐照考验,试件所接受的累积γ射线照射剂量和相应的快中子积分注量均满足技术要求,且辐照罐样品入堆后对功率峰值因子、反应性、发热率等与堆运行安全相关因子的影响均在安全范围内。     

Radiation facilities for fusion reactor first wall and blanket structural materials development

Present and future irradiation facilities for the study of fusion reactor irradiation damage are reviewed. Present studies are centered on irradiation in accelerator-based neutron sources, fast- and mixed-spectrum fission reactors, and ion accelerators. The accelerator-based neutron sources are used to demonstrate damage equivalence between high-energy neutrons and fission reactor neutrons. Once equivalence is demonstrated, the large volume of test space available in fission reactors can be used to study displacement damage, and in some instances, the effects of high-helium concentrations and the interaction of displacement damage and helium on properties. Ion bombardment can be used to study the mechanisms of damage evolution and the interaction of displacement damage and helium. These techniques are reviewed, and typical results obtained from such studies are examined. Finally, future techniques and facilities for developing damage levels that more closely approach those expected in an operating fusion reactor are discussed.     

The collapse of defect cascades to dislocation loops

We describe a number of experiments that we have recently performed to investigate the collapse of defect cascades to dislocation loops. This important ion and neutron irradiation phenomenon has been studied with in situ ion bombardment using the High Voltage Electron Microscope-Ion Accelerator Facility at Argonne National Laboratory in Cu₃Au, Cu, and Fe at temperatures of 30 and 300 K and in Ni at 30, 300 and 600 K. These experiments have demonstrated that individual defect cascades collapse to dislocation loops athermally at 30 K in some materials (Ni, Cu and Cu₃Au), while in Fe overlapping of cascades is necessary to produce dislocation loops. A slight sensitivity to the irradiation temperature is demonstrated in Cu₃Au and Fe, and a strong dependence on the irradiation temperature is seen in Ni. This phenomenon of cascade collapse to dislocation loops in metals at 30 K provides an understanding for previous neutron irradiation data. The more detailed dependencies of the collapse probability on material, temperature, bombarding ion dose, ion energy and ion mass contribute much information to a thermal spike model of the collision cascade which we will describe.     

Sputtering from energetic self-ion cascades

The rather high primary recoil energies that occur under 14 MeV neutron irradiation can be simulated by self-ion bombardment. However, the primary ion always starts at theentrance surface when self-ion bombardment is used. To examine the effects of cascades in which the momentum of the primary atom is directed towards an exit surface, one has to introduce a second surface that will intersect the cascade in the forward direction. Self-ion transmission sputtering on very thin films has been used for this purpose. The analysis was done in situ by He⁺ backscattering. A backsputtering yield of 120 atoms/ion was observed at 540 keV. At the same energy a forward sputtering yield of 70 atoms/ion is obtained for a film of 660 Å in thickness. These yields are in order of magnitude agreement with theoretical estimates, however, the results seem to indicate that collective and lattice effects play a significant role. It was observed that a tensile stress is built up in the films during irradiation, leading to flattening and rupturing of the film along preexisting faults.     

Influence of external action and structural factors on radiation blistering

A survey of experimental results is presented, pertaining to radiation blistering of a considerable number of materials (stainless steels, alloys with high nickel content, alloys of refractory metals) under helium ion irradiation with energies of 20–100 keV under conditions corresponding to the plasma-wall interaction: bombardment at various angles of incidence and cyclic irradiation in a wide spectrum of ion incidence angles; influence of external action, including thermocycling; influence of preceding neutron and proton irradiation. It has been shown that external factors have a complex influence on blister parameters and erosion coefficients of materials. A study has been carried out on the influence of aluminium coatings, alloying additions, phase state of material and microstructure on the nature and degree of surface erosion. Complex influence of element and phase composition, as well as microstructural changes during heat treatment and welding on radiation erosion have been established.     

离子轰击对氮化铀表面氧化行为的影响

采用离子氮化技术制备得到一定厚度的氮化铀层,以不同能量的氩离子轰击考察氮化铀的辐照氧化行为,并与大气中的自然氧化行为进行对比,考察材料在辐照环境下的稳定性。结果表明,氮化铀表面经氩离子轰击后,表面形貌发生了改变;氩离子轰击氧化与大气中的自然氧化行为存在差异,离子轰击增强了氮化铀表面的氧化程度,但其对氧化行为的影响主要在浅表面,大气氧化的氮化铀氧化层更厚;随着氩离子轰击能量的增加,表面氧化物含量及氧化层深度显著增加。总体而言,氩离子辐照对氮化铀层的影响随深度的增加而减弱,并不影响氮化铀的整体稳定性。     

On the simulation of CTR neutron radiation damage by heavy ion irradiation

The primary recoil spectrum in nobium under 33 MeV self-ion bombardment is calculated and compared with a calculation by Logan et al. of the same spectrum under neutron irradiation in a controlled thermonuclear reactor. The two spectra are similar, which suggests that a close simulation of CTR neutron radiation damage by ion bombardment will be possible. The displacement rate per projectile is found to be $\text{3.7 × 10}{}^5$ times higher for ions than for neutrons, allowing very high neutron fluxes, up to about $\text{10}{}^{18}\text{cm}{}^{\mathrm{?2}}\text{· sec}{}^{\mathrm{?1}}$, to be simulated with existing accelerators.     

The effect of cluster formation on the ‘temperature shift’ for accelerator simulation of neutron irradiation

The effect of the nature of the incident particles on the temperature dependence of irradiation-induced void formation in steel is considered. During neutron irradiation small clusters of vacancies are formed in ‘spikes’. At temperatures below the maximum in the swelling-temperature curve these clusters tend to dissolve slowly and hence provide recombination sites for interstitials as well as vacancies which have escaped from other clusters. Consideration of the dissolution kinetics of these clusters leads to the theoretical prediction of a minimum temperature for void formation (under neutron irradiation) of around 350°C. This result is more consistent with experimental observation than the much lower temperatures predicted by previous theory and hence lends support to the cluster dissolution theory. Due to the nature of the interaction of the high-energy electrons with the lattice, no clusters are formed during HVEM simulation of neutron damage, and cluster dissolution kinetics are therefore not controlling. Clusters are, however, produced in heavy-ion bombardment. Consequently the rate-dependent temperature shifts which are used to compare accelerator void formation data with neutron irradiation are expected to be different for electrons and for heavy ions.     

Continuous observation of surface erosion of polycrystalline molybdenum implanted with helium ions with different energies

Surface erosion of polycrystalline molybdenum caused by helium ion bombardment, with various irradiation modes of different energies ranged from 60 to 200 keV, was studied by continuous observation of the surfaces under helium ion bombardment. The development processes of the surface deformation are presented as a function of irradiation dose and the critical fluence for surface deformation was precisely determined. The critical helium concentrations for blistering were obtained from the calculated profiles of implated helium at the critical fluence and it was found that the critical concentrations for both 100 and 200 keV single implantation were almost the same, whereas the critical concentrations for sequential irradiation were distributed around that for a single implantation. In addition, it was observed that the average thickness of the exfoliated layer lay nearly at the peak in the depth profile.     

Electrical and optical surface degradation of silica due to superficial He implantation

Different oxides will be used in ITER and future fusion reactors for electrical insulation and optical components. The vacuum face of these materials will be subjected not only to neutron and gamma irradiation, but also to particle bombardment, due mainly to ionization of the residual gas and acceleration of the resulting ions by local electric fields. Previous work showed that silica suffers electrical and optical degradation when subjected to He bombardment with energies from 300 keV down to 27 keV. As the He ion energy may extend down to some few keV, or less, further work has been performed to study possible degradation for energies from 21 keV down to 5 keV. The results show that both surface and optical degradation occur at these low energies, more rapidly for the lowest energy (5 keV) ions. They also suggest that the superficial narrow implanted He profile plays an important role in the surface degradation.