Best Estimate BWR Transient Analysis with TRACG Assessment using Data from BWR Startup Tests and LOCA Integral Tests

TRACG is a new version of the best estimate BWR transient analysis code, which utilizes a multi-dimensional two-fluid model for the thermal hydraulics and a three-dimensional neutron kinetics model. A three-dimensional neutronics, a fully implicit integration scheme and models for advanced BWR components have been implemented in the code upon TRAC-BF1.

Assessment of TRACG has been performed in this study for the predictive capability of plant transients, which include thermal-hydraulic and neutronic interactions, as affected by responses of the plant control system. Simulations were presented for BWR representative transient tests, which were done as part of a series of BWR5 startup tests. As for the capability to predict thermal hydraulics during the design basis LOCAs, simulations were presented for the LOCA integral tests conducted in the ROSA-III at JAERI and the Hitachi TBL, which had been used for assessment of the TRAC former version.

Consequently, (1)the space-dependent power flow transitions in a BWR were confirmed by TRACG simulations in which the module coupled with neutronics and thermal hydraulics during transients has been newly introduced, and (2) the characteristic thermal-hydraulic phenomena including multi-channel effects during the design basis LOCAs were confirmed, as well as the TRAC former version, by TRACG simulations on which the influence due to a fully implicit integration scheme has not extended. Capability of TRACG to predict BWR transients ranging from simple plant operational transients to design basis LOCAs was successfully demonstrated.     

A Validation of ATR LOCA Thermal-hydraulic Code with a Statistical Approach

When cladding temperatures are measured for a blowdown experiment, cladding temperatures at the same elevation in the fuel bundle have usually some differences due to eccentricity of the fuel bundle and other reasons such as biased two-phase flow. In the present paper, manufacturing tolerances and uncertainties of thermal-hydraulics are incorporated into a LOCA code that is applied with the statistical method. The present method was validated with the results of different blowdown experiments conducted using the 6 MW blowdown facility simulating the Advanced Thermal Reactor (ATR). In the present statistical method, the code was modified to run fast in order to calculate the blowdown thermal-hydraulics a lot of times with the code using different sets of input data. These input data for sizes and empirical correlations are prepared by the effective Monte-Carlo method based on the distribution functions deduced by the measured manufacturing errors and the uncertainties of thermal hydraulics. The calculated curves express uncertainties due to the different input deck. The uncertainty band and tendency of the cladding temperature were dependent on the beak sizes in the experiment. The measured results were traced by the present method.     

圆参数的两步估计

在许多工程技术领域经常会遇到用一个圆形去拟合一组观测数据的问题。本文用异方差线性模型提出了圆心和半径的两步估计。利用模型设计阵的特殊结构,建立了最小二乘估计、最佳线性无偏估计和两步估计的协方差阵的很有用的分解式。据此,导出了两步估计的一些重要统计性质。特别,应用Kantorovich不等式获得了两步估计优于最小二乘估计的条件。同时,本文给出了两步估计相当于最佳线性无偏估计相对效率的下界,这个下界表明,既使样本容量不太大,两步估计也有较高的相对效率。最后、本文还证明了观测点在圆周上均匀分布时最小二乘估计的优良性。     

特征值问题各向异性非协调有限元逼近

利用紧算子谱逼近理论,给出了Stokes特征值问题的各向异性非协调有限元逼近方法及最优误差估计,得到了与剖分网格满足正则性或拟一致性关键假设下相同的收敛效果。     

短波低速率数据传输研究

以第三代短波通信网络标准中的低速数据传输规程为基础,设计了一种低信噪比且存在多径衰落的信道中数据传输的调制解调方案.方案中利用相关搜索、FFT捕获的方法捕获信号,利用滑动相关完成位同步和信道估计,利用RAKE接收机抗多径衰落,并用DSP实现了数据的低误码率传输.     

Estimation of dietary intake of PCB and organochlorine pesticides for children and adults

Levels of organochlorine substances, including a number of organochlorine pesticides and PCB, are monitored in food, including meat, fish and dairy products. The substances are slowly degradable and therefore persist for long periods in the environment, where they accumulate in the fatty tissues of animals and humans. They are included, because of the potential health-hazardous effect of these compounds on humans. The highest average contents are found in cod liver and fatty fish. The Danish population’s average daily intake has been estimated at between 0.03 and 0.3 μg/day for organochlorine pesticides and 0.9 μg/day for the indicator PCB-sum. People with a relatively high intake of these substances (the 95th percentile) are estimated to consume approximately twice as much. In general, the highest contributions to the intake of the organochlorine environmental contaminants are from fish, meat and dairy products. However, children have a relatively higher intake from milk and milk products and a lower intake from fish compared to adults.     

决策树C4.5算法的优化与应用

C4.5算法作为目前最具影响力的决策树分类算法,仍存一些不足之处。针对C4.5算法在对连续值属性离散化处理过程中比较耗时的缺点,基于Fayyad和Irani的边界定理,在连续属性离散化之后使用Gini指标代替信息熵对算法进行了化简。针对决策树算法中的过度拟合问题,基于Occam’s razor,采用再带入估计,对算法进行了改进。将上述思想应用于金融借贷数据,实验结果表明,改进的C4.5算法在保证准确率的前提下,执行时间平均降低8.74%,模型复杂度平均降低6.26%,表明了该算法的有效性。     

基于Snake 的点模型谷脊线提取与优化

基于主动轮廓模型（Snake 模型）,提出一种点模型的谷脊线提取与优化方法。首先 构建点模型的局部隐式曲面,并求出采样点的曲率值;然后通过求解主曲率极值点得到潜在谷脊 点,依据特征点的主方向连接谷脊点生成谷脊折线段;最后利用主动轮廓模型对谷脊折线段进行 优化。实验结果表明,算法是鲁棒的且能够生成光滑的谷脊线。     

Uniformly Stable Explicitly Solvable Finite Difference Method for Fractional Diffusion Equations

A finite difference scheme for the one-dimensional space fractional diffusion equation is presented and analysed. The scheme is constructed by modifying the shifted Grünwald approximation to the spatial fractional derivative and using an asymmetric discretisation technique. By calculating the unknowns in differential nodal point sequences at the odd and even time levels, the discrete solution of the scheme can be obtained explicitly. We prove that the scheme is uniformly stable. The error between the discrete solution and the analytical solution in the discrete $l^2$ norm is optimal in some cases. Numerical results for several examples are consistent with the theoretical analysis.     

An Inverse Diffraction Problem: Shape Reconstruction

An inverse diffraction problem is considered. Both classical Tikhonov regularisation and a slow-evolution-from-the-continuation-boundary (SECB) method are used to solve the ill-posed problem. Regularisation error estimates for the two methods are compared, and the SECB method is seen to be an improvement on the classical Tikhonov method. Two numerical examples demonstrate their feasibility and efficiency.