反应堆压力容器外水冷条件下贯穿件完整性分析

严重事敝下堆芯熔融物坍塌到反应堆压力容器(RPV)下封头时,可能造成贯穿件因高温熔融物热侵袭而失效,使压力容器丧失完整性,熔融物进入到反应堆堆腔中,导致熔融物堆内滞留(IVR)失效.在分析贯穿件脱落和熔融物流入贯穿件两种失效模式基础上,分别运用VTA程序和修正的整体凝固模型(MBF)计算贯穿件焊缝的熔化程度、热膨胀产生的摩擦力,估算贯穿件内熔融物流动的距离.结果表明,在成功实施反应堆压力容器外水冷(EVVC)措施条件下,300 MW压水堆核电厂压力容器的下封头不会因贯穿件失效而丧失完整性,堆芯熔融物小能通过贯穿件失效向堆腔迁移.     

ROAAM应用于ACP1000严重事故下实施IVR策略的有效性概率分析

基于堆芯熔融物与压力容器传热的机理分析模型,采用风险导向事故分析方法(ROAAM)分析压水堆在严重事故情况下通过冷却压力容器外部的手段来实施堆芯熔融物滞留在压力容器内(IVR)策略的有效性。以核电厂一级概率安全评价(PSA)分析结果为参考,计算ACP1000典型严重事故序列,分析影响熔融物传热的重要参数不确定性。概率分析结果表明:ACP1000发生假象的严重事故情况下,IVR策略有效性概率大于99%;由于熔融池顶部的金属层出现集热效应,下封头发生传热危险的主要位置出现在金属层。     

严重事故条件下压力容器完整性评价的研究进展

堆芯熔融物堆内滞留(In-Vessel Retention,IVR)是以AP1000为代表的第三代轻水反应堆严重事故管理的重要策略之一,也是严重事故条件下保证压力容器完整性(Reactor Vessel Integrity,RVI)的典型方法之一.该文综述了国外在严重事故条件下压力容器完整性试验研究和理论分析的现状,总...     

基于ASTEC程序的反应堆严重事故下压力容器下封头传热分析

反应堆压力容器内熔融物滞留是先进反应堆设计严重事故缓解措施中的重要选项之一，在维持反应堆压力容器的完整性，包容堆芯熔融物方面具有重要作用。确保熔融物滞留有效性的关键是保证下封头内壁热负荷不超过下封头外壁面换热能力，而且在整个过程中不发生结构失效，即下封头剩余壁厚能够实现熔融物的承载。应用ASTEC程序，基于大型先进压水堆的设计，针对反应堆压力容器内熔融物滞留系统运行过程中冷却剂热工参数、下封头外壁面临界热流密度和最终下封头厚度进行计算分析，通过研究熔池对下封头的熔蚀和剩余厚度，判断下封头残留厚度对于熔融物的包容，评估系统的有效性。结果表明：在下封头较上部位置的部分区域内，换热较为剧烈，其中热流密度最大值出现在熔融物分两层的交界处，事故过程中下封头内壁将被熔融物金属层熔化，剩余厚度满足包容要求，但是最终剩余厚度十分有限。     

三层熔融池结构情况下反应堆压力容器外水冷有效性分析

通过反应堆压力容器外水冷(ERVC)实现熔融物压力容器内滞留(IVR)是300 MW压水堆核电厂重要的严重事故管理特征。在过去IVR分析中通常对反应堆压力容器(RPV)下封头内两层熔融池结构进行分析,然而核电厂还可能出现一种底部为重金属层的3层熔融池结构,它可能对RPV完整性带来更大的威胁。本文根据建立的模型假设300 MW压水堆核电厂出现的该熔融池结构,并进行分析。结果表明,形成的底部重金属层不会威胁RPV完整性,但厚度变薄的顶部金属层失效裕度较小,可能威胁RPV完整性。     

先进压水堆熔融物堆内滞留参数不确定分析研究

压水堆核电厂在严重事故下将发生堆芯熔化事故而形成熔融池。形成熔融池的过程具有很大的不确定性,这影响到反应堆压力容器熔融物堆内滞留（IVR）策略的有效性。本工作以AP1000核电厂两层IVR模型为研究对象,对成功实施反应堆压力容器外部冷却（ERVC）的假想严重事故进行了熔融池参数不确定性分析,包括参数的敏感性分析和使用拉丁超立方抽样的概率分析。结果表明：衰变功率对IVR评价参数影响最大,应采取措施（如上堆腔注水）尽量延缓堆芯熔化的时间;熔融物中不锈钢的质量将对金属层参数造成较大影响,可考虑在压力容器内布置牺牲性材料来减小金属层的集热效应;氧化物层外压力容器失效的概率仅为1.2%,但金属层外压力容器失效的概率高达20%。本结果对今后IVR策略研究和设计具有一定的指导意义,同时也为压水堆核电厂安全评审提供理论支持。     

反应堆内熔融物冷却的三维数值模拟研究

目前国际上普遍采用堆芯熔融物压力容器内滞留（IVR）策略来缓解严重事故后果。本文基于日本应用能源研究所开发的核电厂事故分析程序SAMPSON,对其压力容器内熔融物冷却分析（DCA）模块进行改进,增加了熔池内金属和氧化物分层模型,开发了熔融物三维直角坐标网格与压力容器三维曲面坐标的交界面几何参数前处理程序,改进了压力容器外冷却的传热关系式。通过AP1000核电机组严重事故下的IVR对改进后的程序进行分析验证,并与实验结果进行对比。结果表明,改进后的SAMPSON程序可对核电厂严重事故下下封头内的熔融物冷却滞留开展有效的模拟分析。     

严重事故IVR下反应堆压力容器耦合传热数值模拟分析

堆芯熔化严重事故下保证反应堆压力容器（RPV）完整性非常重要,高温蠕变失效是堆芯熔化严重事故下反应堆压力容器的主要失效模式。在进行严重事故堆芯熔化物堆内包容（IVR）下RPV结构完整性分析中,RPV内外壁和沿高度方向的温度分布以及剩余壁厚是结构分析的重要输入。本文采用CFD分析方法对RPV堆内熔融物、RPV壁以及外部气液两相流动换热进行热-固-流耦合分析,获得耦合情况下的温度场、流场、各相份额分布以及RPV的剩余壁厚,为RPV在严重事故IVR下的结构完整性分析提供依据。     

增强IVR有效性的堆内注水策略研究

熔融物堆内滞留（IVR）是一项核电厂重要的严重事故管理措施,通过将熔融物滞留在压力容器内,以保证压力容器完整性,并防止某些可能危及安全壳完整性的堆外现象。对于高功率和熔池中金属量相对不足的反应堆,若下封头形成3层熔池结构,则其顶部薄金属层导致的聚焦效应可能对压力容器完整性带来更大的威胁。本文考虑通过破口倒灌及其他工程措施实现严重事故下熔池顶部水冷却,建立熔池传热模型,分析顶部注水的带热能力,建立事件树,分析顶部注水措施的成功概率及IVR的有效性。结果表明,通过压力容器内外同时水冷熔融物,能显著增强IVR措施的有效性。     

熔融物作用下压力容器下封头热应力分析方法研究

堆芯熔融物滞留(IVR)策略是核电厂针对严重事故的一项重要缓解措施。采用有限元方法对IVR策略期间反应堆压力容器(RPV)下封头在熔融物作用下的力学行为进行研究,通过对熔融物传递给压力容器壁面的热载荷和力学载荷进行研究,计算得到下封头的温度场和应力场分布,幵对热膨胀和内压等对结构力学响应的影响进行了研究,对材料的弹性和弹塑性行为进行了比较。结果表明,热膨胀产生的应力和变形远大于容器自重、熔池压力和冷却水压力产生的结果;内压大于1 MPa时其对结构的力学响应有显著影响;熔融物作用下压力容器下封头将产生不可忽视的塑性变形,采用弹塑性方法进行分析更为合理。     

真实表面材料及其老化效应对反应堆压力容器ERVC-CHF影响的试验研究

通过反应堆压力容器外部冷却（ERVC）实现熔融物堆内滞留（IVR）技术是核电厂严重事故缓解的重要措施之一。在本文的研究中,建立了二维切片式、全尺寸的试验台架FIRM,开展严重事故条件下反应堆压力容器ERVC-临界热流密度（CHF）试验研究。试验采用去离子水作为试验工质,获得了反应堆压力容器下封头ERVC过程的CHF限值。研究了真实表面材料对CHF的影响及其影响机理,讨论了在去离子水下表面材料SA508 Gr3. Cl.1钢的老化效应。本试验研究对于认识反应堆压力容器IVR-ERVC条件下的CHF行为、提高反应堆压力容器安全性有重要意义。     

海洋核动力平台严重事故下熔融物堆内滞留分析程序开发

针对海洋核动力平台的设计特点,分析了严重事故下压力容器外冷却实现熔融物堆内滞留技术的可行性。根据海洋核动力平台功率密度较低和压力容器下封头尺寸较小的特点,建立了压力容器下封头内熔池传热理论模型,编制了分析程序SR-IVR,进行了基准例题验证。结果表明,本文所建分析模型和程序可用于海洋核动力平台严重事故下熔融物堆内滞留分析。     

Corium retention for high power reactors by an in-vessel core catcher in combination with External Reactor Vessel Cooling

If there were inadequate cooling during a reactor accident, a significant amount of core material could become molten and relocate to the lower head of the reactor vessel, as happened in the Three Mile Island Unit 2 (TMI-2) accident. If it is possible to ensure that the vessel lower head remains intact so that relocated core materials are retained within the vessel, the enhanced safety associated with these plants can reduce concerns about containment failure and associated risk. For example, the enhanced safety of the Westinghouse Advanced 600 MWe Pressurized Water Reactor (AP600), which relied upon External Reactor Vessel Cooling (ERVC) for in-vessel retention (IVR), resulted in the United States Nuclear Regulatory Commission (US NRC) approving the design without requiring certain conventional features common to existing Light Water Reactors (LWRs). Accordingly, IVR of core melt is a key severe accident management strategy adopted by some operating nuclear power plants and proposed for some advanced light water reactors. However, it is not clear that currently-proposed methods to achieve ERVC will provide sufficient heat removal for higher power reactors. A US–Korean International Nuclear Energy Research Initiative (INERI) project has been initiated in which the Idaho National Engineering and Environmental Laboratory (INEEL), Seoul National University (SNU), Pennsylvania State University (PSU), and the Korea Atomic Energy Research Institute (KAERI) will determine if IVR is feasible for reactors up to 1500 MWe. This paper summarizes results from the first year of this 3-year project.     

A simple novel analysis procedure for IVR calculation in core-molten severe accident

In-Vessel Retention (IVR) of core melt is a key severe accident management strategy adopted by operating nuclear power plants and advanced light water reactors (ALWRs), AP600, AP1000, etc. External Reactor Vessel Cooling (ERVC), which involves flooding the reactor cavity to submerge the reactor vessel in an attempt to cool core debris relocated to the vessel low head, is a novel severe accident management for IVR analysis. In present study, IVR analysis code in severe accident (IVRASA) has been proposed to evaluate the safety margin of IVR in AP600 with anticipative depressurization and reactor cavity flooding in severe accident. For, IVRASA, a simple novel analysis procedure has been developed for modeling the steady-state endpoint of core melt configurations. Furthermore, IVRASA was developed in a more general fashion so that it is applicable to compute various molten configurations such as UCSB Final Bounding State (FIBS). The results by IVRASA were consistent with those of the UCSB and INEEL. Benchmark calculations of UCSB-assumed FIBS indicate the applicability and accuracy of IVRASA and it could be applied to predict the thermal response of various molten configurations.     

Flow analyses using RELAP5/MOD3 code for OPR1000 under the external reactor vessel cooling

External reactor vessel cooling (ERVC) is considered as one of the most promising severe accident management strategies for an in-vessel corium retention (IVR). Heat removal capacity and water availability at the vessel outer surface can be key factors determining the success of ERVC measures. In this study, for the investigations on the effect of water availability in case of ERVC, flow analyses using the RELAP5/MOD3 code were performed. The analyses were focused to examine the flow behavior inside the reactor pressure vessel (RPV) insulator of the OPR1000 (Optimized Power Reactor 1000 MWe) under a cavity flooding. The current flow analyses results show that for the accident scenarios of station black out (SBO) and 9.6 in. large break loss of coolant accident (LBLOCA) under the ERVC, steam could not ventilate through the insulator and the pressure inside the RPV insulator increased abruptly. This induced a water sweep out and steam domination in the flow path inside the insulator. These flow analyses results indicate that sufficient water ingression and steam venting through the insulator can be a key factor determining the success of the ERVC in the operating nuclear power plant, OPR1000. According to the results of the sensitivity studies for the venting area, in terms of an effective flow circulation inside the insulator, an optimal venting is to assign four holes having a diameter of 0.3 m at the upper exit (hot leg level) of the insulator. And the effect of the inlet flow area at the insulator bottom is rather minor when compared to that of the outlet flow area of a steam venting.     

CHF enhancement by vessel coating for external reactor vessel cooling

In-vessel retention (IVR) is a key severe accident management (SAM) strategy that has been adopted by some operating nuclear power plants and proposed for some advanced light water reactors (ALWRs). One viable means for IVR is the method of external reactor vessel cooling (ERVC) by flooding the reactor cavity during a severe accident. As part of a joint Korean–United States International Nuclear Energy Research Initiative (K-INERI), an experimental study has been conducted to investigate the viability of using an appropriate vessel coating to enhance the critical heat flux (CHF) limits during ERVC. Toward this end, transient quenching and steady-state boiling experiments were performed in the subscale boundary layer boiling (SBLB) facility at the Pennsylvania State University using test vessels with micro-porous aluminum coatings. Local boiling curves and CHF limits were obtained in these experiments. When compared to the corresponding data without coatings, substantial enhancement in the local CHF limits for the case with surface coatings was observed. Results of the steady-state boiling experiments showed that micro-porous aluminum coatings were very durable. Even after many cycles of steady-state boiling, the vessel coatings remained rather intact, with no apparent changes in color or structure. Moreover, the heat transfer performance of the coatings was found to be highly desirable with an appreciable CHF enhancement in all locations on the vessel outer surface but with very little effect of aging.     

严重事故下大功率先进压水堆IVR-ERVC有效性分析

通过压力容器外部冷却(ERVC)以实现堆内熔融物滞留(IVR)作为反应堆严重事故缓解管理的一项重要举措一直以来广泛受到关注和研究。本文使用严重事故分析程序MELCOR,从瞬态角度对大型先进压水堆进行了IVR-ERVC相关研究。过程中重点关注了堆芯熔毁和重新定位,熔池形成、生长及其传热过程,并且对压力容器外部流动传热进行了分析。MELCOR计算所得下封头热流密度分布的瞬态结果与临界热流密度(CHF)比较和分析表明,1700 MWe大功率压水堆发生严重事故后在IVRERVC条件下能够保证压力容器的完整性,即,IVR-ERVC能够有效带出下封头熔融物的衰变热量,缓解严重事故后果。     

Late-phase melt conditions affecting the potential for in-vessel retention in high power reactors

If cooling is inadequate during a reactor accident, a significant amount of core material could become molten and relocate to the lower head of the reactor vessel, as happened in the Three Mile Island Unit 2 accident. In such a case, concerns about containment failure and associated risks can be eliminated if it is possible to ensure that the lower head remains intact so that relocated core materials are retained within the vessel. Accordingly, in-vessel retention (IVR) of core melt as a key severe accident management strategy has been adopted by some operating nuclear power plants and planned for some advanced light water reactors. However, it is not clear that currently proposed external reactor vessel cooling (ERVC) without additional enhancements can provide sufficient heat removal to assure IVR for high power reactors (i.e., reactors with power levels up to 1500 MWe). Consequently, a joint United States/Korean International Nuclear Energy Research Initiative (I-NERI) has been launched to develop recommendations to improve the margin of success for in-vessel retention in high power reactors. This program is initially focussed on the Korean Advanced Power Reactor—1400 MWe (APR1400) design. However, recommendations will be developed that can be applied to a wide range of existing and advanced reactor designs. The recommendations will focus on modifications to enhance ERVC and modifications to enhance in-vessel debris coolability. In this paper, late-phase melt conditions affecting the potential for IVR of core melt in the APR1400 were established as a basis for developing the I-NERI recommendations. The selection of ‘bounding’ reactor accidents, simulation of those accidents using the SCDAP/RELAP5-3D^© code, and resulting late-phase melt conditions are presented. Results from this effort indicate that bounding late-phase melt conditions could include large melt masses (>120,000 kg) relocating at high temperatures (3400 K). Estimated lower head heat fluxes associated with this melt could exceed the maximum critical heat flux, indicating additional measures such as the use of a core catcher and/or modifications to enhance external reactor vessel cooling may be necessary to ensure in-vessel retention of core melt.     

熔融物堆内滞留条件下压力容器变形

熔融物堆内滞留(In-Vessel Retention,IVR)已经成为第三代反应堆一项关键的严重事故缓解策略,而压力容器外部冷却(External Reactor Vessel Cooling,ERVC)技术则是保证IVR得以成功实施的关键。当发生堆芯熔化时,高温熔融物对压力容器(Reactor Pressure Vessel,RPV)下封头的热冲击会导致RPV壁面和由其构成的外部冷却通道的形状发生变化,使局部传热恶化,进而造成IVR的失效。因此,有必要对IVR条件下RPV壁面的变形进行研究。本文利用有限元软件ANSYS对RPV进行了几何建模、温度场分析和力学场分析。结果表明,在RPV外部实现冷却、内部实现泄压的前提下,壁面变形为13.85-18.75 mm。在1 MPa内压的作用下,高温蠕变会使壁面变形随时间增大,但其增量有限。热膨胀是造成壁面变形的主要因素。