Acceleration of source convergence in Monte Carlo k-eigenvalue problems via anchoring with a p-CMFD deterministic method

The Monte Carlo method is widely used in neutron transport calculations, especially in complex geometry and continuous-energy problems. However, an extended application of the Monte Carlo method to large realistic eigenvalue problems remains a challenge due to its slow convergence and large fluctuations in the fission source distribution. In this paper, a deterministic partial current-based Coarse-Mesh Finite Difference (p-CMFD) method is proposed that achieves fast convergence in fission source distribution in Monte Carlo k-eigenvalue problems. In this method, the high-order Monte Carlo method provides homogenized and condensed cross section parameters while the low-order deterministic p-CMFD method provides anchoring of the fission source distribution. The proposed method is implemented in the MCNP5 code (version 1.30) and tested on realistic one- and two-dimensional heterogeneous continuous-energy large core problems, with encouraging results.     

准噶尔盆地热演化历史模拟

根据磷灰石裂变径迹和镜质体反射率(Ｒ。)动力学模型模拟了准噶尔盆地腹部莫索湾、陆南和盆地南缘等地区的地温演化历史。研究结果表明,尽管准噶尔盆地现今的地温较低,但由于受构造运动的影响,各地质历史时期的地温演化不同,盆地的古地温较现今地温高。特别是在古生代和三叠纪,地温梯度很高。古生代的地温梯度平均大于38℃／ｋｍ,中生代三叠纪的地温梯度仍很高,为34．6－41℃／ｋｍ．侏罗纪的地温梯度变化较大,这可能与该时期的构造运动频繁有密切关系。白垩纪以后盆地的地温梯度演化基本不变,与现今相当。     

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文章首先利用地震层速度法、镜质体反射率法、声波时差法、地质外推法、磷灰石裂变径迹法等确定渤海湾盆地区中生界三叠系、侏罗系、白垩系的剥蚀量，恢复了其原始地层厚度，分析了中生代不同时期地层的分布状态，盆地性质和展部特点。认为渤海湾盆地三叠系沉积时期为大型内陆盆地，末期抬升遭受剥蚀。侏罗系和白垩系沉积时期为北东向展布的小型山间盆地群。进入新生代后，形成了一个受NNE、NE向断层控制的半地堑式复合盆地，叠置于中生代盆地之上。不同时代的地层的不同叠合方式形成了中坳新坳、中坳新隆、中隆新坳、中隆新隆4种叠合单元类型，不同类型的叠合单元经历了不同的沉降史，具有不同的石油地质意义。     

中子活化分析参量化的进一步研究——Ⅰ.裂变干扰的参量法校正

112个活化分析感兴趣的(n,γ)反应k_0值的建立,已经使得63种元素的参量法堆中子活化测定成为可能。然而,为了实现堆中子活化分析的全面参量化,尚需进一步解决几个问题。作者对实现裂变干扰和阈反应干扰的参量化修正,以及“远”、“近”测量几何效率的参量化归一提出一些新的建议。 本工作基于~(235)U(n,f)反应在热中子能区的截面服从1/v定律且具有小的Q_0(I_0/σ_0)值,首次建议了“组合核常数”Ik_0,从而实现了堆中子活化分析中裂变干扰的参量法校正。在我院3座反应堆的6个照射孔道上测定了8个主要裂变干扰反应的Ik_0值。这些Ik_0值的堆中子谱无关性质。证实了本法的可靠性。     

测定混合核燃料裂变数的多核素法

提出了一种测定混合核燃料裂变数的新方法－多核素法。通过分析样品中若干个裂变产物的核数，按虚拟变数对两种核燃料裂变产额比进行线性回归，可同时计算总裂变数和两种核材料的分裂变数。中给出了分析核素的选择要求和裂变产额的确定原则。     

从混合裂变产物中分离铪

进行了从短期冷却的混合裂变产物中分离铪的研究。测定了在不同Zr,Hf载体量时的分离因子α和分离度R_3值,推荐了一个分离放化纯~(181)Hf的流程。方法简单,对裂变产物的去污因子为10~8～10_9,对~(95)Zr的分离因子为～10_6,化学产率为60～70％。     

Discrimination of pile up in a fission fragment detection experiment

In this work the problem introduced in a fission experiment by the pile-up due to a strong -background has been addressed. A novel scheme has been developed, able to reject more than 90% of pile-up affected pulses in a plutonium sample with an activity of 1 MBq. This procedure is necessary in order to improve the resolution to an acceptable level. With a proper calibration, however, the global mean energy and mass of the fragments are correctly reproduced both with and without pile-up rejection.     

人肺中钚积沉量体外测量装置的改进及裂变核素干扰的扣除

本文叙述了一套人肺中钚积沉量体外测量装置,该装置是对原有装置的改进。用四个大面积薄碘化钠闪烁探测器(二个为φ100×1毫米,另二个为φ100×2毫米)分别置于胸腔上方及左、右两侧进行肺中钚测量;用两个φ100×100毫米碘化钠闪烁探测器测量人体中裂变核素负荷量,并从肺中钚测量数据中扣除体内裂变核素的干扰。依照三倍本底标准偏差估计肺中钚测量的灵敏度为10.2纳居里(毫微居里),体内裂变核素测量的灵敏度为10~(-2)微居里量级。     

Compositional design of an amphoteric chemical trap for the capturing of gaseous cesium and iodine in UO2 nuclear fuel

A chemical trap in the form of Ba-Al-Si-O that captures gaseous cesium and iodine has been developed for application to UO₂ nuclear fuel. A key issue for better trapping efficiency is to secure the ability to capture individual fission gases, in this case for cesium and iodine. This can be done through chemical trapping with the presence of chemical compounds that spontaneous react with them. In this study, based on thermodynamic estimations, a promising composition of 1BaO-1Al₂O₃-1SiO₂ (mole ratio) is suggested for amphoteric trapping. The chemical design was confirmed experimentally under simulated conditions approximating an actual fuel environment. In each experiment for cesium and iodine, the trapping reaction was confirmed to occur at 650 °C in a reducing atmosphere. This study provides a methodology for compositional design and empirical confirmation to shed light on an accident-tolerant fuel development strategy that reduces the release of fission gases.