WIMS/CITATION在IHNI-1堆芯物理计算中的应用

建立了利用WIMS+CITATION计算医院中子照射器Ⅰ型堆堆芯中子学参数的模型,计算了堆芯的功率分布、顶铍反应性价值、控制棒价值、温度系数、堆芯燃耗等中子学参数,计算结果与文献数据一致,表明文章所建立的计算模型可用于医院中子照射器I型堆堆芯的物理计算。     

医院中子照射器I型堆堆芯热工水力分析

针对医院中子照射器Ⅰ型堆(IHNI-1)的堆芯特点和运行工况,建立了适用于IHNI-1反应堆堆芯的热工分析模型,并对模型进行了验证.利用所建模型,计算了 IHNI-1反应堆堆芯热工参数.最后分析了IHNI-1反应堆堆芯入口流量对堆芯出口温度的影响,同时给出了堆芯发生过冷沸腾时的功率计算结果.     

事故工况下医院中子照射器I型堆瞬态特性研究

采用RELAPS/SCDAP/MOD3.4程序对医院中子照射器Ⅰ型堆(IHNI-1)在事故工况下的瞬态特性进行研究,对意外大反应性引入和池水丧失事故工况进行了计算和分析,计算结果表明:IHNI-1堆具有良好的固有安全性,在发生大反应性引入和池水丧失事故时,最终能够稳定在较低功率,确保反应堆安全.     

医院中子照射器I型堆热中子束流孔道等效平面源的模拟计算

采用蒙特卡罗程序MCNP模拟计算了医院中子照射器Ⅰ型堆(IHNI-1)热中子束流孔道出口处的等效平面源.对B堆芯进行了临界搜索计算,模拟计算了热中子束流孔道及出口处中子、γ的束流参数,应用等效平面源模型建立了BNCT等效中子、γ平面源.为人体头颅等效模型剂量分布的快速计算提供了较为可靠的平面源.     

反应堆实际提棒的中子倍增公式

针对实际的反应堆启动过程中采用步进提棒的方式．并考虑单组缓发中子效应，以点堆中子动力学方程为基础，导出了反应堆启动的中子倍增公式。此公式的计算结果与用纯数值计算结果相同．     

基于WIMS和MCNP耦合程序的医院中子照射器I型堆燃耗计算

建立了基于WIMS和MCNP的临界-燃耗耦合计算方法,并对此方法进行了验算.通过栅元和组件问题的分析计算以及西安脉冲堆燃耗实验对比,验证了此耦合程序的可靠性和正确性.最后应用此耦合程序对医院中子照射器Ⅰ型堆的燃耗进行了计算和分析.     

基于医院中子照射器I型堆的MCNP中子截面库研制

利用NJOY程序制作了用于医院中子照射器Ⅰ型堆(in-hospital neutron irradiator mark 1 reactor,IHNI-1)物理计算的MCNP中子截面库。着重考虑了反应堆运行温度范围内的温度点,制作了多温度点ACE(a compact ENDF)格式中子截面数据库。利用MCNP/4B自带库验证了自制库的正确性,利用ICSBEP(International Criticality Safety Benchmark Evalution Project,国际临界安全基准评价工程手册)基准题对结果进行了验证和反应性温度系数计算,分析了不同参数的影响作用。结果表明,所制作的截面库是正确的,能够用于IHNI-1反应堆物理设计计算。     

考虑单群缓发中子时中子增殖的统一公式

迄今为止，人们只分别导出了深度次临界、缓发临界附近和瞬发超临界的几个特定条件下的中子增殖公式，各公式都不具有通用性，使用很不便,文中导出了反应性阶跃变化时，只考虑单群缓发中子从深度次临界直到缓发超临界整个区间上的中子增殖统一公式。实例计算表明，该公式计算准确，实用性强，具有重要的理论意义与应用价值。     

医院中子照射器I型堆超热中子束流孔道的优化设计

采用蒙特卡罗程序(Monte Carlo neutron and photo transport code,MCNP)对医院中子照射器Ⅰ型堆(IHNI-1)超热中子束流孔道的慢化层、反射层进行了优化设计。首先对FLUENTAL、Al等材料组成的6种慢化体方案进行了分析比较,给出了孔道出口处超热中子通量密度较大的两种设计方案;基于此两种慢化体设计方案,在保持束流孔道外框尺寸不变情况下,对慢化体周围的反射层进行了分析比较,给出了反射层的推荐方案;基于慢化体和反射层优化方案,最后给出了超热中子束流孔道出口处束流参数的空间分布。     

低浓化医院中子照射器（IHNI-1）堆芯的物理方案设计

采用蒙特卡罗程序MCNP／4B模拟计算了功率为30kW的低浓化医院中子照射器的堆芯物理参数,设计了合理的堆芯布置方案、235U富集度、控制棒价值、后备反应性和停堆深度,得到固有安全性较高、寿期达10年且无需换料、采用低浓化UO2燃料的医院中子照射器的堆芯物理设计方案,为后续反应堆工程设计以及硼中子俘获治疗肿瘤用中子束的设计提供理论依据。     

BNCT医院中子照射器辐射场特性参数初步测量

为验证BNCT医院中子照射器的设计效果,对其辐射场的特性参数如中子能谱、中子通量密度及其空间分布、中子和γ吸收剂量率及其空间分布等进行了测量。针对该照射器的特点,建立了一套由多球谱仪、235U裂变电离室、金箔、组织等效正比计数器和热释光探测器组成的测量系统,利用蒙特卡洛计算方法优化设计探测器的结构,以提高超热能区的分辨率和甄别不同能量成分中子的能力。初步测量结果表明,该照射器的中子通量密度达到了预期设计要求。     

Neutron imaging at Peking University

Neutron imaging techniques were investigated at Peking University based on a 4.5 MV Van de Graaff accelerator. The thermal neutron radiography, fast neutron radiography and fast neutron resonance radiography were tested. The low neutron flux limits the image quality. A new radio frequency quadrupole (RFQ) accelerator based neutron source with a yield of 1012 n/s is being set up.     

MARS14 deep-penetration calculation for the ISIS target station shielding

The calculation of neutron penetration through a thick shield was performed with a three-dimensional multi-layer technique using the MARS14(02) Monte Carlo code to compare with the experimental shielding data in 1998 at the ISIS spallation neutron source facility of Rutherford Appleton Laboratory. In this calculation, secondary particles from a tantalum target bombarded by 800-MeV protons were transmitted through a bulk shield of approximately 3-m-thick iron and 1-m-thick concrete. To accomplish this deep-penetration calculation, a three-dimensional multi-layer technique and energy cut-off method were used considering a spatial statistical balance. Finally, the energy spectra of neutrons behind the very thick shield could be calculated down to the thermal energy with good statistics, and the calculated results typically agree well within a factor of two with the experimental data over a broad energy range. The ¹²C(n,2n)¹¹C reaction rates behind the bulk shield were also calculated, which agree with the experimental data typically within 60%. These results are quite impressive in calculation accuracy for deep-penetration problem.     

14 MeV neutron irradiation effects on cryostability of a composite superconductor for a fusion reactor

The neutron irradiation effects on cryostability of composite superconductors for fusion reactors are studied based on Maddock's condition. In particular, to estimate the effects of 14 MeV neutrons we assumed that the irradiation-induced degradation of critical temperature, critical current density and conductivity of stabilizer are determined by the damage energy depending on the neutron energy spectrum. The cryostability is found to decrease sensitively with increasing the fraction α of fusion neutrons with energy of 10 ～ 14 MeV to the total neutrons, ie, the Cu/superconductor ratio R_ns, to stabilize the conductor, must be increased remarkably with increasing α as well as the total dose of the neutron fluence. For the small R_ns (～4) the stabilized overall current density decreases by several ten percents even at the fluence when T_c and J_c change by only a few percent. This effect is dominated by the severe increase of ρ.     

一种碳前驱物热解反应的热力学和动力学研究

根据量子化学理论研究了碳前驱物CH3－Ar-CH2-NH2的热裂解机理,利用Gaussian98程序包听AM1法,用UHF计算对化合物五种可能的热裂解路径进行了热力学和动力计算,结果表明,碳前驱物CH3－Ar-CH2-NH2将首先发生生成自由基CH3－Ar-CH2和NH2．的热裂解主反应,活化能Ea=230.78kg/mol,而碳前驱物CH3－Ar-CH2-NH2的实验表观活化能Ea=206.78kg/mol.键能的计算值与实验值符合得比较好,通过分析优化的反应物及产物自由基的部分结构参数,了解了理论支持主反应原因,计算的产物自由基的空间构型表明主反应路径生成的产物自由基相互间若进行筒环缩合反应,获得得分子平面取向性很好的稠环芳烃产物。     

Plasma parameter analysis of Ag sputter deposition using cathodes with different magnetic flux densities

The effects of the magnetic flux density of the Ag sputter target surface on plasma parameters were investigated using the Langmuir probe system in this work. It was found that the electron energy and electron density near the substrate clearly decreased at a high magnetic flux density. In addition, the difference between plasma potential and floating potential (V_p−V_f) decreased at the high magnetic flux density relative to the potentials at the low magnetic flux density. The changes in plasma parameters could be interpreted as the result of many electrons being trapped in the neighborhood of the target surface (cathode sheath) at the high magnetic flux density; hence, the number of electrons in the space near the substrate is reduced. The Ag thin films exhibited low resistivity at a high magnetic flux density. The reduction in resistivity was attributed to the following factors: the low electron energy and electron density near the substrate; the low kinetic energy of positive argon ions; the low kinetic energy of argon atoms backscattered onto the target surface.