LBB和BP在核电站管道设计中的异同性分析

对LBB（破前漏）和BP（破裂排除）两种设计理念进行了比较，从材料质量要求、制造要求、应用范围、泄漏监测、裂纹分析及局部效应、全局效应等方面，对BP和LBB管道设计中的异同性进行了分析。分析结果表明：BP的“纵深防御”体系能包络LBB的主体内容；相对于LBB，BP对管道设计的要求更复杂；主冷却剂管道采用LBB和BP后的局部效应和全局效应大体相同。     

LBB裂纹稳定性分析方法研究

破前漏（LBB）分析是一种先进的管道分析评价技术,其关键技术是裂纹的稳定性分析,决定着LBB技术的可用性。本文从核级管道的失效模式出发研究了LBB分析的裂纹稳定性分析问题,并探讨了修正J积分撕裂模量汇交方法(J-T方法)、修正极限载荷分析法以及两倍弹性斜率法的优缺点和适用范围,最后通过工程算例对不同分析方法进行检验,其结论可为我国核电站管道的LBB设计提供参考。     

核反应堆压力容器接管安全端堆焊修复结构的LBB分析

核反应堆压力容器接管安全端异种金属焊接接头在服役中通常会产生高温高压水环境中的应力腐蚀裂纹扩展。目前减轻和修复这种裂纹的技术是在安全端管接头外表面堆焊一层更抗腐蚀的镍基合金(Alloy52M)材料。本文通过三维结构的有限元断裂力学分析,计算得到了堆焊修复结构的"先漏后断"(Leak-before-break,LBB)曲线和韧带失稳线,并分析了堆焊层厚度对LBB安全边际的影响。结果表明,堆焊修复后结构的LBB曲线和韧带失稳线在没有堆焊层结构的曲线上方,且随堆焊层厚度的增加,LBB曲线和韧带失稳线上移,表明堆焊修复及堆焊层厚度的增加使安全端结构的LBB安全边际增大。     

基于声发射的压力管道LBB监测系统研制

核反应堆压力管道应用破前漏(LBB)技术可提高反应堆的安全性、经济性,设置LBB监测系统则是应用的前提和关键。通过分析LBB监测需求,提出了基于声収射的LBB监测方法,幵通过开展相关试验建立了LBB鉴别方法和定位定量模型。为了适应核反应堆压力管道应用环境要求,研制出一体式声収射传感器,实现了高温辐照环境下LBB探测。通过开展信号调理、抗误报警、在线自检等关键技术研究,研制出LBB监测系统。试验验证结果表明,研制的LBB监测系统各项指标满足核电厂应用要求,幵在华龙一号得到应用。     

不同材料的核电厂主管道LBB评估对比研究

我国核电厂主管道的材料主要有铸造奥氏体不锈钢(CASS)和锻造不锈钢(WSS)。针对CASS和WSS两种材料的主管道,依据美国核管会的SRP3.6.3进行主管道硬前漏(LBB)评估的对比研究。考虑热老化效应获取可信的材料性能数据,根据材料性能差异采用极限载荷法或J积分撕裂模量汇交法计算临界裂纹尺寸。根据Henry均匀非平衡双相流模型计算泄漏裂纹尺寸,并通过环向表面裂纹和贯穿裂纹的扩展分析论证了裂纹疲劳扩展不会导致管道的突然断裂。研究结果表明,WSS材料和CASS材料相比具有更好的LBB性能。     

核反应堆管道LBB设计关键软件研发

破前漏(LBB)设计是三代核电技术的重要技术特征之一,但国内直到现在也没有受认可的LBB设计专用程序,开发出受认可的LBB设计程序具有重要意义。简单介绍LBB设计中断裂力学分析、裂纹张开位移分析以及泄漏率计算的技术背景以及我国相关关键程序的研发。算例验证结果表明,自主开发的程序具有较高的精度,进一步完善和验证后可以应用于实际工程。     

LBB在蠕变温度以上核级管道设计中的应用

LBB（Leak-Before-Break）技术是保证核反应堆结构安全和可靠的一种重要分析方法。对于在蠕变温度以上高温堆（如快堆）的核级管道,运用LBB分析时应考虑疲劳和蠕变对裂纹扩展的影响。本工作以法国规范RCC-MR的A16为基础、以快堆余热排放系统的一段管道为研究对象进行LBB分析,总结出一套运用于蠕变温度以上核级管道安全分析的LBB方法。经计算得到,在蠕变温度以上,蠕变对裂纹扩展的影响较大。经验证,该管道符合LBB技术对于裂纹稳定性及泄漏量可探测性的条件,满足从开始泄漏到裂纹失稳的时间要求。     

非中心穿透裂纹对LBB技术应用的影响分析

随着LBB技术的发展和应用推广,可运用详细的裂纹扩展分析技术,通过周密的分析论证,以证明带缺陷管系在使用寿期内同样能够满足SRP3.6.3中关于LBB技术应用的、与泄漏探测能力、裂纹稳定性和载荷相关的裕量要求。在这种前提下,一些额外的分析就必不可少。其中之一即为需要考虑载荷对称中心与裂纹对称中心不重合情况,即所谓的非中心裂纹,对LBB技术应用的影响。本文以压水堆核电厂中DN150、DN350和DN550管径的核1级高能管道中非中心裂纹为研究对象,先从偏心角度对裂纹张开面积的分析着手,进而研究其对泄漏率分析与裂纹稳定性分析的影响,并对非中心裂纹对LBB技术应用的影响做了综合性的分析总结,为今后含缺陷管道应用LBB技术的分析提供参考与借鉴。     

含环向穿透裂纹管道LBB裂纹扩展稳定性计算程序开发

在管道LBB设计和评定中,J积分和裂纹扩展稳定性的计算过程复杂,为提高计算精度和效率,需采用改进的计算方法,并实现程序软件的计算。本文基于增强参考应力法(ERS法)的J积分计算和J积分稳定性评定图法,开发LBB裂纹扩展稳定性计算程序,此程序可计算含环向穿透裂纹管道的LBB失稳载荷和临界裂纹长度。所开发的程序实现了单纯拉伸载荷、弯曲载荷及拉弯复合非比例加载下的裂纹扩展稳定性计算,并提供了两种材料真应力-真应变关系参数的输入计算方法,拓宽了现有计算方法的局限性。通过有限元计算结果和文献中管线试验结果与程序计算结果的对比分析,验证了计算程序的准确性。     

核电厂高能管道应用破前漏技术对材料力学性能的要求

核电厂高能管道应用破前漏(LBB)技术可提高其安全性与经济性,同时对材料提出了新的力学性能测试要求。文章研究和分析了美国核管理委员会颁布的LBB有关的标准评审大纲和实施规范等,梳理和归纳了测试项目、对象、温度、数量与热老化效应等5项总体要求,以及试样尺寸、侧槽效应、应变范围、试样方向等4项测试关键技术要求,以确保测试数据的有效性。本研究可为国内开展此领域的测试工作提供一定的指引作用。     

Development of modified piping evaluation diagram for leak-before-break application to Korean next generation reactor

Recently, the piping evaluation diagram (PED) is accepted in nuclear industry for an efficient application of leak-before-break (LBB) concept to piping system at an initial piping design stage. The objective of this paper is to develop the modified PED, which can account for the variation of the material properties of the PED development stage and those of the assembly stage. For this purpose, a parametric study was performed to investigate the effect of stress–strain curve on the detectable leakage crack length and the effect of fracture resistance curve on the LBB allowable load. Finite element analyses were also performed to investigate the effect of stress–strain curve on the LBB allowable load. Finally, a modified PED was proposed as a function of crack length and the allowable safe shutdown earthquake load. The LBB analyses based on the modified PED are in good agreement with those based on the traditional PED. By adopting the modified PED, the variation of material properties can be considered in the LBB analysis and the computing times required for the application of LBB during the design process can be considerably reduced.     

Application of LBB to high energy pipings of a pressurized water reactor in Korea

The application of the leak before break (LBB) technology to the newly constructed pressurized water reactors (PWRs) has been approved in Korea for several high energy systems that can meet rigorous acceptance criteria. The LBB application in Korea is based on the US Nuclear Regulatory Commision (USNRC) requirements. The purpose of the LBB evaluation is to eliminate the dynamic effects associated with the postulated double-ended guillotine break (DEGB) from design basis loads, as well as to eliminate pipe whip restraints and jet impingement barriers. There were several issues on the application of LBB to the primary coolant loop and the pressurizer surge line. Of concern were the material properties for the carbon steel for the primary coolant loop, estimation of the crack opening area at the pipe-to-nozzle interface considering the asymmetry, and the leakage crack size which barely meets the required margin of 2 for the surge line, etc. Some additional work was required by the safety authority to maintain the global safety of the plant at a sufficient level. This paper describes the regulatory application of LBB in Korea, and the issues encountered during the regulatory review.     

破前漏分析中泄漏率模型研究进展

破前漏（LBB）分析对商业核电站承压设备的安全分析至关重要,并有许多突出的优点。目前,LBB在高温气冷堆上的应用尚不成熟,而提出较为精确的破前漏泄漏率模型是破前漏思想能否在高温气冷堆上得以应用的关键。文章主要概述目前各国破前漏分析中泄漏率模型方面的研究进展。通过分析各个泄漏率模型的基本假设,理论分析、计算流体力学分析、实验验证及应用实例,分析各模型的优缺点,理清各因素对泄漏率的影响,并筛选可能应用到高温气冷堆破前漏分析泄漏率模型中的合理部分,为后期高温气冷堆破前漏泄漏率模型研究提供建议。     

Extended applications of LBB piping evaluation diagrams for a new plant design

Plant specific data, such as pipe geometry, material properties and pipe loads, are required to apply leak-before-break (LBB) to a piping system. Thus, LBB evaluation cannot be done until piping design and routing are completed. A simple method for evaluating LBB for piping systems during design process considering the effects of nozzle and the change in local and global compliance in cracked piping system is developed in this paper. This method produces piping evaluation diagrams for intermediate pipe locations and pipe-nozzle interface locations which defines the LBB requirements to the piping designer for use during the design process and is independent of pipe routing. Piping evaluation diagrams can be used for the LBB evaluation for a new plant design.     

压力管道破前漏分析的一种简化方法

介绍了一种用于核反应堆管道和压力容器破前漏（ＬＢＢ）分析的简化方法，它主要以线弹性断裂力学的基础，将ＬＢＢ分析中应力强度因子，裂纹张开面积和泄漏率等计算以解析公式表达出来。这种方法使用方便，而且满足有关的国家标准和国际规范的要求，适用于一些应力分布和几何形状比较简单的管道和压力容器，或用于ＬＢＢ性质的近似估计。     

Leak-before-break behavior of statically indeterminate piping system

Structural integrity considering the fatigue have become to be important, as energy-related structures such as nuclear piping systems especially have been usually operating under cyclic loads. This study is concerned about the leak-before-break (LBB) behavior when pipe including a circumferential crack is subjected to a cyclic load. Attentions were paid to the proposal of assessment models and conditions on the LBB behavior considering a crack shape at wall penetration under a cyclic load, the comparison of LBB condition between a static load and a cyclic load, and the characteristic of the fatigue LBB behavior under statically indeterminate system. It is concluded that LBB behavior is more likely to be occurred in statically indeterminate piping system, as the reduction of ultimate strength due to a sufficient redistribution of bending moment in this system was relatively small. This benefit on structural integrity of statically indeterminate system was applied to the fatigue LBB behavior envisioned the validity and the superiority of the fatigue LBB behavior in statically indeterminate piping system.     

New leak detection technique using ceramic humidity sensor for water reactors

Leak-before-break (LBB) approach has been considered for its application to the main steam line (MSL) of Korean Next Generation Reactor (KNGR) — an advanced pressurized water reactor under development. Unlike the primary water leakage, the MSL leak detection must be based on principles other than radioactivity measurements. Among potential options that are being considered as indicators of leakage, it is believed that humidity at the proximity of the piping system is an effective one. A ceramic-based humidity sensor was developed, which can be qualified for LBB applications. The ceramic material, sintered and annealed MgCr₂O₄–TiO₂, is shown to increase its electrical conductivity upon water vapor adsorption without any negative impact due to gamma radiation over the entire temperature range of interest. In the plant applications, the sensor array can be positioned in the annulus between the piping and surrounding insulation. By the analysis of humidity distribution in the annulus, a leak rate of 1 l h⁻¹ can be detected within an hour when the distance between two adjacent sensors does not exceed 1 m. In order to minimize the number of signal wires, the use of AC impedance technique is shown to be advantageous. In this paper, the results of the development and the performance characterization of ceramic humidity sensor for the LBB application to the MSL of KNGR are summarized.