严重事故下安全壳卸压箱隔间氢气浓度场模拟

根据MELCOR程序对全厂断电诱发的严重事故下安全壳内各隔间的氢气浓度分布的计算结果,参考美国联邦法规关于氢气控制和风险分析的标准,分析安全壳内氢气的燃烧风险。结果表明：安全壳内平均氢气浓度不会导致整体性氢气燃烧,但存在局部燃烧的风险。通过CFD程序对氢气浓度较高的卸压箱隔间进行氢气释放和空间气体流动过程的模拟,得到更细致的卸压箱隔间内氢气浓度场分布,给出氢气聚集区域的准确位置,为采取严重事故缓解措施,设计氢复合器布置方案提供了参考依据。     

大亚湾和岭澳核电站安全壳氢气风险及消氢措施有效性分析

使用MAAP程序计算大亚湾和岭澳核电站严重事故条件下安全壳内的相关质能释放和氢气源项;利用TONUS程序建立安全壳集总参数模型,计算分析氢气在安全壳内的分布情况;结合非能动氢复合器消氢性能、现场条件和氢气分布情况,提出氢复合器布置方案;借助TONUS和GASFLOW程序,分别使用集总参数法和CFD法,验证消氢方案的有效性。验证结果表明,安全壳内氢气浓度满足相关法规要求。     

核电厂非能动氢复合器研制

核电厂非能动氢复合器主要用于消除严重事故后安全壳内产生的氢气,避免氢气聚集而产生爆炸。根据H2和O2催化反应消氢的工作原理,设计以Pt、Pd混合配比作为催化剂的催化板,并以此为核心部件,设计制造能够在非能动条件下持续消氢的非能动氢复合器。针对核电厂安全壳严重事故后的消氢要求,开展非能动氢复合器在不同温度、压力、氢气体积分数等条件下的消氢速率试验,不同毒物对消氢效果影响试验以及启动和停止阈值试验。研究结果表明,非能动氢复合器达到了核电厂事故后消氢技术要求,可直接应用于二代堆型核电厂,还可以应用于EPR或AP1000等三代堆型核电厂。     

秦山二期核电站氢气风险的CFD研究

利用计算流体力学(CFD)程序GASFLOW模拟了波动管大破口事故发生后7 000 s内装有22台氢气复合器的秦山二期核电站安全壳内的水蒸汽及氢气行为,得到了不同阶段的特征性流场及氢气浓度的分层情况,给出了所采用的复合器布置方案的稳定消氢速率为20 g/s,并指出了破口所在蒸汽发生器隔间内发生氢气燃烧火焰加速的可能性.同时,计算结果表明,安全壳内构筑物吸热带走了大部分从一回路释放的热量;压力变化同时受气体总质量(主要是水蒸汽质量)与温度的控制.     

基于Gasflow程序的非能动安全压水堆氢气行为计算和分析

本文利用Gasflow程序对非能动压水堆发生假想的严重事故后,安全壳内的氢气流动、分布和积聚行为进行了计算和分析,对安全壳内各房间的氢气风险进行了评价并给出了降低氢气燃烧风险的建议。计算结果表明,在发生大破口事故中,安全壳内氢气浓度较高的区域为破损蒸汽发生器隔间,内置换料水箱隔间和上部隔间,需要设置消氢系统来降低隔间内的氢气浓度。     

压水堆核电厂消氢装置选用探讨

为消除核电厂在严重事故工况下积聚在安全壳内的氢气,需要在核电厂安全壳内增加消氢装置。本文分析了严重事故工况下目前主要采用的氢气点火器和非能动氢复合器的原理,并结合某核电厂增加非能动氢复合器改造的工程实践,给出了压水堆核电厂消氢装置选用方案。实践结果表明,此最优消氢方案既可以保证电厂安全,又可以节约成本,具有巨大的社会效益和经济效益。     

先进压水堆核电厂氢气控制策略分析研究

新建核电厂的设计必须做到"实际消除"早期与大量放射性释放的可能性,氢气燃爆导致的安全壳失效是必须要"实际消除"的严重事故工况之一。因此对各种消氢措施的特点进行分析研究,建立联合消氢策略评价方法,可为先进压水堆核电厂氢气控制策略选择设计评价提供支持手段。根据严重事故管理中对氢气控制策略的考虑,研究安全壳内局部位置的可燃性是相关设计评价的关键问题。根据可燃性准则、火焰加速准则、燃爆转变准则,本文使用三维CFD程序对典型严重事故工况下安全壳蒸汽发生器隔间内的可燃性及氢气风险进行模拟分析。研究结果表明,虽然喷放源项中有大量水蒸气,蒸汽发生器隔间中仍有较大区域处于可燃限值以内,合理布置的点火器能在设计中点燃并消除氢气。本研究建立的分析方法能用于对核电厂氢气控制策略选择设计的评价。     

严重事故下安全壳内氢气行为与风险分析

福岛事故后的核电厂安全审评过程中,国家核安全局对于严重事故下的氢气安全问题提出了更高的要求,从满足当前高标准的氢气安全要求的角度出发,有必要对安全壳内氢气行为开展更为细致深入的研究,开展氢气的三维分析,为集总参数程序的分析结果提供有益补充。本文采用一体化严重事故分析程序和流体力学程序对国产先进压水堆核电厂进行系统建模,选取大破口触发的严重事故序列,对严重事故工况下的氢气行为及氢气控制系统性能进行分析评价。首先采用一体化严重事故分析程序计算氢气产生源项、氢气产生速率和安全壳内氢气浓度分布等,评价安全壳隔间内的氢气风险。并采用计算流体力学程序,进一步对安全壳内重要隔间的氢气分布进行三维分析,研究安全壳内氢气和水蒸汽的行为,获得重要隔间内的流场、温度场、压力场、氢气分布及浓度变化等计算结果。CFD程序在计算气体分布方面要比集总参数程序更加精确和详细,通过更精细地模拟安全壳内的氢气行为,可以为集总参数程序的计算结果提供补充,为氢气控制系统的设计优化和严重事故氢气风险管理等提供有力的支持。     

先进压水堆核电厂氢气控制策略分析研究

新建核电厂的设计必须做到“实际消除”早期与大量放射性释放的可能性,氢气燃爆导致的安全壳失效是必须要“实际消除”的严重事故工况之一。因此对各种消氢措施的特点进行分析研究,建立联合消氢策略评价方法,可为先进压水堆核电厂氢气控制策略选择设计评价提供支持手段。根据严重事故管理中对氢气控制策略的考虑,研究安全壳内局部位置的可燃性是相关设计评价的关键问题。根据可燃性准则、火焰加速准则、燃爆转变准则,本文使用三维CFD程序对典型严重事故工况下安全壳蒸汽发生器隔间内的可燃性及氢气风险进行模拟分析。研究结果表明,虽然喷放源项中有大量水蒸气,蒸汽发生器隔间中仍有较大区域处于可燃限值以内,合理布置的点火器能在设计中点燃并消除氢气。本研究建立的分析方法能用于对核电厂氢气控制策略选择设计的评价。     

非能动氢复合器布置浅析

本文阐述了反应堆厂房内布置非能动氢气复合器的目的,对非能动氢气复合器的结构进行了描述,详细分析了反应堆厂房内的氢气来源及氢气分布,给出了氢复合器的布置原则,并在布置原则的指导下对岭澳二期氢复合器进行了布置,通过对布置结果的分析证明其是可行的。     

Analysis of steam and hydrogen distributions with PAR mitigation in NPP containments

The 3-D-field code, GASFLOW is a joint development of Forschungszentrum Karlsruhe and Los Alamos National Laboratory for the simulation of steam/hydrogen distribution and combustion in complex nuclear reactor containment geometries. GASFLOW gives a solution of the compressible 3-D Navier–Stokes equations and has been validated by analysing experiments that simulate the relevant aspects and integral sequences of such accidents. The 3-D GASFLOW simulations cover significant problem times and define a new state-of-the art in containment simulations that goes beyond the current simulation technique with lumped-parameter models. The newly released and validated version, GASFLOW 2.1 has been applied in mechanistic 3-D analyzes of steam/hydrogen distributions under severe accident conditions with mitigation involving a large number of catalytic recombiners at various locations in two types of PWR containments of German design. This contribution describes the developed 3-D containment models, the applied concept of recombiner positioning, and it discusses the calculated results in relation to the applied source term, which was the same in both containments. The investigated scenario was a hypothetical core melt accident beyond the design limit from a large-break loss of coolant accident (LOCA) at a low release location for steam and hydrogen from a rupture of the surge line to the pressurizer (surge-line LOCA). It covers the in-vessel phase only with 7000 s problem time. The contribution identifies the principal mechanisms that determine the hydrogen mixing in these two containments, and it shows generic differences to similar simulations performed with lumped-parameter codes that represent the containment by control volumes interconnected through 1-D flow paths. The analyzed mitigation concept with catalytic recombiners of the Siemens and NIS type is an effective measure to prevent the formation of burnable mixtures during the ongoing slow deinertization process after the hydrogen release and has recently been applied in backfitting the operational German Konvoi-type PWR plants with passive autocatalytic recombiners (PAR).     

Improvements to hydrogen depleting and monitoring system for Chinese Pressurized Reactor 1000

We evaluate the hydrogen depletion ability of the hydrogen depletion system for Chinese Pressurized Reactor 1000 (CPR1000),which has been applied in nuclear power plants with pressurized water reactors;moreover,we introduce a new device that can continuously monitor hydrogen concentration inside the CPR1000 containment building.Experimental studies show that a moveable hydrogen autocatalytic recombiner alone can sufficiently deplete hydrogen under the condition of a design-basis accident,and 33 passive autocatalytic recombiners placed in the areas of high hydrogen concentration satisfy the hydrogen depletion requirements under the condition of a beyond-design-basis accident.Meanwhile,the hydrogen concentration monitoring system is designed and installed based on the approach of detecting the temperature increase caused by the catalytic reaction of hydrogen.In conclusion,the hydrogen depletion capacity of the CPR1000 meets the requirements,and the system's safety can be enhanced by the improved hydrogen concentration monitoring system.     

氢气催化复合器对核电厂严重事故的缓解效果

在严重事故条件下,安全壳内的氢气燃烧或爆炸威胁安全壳完整性,必须采取措施减小或消除安全壳的氢气风险。针对600MWe级核电厂的大型干式安全壳,以小破口失水诱发的严重事故序列为基准事故,计算分析了氢气催化复合器（PAR）消除安全壳内氢气的效果,及复合效应对安全壳压力温度的影响。研究表明：氢气催化复合器能够持续稳定地消除安全壳内氢气,但对于极其快速的氢气释放,它的消氢能力受到一定限制。     

Three-dimensional behaviors of the hydrogen and steam in the APR1400 containment during a hypothetical loss of feed water accident

During a hypothetical severe accident in a nuclear power plant (NPP), hydrogen is generated by an active reaction of the fuel-cladding and the steam in the reactor pressure vessel and released with the steam into the containment. In order to mitigate hydrogen hazards which could possibly occur in the NPP containment, a hydrogen mitigation system (HMS) is usually adopted. The design of the next generation NPP (APR1400) developed in Korea specifies that 26 passive autocatalytic recombiners and 10 igniters should be installed in the containment for a hydrogen mitigation. In this study, an analysis of the hydrogen and steam behavior during a total loss of feed water (LOFW) accident in the APR1400 containment has been conducted by using the computational fluid dynamics (CFD) code GASFLOW. During the accident, a huge amount of hot water, steam, and hydrogen is released into the in-containment refueling water storage tank (IRWST). The current design of the APR1400 includes flap-type openings at the IRWST vents which operate depending on the pressure difference between the inside and outside of the IRWST. It was found from this study that the flaps strongly affect the flow structure of the steam and hydrogen in the containment. The possibilities of a flame acceleration and a transition from deflagration to detonation (DDT) were evaluated by using the Sigma–Lambda criteria. Numerical results indicate that the DDT possibility was heavily reduced in the IRWST compartment by the effects of the flaps during the LOFW accident.     

Studies on innovative hydrogen recombiners as safety devices in the containments of light water reactors

In order to prevent the containment and other safety relevant components from incurring serious damage caused by a detonation of the hydrogen/air-mixture generated during a severe accident in light water reactors (LWR) passive autocatalytic recombiners (PAR) are used for hydrogen removal in an increasing number of European plants. These devices make use of the fact that hydrogen and oxygen react exothermally on catalytic surfaces generating steam and heat.

Experimental investigations at several research facilities indicate that existing PAR systems bear the risk of igniting the gaseous mixture due to an overheating of the catalyst elements caused by strong reaction heat generation. Innovative devices could overcome existing limitations making use of the knowledge deduced from experiments performed at the REKO facilities at Forschungszentrum Juelich (FZJ).

The paper analyses the mechanisms of the thermal behaviour of catalytic plate-type recombiners and presents experimental results on existing and innovative devices for hydrogen removal introducing the modular recombiner concept.     

安全壳消氢系统催化板效率试验影响因素分析

本文通过对某核电站安全壳消氢系统(EUH)非能动氢复合器催化板效率试验的试验方法和催化板本身特性的分析,确认对催化板消氢效率试验结果影响较大的因素,并且针对这些影响因素给出相应的应对措施。大修期间的试验数据表明本文给出的各项应对措施是非常有效的,对其他核电项目具有参考意义。     

Simulation of hydrogen mitigation in catalytic recombiner. Part-II: Formulation of a CFD model

This paper aims at formulation of a model compatible with CFD code to simulate hydrogen distribution and mitigation using a Passive Catalytic Recombiner in the Nuclear power plant containments. The catalytic recombiner is much smaller in size compared to the containment compartments. In order to fully resolve the recombination processes during the containment simulations, it requires the geometric details of the recombiner to be modelled and a very fine mesh size inside the recombiner channels. This component when integrated with containment mixing calculations would result in a large number of mesh elements which may take large computational times to solve the problem. This paper describes a method to resolve this simulation difficulty. In this exercise, the catalytic recombiner alone was first modelled in detail using the best suited option to describe the reaction rate ( [Prabhudharwadkar et al., 2005] and [Prabhudharwadkar et al., 2011]). A detailed parametric study was conducted, from which correlations for the heat of reaction (hence the rate of reaction) and the heat transfer coefficient were obtained. These correlations were then used to model the recombiner channels as single computational cells providing necessary volumetric sources/sinks to the energy and species transport equations. This avoids full resolution of these channels, thereby allowing larger mesh size in the recombiners. The above mentioned method was successfully validated using both steady state and transient test problems and the results indicate very satisfactory modelling of the component.     

A study on evaluating a passive autocatalytic recombiner PAR-system in the PWR large-dry containment

A systematic step-by-step framework for analyzing hydrogen behavior and implementing passive autocatalytic recombiners (PARs) to mitigate hydrogen deflagration or detonation risk in severe accidents (SAs) is presented. The procedure can be subdivided into five main steps: (1) modeling the containment based on the plant design characteristics, (2) selecting the typical severe accident sequences, (3) calculating the hydrogen generation including in- and ex-vessel period, (4) modeling the gas distribution in containment atmosphere and estimating the hydrogen combustion modes and (5) evaluating the efficiency of the PAR-system to mitigate the hydrogen risk with and without catalytic recombiners, according to the safety criterion. For the Chinese 600MWe pressurized water reactor (PWR) with a large-dry containment, large break loss-of-coolant accident (LB-LOCA) is screened out as the reference severe accident sequence, considering the nature of hydrogen generation and the probabilistic safety assessment (PSA) result on accident sequences. The results show that a certain number of recombiners could remove effectively hydrogen and oxygen, to protect the containment integrity against hydrogen deflagration or detonation.     

Fluid dynamic analysis of a catalytic recombiner to remove hydrogen

Catalytic reacting surfaces in recombiners are a reliable way to remove hydrogen as well as other burnable gases like CO in a passive way from the containment atmosphere of a nuclear power plant (NPP) during an accident. Industrial mature designs are ready to be installed in large dry containments to act as a mitigation measure preferably in the case of severe accidents. Experiments have been carried out to study manifold aspects of recombiners like the efficiency of hydrogen removal, start-up conditions, poisoning, oxygen starvation, steam and water impact and others. Mostly the global behaviour of a given device in a larger environment has been investigated in order to demonstrate the effectiveness and to facilitate the derivation of simplified models for long-term severe accident analyses. There are a number of reasons to look inside a recombiner to understand the interaction of chemistry and flow. This can help in understanding the dependencies of non-measurable variables (e.g. reaction rate), of local surface temperatures and more. It also offers possibilities to increase the chemical efficiency by optimising the geometry properly. Computational fluid dynamics (CFD) codes are available to be used as development tools to include the specifics of catalytic surface reactions. The present paper describes the use of the code system CFX (CFX 4.1 Flow Solver User Guide. 1995, Computational Fluid Dynamics Services, AEA Technology plc, Oxfordshire, UK) for creating a recombiner model. Finally its comparison with existing test data is discussed.     

氢气缓解措施中点火器特点及有效性分析

为保证严重事故下安全壳的完整性，氢气缓解措施广泛应用于核电站内。本文应用三维计算流体力学程序GASFLOW分析了氢气缓解措施中的点火器系统与复合器系统，并总结出各自的特点。点火器通过点燃的方式能够快速有效地降低氢气总量，同时会明显增大安全壳内压力与温度；复合器需长时间运行才能够消除大量的氢气，工作的同时不会引起平均温度与压力的明显上升。如果点火器的布置位置及启动时间均合理，有可能在不引起大范围火焰加速或爆炸的情况下迅速有效地消除氢气。