蒋家沟流域古泥石流物质选频释光特征研究

采用BG2003释光仪研究云南蒋家沟流域泥得坪台地、多照台地、大凹子沟、蒋家沟4个地点的8个古泥石流物质样品的选频释光特征,确定了发射光子的特征发射频率.在蓝光(488 nm)激发下,各样品的发射光子分别出现在波长为300、310、320、400、460 nm处.用绿光(532 nm)激发上述相同样品,发现其在波长为300、310、320、460 nm时的计数最为明显.进而确定出泥得坪堆积台地在不同时期泥石流物质释光谱图大体一致,但大凹子沟与多照古泥石流堆积台地不同时期的泥石流物质释光谱图表现出差异.以泥得坪堆积台地为例,该台地的上部、中上部、下部泥石流物质样品在绿光激发下,在波长为310、320、460 nm处,随辐照剂量的加大,样品的释光光子数递增.由这一规律可确定泥得坪堆积台地泥石流物质用于年龄测定的波长.     

云南东川地区达朵台地泥石流释光测年研究

采用RGD-3B热释光仪对达朵泥石流堆积台地进行研究,以单片再生剂量法测定其剖面样品的等效剂量值(E.D.),结果表明:达朵台地剖面随深度的增加,埋藏时间增加,接受周围环境U、Th、K等的辐射剂量增多,等效剂量值总体上呈上升趋势,范围为92.91～155.38 Gy。说明采用热释光技术对古泥石流堆积台地进行年龄测定是可行的。确定达朵台地堆积时的年龄范围,对于云南小江流域划分泥石流活动期次、第四纪地层以及年代学标尺的建立具有基础性意义,同时为古泥石流堆积台地这种事件性的环境记录载体测年提供了一种新的思路和方法。     

北京清水河流域古泥石流堆积物的热释光测年研究

通过对北京清水河流域灵山、洪水口两个古泥石流台地堆积物质样品的热释光研究,测定了古泥石流剖面各样品的热释光年龄。两个古泥石流剖面的年龄均随深度增加而增大,泥石流堆积物质层位越深,受到的环境辐射剂量则越大。剖面U、Th和K的含量随深度的变化趋势与年剂量随深度的变化趋势基本一致, Th含量随深度的变化比U、K含量随深度的变化离散。     

蒋家沟流域现代泥石流物质选频光释光特征初步研究

采用BG2003释光仪研究了云南蒋家沟流域的大凹子沟、蒋家沟、泥得坪沟及其多照沟4个泥石流沟底泥石流物质的选频释光特征,确定了发射光子的特征发射频率.在蓝光(480 nm)激发下,在波长为300nm、310nm、320 mn、400 nm和460nm下,大凹子沟与蒋家沟泥石流物质吸收的光子数都极为接近.用绿光(532nm)激发上述相同的样品,发现大凹子沟与多照沟底的泥石流物质吸收的光子数在波长为310nm、320 nm时也十分相近;进而在相同实验条件下,用绿光激发东北地区沙漠砂样品,得出沙漠砂物质的吸收光子数远大于泥石流物质的吸收光子数.     

龙泉窑古陶瓷年代断定的中子活化分析和Bayes判别

为实现龙泉窑古陶瓷年代的准确判定,利用中子活化分析（NAA）方法准确测定了南宋-元(AD1127—1368)和明代(AD1368—1644)龙泉窑古瓷胎中La、Sm、U、Ce等18种元素的含量。为提高实验数据的可靠性,利用马氏距离准则排除实验数据的异常值,并对实验数据进行了正态分布检验。在一定的假设前提下,应用Bayes判别法用预处理的实验数据对样品进行年代判别。结果表明：明代69个古陶瓷样品全部正确归类,南宋-元时期96个古陶瓷样品仅有3个未能正确归类,全部样品归类的正确率为98.2%,说明NAA技术和Bayes判别法可望在古陶瓷的年代断定研究中发挥重要作用。     

北京白河流域现代泥石流物质热释光本底研究

通过对北京白河流域柯太沟、西白莲峪两条泥石流沟谷堆积物的热释光测定,研究现代泥石流物质的热释光本底,得出泥石流物质在流动过程中其热释光信号存在明显的减弱现象.物源区、流通区和堆积区的等效剂量平均值分别为63.19、52.42和49.54 Gy.且因光晒退的影响,两条沟谷每个样点的表层本底值均小于距表层5～10 em的深层本底值.北京白河流域泥石流堆积表层物质的残留本底值在11.2～28.5 ka之间,这一结果是应用古泥石流物质进行热释光测年的基础,为古泥石流测年提供了依据.     

北京清水河流域现代稀性泥石流表层物质热释光本底初步研究

应用热释光技术对北京清水河流域稀性泥石流表层物质进行热释光信号测定,西北山沟、达摩沟、前桑峪沟三沟的形成区等效剂量平均值为48.38 Gy,流通区的平均值为91.75 Gy,堆积区的平均值为62.02 Gy。三个沟的表层泥石流物质本底小,说明原有的认为泥石流由于受物源本底影响无法测年的认识是有局限性的。这个事实可以为应用热释光对老泥石流测年提供依据,对于在泥石流堆积物质中应用热释光技术进行年代测定具有基础性的意义。     

蒋家沟现代泥石流表层堆积物热释光信号的沿沟变化

连续两年对沿蒋家沟主沟(门前沟和多照沟交汇处至蒋家沟与小江交汇处)新发生的泥石流表层堆积物等距取样,测定热释光信号,计算出本底年龄值.研究表明:2010年泥石流表层堆积物的等效剂量和本底年龄沿沟向下游总体增大,2011年总体减小.2011年呈规律性波动,2010年相对于2011年规律不明显.2010年泥石流表层堆积物的辐照响应有较大差异,2011年则基本相同.随着支沟泥石流堆积物汇入主沟,本底年龄值先增大后减小,支沟泥石流堆积物的加入重置了主沟的退火起点.为确保泥石流释光测年机制的可对比性,应该选用对辐照响应较一致的样品,以不同的支沟退火过程为基础研究主沟的退火机制.本工作为进一步揭示泥石流的释光退火机制,开展古泥石流的释光测年提供技术支撑.     

辐照剂量增量对泥石流物质热释光等效剂量的影响

等效剂量的准确测定是进行地质样品热释光年龄测定的关键。采用不同辐照间隔增量测量泥石流物质标样,测得的等效剂量值是不同的,说明辐照剂量增量对泥石流物质样品等效剂量值存在影响。测试选用已知等效剂量为30 Gy的泥石流标样,按不同的辐照剂量增量进行等效剂量测定。2.5Gy/min的β源(90Sr-90Y)辐照剂量增量分别选用1、2、4、6 min时,测得的等效剂量分别为19.3、22.3、26.4、23.0 Gy;8 Gy/min的β源(90Sr-90Y)辐照剂量增量分别选用0.5、1、1.5、2 min时,测得的等效剂量分别为17.6、19.6、25.3、15.6 Gy。研究表明:对于30 Gy的泥石流标样,剂量率为2.5 Gy/s的β源(90Sr-90Y)测定泥石流物质时最适合的辐照剂量增量为4 min。剂量率为8 Gy/s的β源(90Sr-90Y)测定泥石流物质时最适合的辐照剂量增量为1.5 min。     

郊坛官窑瓷器的原料来源和着色机理研究

选取28个效坛官窑残片样品、1个效坛官窑遗址缸内泥料、1个练泥池内泥料、1个官窑所在地的紫金土样品和4个现代仿古官瓷的釉和胎样品进行中子活化分析，测定每个样品中36种元素的含量。将测量数据进行模糊聚类分析，得到动态模糊聚类分析图。结果表明：效坛官瓷胎和釉的原料来源明显不同，郊坛官窑有着稳定的釉料和胎料产地。铁是古官瓷釉的主要着色元素。用色彩分析仪测量古官瓷釉的反射光谱，确定了各种釉色的主波长；用穆斯堡尔谱测定釉中结构铁(Fe^2 、Fe^3 )的相对含量与各种釉色主波长之间的定量关系，从而揭示郊坛官瓷的着色机理。     

小江断裂沿线低阶地面热释光年代学标尺的研究

用ＴＬ测年技术测定了沿小江断裂发育的主要河流低阶地沉积物的堆积年龄，结合毗邻地区同级阶地沉积物的堆积年代，估算了研究区低阶地面的形成时代，为建立研究区最新气候，构造事件的序列提供年代学依据。     

Applicability of Annular Flow Model to Counter-Current Flow in Debris Beds

Counter-current flow limitation (CCFL) is dominant phenomena for dryout in a debris bed which may be formed during a severe accident as observed in the Three-Mile Island unit-2. Actual CCFL situation in debris bed is very complex. It is difficult to treat the CCFL in the debris bed as it is. On the other hand, an annular flow model was developed to predict CCFL in a pipe by assuming a two-dimensional turbulent flow. If hypothetical flow channel were assumed for CCFL in the debris bed, CCFL in the debris bed could be treated with the same manner as for CCFL in a pipe. 'The purpose of this study is to investigate whether the annular flow model developed for CCFL in a pipe is applicable for CCFL in the debris bed or not. As the results, it is clarified that qualitative tendency of the CCFL in the debris bed consisting of larger particles than 3 mm is estimated by the annular flow model developed for CCFL in a pipe, although the difference between the calculation and the data is large in higher and lower gas velocity. It is also clarified that wall friction factor calculated with the present analysis is twice to forth larger than that in the single phase flow through porous media.     

Experimental measurement of frictional law under CCFL in porous debris

Counter-current flow limitation (CCFL) is the dominant phenomena for dryout in porous debris, which would be formed during a severe accident of a nuclear power plant. Since flow at CCFL in porous debris is far away from normal two-phase flow in a pipe, it is not clear whether the interfacial friction laws in a pipe can be applied to the CCFL in porous debris. In the present experimental research, the void fraction in porous debris is measured simultaneously with the differential pressure and flow rates for gas and liquid. The combination of these simultaneously measured data makes it possible to estimate the shear stresses and friction factors in a porous debris at CCFL. It results that the wall friction factor estimated is larger than the Ergun equation proposed for single-phase flow in a porous bed. Furthermore, the interfacial friction factor estimated is well correlated by the theoretical correlation derived here from a force balance for a hypothetical flow channel in porous debris at CCFL.     

阳光晒退对泥石流表层物质热释光信号的影响

应用热释光技术对模拟阳光晒退后的泥石流标样和实际阳光晒退后的泥石流样品进行了热释光信号分层测定。实验结果表明：泥石流发生后经过曝光,样品积存热释光晒退程度随深度增加逐渐减弱,光晒退明显。光晒退随光照强度和时间增大而增强,深度增大,但深度变化总体不大。模拟的阳光晒退实验晒退深度达1 mm左右,实际阳光晒退实验晒退深度达6 mm左右。根据等效剂量随深度的变化可知,天然泥石流块状样由两次泥石流堆积形成。这一结果可为利用热释光技术开展泥石流测年和发生期次研究提供依据。     

Development of debris bed cooling evaluation code,DPCOOL, based on heating porous media submerged in two-phase pool

ABSTRACT

A framework of the modular code system, THERMOS, aiming to evaluate cooling of a debris bed having complex configurations was introduced with a focus on one of the major modules, DPCOOL, which models heating or non-heating porous media of particulate debris in a two-phase pool. In DPCOOL, pool and debris bed regions are discretized in a three-dimensional Cartesian coordinate system. A pool region is formulated based on the two-fluid model. A two-phase flow in the debris bed region is formulated based on the Tung & Dhir model with modifications for smaller particles proposed by Schmidt. In order to synthesize the momentum equations of the two regions, interpolation factors as piecewise linear functions of porosity are introduced. The interfacial friction model was validated based on Chu’s test using a debris bed composed of non-heating SUS spheres in a water pool with air injection from below where the net water flow in the layer became zero so that pressure loss of the layer was governed by interfacial friction. The sum of the two-phase flow friction and the interfacial friction models was validated based on top flooding and bottom flooding tests conducted in IKE’s DEBRIS test facility loaded with mixed steel and alumina spheres that were heated by an induction coil system.     

An experimental study on quenching of a radially stratified heated porous bed

The quenching characteristics of a volumetrically-heated particulate bed composed of radially stratified sand layers were investigated experimentally in the POMECO facility. The sand bed simulates the corium particulate debris bed which is formed when the molten corium released from the vessel fragments in water and deposits on the cavity floor during a postulated severe accident in a light water reactor (LWR). The electrically-heated bed was quenched by water from a water column established over top of it, and later also with water coming from its bottom, which was circulating from the water overlayer through downcomers. A series of experiments were conducted to reveal the effects of the size of downcomers, and their locations in the bed, on the quenching characteristics of the radially stratified debris beds. The downcomers were found to significantly increase the bed quenching rate. To simulate the non-condensable gases generated during the MCCI, air and argon were injected from the bottom of the bed at different flow rates. The effects of gas flow rate and its properties on the quenching behaviour were observed. The results indicate that the non-condensable gas flows reduce the quenching rate significantly. The gas properties also affect the quenching characteristics.     

径向分层碎片床内流动特性研究

为研究非均质结构碎片床内的流动特性,采用两种尺寸颗粒构建了具有径向分层结构的颗粒堆积碎片床,为了对比分析,同时构建了均质结构颗粒堆积碎片床。实验研究了流体在不同堆积结构床内的流动阻力特性,并通过数值模拟揭示了流体在分层床分层界面处的流量再分配现象。研究结果表明,当流体自下而上通过碎片床时,对于均质结构颗粒堆积床,流体呈现一维流动特性;对于具有不同渗透率的径向分层床,除大部分流体自下而上通过分层床外,还存在部分流体从低渗透率层流向高渗透率层,呈现二维流动特性,且绝大部分横流仅发生在分层床的初始部分。     

An experimental study on pressure drop and dryout heat flux of two-phase flow in packed beds of multi-sized and irregular particles

This paper is concerned with debris bed coolability in a postulated severe accident of light water reactors, where the debris particles are irregular and multi-sized. To obtain and verify the friction laws predicting the hydrodynamics of the debris beds, the drag characteristics of air/water single- and two-phase flow in a particulate bed packed with multi-sized spheres or irregular sand particles were investigated on the POMECO-FL test facility. The same types of particles were then loaded in the test section of the POMECO-HT facility to obtain the dryout heat fluxes of the particulate beds heated volumetrically. The effective (mean) particle diameter is 2.25 mm for the multi-sized spheres and 1.75 mm for the sand particles, determined from the Ergun equation and the measured pressure drop of single-phase flow through the packed bed. Given the effective particle diameter, both the pressure drop and the dryout heat flux of two-phase flow through the bed can be predicted by the Reed model. The experiment also shows that the bottom injection of coolant improves the dryout heat flux significantly and the first dryout position is moving upward with increasing bottom injection flowrate. Compared with top-flooding case, the dryout heat flux of the bed can be doubled if the superficial velocity of coolant injection is 0.21–0.27 mm/s. The experimental data provides insights for interpretation of debris bed coolability (how to deal with the multi-sized irregular particles), as well as high-quality data for validation of the coolability analysis models and codes.