Demonstrative testing of honeycomb passive autocatalytic recombiner for nuclear power plant

Passive autocatalytic recombiners (PAR) are widely being used as hydrogen control device in the current and advanced light water reactors (ALWRs). The PARs lend themselves to very effective means of circumventing buildup of combustible or detonable hydrogen gas mixtures in the reactor containment. Korea Nuclear Technology Inc. has recently developed a new PAR system with high porous catalyst material in the shape of honeycomb. The honeycomb PAR catalyst has a design characteristic of improved hydrogen removal performance by increasing the surface area and enhancing the flow rate through the catalyst at the same time, without increasing PAR size compared to the conventional PARs. The experimental study was focused on the development of the hydrogen depletion rate correlation of the honeycomb PAR. Two different sizes of PARs, KPAR-40 and KPAR-T2, have been employed in the tailor-made Integral Test Facility and Performance Test Facility. Multiple tests were conducted in various conditions of pressure, temperature, and hydrogen concentration. The hydrogen depletion rate correlation and the PAR performance constant were determined from the experimental results, which can be applied to the honeycomb PAR system. Also determined was the scale effect due to the PAR size, i.e., the number of catalysts in a PAR.     

非能动氢复合器性能验证试验方法研究

消氢启停阈值和消氢速率是非能动氢复合器的关键性能参数。本文设计了一种直观方便的非能动氢复合器性能验证试验方法:将非能动氢复合器放于密闭容器中，并通入氢气，只要氢复合器启动消氢反应且整条消氢过程曲线在给定值直线A以下，则验证了启动阈值不大于给定值A；只要消氢过程曲线最终的水平段在给定值直线B以下，则验证了停止阈值不大于给定值B；只要氢复合器达到稳定消氢状态，通入容器的氢气质量流量即为消氢速率。本文设计并搭建了试验装置，采用非能动氢复合器样机PARQX-15进行消氢性能验证试验，成功验证了消氢启动阈值<2%（体积浓度，下同），停止阈值<0.5%，消氢速率大于536 g/h，证明了试验方法的实用性和有效性。      

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.     

Analysis of hydrogen risk mitigation with passive autocatalytic recombiner system in CPR1000 NPP during a hypothetical station blackout

Hydrogen safety has attracted extensive concern in severe accident analysis especially after the Fukushima accident. In this study, a similar station blackout as happened in Fukushima accident is simulated for CPR1000 nuclear power plant (NPP) model, with the computational fluid dynamic code GASFLOW. The hydrogen risk is analyzed with the assessment of efficiency of passive autocatalytic recombiner (PAR) system. The numerical results show that the CPR1000 containment may be damaged by global flame acceleration (FA) and local detonation caused by hydrogen combustion if no hydrogen mitigation system (HMS) is applied. A new condensation model is developed and validated in this study for the consideration of natural circulation flow pattern and presence of non-condensable gases. The new condensation model is more conservative in hydrogen risk evaluation than the current model in some compartments, giving earlier starting time of deflagration to detonation transition (DDT). The results also indicate that the PAR system installed in CPR1000 could prevent the occurrence of the FA and DDT. Therefore, HMS such as PAR system is suggested to be applied in NPPs to avoid the radioactive leak caused by containment failure.     

Effect of spray on performance of the hydrogen mitigation system during LB-LOCA for CPR1000 NPP

During the course of the hypothetical large break loss-of-coolant accident (LB-LOCA) in a nuclear power plant (NPP), hydrogen is generated by a reaction between steam and the fuel-cladding inside the reactor pressure vessel (RPV). It is then ejected from the break into the containment along with a large amount of steam. Management of hydrogen safety and prevention of over-pressurization could be implemented through a hydrogen mitigation system (HMS) and spray system in CPR1000 NPP. The computational fluid dynamics (CFD) code GASFLOW is utilized in this study to analyze the spray effect on the performance of HMS during LB-LOCA. Results show that as a kind of HMS, deliberate igniter system (DIS) could initiate hydrogen combustion immediately after the flammability limit of the gas mixture has been reached. However, it will increase the temperature and pressure drastically. Operating the DIS under spray condition could result in hydrogen combustion being suppressed by suspended droplets inside the containment. Furthermore, the droplets could also mitigate local the temperature rise. Operation of a PAR system, another kind of HMS, consumes hydrogen steadily with a lower recombination rate which is not affected noticeably by the spray system. Numerical results indicate that the dual concept, namely the integrated application of DIS and PAR systems, is a constructive improvement for hydrogen safety under spray condition during LB-LOCA.     

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.     

反应堆非能动氢气复合器严重事故下消氢性能研究

非能动氢气复合器（PAR）是核电厂主要的消氢措施。在严重事故下,某些裂变反应产生的特殊杂质(如I₂、CsI、CO等)可能对催化剂产生有害的影响,为保证PAR消氢性能的可靠性,中毒机理研究十分必要。本文根据相关试验研究结果,从铂、钯金属原子分布结构、催化反应性面积两个方面对催化剂中毒效应进行机理分析,研究得出催化剂中金属原子的分布结构、进入PAR的实际毒物浓度等均是影响催化剂中毒效应的关键因素。     

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.     

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).     

Ensuring the long-term functionality of passive auto-catalytic recombiners under operational containment atmosphere conditions—An interdisciplinary investigation

In order to sustain the structural integrity of the containment and other safety relevant components i.e. to avoid a detonation of the hydrogen-air mixture generated during a severe accident in light water reactors, passive auto-catalytic recombiners (PAR) are used for hydrogen removal in many European nuclear power plants (NPP). In 1999, the German NPP Emsland (KKE) was equipped with 58 PAR of AREVA design as an internal accident management measure for a beyond-design accident. Since that time the recombiners are in a stand-by state. As the catalyst elements are exposed to various airborne substances during normal plant operation their function is controlled periodically by testing selected catalyst sheets in a specially designed device. Under the conservative test conditions during this procedure some catalyst sheets showed a delayed responding behavior. First internal analysis gave indication of a beginning fouling on the catalytic surface.The aim of a precautionary investigation performed in cooperation between KKE, Forschungszentrum Juelich and RWTH Aachen University was to characterize the composition of the fouling and to correlate it with potential sources within the containment.In the framework of the investigation the reports of the periodic inspections were analyzed and appropriate sample sheets were selected from the installation. These samples were subjected to a comprehensive chemical surface analysis in order to identify effects like thermal sintering, poisoning or a blocking of the catalytic surface (Baerns, M., 2004. Basic Principles in Applied Catalysis, Springer Verlag). Along with the chemical analysis the catalytic activity of the samples was assessed in several test series in order to correlate the chemically quantified deposition on the catalyst samples with the characteristics of the start-up and the steady-state performance of the recombination reaction. In a final step, possible sources of the fouling were analyzed with regard to their possible contribution to the phenomena. According to the results achieved, measures have been implemented at KKE in order to optimize procedures and to enhance the performance of the PARs.     

Study of H loss from hydrogenated Hg1−xCdxTe under high electronic excitation by elastic recoil detection analysis (ERDA)

Large erosion (∼1.1 × 10⁴ atoms/ion) of H from hydrogenated MCT wafers is observed due to the bombardment with 80 MeV Ni⁹⁺ ions. The initial H areal concentration and hydrogen depletion rate is monitored by elastic recoil detection analysis. The ion-damaged zones from where depletion of H takes place have been calculated from fluence-dependent hydrogen areal content analysis. The results are explained on the basis of the thermal spike model of ion-solid interaction.     

Stress corrosion cracking on irradiated 316 stainless steel

Tests on irradiation-assisted stress corrosion cracking (IASCC) were carried out by using cold-worked (CW) 316 stainless steel (SS) in-core flux thimble tubes which were irradiated up to 5×10²⁶ n/m² (E>0.1 MeV) at 310°C in a Japanese PWR. Unirradiated thimble tube was also tested for comparison with irradiated tubes. Mechanical tests such as the tensile, hardness tests and metallographic observations were performed. The susceptibility to SCC was examined by the slow strain rate test (SSRT) under PWR primary water chemistry condition and compositional analysis on the grain boundary segregation was made. Significant changes in the mechanical properties due to irradiation such as a remarkable increase of strength and hardness, and a considerable reduction of elongation were seen. SSRT results revealed that the intergranular fracture ratio (%IGSCC) increased as dissolved hydrogen (DH) increased. In addition, SSRT results in argon gas atmosphere showed a small amount of intergranular cracking. The depletion of Fe, Cr, Mo and the enrichment of Ni and Si were observed in microchemical analyses on the grain boundary.     

Angular Distributions of Resonance Neutron Scattering from Fe-56

Chromium depletion near grain boundaries of austenitic stainless steel during irradiation was investigated. Specimens were kept at 1,473 K for 30 min, and were quenched into the water. Irradiations were done using 400 keV He⁺ ions at 573, 673 and 773 K up to 10dpa with a dose rate of 2.4×10^?4 dpa/s. After irradiation, the Cr concentration profile near the grain boundary was measured using an analytical electron microscope with a 1 nm beam diameter. At 573 K, Cr depletion is small, and its concentration at the grain boundary decreases to 15.5 mass% at 3 dpa from the initial concentration of 18.5 mass%. At 673 and 773 K, Cr concentration at the grain boundary rapidly decreases between 0 and 0.2dpa, and then gradually approaches a constant value, 7.0 mass% at 673 K and 5.0 mass% at 773 K. Two stages are found in radiation induced segregation (RIS) behavior, one stage in which Cr depletion and Ni enrichment balance and another in which Fe depletion and Ni enrichment balance.

These experimental results were compared with the calculations based on the vacancy-induced inverse Kirkendall effect. Predicted Cr segregation at 673 and 773 K above 3dpa agrees with the experimental results. But Cr depletions at low doses which were obtained in the experiments are much faster than calculated. At 573 K in the experiments, depletion is smaller than calculated up to 10dpa.     

Simulation of hydrogen distribution in an Indian Nuclear Reactor Containment

The management of hydrogen in a Nuclear Reactor Containment after LOCA (Loss Of Coolant Accident) is of practical importance to preserve the structural integrity of the containment. This paper presents the results of systematic work carried out using the commercial Computational Fluid Dynamics (CFD) software FLUENT to assess the concentration distribution of hydrogen in a typical Indian Nuclear Reactor Containment. In order to obtain an accurate estimate of hydrogen concentration distribution, a suitable model for turbulence closure is required to be selected. Using guidelines from the previous studies reported in the literature and a comparative simulation study using simple benchmark problems, the most suitable turbulence model for hydrogen mixing prediction was identified. Subsequently, unstructured meshes were generated to represent the containment of a typical Indian Nuclear Reactor. Analyses were carried out to quantify the hydrogen distribution for three cases. These were (1) Uniform injection of hydrogen for a given period of time at room temperature, (2) Time varying injection as has been computed from an accident analysis code, (3) Time varying injection (as used in case (2)) at a high temperature. A parametric exercise was also carried out in case (1) where the effect of various inlet orientations and locations on hydrogen distribution was studied. The results indicate that the process of hydrogen dispersal is buoyancy dominated. Further for typical injection rates encountered following LOCA, the dispersal is quite poor and most hydrogen is confined to the fuelling machine vault.     

Effect of prior thermal treatment on the microchemistry and crack propagation of proton-irradiated AISI 304 stainless steels

The effect of prior thermal treatment on crack growth was investigated on proton-irradiated Type 304 stainless steel (SS) of initially solution annealed (SA) and thermally sensitized (SEN) conditions. The Cr depletion profiles were measured by field emission gun transmission electron microscopy/energy dispersive spectroscopy (FEGTEM/EDS) in an attempt to correlate grain boundary chromium composition with the measured crack growth rate. The results showed that the crack growth of the 1-dpa-irradiated SEN 304SS is substantially higher than that of SA 304SS with the same irradiation dose. The unirradiated SEN material initially started with a shallow Cr depletion profile near grain boundary. After 1 dpa irradiation with proton, the Cr depletion profile becomes narrower and deeper. In contrast, the grain boundary Cr concentration in the SA specimen at the same irradiation dose was higher than that of the SEN specimen, mainly due to an initial Cr enriched condition. Consequently, the irradiated SEN specimen exhibited a higher degree of sensitization in electrochemical potentiokinetic reactivation test and faster crack growth rate in the stress corrosion crack test. The absence of irradiation enhanced crack growth in heavily thermal-sensitized 304SS is probably attributed to slower radiation-induced Cr depletion as a result of pre-existing thermally induced grain boundary Cr depletion. It is a clear indication that the inverse Kirkendall effect was hampered by the back diffusion of Cr due to initially depleted Cr concentration gradient near grain boundary.     

Ti-Mo互扩散界面吸氢同位素效应的离子束分析研究

为探究Ti-Mo互扩散对金属吸氢的影响,本文采用离子束分析方法对Ti-Mo薄膜的膜-基互扩散界面的吸氢同位素（H和D）效应进行了研究。通过氩离子刻蚀减薄的方法有效降低了表面碳、氧杂质对样品吸氢的影响。吸氢结果表明,对于表面洁净的样品,氢化后固相中氢或氘的浓度均沿着深度随钼原子含量的增加而减小。在单一气体吸氢实验中,氢原子浓度减小的趋势较氘原子缓慢;而在氢氘混合气体吸氢实验中,当容器中的氢氘压强比p(H2)∶p(D2)≥05∶1时,固体中氘氢浓度之比随钼浓度的增加而降低,但当p(H2)∶p(D2)<05∶1时,氘氢浓度之比随钼浓度的增加而升高。因此,由于Ti Mo界面的互扩散,吸氢出现了显著的氢同位素效应,钼的存在不利于体系对氢同位素气体的吸收。     

Characterization of hydrogen concentration in Zircaloy-4 using ultrasonic techniques

The relationship between hydrogen concentration precipitated as hydride particles and ultrasonic parameters, such as velocity and attenuation, was examined in Zircaloy-4 samples for potential applications in the Non-Destructive Test Field. Different amounts of hydrogen (up to 517 ppm) were introduced in the samples by gaseous charging. Ultrasonic attenuation measurements were performed with compressive waves at frequencies of 10 and 30 MHz, and propagation velocity measurements were performed at 10 MHz. Ultrasonic velocity showed an approximately linear increase with hydrogen concentration and it could be used as an assessment parameter when the hydrogen level is high enough. Attenuation versus hydrogen concentration has been fitted by a logarithmic equation at 10 MHz. At 30 MHz a fluctuating behavior of the attenuation prevented measurement of the hydrogen concentration.     

PET/CT对非小细胞肺癌精确放疗计划的影响

探讨PET/CT对非小细胞肺癌(Non-small Cell Lung Cancer,NSCLC)精确放疗(Precise and Accurate Radiotherapy,PAR)计划的影响。对21例非小细胞肺癌患者行PET/CT检查,分别根据CT和PET/CT进行TNM分期,并将PET/CT图像上的TNM分期和CT分期结果进行比较分析。利用CMS治疗计划系统图像融合软件,组织5名放疗科不同年资医师分别在CT和PET/CT三维图像上独立勾画大体肿瘤体积(Gross Tumor Volume,GTVCT和GTVPET/CT),计算患者GTV的体积值和变异系数,比较放疗科不同医师分别在CT和PET/CT上勾画GTV的差异。结果发现52.38%(11/21例)的患者TNM分期改变,21例患者GTVCT和GTVPET/CT均不相同。PET/CT可改变NSCLC临床分期,进而改变整个治疗计划。PET/CT可明显减小放疗科不同级别医师勾画GTV的差异。     

Effect of Metallographic Factor on Hydrogen Pick-up Properties of Zircaloy-2

Zirconium alloy sheets were prepared with varying Fe, Cr and Ni systematically. The corrosion and hydrogen pickup property were estimated in steam at 673 K, in water at 633 K and in super critical water at 673 K. The effect of the SPP and the oxide film on the hydrogen pick-up was studied from the hydrogen pick-up route using D₂O and the microstructure of the oxide film and secondary phase particle (SPP) in the oxide film. The hydrogen pick-up ratio decreased with increase of Fe and decrease of Ni. It was affected by Fe/Ni ratio of the matrix. The hydrogen pickup was not related to SPP but was related to the oxide film when the oxide film was relatively thick. The tetragonal ZrO₂ is considered to act as a barrier for hydrogen pick-up.     

Improvement of HYCA3D code and experimental verification in rectangular geometry

Concerns about the local hydrogen behavior in a nuclear power plant (NPP) containment during severe accidents have increased with the 10CFR50.34(f) regulation after TMI accident. Consequently, investigations on the local hydrogen behaviors under severe accident conditions were required. An analytical model named HYCA3D was developed at Seoul National University (SNU) to predict the thermodynamics and the three dimensional behavior of a hydrogen/steam mixture, within a subdivided containment volume following hydrogen generation during a severe accident in NPPs. In this study, the HYCA3D code was improved with a steam condensation and spray model, and verified with hydrogen mixing experiments executed in a SNU rectangular mixing facility. Helium was used to simulate hydrogen in both the calculations and the experiments. The calculation results show good agreement with the experimental data.