Core Burnup Calculation of Plutonium Burning Inert-Matrix Fueled High Temperature Gas Cooled Reactor

For the efficient reduction of excess plutonium amount, Japan Atomic Energy Research Institute (JAERI, now Japan Atomic Energy Agency) has studied a concept of rock-like oxide (ROX) fuel as a kind of inert matrix fuel (IMF). In the JAERI study, ROX fuel is burnt in existing light water reactors (LWRs), while in this study, pebble bed type high temperature gas cooled reactor (HTGR) is studied, mainly because of its high neutron economy and softer neutron spectrum than LWRs. Here, PuO₂-yttria stabilized zirconia (YSZ: (Zr,Y)O_2-x) particles are dispersed in graphite matrix. In the ROX fueled LWR study, it was necessary to improve fuel temperature reactivity coefficients by adding such additives as ²³⁸U and Er. Here in HTGR, although the negative temperature coefficient is much larger than that in LWR without any improvements, temperature coefficient was improved as large as possible to the level of UO₂ HTGR case by adding Er in the fuel. Burnup calculations on PuO_2-YSZ fueled HTGR, by simulating the continuous refueling of fuel pebbles with the batch fuel loading, showed almost complete transmutation for ²³⁹Pu and more than 80% for the total plutonium. As the maximum power density of the fuel pebble obtained by the core burnup calculation was very large in comparison with the UO₂ HTGR, the maximum temperature in YSZ fuel particle was also evaluated. Despite the low thermal conductivity of YSZ, the evaluated YSZ temperature was well below the melting point, thanks to the high thermal conductivity of graphite and small YSZ particle size. Here, the high power density in the Pu-YSZ fueled core might become a problem, but is possible to be reduced by adjusting the initial plutonium enrichment.     

强内热源球床通道单相对流换热特性实验研究

球床水冷反应堆的堆芯为球形燃料元件堆积成的多孔通道,具有显著的强化换热作用。球床通道内的孔隙因具有多变性、随机性的特点,换热情况非常复杂,相关研究较少。为了研究含内热源球床通道内的换热特性,本文用直径为8 mm碳钢球堆积形成球床,以蒸馏水为工质,采用电磁感应加热方式对球床进行整体加热,研究球床通道内部的换热特性。通过对实验数据进行分析,得到了球床通道内部的功率分布和换热系数随热流密度、工质Re的变化规律,根据实验数据拟合得到了球床通道内平均换热系数的无量纲准则关联式,拟合结果与实验结果的相对偏差在12%以内,符合良好。     

球床式高温气冷堆MOX燃料循环优化

与压水堆相比,球床式高温气冷堆能在堆芯结构不做明显改变的情况下采用全堆芯装载混合氧化物（MOX）燃料元件。基于250 MW球床模块式高温气冷堆堆芯结构,设计了4种球床式高温气冷堆下MOX燃料循环方式,包括铀钚混合的燃料球和独立的钚球与铀球混合装载的等效方式,采用高温气冷堆设计程序VSOP进行分析,比较了初装堆的有效增殖因数、燃料元件在堆芯内滞留时间、卸料燃耗、温度系数等主要物理特性。结果表明：采用纯铀和纯钚两种分离燃料球且铀燃料球循环时间更长的方案,平均卸料燃耗较高,总体性能较其他循环方式优越。     

球床堆内冷却剂流动与传热特性的CFD研究

以计算流体力学(CFD)为基础,利用大型商业软件ProE和CFX,对球床式水冷堆堆芯燃料元件进行三维建模、网格划分和数值计算,对堆芯内冷却剂热工水力特性进行了初步的研究.计算比较了燃料元件球间隙和接触情况下冷却剂的速度场、温度场和压力分布,分析了其对堆芯安全的影响.     

Using thorium to reduce the maximum fuel temperatures during depressurized loss of coolant accidents in a once-through-then-out (OTTO) PBMR DPP-400 core

This article presents the results for the PBMR-DPP-400, but for a once-through-then-out (OTTO) refueling scheme. An optimization attempt of the axial and radial power profiles is reported. The main aim was to reduce the maximum depressurized loss of forced coolant (DLOFC) temperature by adding thorium to the fuel and making the fuel layout radially asymmetric by placing lower enriched fuel in the inner and higher enriched fuel in the outer fuel flow regions. These measures (1) flattened the peaks in the axial power profiles and thus suppressed the hotspots in the axial DLOFC temperature profiles and (2) ‘pushed’ the power radially outwards, so as to reduce the distance that the decay heat must be evacuated towards the outside of the fuel core. This resulted in a huge reduction in the maximum DLOFC temperature for the OTTO cycle from 2273 to 1811 °C, which is still above the 1600 °C limit but represents a remarkable result. Maximum DLOFC temperature below the 1600 °C limit was obtained by reducing the power output. The results obtained and the proposed strategies for further improvement are applicable to the Chinese HTR-PM and could produce even better results in Prismatic Block Reactors such as the Japanese HTTR.     

高温气冷堆和轻水堆超铀元素管理特性研究

乏燃料中长寿命锕系元素对环境造成长期潜在危害,本文研究球床高温气冷堆不同燃料循环中超铀元素的产生和焚烧特性。在250 MW球床模块式高温气冷堆示范电站HTR-PM铀钚循环的乏燃料中提取铀和钚作为核燃料,设计了PuO₂和MOX燃料元件,将新设计的燃料元件重新装入与HTR-PM相同结构和尺寸的堆芯,分别形成纯钚燃料循环和MOX燃料循环。采用高温气冷堆物理设计程序VSOP,研究了高温气冷堆一次通过燃料循环和不同闭式燃料循环的超铀元素焚烧特性,并与轻水堆燃料循环结果进行比较和分析。结果表明：高温气冷堆一次通过燃料循环超铀元素生成率约为轻水堆的1/2;高温气冷堆闭式燃料循环能有效嬗变超铀元素。     

球床高温气冷堆使用可燃毒物的方案探讨

为改善球床高温气冷堆在特定情况下功率分布的形状和峰值,可在燃料球内添加可燃毒物。本文分析两种可燃毒物的添加方式,燃料球石墨基体均匀添加可燃毒物和燃料球内添加可燃毒物颗粒。由于¹⁰B的强吸收性能,均匀添加可燃毒物的消耗速度过快,不易控制,而通过添加不同尺寸的可燃毒物颗粒可优化燃耗速度,有效改善堆芯功率分布的形状和峰值。     

球床反应堆燃料元件脉冲气力提升动力特性分析

球床反应堆采用球形燃料元件多次通过堆芯的循环运行方式,燃料元件从堆芯底部连续单列排出后依靠管路气动推力逐一被提升至堆芯顶部。本文建立了球形燃料元件“近等径”管路脉冲气力提升运动模型,并在此基础上分析了气源压力、控制阀有效截面积、球外径与管内径的直径比等参数对提升过程燃料元件运行速度的影响。利用测速装置测量了10 MW球床反应实验堆提升器出口燃料元件的运行速度,实验结果接近理论分析结果。近等径球流管路脉冲气力提升运动模型的建立及实验研究为球床反应堆燃料输送系统优化设计及运行调控提供了理论依据。     

球床堆流动与传热数值模拟

采用离散元方法(DEM)模拟球床反应堆内燃料球的随机分布,通过计算流体力学(CFD)方法研究球床堆内的流动与传热。结果表明:球与球之间的间隙处压力较低;而流速、温度、涡强度较高。沿径向分布,压力、涡强度、换热系数随孔隙率的增加而降低;流速随孔隙率的增加而增加。     

球床模块堆停堆后自然对流传热特性数值研究

对冷却流体在球床模块堆内燃料颗粒填充区域中的流动和传热过程进行了研究.数值模拟突然停堆后燃料颗粒区在温差作用下的自然对流过程,分析了瑞利数Ra对燃料填充区域内流场、温度场和局部努塞尔数Nu以及壁面摩擦阻力系数的影响.计算结果表明:当球床模块堆突然停堆时燃料填充区域可形成加热壁面流体上升流动、冷却壁面下降流动的自然循环流动;随着Ra数增大,回流中心向上移动;沿轴向壁面局部Nusselt数和摩擦阻力系数存在极值,并且极值点随Ra数增大而向上移动;与氮气相比,氦气作为冷却介质停堆后具有更均匀的堆芯轴向温度分布.     

硅酸锂球床传热传质特性与吹扫气体流动的DEM-CFD耦合模拟

氦冷固态增殖包层是中国聚变工程实验堆（CFETR）的3种候选包层概念之一,氚增殖球床是包层的核心部件,采用硅酸锂颗粒作为氚增殖材料。球床结构对氚在球床内的输运行为及流动和传热均有重要影响。本文基于离散单元法（DEM）生成了满足氚增殖球床填充率要求的随机堆积结构,通过CFD计算获取了球床结构下氚在吹扫气体内的等效扩散系数及吹扫气体的流动特性,包括速度分布、压力分布及进出口压降;开展了外加热流及有内热源两种工况下球床等效导热系数的模拟。计算结果表明,球床结构下氚在吹扫气体内的等效扩散系数为二元气体扩散系数的40%;受球床结构影响,球床内存在流动迟滞区,壁面出现流动加速;拟合得到Ergun方程的黏性阻力系数C1=87;有内热源工况下的球床等效导热系数低于外加热流工况下的球床等效导热系数。     

Evaluation of Hot Spot Factors for Thermal and Hydraulic Design of HTTR

Abstract

High Temperature Engineering Test Reactor (HTTR) is a graphite-moderated and helium gas-cooled reactor with 30 MW in thermal power and 950°C in reactor outlet coolant temperature. One of the major items in thermal and hydraulic design of the HTTR is to evaluate the maximum fuel temperature with a sufficient margin from a viewpoint of integrity of coated fuel particles. Hot spot factors are considered in the thermal and hydraulic design to evaluate the fuel temperature not only under the normal operation condition but also under any transient condition conservatively. This report summarizes the items of hot spot factors selected in the thermal and hydraulic design and their estimated values, and also presents evaluation results of the thermal and hydraulic characteristics of the HTTR briefly.     

氟盐冷却球床高温堆燃料管理程序的开发与分析

基于确定论的中子学分析程序在计算氟盐冷却球床高温堆（PB-FHR）时需解决双重非均匀性的燃料球均匀化、燃料球均匀化时出现的泄漏效应及燃料球在堆芯内连续移动与多次通过堆芯的燃料循环模式问题。本文基于DRAGON5与DONJON5程序开发了PB-FHR的燃料管理程序PBMSR,并进行了验证。使用PBMSR对PB-FHR在不同燃料循环模式下进行计算与初步分析,结果显示在多次通过的燃料管理模式下,燃料球的通过次数对最深卸料燃耗影响较小,但对轴向功率分布影响较大。     

压水堆堆芯熔融物的运动及传热数值分析

针对HPR1000堆型堆芯熔融坍塌问题建立了精确的三维堆芯模型,使用时间推进方法通过求解熔融物的瞬态运动、传热微分方程,确定熔融物在堆芯中的瞬态位置和瞬时温度,以模拟堆芯升温及堆芯熔融进程。研究结果表明：停堆后约2 400 s开始出现熔融现象,熔融物在堆芯活性区域内下落且发生多重相变过程;在4 900 s后,熔融物在堆芯底部形成约1.5 m高的稳定熔池;由于外围组件与低温围栏装置换热,最外围的组件不会发生熔融。本文建立的堆芯熔融物运动与传热分析模型及相关计算结果,可为事故缓解和处理提供技术参考。     

带交混翼矩形流道内超临界流动传热CFD研究

针对超临界水堆使用的棒束,取1根加热棒为中心的矩形区域作为研究对象,采用CFD中CFX10作为数值计算方法,研究了25MPa超临界压力下,有无交混翼时流体的流动和传热特点。计算结果表明：交混翼可增加流道内温度分布的均匀性,同时具有强化传热作用。     

Heat Transfer Characteristics of Zircaloy-2 Oxide Film

A neural network model is under development to predict the local power distribution in a BWR fuel bundle as a high speed simulator of precise nuclear physical analysis model. The relation between ²³⁵U enrichment of fuel rods and local peaking factor (LPF) has been learned using a two-layered neural network model ENET. The training signals used were 33 patterns having considered a line symmetry of a 8x8 assembly lattice including 4 water rods.

The ENET model is used in the first stage and a new model GNET which learns the change of LPFs caused by burnable neutron absorber Gadolinia, is added to the ENET in the second stage. Using this two-staged model EGNET, total number of training signals can be decreased to 99. These training signals are for zero-burnup cases. The effect of Gadolinia on LPF has a large nonliniality and the GNET should have three layers. This combined model of EGNET can predict the training signals within 0.02 of LPF error, and the LPF of a high power rod is predictable within 0.03 error for Gadolinia rod distributions different from the training signals when the number of Gadolinia rods is less than 10. The computing speed of EGNET is more than 100 times faster than that of a precise nuclear analysis model, and EGNET is suitable for scoping survey analysis.     

氚增殖剂球床组件堆内辐照物理热工计算分析

为验证在中国先进研究堆(CARR)内进行国际热核聚变实验堆(ITER)氚增殖包层模块(TBM)辐照实验的可行性和安全性,进行了氚增殖剂球床组件堆内辐照物理及热工计算分析。氚增殖剂包层模块主要是固态氚增殖剂陶瓷球床。本文采用Monte Carlo粒子输运模拟程序对氚增殖剂球床进行堆内建模,计算球床的中子注量率、能量沉积和产额,得到不同功率下球床的中子注量率、发热功率和产氚速率以及球床组件引入反应堆的反应性。根据物理计算得到的组件各部件发热情况建立热工计算一维模型,通过更改反应堆功率得到满足实验要求的工况并采用三维程序进行验证。物理与热工计算分析的结果表明,在反应堆运行功率为20 MW的工况下球床组件各部件的温度均不超过限值。     

Numerical Simulation of Fluid Flow and Heat Transfer of Supercritical Fluids in Fuel Bundles

A supercritical water-cooled reactor (SCWR) was proposed as a kind of generation IV reactor in order to improve the efficiency of nuclear reactors. Although investigations on the thermal-hydraulic behavior in SCWR have attracted much attention, there is still a lack of CFD study on the heat transfer of supercritical water in fuel channels. In order to understand the thermal-hydraulic behavior of supercritical fluids in nuclear reactors, the local fluid flow and heat transfer of supercritical water in a 37-element fuel bundle has been studied numerically in this work. Results show that secondary flow appears and the cladding surface temperature (CST) is very nonuniform in the fuel bundle. The maximum cladding surface temperature (MaxCST), which is an important design parameter for SCWR, can be predicted and analyzed using the CFD method. Due to a very large circumferential temperature gradient in cladding surfaces of the fuel bundle, the precise cladding temperature distributions using the CFD method is highly recommended.     

钠冷快堆六角形组件换热特性分析

钠冷快堆乏燃料组件在转运过程中,会暴露在传热性能较差的氩气环境中。为保证燃料组件温度在转运过程中低于安全限值,本研究基于37棒燃料组件开展了在氩气环境下的实验研究及数值模拟计算。研究结果表明：可采用等效导热法对组件内绕丝模型进行简化,简化模型能满足计算精度要求。将计算结果与实验研究结果进行对比分析,结果表明数值模拟方法能较好模拟组件在氩气环境下的换热。六角形燃料组件在氩气中的换热分析中,辐射换热具有重要的影响,实验工况下辐射换热占总换热量的36%～57%。     

燃料棒周向导热对超临界水堆堆芯子通道分析的影响

本文在子通道程序的燃料棒模型中引入三维导热方程,使该模型能用来模拟燃料棒的周向导热情况。采用改造后的子通道程序对混合谱超临界水堆设计中的两种燃料组件结构进行计算分析,研究燃料棒周向导热对超临界水堆燃料组件子通道分析的影响。结果表明：热谱组件的子通道计算中,燃料棒周向导热的影响不能忽略;快谱组件的子通道计算中,燃料棒周向导热的影响基本可忽略。