氦气杂质对中间换热器材料的影响初探

中间换热器是高温气冷堆氦气透平间接循环和高温工艺热应用的关键部件.中间换热器属于一回路压力边界,它将堆芯出口温度达900～1 000 ℃氦气的热量传递给二回路氦气,此外还承受一、二回路氦气压差,因此,目前能够用于中间换热器的耐热金属材料非常有限.高温气冷堆一、二回路氦气中含有H_2、H_2O、CO、CH_4等杂质,在高温下,氦气杂质对中间换热器材料的影响主要是氧化、碳化和脱碳,降低材料的机械性能,其影响不可忽视.对于中间换热器设计,现有规范的温度范围需扩展,氦气杂质对材料强度的影响也需考虑.     

Formation of Gas Pores in Nickel Alloys and Structural Steel under Irradiation by Helium Ions

Transmission electron microscopy is used to study the development of helium porosity in binary alloys of nickel with elements possessing a different dimensional atomic mismatch with nickel – from negative (beryllium and silicon) to positive (molybdenum, tungsten, aluminum, titanium, tantalum, tin, and zirconium), in structural steels ChS-68, ÉP-150, and the nickel alloy KhNM. The gas pores were produced by irradiation with 40 keV He⁺ up to fluence 5·10²⁰ m^–2 at 650 and 20°C followed by annealing at 650°C for 1 h. It is shown that under high-temperature annealing beryllium and silicon, relative to nickel, give rise to the formation of larger bubbles, while elements with a larger positive size mismatch with nickel atoms substantially decrease the size and increase the density of the bubbles. On the whole, as atomic radius and the concentration of the alloying element increases in alloys, the gas swelling of the irradiated layer decreases. Under post-irradiation annealing, bubbles with the largest diameter and the lowest density develop in nickel. Any alloying used decreases the size and increases the density of bubbles. The data obtained are discussed from the standpoint of the formation of various vacancy complexes of helium and their thermal stability.     

Impact of Material Configuration Behind First Wall on Helium Formation in In-Vessel Components of Fusion Reactor

The results of neutron transport calculations of the He formation based on the JENDL gas-production cross section file are discussed for some metals and alloys, namely ²⁷A1, Ti, ⁵¹V, Cr, ⁵⁵Mn, Fe, Ni, Zr, Mo, austenitic stainless steel (Ti modified 316 SS: PCA), Ni-base alloy (Inconel 625), ferritic steel (Fe-11Cr-1Mo: HT-9), Ti-base alloy (Ti-6A1-4V) and V-base alloy (V-5Cr-5Ti). Impacts of the two shields having the steel-rich and the H₂O-rich compositions and the two blankets having the Li₂O/Be-base and the liquid Li/Be-base compositions on the He formation rate in the above-mentioned metals and alloys are discussed. The relation between the He formation rate and the fast neutron flux (14.1 MeV>E>0.1 MeV) is investigated. The decrease of He formation at any distance Δ from the first wall more than Δ_as, the distance where the shape of neutron spectrum reaches its asymptotic form, is modelled by the simple formula based on the exponential dependence, as those reported so far for the fast neutron flux and the displacement damage rate.     

Helium Production in Solid Target and Metallic Window Materials Irradiated with Intermediate and High Energy Protons

The helium isotope formation cross-section has been obtained for iron, tantalum and tungsten irradiated with protons at energies from the reaction threshold up to several GeV. The cross-section evaluation has been performed using the results of model calculations and by the analysis of available experimental data.

The numerical calculations were carried out using the modified ALICE code and the CASCADE/INPE code.     

Helium and hydrogen re-emission during implantation of molybdenum,vanadium and stainless steel

He re-emission has been measured during 300 keV He⁺ implantation from 400°C to 1200°C in V and Mo between ?170°C and 700°C in 316 SS. H re-emission has been measured during 150 keV H⁺ implantation of Mo, V, and 316 SS between ?90°C and 115 °C. In general the He re-emission is low until a critical dose is reached, at which time the re-emission abruptly rises to higher values. Both the critical dose and re-emission are strongly temperature dependent. The H re-emission generally rises smoothly to an equilibrium value which is both temperature and material dependent. Only at the lowest temperature does the H re-emission in Mo bear a qualitative resemblance to He re-emission.     

固溶处理时Inconel 718焊接试样中铌的扩散

根据非稳态扩散方程,对Inconel718焊接试样中铝在固溶处理时的均匀化过程进行了计算,以此说明了要求高温长时间固溶处理的原因,表明了减少条状组织中β-Ni3Nb相的间距是进一步提高延伸率的有效方法。     

Development of Fast Helium Reactors in Russia

The need for fast reactors in nuclear power is discussed. The advantages of fast helium reactors over fast liquid-metal reactors are shown. Fast helium reactor concepts and the possibilities of improving breeding by using fuel of higher density than oxide fuel, specifically, carbides and nitrides, are examined. It is indicated that the development and use of high-temperature helium-cooled thermal- and fast-neutron reactors are promising as part of an international collaboration in nuclear power in the 21st century.     

Unified Model of Damage Annealing in CMOS, from Freeze-In to Transient Annealing

Irradiation studies at 76°K are described which demonstrate that radiation-produced holes in SiO2 are immobile at this temperature. If an electric field of either polarity is present in the SiO2 during 76°K irradiation, to sweep out the mobile electrons, the holes will virtually all be trapped where created and produce a uniform positive charge density in the oxide. This predicts ?VT ? dox2 , which is observed. The magnitude of the observed shift is consistent with 18 eV required per hole-electron pair generated. All CMOS transistors of the same oxide thickness exhibit the same initial ?VT, for a given exposure level, regardless of oxide type or process. The rate of annealing differs, both as a function of oxidation process and oxide thickness. Thin oxides have two advantages: a smaller ?VT (stable shift) and faster annealing. If a CMOS device is irradiated for sufficient time at 76°K to build in an appreciable field, further irradiation with zero gate-substrate bias will produce little additional change in VT, since the field in the oxide tends to keep all generated electrons in the oxide, where they recombine with trapped holes. Room temperature annealing following a pulsed gamma exposure occurs in two regimes. The first regime can be quite fast, and occurs prior to 10-4 seconds. The magnitude of this early-time recovery is both process dependent and thickness dependent.     

Helium solubility and behaviour in uranium dioxide

A set of devices was developed in order to infuse UO₂ disks with helium, at high temperature and pressure, to measure the helium infused quantity and from these data to calculate the helium solubility in the UO₂ matrix. Samples of UO₂ single crystal and UO₂ polycrystal were infused at a temperature of 1473 and 1743 K in a helium atmosphere ranging between 50 and 100 MPa. These samples were then annealed and the helium released was measured with a mass spectrometer. From the obtained spectra it was possible to give an interpretation of the helium release mechanism and to calculate its solubility in the UO₂ lattice in these specific thermodynamic conditions. Additionally to the helium solubility measurement from infused samples, a 37 years old sample of ²³⁸PuO₂, retrieved from an old ²⁴²Cm radioisotope thermoelectric generator (RTG), containing radiogenic helium, was also measured to widen perspectives of this kind of measurements to damaged sample more representative of spent fuel.     

Helium diffusion in uranium and plutonium oxides

Samples of UO₂, (U,Pu)O₂ and PuO₂ containing up to several 100 at. ppm helium were submitted to thermal annealing in a Knudsen-cell provided with a mass spectrometer. Gas release was measured on line with a great accuracy. In the examined materials helium was created by α-decay of plutonium or laboratory infused at high temperature and high pressure. The selected samples exhibited different types of lattice damage, including reactor burn-up and high α-radiation doses. Analysis of helium release as a function of temperature enabled the elementary diffusion processes to be investigated and the atomic diffusion coefficient to be deduced for a defined state of helium-in-solid. The helium diffusion coefficient has the expression:

     

Formation process of β-SiC during reaction-sintering

Reaction-sintered bodies of β-SiC were prepared from various carbon powders, such as non-graphitizable carbon, petroleum coke, artificial graphite and kish graphite. The maximum particle size of carbon powder that can be completely siliconized was estimated from the difference of particle size distribution between carbon raw materials and unreacted carbon observed in the reaction-sintered bodies. The lattice strain of β-SiC formed in situ was measured by an X-ray line broadening method. It was suggested from these data that the formation process of β-SiC during the reaction-sintering was influenced by the microstructure of carbon raw materials; the crystallite size and the degree of preferred orientation of crystallite.     

Behavior of Helium Gas Bubbles in Neutron-Irradiated Beryllium

Transmission electron microscopic observations were made on hot-rolled Be sheet prepared from cast ingots irradiated to about 5 × 10¹⁹ nvt(fast) in JRR-2.

The aim of the study was to elucidate the effect of irradiation on changes in microstructure and the effect of pre-irradiation heat treatment on the formation of He gas bubbles during post-irradiation annealing.

The formation and growth of He bubbles during post-irradiation annealing was distinctly less inhibited in the Be irradiated as hot-rolled than in the metal irradiated after recrystallization treatment. In the former case, He bubbles could be observed upon post-irradiation treatment of only 3hr at 750°C, while in the latter case, a similar formation of bubbles could, only be seen after a final treatment at 900°C for 50 hr.

The difference thus observed in the tendency of bubble formation depends upon the grain boundary mobility during post-irradiation heat treatment.

The nucleation and growth of bubbles occurred preferentially at the grain boundaries, inclusions and dislocation sites. The recrystallization of irradiated Be was retarded by the interaction between dislocations and He atoms.

The inclusion which has the largest affinity to the bubbles in Be is Be₁₁Fe.     

氦回路用风机的特点及与堆用主风机的比较

由于采用了平衡结构、气动轴承，置入式电机，抽气冷却和交直流机组调速等手段，清华大学核研院高压氦气试验回路的二级涡轮式氦气循环风机具有轴向推力小、无油、无动密封、不引入其它介质和调速方便等特点。本文还将这些特点和高温气冷堆－加路氦气风机的技术要求作用比较。     

Effect of Different Structural Materials on Neutronic Performance of a Hybrid Reactor

Selection of structural material for a fusion–fission (hybrid) reactor is very important by taking into account of neutronic performance of the blanket. Refractory metals and alloys have much higher operating temperatures and neutron wall load (NWL) capabilities than low activation materials (ferritic/martensitic steels, vanadium alloys and SiC/SiC composites) and austenitic stainless steels. In this study, effect of primary candidate refractory alloys, namely, W-5Re, T111, TZM and Nb–1Zr on neutronic performance of the hybrid reactor was investigated. Neutron transport calculations were conducted with the help of SCALE4.3 System by solving the Boltzmann transport equation with code XSDRNPM. Among the investigated structural materials, tantalum had the worst performance due to the fact that it has higher neutron absorption cross section than others. And W-5Re and TZM having similar results showed the best performance.     

Behavior of Helium Bubbles in Cold Worked Aluminium-Lithium Alloys

Abstract

Various kinds of cold worked Al-Li alloys were irradiated in JRR-2 and the change in microstructure with post-irradiation annealing was examined in an electron microscope. In 30% cold worked specimen, bubbles are preferentially distributed on sub-boundaries. The grain interior contains only a small amount of bubbles. On the contrary, in 2% cold worked specimen, in which distinct sub-boundaries are rarely formed, most of bubbles are distributed within the grains. Bubbles aligned on a dislocation are frequently observed.

These experimental results are explained as follows. In heavily cold worked specimen, moving dislocations collect most of He atoms or their clusters in the course of sub-boundary formation after irradiation. In slightly cold worked specimen, dislocation density is insufficient to perform this process and He atoms or their clusters precipitate either upon dislocations or within the grains.     

高温气冷堆氦气气氛下的固体润滑技术

由于高温气冷堆采用氦气作为冷却剂,堆内构件在氦气下的摩擦学性能变化成为高温气冷堆必须研究的一个问题。在氦气环境中,材料的摩擦学性能一般要变差,而且很难采用流体润滑技术。本文讨论了粘结固体润滑膜和熔烧固体润滑膜技术在高温气冷堆控制棒驱动机构上的应用,并探讨了对于连续动转的摩擦副、固体润滑剂的几种补给方式以及固体润滑技术在氦风机上应用的必要性和可能性。