先进核能系统结构材料辐照性能研究

首先简要介绍第一代到先进的第四代核能系统的发展、与核能系统发展密切的抗辐照结构材料研发进展、第四代核能系统结构材料辐照性能研究新方法。第四代核能系统发展中,辐照引起材料性能退化是一个需要研究和解决的瓶颈问题。现有中子源都不能满足第四代核能系统结构材料高剂量中子辐照性能研究的要求。为此,发展了用于核能系统结构材料高剂量辐照性能快速检测加速器重离子辐照方法和第四代核能系统实际辐照工况模拟的重离子与氢和氦三束同时辐照新方法,文中进行了详细的介绍。最后介绍了中国原子能科学研究院核能系统结构材料辐照性能研究现状和近期发展计划。该院在HI-13串列加速器器上建立了多种不同用途的重离子辐照装置、三个独立加速器构成的重离子与氢和氦三束同时辐照实验平台,开展了一系列核能结构材料,例如国产改进型奥氏体钢、CLAM钢、1515钢、钽、钨等的辐照性能的系统测试和研究。为了更好地开展核能结构材料性能研究,从国外引进了一台超导直线加速器和一台可变能量重离子回旋加速器。结合现有2×13 MeV,2×1.7 MV串列加速器、30 MeV和100 MeV质子回旋加速器、高压倍加器,中国实验快堆、中国先进研究堆、微堆等,CIAE将建成一个比较完整和先进的核能系统结构材料辐照实验平台系统供国内外用户使用。This paper introduces briefly the development of nuclear energy systems from the GEN I to the advanced GEN IV, the progress of manufacturing radiation resistant materials associated with the development of nuclear energy systems and the new methods of investigating radiation properties of the structural materials for the GEN IV nuclear energy systems at first. Irradiation induced deterioration of materials properties is a bottle neck problem, which must be investigated and solved for the development of the GEN IV nuclear energy systems. Unfortunately, all the currently available neutron sources cannot meet the requirements of investigating radiation properties of structural materials irradiated by high dose neutron irradiation in the GEN IV nuclear energy systems. Therefore, two new methods of the accelerator heavy ion irradiation that simulates the high-dose neutron irradiation and the triple beam irradiation that mimics the real neutron irradiation environment in the GEN IV nuclear energy systems have been developed. These two methods are introduced in this paper. The present status of the study on radiation properties of structural materials for nuclear energy systems of the new generation and the near future development plan at China Institute of Atomic Energy (CIAE) are described also. The accelerator heavy ion irradiation facilities for different applications and the simultaneous triple beam irradiation platform with three separate accelerators or implanters have been established at the HI-13 tandem accelerator of CIAE. A series of structural materials for nuclear energy systems, such as the home-made modified austenic steel, CLAM steel, 1515 steel, Tantalum, Tungsten, etc. have been tested and investigated systematically. A superconducting linear accelerator and a variable energy heavy ion cyclotron have been imported from abroad for a better performance of the study. Combined with the currently existing facilities of 2×13 MeV and 2×1.7 MV tandem accelerators, 30 and 100 MeV proton cyclotrons, China experimental fast reactor, China advance research reactor, Miniature neutron source reactor, etc. a comprehensive and advanced system of experimental irradiation platform for structural materials of nuclear energy systems will be established in the near future for both domestic and foreign users.     

Method of H1(10) evaluation using a spherical-type energy-independent neutron dose monitor

A spherical-type neutron dose monitor has been developed for the use of area monitoring around the neutron producing fields. Considering the practical fields that neutrons coming from multiple directions, the study has been performed using MCNP simulation, in order to estimate the resultant direction of the sources and to find a suitable method of H¹(10) evaluation. This was done by irradiating the monitor using two neutron sources of different energies and intensities; placed at an angle between them. A parallel neutron beam of 50 cm radius with wide energy was used for the irradiation. The direction of the neutron sources was determined comparing the responses of 12 thermo-luminescent detectors (TLDs) of first layer between single and two directional sources. It was found that in most of the cases, the direction of the source was estimated to be the average angle or near the average angle of single sources. Using a linear combinational equation the method has been developed for evaluating the dose from the mean values of selected detectors of two consecutive depths of TLDs and the TLD of core depth. It was found that the ratio of the calculated to the expected dose was almost close to unity which indicates that the method can be used for evaluating the dose with good accuracy.     

The measurement using passive dosemeters of the neutron component of aircraft crew dose

The cosmic radiation field at aviation altitudes can be measured with simple passive detectors. The non-neutron component may be measured by means of thermoluminescence dosimetry or other techniques, and the neutron component may be measured using poly allyl diglycol carbonate (PADC) dosemeters as described in this paper. Effective dose from neutron radiation becomes the larger component for altitudes above about 10 km, in general. The dominance is more pronounced for higher latitudes. The neutron energies range up to the maximum of the incident protons, that is many GeV. However the majority of the dose is contributed by neutrons of a few hundred MeV and less, with two maxima in the fluence spectrum, one between 1 and 10 MeV and the other between 50 and 150 MeV. We have used PADC dosemeters, electrochemically etched, to estimate the neutron component of effective dose. Up to 50 dosemeters are used in a single measurement to obtain an estimate of sufficient precision for total neutron effective doses of 50 microSv and less. The neutron fluence response characteristics of the dosemeter have been measured up to 70 MeV. These are extrapolated up to 180 MeV. This extrapolation is validated, partially, by a comparison of measured and predicted readings in the CERN reference field. From the dosemeter readings for exposure on board aircraft, neutron fluence may be estimated assuming an isotropic radiation field and the estimated neutron fluence spectrum. The neutron fluence may then be converted to effective dose using published values of conversion coefficients with the same assumptions of isotropy and known fluence spectrum. For the measurement results reported here, the calculated spectrum for the CERN concrete shielded field is used.     

氘核与聚变中子耦合输运方法及应用

对加速器驱动中子发生器的数值模拟包括离子输运、聚变反应、中子输运等。由于核反应截面远低于带电粒子输运的库仑截面,且核反应平均自由程远大于靶厚度,直接蒙卡抽样难以抽到聚变反应。在MCNPX程序基础上,采用“强迫”聚变方法,即每个入射氘核必发生一次聚变反应,聚变反应处氘核的真实状态(位置、能量和方向)以抽样产生,并以此状态来确定聚变中子的出射状态,实现了氘核与聚变中子的耦合输运模拟计算。研究结果表明,该方法能够给出氘核输运对聚变中子能谱和角分布的影响,中子产额计算结果符合预期。     

Study of the improvement of TLD cards for personal neutron dosimetry

In this work, personal thermoluminescence dosimeter (TLD) cards type of GN-6770 (holder type 8806) from Harshaw were used for personal neutron dosimetry. The response of the dosimeters has been determined in terms of the personal absorbed dose and personal dose equivalent for different neutron energy components, based on the recommendations of ICRP-60 and ICRU-49. Neutron irradiation was performed using a 5 mCi Am–Be neutron source. The TLD reader, type Harshaw 6600, was installed and calibrated for accurate neutron doses equivalent to gamma-ray doses. It was found that fast neutron doses measured by TLD (badges or cards) are in agreement with those measured by neutron TE (tissue equivalent gas) ionization chambers and neutron monitors. Thermal neutron doses measured by TLD cards were overestimated when compared with those measured by neutron monitors. Additional Cd was used to reduce thermal neutron doses to be in agreement with actual thermal doses. Other configurations for TLD crystals are also suggested for accurate thermal neutron dose measurements.     

基于北京大学4.5 MV静电加速器的核技术应用

北京大学4.5 MV静电加速器是20世纪80年代我国自主研发的静电加速器。该器端电压在0.7~3.8 MV连续可调,主要加速氢/氦同位素离子,并可通过打靶产生准单能直流/脉冲中子场,具有多条束线及多个实验终端。该器作为开放仪器多年来为国内外从事核技术研究的团队提供了实验平台。近年来,针对我国在能源、航天和国防等领域材料研究的重要需求,该器进行了多次升级改造。一方面通过产生7 MeV以下和14~19 MeV的准单能中子场,应用于(n, a)核反应截面的测量和聚变堆中子谱仪刻度;另一方面,通过温控辐照、核反应分析等实验终端,实现了材料辐照损伤及聚变堆材料元素定量分析等研究方向的功能拓展。此外,设计新增用于半导体材料电学性能测试的原位在线辐照终端和用于研究材料微观尺度元素分布的离子束综合分析实验终端。目前部分新终端已设计组装完成,相关搭建和调试工作正在进行中。     

Sm_2Co_(17)型永磁合金的辐照效应研究

Sm_2Co_(17)型永磁合金大量使用在上海同步辐射光源储存环的永磁型波荡器上,在受到长期辐照后会发生磁性能损失的现象,进而影响同步辐射光的品质.为了探索其潜在的微观机理,本文首先对Sm_2Co_(17)型永磁合金所处混合辐射场的粒子及相关物理量进行了计算分析,确定引发磁性能损失的主要粒子是中子.然后采用Ar离子模拟中子辐照损伤的方法对其进行辐照,采用透射电镜对其辐照前后的微观形貌及微观结构进行了研究探讨,采用振动样品磁强计对永磁合金辐照前后的饱和磁化强度进行了分析对比,并讨论了微观结构演化与宏观磁性能变化的联系.结果表明,Ar离子辐照后Sm_2Co_(17)型永磁合金饱和磁化强度的不可逆损失与微观结构变化有直接的关系,其2:17相从单晶结构转变为非晶结构是造成其磁性能损失可能的微观机制.     

Search for heavy neutron clusters in nuclear fission

An experiment on search for heavy neutron clusters in fission of ²³⁵U nuclei has been carried out on a nuclear reactor. The method of searching for neutron clusters is based on irradiation of tellurium dioxide and lead oxide targets in reactor channels near the active zone and far from it. The method of γ-spectrometric analysis of irradiated targets was used to search for nuclei whose occurrence in the targets cannot be explained by other nuclear reactions, except for the reactions of original target nuclei with neutron clusters. The reactions of tellurium and lead nuclear fission by neutron clusters (nuclei) and direct capture of neutron clusters have been revealed.     

质子与中子辐照对电荷耦合器件暗信号参数的影响及其效应分析

对科学级电荷耦合器件(charge-coupled device, CCD)进行了质子和中子辐照试验及退火试验, 应用蒙特卡洛方法计算了质子和中子在CCD中的能量沉积, 分析了器件的辐射损伤机理. 仿真计算了N⁺埋层内沉积的位移损伤剂量, 辐照与退火试验过程中主要考察暗信号的变化规律. 研究结果显示, 质子与中子辐照均会引发暗信号退化, 其退化的规律与位移损伤剂量变化一致; 退火后, 质子辐照所致CCD暗信号大幅度恢复, 其体暗信号增加量占总暗信号增加量的比例最多为22%; 中子辐照引发的暗信号增长主要为体暗信号. 质子和中子在N⁺埋层产生相同位移损伤剂量的情况下, 两者导致的体暗信号增长量相同, 质子与中子辐照产生的体缺陷对体暗信号增长的贡献是同质的.     

Magnetic hysteretic characterization of the irradiation-induced embrittlement of Fe,Fe–Cu model alloys,and reactor pressure vessel steel

Neutron irradiation is known to cause embrittlement of iron-based materials; in the nuclear industry, this effect can be detrimental for reactor pressure vessel steels. In this paper, we investigate the variations of the magnetic hysteretic behavior due to neutron irradiation, for four materials, i.e. nominally pure Fe, Fe-0.1 wt% Cu and Fe-0.3 wt%Cu model alloys, and a reactor pressure vessel steel, JRQ A533-B. Two parameters related to the magnetization loop shape, i.e. maximum relative differential permeability and peak intensity of local interaction field distribution, are measured as a function of neutron fluence. For all materials both parameters decrease with increasing fluence, due to the irradiation-induced formation of nano-size defects. This decreasing trend in magnetic parameters during embrittlement is noticeable regardless the origin of the embrittlement, which can be only Cu-precipitation (thermal aging of Fe–Cu), only matrix damage (irradiation of pure Fe), or both mechanisms (irradiation of Fe–Cu or steel). The magnetic parameters relatively change up to 40%, which indicates the potential of magnetic characterization to assess irradiation-induced material hardening and embrittlement.     

ST嬗变堆中心柱的中子学及中子辐照效应研究

基于先进核数据库ENDF/B-VI和计算机程序对ST嬗变堆中心柱的中子学及辐照损伤的二维分析计算结果，分别对中心柱导体因中子辐照影响而引起电阻率、电阻、电流和欧姆电阻功率等的沿径向不均匀分布，以及辐照损伤对中心柱热工水力问题及更换寿命的影响进行了分析和计算。结果表明，中子辐照直接改变了中心柱导体材料的电阻率分布。热工-水力学分析和计算表明，电流不均匀分布可显著地延长中心柱的使用寿命，并估算出ST嬗变堆中心柱设计的更换寿命大约8年。     

The weak center nature and their pinning anisotropy of radiation damage defects in Y1Ba2Cu3O7−δ single crystals

A field induced weak pinning center, in MeV proton irradiated Y₁Ba₂Cu₃O_7−δ (YBCO) single crystal and in ⁶Li-doped sintered YBCO exposed to thermal neutron irradiation, has been identified. The pinning contribution of those radiation caused weak centers (RWCs) showed strong field dependence, which resembles that of the common weak centers of oxygen deficient regions (OWCs) in most of the bulk YBCO materials. The radiation dose dependence of the pinning enhancement, in proton irradiated single crystal, showed strong angular dependence, when the field orientation relative to the crystal was changed. This is believed to be due to the different flux line size (orξ) in different directions, and the so caused volume or line pinning effects. No angular dependence has been observed in neutron irradiated YBCO, which is polycrystalline in nature.     

The simulated workplace field with a high-energy neutron component produced by irradiating a Fe-target with 200 MeV/u 12C-ions

Recent developments in accelerator physics have led to new challenges for radiation protection dosimetry. Doses have to be determined for workplace fields which are characterized by high-energy radiation, a dominant contribution from neutrons, high intensities and pulsed time structure This may present problems for active measuring devices. As is well known, the ambient dose equivalent is often underestimated by area monitors operating in high-energy neutron fields behind shielding. Therefore, it is desirable to calibrate survey monitors in a characterized neutron field with the type of spectral fluence distribution that is expected behind shielding, i.e. where the main dose from neutrons arises from two peaks with mean energies of about 1 MeV and 100 MeV, respectively. Such a neutron fluence distribution is produced by the irradiation of a Fe-target with 200 MeV/u ¹²C-ions. Measurements with the extended range Bonner sphere spectrometer NEMUS of PTB were performed at two positions inside the experimental area Cave A of the heavy-ion synchrotron SIS at GSI. The measured neutron spectra show different fluence contributions for the two peaks at the two positions. The results were compared to Monte Carlo Simulations with MCNPX and FLUKA.     

Grain boundary impurity segregation and neutron irradiation effects in ferritic alloys

Segregation of alloying and impurity elements to grain boundaries in ferritic steels and alloys is known to modify the mechanical properties. This paper considers segregation of such elements, in particular phosphorus and carbon, that occur in ferritic nuclear pressure vessel steels subject to neutron irradiation and temperature typical of that encountered in service. Models are presented that allow the prediction of equilibrium and non-equilibrium segregation of phosphorus to grain boundaries and also take into account synergistic interaction with carbon under various combinations of neutron-irradiation temperature. These are related to a wide range of experimental observations compiled from data in the literature for mainly phosphorus and carbon measured at grain boundaries in neutron-irradiated ferritic vessel steels and alloys. The predictions from the segregation models are compared with these experimental data. The discussion provides a rationalization for the apparent variability in the measured grain boundary phosphorus compositions and thereby fracture susceptibility for various nuclear pressure vessel ferritic steels.     

Neutron ambient dose equivalent from 5 MeV/u 10,11B, 12,13C and 16,18O projectiles incident on a thick Al target

The neutron ambient dose equivalent has been measured from ¹⁰B, ¹¹B, ¹²C, ¹³C, ¹⁶O and ¹⁸O projectiles of energy 5 MeV/amu incident on a thick Al target at 0°, 30°, 60° and 90° with respect to the beam direction using a conventional dose equivalent meter. The calculated results obtained using previously reported empirical relations do not reproduce the experimental data. The results obtained from the PACE nuclear reaction code are closer to the experimental data as compared to the various empirical expressions. The ratio of the increase in the dose rates when the projectile is changed from the lighter to the heavier isotopes is fairly reproduced by most of the empirical formulations and the PACE code. A previously reported relation for the slope parameter is used to predict the directional distribution of the neutron dose for the projectiles used in this study. The calculated doses are lower than the experimental results in the forward directions but agree within the uncertainties at the backward directions. A new set of projectile-based parameters have been derived from the present experimental data which can be used in an empirical formulation.     

On the dielectric loss and thermal bleaching of calcite irradiated by X-rays

The changes produced by X-ray irradiation in the dielectric and optical properties of calcite crystals are reported. At ordinary temperatures, the dielectric constant as well as the dielectric loss of the uncoloured crystal remains practically unchanged in the frequency region of 10 kc/s-15 Mc/s. It has been found that the temperature variation of its dielectric loss can be represented by an equation tan where A and B are constants; this is attributed to the movement of vacancies in the crystal.

On irradiation by X-rays, calcite exhibits pronounced optical absorption in the ultraviolet region beyond 400 mμ; the dielectric loss of calcite also increases considerably on colouration. The thermoluminescence shows a very strong glow peak at 85°C with minor ones at higher temperatures. During thermal bleaching, the dielectric loss of the coloured crystal shows a prominent maximum in the temperature range 70–120°C and beyond 230°C, it varies in the same way as in the case of the uncoloured crystal. The correspondence between the change in dielectric loss and the first glow peak is possibly due to thermal release of trapped electrons. The optical absorption disappears when the crystal is heated to 350°C and on cooling to room temperature, its dielectric loss returns to its original value before colouration.     

Response functions of Cs2LiYCl6: Ce scintillator to neutron and gamma radiation

Research into advanced screening technologies has become high priority in all aspects of occupational nuclear safety and environmental radiation protection. Neutrons are a fundamental part of radiation encountered in various fields of nuclear science and technology and their detection is still employing detectors with a high thermal neutron response embedded in a thermalizing medium where helium based devices have been a dominant choice in many applications. Recently, there have been newly developed sensors based on multi-elements that include ⁶Li and ³⁵Cl isotopes to detect neutrons and gamma radiation. Among these new sensors one can cite the elpasolite scintillator, known as CLYC. This sensor contains two neutron sensitive isotopes and may serve as a dual detector for gamma as well as for neutron radiation. In this paper, the response functions of this sensor have been investigated in different fields of neutron and gamma-radiation. The sensor responses have been simulated using Monte Carlo N-Particle MCNPX code and a series of experiments have been carried out to validate the simulated data. Both sets of data are presented and discussed.     

The neutron interferometer as a macroscopic quantum device

Neutron interferometry is a unique tool for investigations in the field of particle-wave dualism because massive elementary particles behave like waves within the interferometer. The invention of perfect crystal neutron interferometers providing widely separated coherent beams stimulated a great variety of experiments with matter waves in the field of basic quantum mechanics. The phase of the spatial and spinor wave function become a measurable quantity and can be influenced individually. High degrees of coherence and high order interferences have been observed by this technique. The 4π-symmetry of a spinor wave function and the mutual modulation of nuclear and magnetic phase shifts have been measured in the past. Recent experiments dealt with polarized neutron beams, which are handled to realize the spin-superposition of two oppositionally polarized subbeams resulting in a final polarization perpendicular to both initial beam polarizations. The different actions on the coherent beams of static (DC) and dynamic (HF) flippers have been visualized.     

Lattice dynamics and inelastic neutron scattering experiments on andalusite,Al2SiO5

We report coherent inelastic neutron scattering measurements of the phonon dispersion relations and lattice dynamics shell model calculations of several microscopic and macroscopic properties of andalusite, Al₂SiO₅. Andalusite has an orthorhombic structure with 32 atoms/unit cell. The inelastic neutron scattering measurements (up to energy transfers of 45 meV) were carried out using the triple axis spectrometer at Dhruva reactor, India using a single crystal of andalusite and the phonon dispersion relations along the [100] direction have been measured. The shell model calculations have been used to compute the crystal structure, elastic constants, phonon frequencies, dispersion relations, density of states and the specific heat. The calculated results are in good agreement with available experimental data. The computed one-phonon neutron scattering structure factors based on the shell model have been very useful in the planning and analysis of the inelastic neutron scattering experiments.     

引入源-样品距离影响的主动中子多重性质量反演公式北大核心CSCD

主动中子多重性计数测量方法是常用的核材料质量无损测量方法,已广泛应用于核材料衡算、核安保测量与军控核查等领域。我们通过对JMCT中子-光子输运程序的二次开发,实现了对经典点模型铀样品质量估算实验的数值模拟,并提出了改进的铀样品质量计算公式。该算法可以显著降低本实验中源-样品耦合与源中子反照等作用对铀样品质量估算精度的影响。建立了主动中子多重性计数测量探测系统模型和32个铀样品半球壳模型,模拟得到了与铀样品距离不同的DT源和AmLi源主动中子多重性计数,利用数值模拟手段检验了质量估算算法的有效性。数值模拟结果表明,改进的铀质量估算算法可以使质量估算的平均偏差率降低到10%以下。