Filtered Containment Venting Research Articles

Measurement for Surface Tension of Aqueous Inorganic Salt

Bubble columns are effective means of filtration in filtered containment venting systems. Here, the surface tension has a significant influence on bubble size distribution and bubble deformation, which have a strong impact on the behavior of the bubble column. The influence of aqueous inorganic compounds on the surface tension depends on the electrolytic activity, Debye length, entropy of ion hydration and surface deficiencies or excess. In this work the surface tensions of same specific aqueous solutions have been measured by different methods including platinum plate method, platinum ring method and maximum bubble pressure method. The measured surface tensions of both sodium hydroxide and sodium thiosulfate are less than that of water. As solution temperature ranges from 20 ℃ to 75 ℃, the surface tension of 0.5 mol/L sodium hydroxide solution decreases from 71 to 55 mN/m while that of 1 mol/L solution decreases from 60 to 45 mN/m. Similarly during the same temperature range, the surface tension of 0.5 mol/L sodium thiosulfate decreases from 70 to 38 mN/m and that of 1 mol/L sodium thiosulfate is between 68 and 36 mN/m. The analysis for the influence mechanism of aqueous inorganic on surface tension is provided. In addition, experimental results show that the surface tension of solid aerosol suspension liquid has no obvious difference from that of distilled water.

Research Works on Iodine and Ruthenium Behavior in Severe Accident Conditions

This paper deals with near past, ongoing, and planned R&D works on fission products (FPs) behavior in reactor cooling system (RCS), containment building and in filtered containment venting systems (FCVS) for severe accident (SA) conditions. All the researches are collaborative works; the overall objective is to develop confident models to be implemented in simulation software. After being initiated in 2004, researches on iodine transport through the RCS are still ongoing and for containment, the last advances are linked to the source term (ST) evaluation and mitigation (STEM) OECD/NEA project. The objective is to improve the evaluation of ST for a SA on a nuclear power plant and to reduce uncertainties on specific phenomena dealing with the chemistry of two major FPs: iodine and ruthenium. For ruthenium attention has been paid to study the amount and nature (gas/aerosol partition) of ruthenium species along the RCS. A follow-up, called STEM2, has started to reduce some remaining issues and be closer to reactor conditions. For FCVS works, the efficiencies for trapping iodine covering scrubbers and dry filters are examined to get a clear view of their abilities in SA conditions. Another part is focused on specific porous materials able to trap volatile iodine. Influence of zeolite materials parameters (nature of the counter-ions, structure, Si/Al ratio…) are tested as well as new kind of porous materials constituted by Metal organic Frameworks will also be looked at.

Investigation of dust particle removal efficiency of self-priming venturi scrubber using computational fluid dynamics

Abstract A venturi scrubber is an important element of Filtered Containment Venting System (FCVS) for the removal of aerosols in contaminated air. The present work involves computational fluid dynamics (CFD) study of dust particle removal efficiency of a venturi scrubber operating in self-priming mode using ANSYS CFX. Titanium oxide (TiO2) particles having sizes of 1 micron have been taken as dust particles. CFD methodology to simulate the venturi scrubber has been first developed. The cascade atomization and breakup (CAB) model has been used to predict deformation of water droplets, whereas the Eulerian–Lagrangian approach has been used to handle multiphase flow involving air, dust, and water. The developed methodology has been applied to simulate venturi scrubber geometry taken from the literature. Dust particle removal efficiency has been calculated for forced feed operation of venturi scrubber and found to be in good agreement with the results available in the literature. In the second part, venturi scrubber along with a tank has been modeled in CFX, and transient simulations have been performed to study self-priming phenomenon. Self-priming has been observed by plotting the velocity vector fields of water. Suction of water in the venturi scrubber occurred due to the difference between static pressure in the venturi scrubber and the hydrostatic pressure of water inside the tank. Dust particle removal efficiency has been calculated for inlet air velocities of 1 m/s and 3 m/s. It has been observed that removal efficiency is higher in case of higher inlet air velocity.

Experimental study on aerosol scrubbing efficiency of self-priming venturi scrubber submerged in water pool

Scrubber nozzles are key pieces of equipment used to remove aerosols in a wet-type filtered containment venting system (FCVS). This study deals with the aerosol scrubbing efficiency of a scrubber nozzle operating in self-priming mode. The scrubber nozzle that has been developed in this work consists of a reducer, a throat, a diffuser, a liquid suction slit, and an end cap with a rectangular section area. The aim of this study was to characterize scrubbing efficiency under various thermal hydraulic and aerosol conditions including nozzle inlet pressure (250–600 kPa(g)), nozzle inlet temperature (102–164 °C), nozzle inlet flow rate (air: 42–132 m3/h, steam: 112–269 m3/h), submergence from the nozzle exit (0.7–2.7 m), aerosol size (0.5, 0.7, 3 µm), nozzle inlet aerosol concentration (0.1–3 g/m3), and steam mass fraction in the main carrier gas (0–1). Aerosol scrubbing efficiency was measured based on the inlet and outlet aerosol concentrations of the scrubbing vessel with isokinetic sampling systems including a glass microfiber filter. Experimental results show that the scrubbing efficiency increased with increasing aerosol size, steam mass fraction, nozzle submergence, and inlet aerosol concentration. We also showed that the scrubbing efficiency increased with an increase in inlet pressure at low scrubber nozzle submergence. However, at higher scrubber nozzle submergence, the nozzle inlet pressure did not significantly influence the scrubbing efficiency. The aerosol scrubbing efficiency with the developed self-priming scrubber nozzle submerged in the pool was over 97% for various thermal–hydraulic conditions. Thus, the experimental results can be used to design a wet scrubber system considering upstream conditions such as operation of the FCVS.

A transient performance of the Organic Iodine Filter for Filtered Containment Venting System of Nuclear Power Plants

A transient performance of the Organic Iodine Filter for Filtered Containment Venting System of Nuclear Power Plants

Measurement of scrubbing behaviour of simulated radionuclide in a submerged venturi scrubber

Post Fukushima accident, the societal impact of radiological leakage to the environment necessitated further exploration and robust strategy to safeguard the nuclear reactor containment. In view of this, design of Filtered Containment Venting System (FCVS) plays an important role in depressurizing the reactor and preventing release of radionuclides to the environment. In this context, a venturi scrubber submerged in alkaline solution along with demister pad housed in a scrubber tank is investigated experimentally at prototypic conditions for retention of iodine vapors in the scrubber system. The hydrodynamics and the scrubbing performance of the submerged venturi scrubber is simulated at air flow rates of 1500–3500 lpm at the submergence height of 4 m. The iodine concentration retained in the scrubber tank and its bulk decontamination is measured by ICP-OES and ICP-MS analysis respectively.It is observed that the overall pressure drop in the venturi scrubber increases with an increase in flow rate. The two phase axial pressure drop characteristics reveal an increase in the pressure drop in the converging section with increase in flow rate. The pressure drop also increases after the scrubbing liquid from the hydrostatic pool is suctioned and no recovery is found in the diverging section of the venturi scrubber. The iodine retention in the scrubber tank increases sharply with an air flow rates up to 2200 lpm after that the increase is gradual with the maximum of 95% retention at 3400 lpm. It is seen that in all the experiments the amount of iodine leaving the facility is negligible and the bulk decontamination is high. Further, effect of submergence height on the retention of iodine vapors in the scrubber tank is compared at 3 m and 4 m. It is seen that an increase in submergence height significantly increased the percentage of iodine arrested in the scrubber tank at 1700 lpm air flow but further increase in air flow rate has lesser impact on the iodine retention in the scrubber tank despite the increase in submergence height.

Study on the hydrogen risk in venturi scrubber filter of filtered containment venting system under PWR severe accident

As the third barrier to prevent radioactive material from leaking into the environment, containment vessel plays an important role in nuclear safety of the Nuclear Power Plant (NPP). Severe accident may result in massive production of hydrogen in the vessel, and vessel pressure may increase rapidly. That may further threat the integrity of the containment vessel. Based on this phenomenon, the Filtered Containment Venting System (FCVS) has been proposed by researchers, which is very essential to protect the integrity of the containment vessel and remove contaminated particles from exhausting gaseous stream under PWR severe accident. The key equipment in FCVS is venturi scrubber filter. When the system is activated under severe accident, the hydrogen produced in the containment vessel will flow into the filtering equipment, which may lead to high hydrogen concentration in some regions of it. High hydrogen concentration may result in combustion, deflagration, and endanger the whole system. In the present study, the temperature and velocity distribution of gaseous mixture in the filtering equipment was simulated on the basis of CFD technology, and high hydrogen concentration region was recognized according to the simulation results of gas concentration distribution. Meanwhile, in order to mitigate the consequence of hydrogen aggregation, the nitrogen injection condition was taken into consideration in simulation process, and the effects of different injection conditions on hydrogen inerting performance was also analyzed in detail. The present study is significant for hydrogen risk management and further design of FCVS under PWR severe accident.

Prediction of hydrodynamic characteristics of a venturi scrubber by using CFD simulation

The filtered containment venting system (FCVS) is a safety relevant system, which consists of venturi scrubber and a mesh filter. FCVS needs to be further assessed to improve the existing performance of the venturi scrubber. Therefore, hydrodynamics is an important counter-component needs to be investigated to improve the design of the venturi scrubber. In the present research, Computational Fluid Dynamic (CFD) has been used to predict the hydrodynamic behaviour of a newly designed venturi scrubber. Mesh was developed by gambit 2.4.6 and ansys fluent 15 has been used to predict the pressure drop profile inside the venturi scrubber under various flow conditions. The Reynolds Renormalization Group (RNG) k-ε turbulence model and the volume of the fluid (VOF) were employed for this simulation. The effect of throat gas velocity, liquid mass flow rate, and liquid loading on pressure drop was studied. Maximum pressure drop 2064.34 pa was achieved at the throat gas velocity of 60 m/s and liquid flow rate of 0.033 kg/s and minimum pressure drop 373.51 pa was achieved at the throat gas velocity of 24 m/s and liquid flow rate of 0.016 kg/s. The results of the present study will assist for proper functioning of venturi scrubber.

Application of Moment Method for Predicting Condensational Growth of Nuclear Aerosols in a Severe Accident

Because most radioactive materials that can escape from a nuclear power plant during a severe accident are expected to be in the form of aerosols, the installation of a filtered containment venting system (FCVS) will be effective to mitigate the risks caused by radioactive aerosols. Aerosol size is a parameter important to the design requirements of an FCVS because the collection efficiency of the venting system depends on the size of the aerosol. In this study, the size distribution change of aerosols by condensation was calculated by using the moment method. Sodium chloride was used as nuclei that underwent condensational growth, and Di-Ethyl-Hexyl-Sebacate (DEHS) was used as a vapor that participated in condensational growth. Then, a condensation experiment was conducted to verify the results calculated by the moment method. However, in an actual severe accident, water vapor in the containment would condense on particles. Therefore, after model verification, calculation was performed with water vapor as the condensation vapor to predict the condensation scenario under a severe accident. This paper reports that the aerosol condensation model based on the moment method can be an auxiliary tool in an existing aerosol modeling program to estimate the particle size distribution change during a severe accident.

Effects of Filtered Containment Venting on Fission Product Releases During CANDU Reactor Severe Accidents

Severe accidents are of increasing concern in the nuclear industry worldwide since the accidents at Fukushima Daiichi (March 2011). These events have significant consequences that must be mitigated to ensure public and employee safety. Filtered containment venting (FCV) systems are beneficial in this context as they would help to maintain containment integrity while also reducing radionuclide releases to the environment. This paper explores the degree to which filtered containment venting would reduce fission product releases during two Canada Deuterium Uranium (CANDU) 6 severe accident scenarios, namely a station blackout (SBO) and a large loss of coolant accident (LLOCA) (with limited emergency cooling). The effects on the progression of the severe accident and radionuclide releases to the environment are explored using the Modular Accident Analysis Program (MAAP)–CANDU integrated severe accident analysis code. The stylized filtered containment venting system model employed in this study avoids containment failure and significantly reduces radionuclide releases by 95–97% for non-noble gas fission products. Filtered containment venting is shown to be a suitable technology for the mitigation of severe accidents in CANDU, maintaining containment integrity and reducing radionuclide releases to the environment.

Severe accident consequence mitigation by filtered containment venting at Canadian nuclear power plants

Having the capability to use filtered containment venting during a severe nuclear accident can significantly reduce its overall consequences. This study employs the MAAP-CANDU severe accident analysis code and the ADDAM atmospheric dispersion code to study the progression of: an unmitigated station blackout accident at a generic pressurized heavy water reactor, the release of radioactive material into the environment, the subsequent dispersion of the fission products through the atmosphere and the subsequent consequences (evacuation radius). The goal is to evaluate the application of filtered venting as an accident mitigation technology. Several aspects of filtered containment venting system design, like flow capacity, initiation protocols, filter efficiency, mass loading, and thermal loading are considered. An efficient and robust filtered containment venting system can reduce the amount of radiological materials emitted during an accident by 25 times or more, and as a result considerably reduce the off-site consequences of an accident.

原子炉格納容器フィルタベント用有機ヨウ素フィルタの除去性能

After the Fukushima Dai-ichi nuclear accident, Filtered Containment Venting Systems (FCVSs) were developed and installed at nuclear power plants in Japan. Using silver zeolite, a design of an additional filter had been developed for FCVSs to capture radioactive organic iodine, which cannot be captured by conventional aerosol filters. For expanding the design flexibility of the FCVS with the organic iodine filter, additional laboratory tests were conducted in this study. To secure the absorption performance, silver zeolite must be kept dry during the operation of the FCVS. The additional tests were conducted to evaluate the absorption performance of silver zeolite under the conditions of relatively low degrees of superheat. And the test results demonstrated that the decontamination factor of the silver zeolite was over 50 even under the condition that the difference between gas temperature and dew point was 2.1 K and contact time was 0.129 s. In addition, absorption performance tests simulating FCVS start-up conditions were conducted. Although similar tests had been conducted in previous studies, the tests in this study demonstrated the performance under relatively short contact time conditions.

格納容器フィルタベント総合解析ツールの開発

格納容器フィルタベント総合解析ツールの開発

Filtered Containment Venting: Reasons, Technology, Impact on Environment

Filtered Containment Venting: Reasons, Technology, Impact on Environment

Experiments on aerosol removal by high-pressure water spray

An experimental research was managed in the framework of the PASSAM European Project to measure the efficiency of high-pressure sprays in capturing aerosols when applied to a filtered containment venting system in case of severe accident.The campaign was carried out in a purposely built facility composed by a scrubbing chamber 0.5×1.0m and 1.5m high, with transparent walls to permit the complete view of the aerosol removal process, where the aerosol was injected to form a cloud of specific particle concentration. The chamber was equipped with a high pressure water spray system with a single nozzle placed on its top.The test matrix consisted in the combination of water pressure injections, in the range 50–130bar, on a cloud of monodispersed SiO2 particles with sizes 0.5 or 1.0μm and initial concentration ranging between 2 and 99mg/m3. The spray was kept running for 2 min and the efficiency of the removal was evaluated, along the test time, using an optical particle sizer.With respect to low-pressure sprays, the removal efficiency turned out much more significant: the half-life for 1μm particles with a removal high-pressure spray system is orders of magnitude shorter than that with a low-pressure spray system.The highest removal rate was detected with 1μm particles at the highest water injection pressure, mainly because of the high concentration of droplets with high velocity, while lower removal was measured for 0.5μm particles. No influence of the initial aerosol concentration was observed for both particle sizes.

The Hydrogen Issue in the Initial Operation of a Filtered Containment Venting System

This study evaluated the hydrogen issue in the initial operation of a filtered containment venting system (FCVS). We calculated the volumetric concentration of hydrogen, steam, and air in the postulated FCVS connected with the OPR 1000, as a target nuclear power plant, under a station blackout using the MELCOR computer code (version 1.8.6). A large amount of steam and a flammable mixture generated during a severe accident are immediately released from the containment building to the FCVS when the pressure in the containment building approaches a set value. The constituent ratio of the flammable mixture of hydrogen, steam, and air can change due to the different thermal-hydraulic conditions between those due to a severe accident in the containment building and the initial condition in the FCVS. The volumetric concentration of hydrogen was 6% in the containment building just before the operation of the FCVS. It increased up to 9% in the FCVS vessel during the early operation, and steam condensation occurred simultaneously. The atmospheric condition including steam, hydrogen, and air in the FCVS can enter the combustion zone in the Shapiro diagram.

A Scaling Analysis for a Filtered Containment Venting System

A scaling method is proposed for the design of a reduced-scale experimental facility for testing the performance of a newly proposed filtered containment venting system (FCVS). A full-height facility at prototypic pressure and temperature conditions is chosen to preserve the fundamental physics such as depressurization rate, two-phase mixture level, and scrubbing process. The geometrical similarities in terms of the ratio of the cross-sectional area and geometric and frictional loss coefficient are preserved for each component in the FCVS. Scaling of the number of components in the reduced-scale test facility is suggested using the prototypic components of the FCVS including a venturi scrubber, a cyclone, a metal fiber filter, and a molecular sieve. This approach minimizes scaling distortions. A properly scaled test facility allows testing in a wide range of initial and boundary conditions such that it can predict the full performance of the prototypic FCVS.

Development of an aerosol decontamination factor evaluation method using an aerosol spectrometer

During a severe nuclear power plant accident, the release of fission products into containment and an increase in containment pressure are assumed to be possible. When the containment is damaged by excess pressure or temperature, radioactive materials are released. Pressure suppression pools, containment spray systems and a filtered containment venting system (FCVS) reduce containment pressure and reduce the radioactive release into the environment. These devices remove radioactive materials via various mechanisms. Pressure suppression pools remove radioactive materials by pool scrubbing. Spray systems remove radioactive materials by droplet−aerosol interaction. FCVS, which is installed in the exhaust system, comprises multi-scrubbers (venturi-scrubber, pool scrubbing, static mixer, metal−fiber filter and molecular sieve). For the particulate radioactive materials, its size affects the removal performance and a number of studies have been performed on the removal effect of radioactive materials.This study has developed a new means of evaluating aerosol removal efficiency. The aerosol number density of each effective diameter (light scattering equivalent diameter) is measured using an optical method, while the decontamination factor (DF) of each effective diameter is evaluated by the inlet outlet number density ratio. While the applicable scope is limited to several conditions (geometry of test section: inner diameter 500mm×height 8.0m, nozzle shape and air-water ambient pressure conditions), this study has developed a numerical model which defines aerosol DF as a function of aerosol diameter (d) and submergences (x).

Methodology developed for the definition of the design parameters and associated safety criteria of the Filtered Containment Venting Systems for Belgian NPPs

Following the post-Fukushima stress tests performed in Belgium, Filtered Containment Venting Systems (FCVS) are foreseen to be installed on Belgian Nuclear Power Plants (NPPs) as ultimate means to cope with slow pressurizations of the containments that could occur during potential Severe Accidents (SA).The present paper discusses the methodology supporting the definition of the FCVS main design parameters and associated safety criteria.This methodology, developed by Tractebel Engineering and accepted by the Belgian nuclear Safety Authorities, followed a series of subsequent steps starting with the definition of the safety referential applicable to the FCVS and leading to the identification of a reference sequence, namely the Complete Station BlackOut (CSBO).Then, key parameters for the FCVS design were defined (e.g. pressure range, venting flow, stored decay heat, stored mass, Decontamination Factors (DF)) along with the associated safety criteria. Several of them were assessed through a well-defined set of supporting calculations. This set included both best estimate representative cases as well as conservative bounding cases performed with state-of-the-art SA codes.The SA codes used were first of all the MELCOR 1.8.6 code and, subsequently, the ASTEC V2.0 code (CPA/IODE modules), considering a chaining methodology. The aim of this approach was to take advantage of the iodine chemistry models features in the CPA/IODE modules of ASTEC to calculate the iodine speciation in the containment and in the FCVS, without having to run a full scope ASTEC calculation.In conclusion, appropriate values for the safety criteria of each design parameters were assessed. In particular, the ones related to the minimum DF relied on a marginal gain approach to cope with the large uncertainties existing when performing dedicated radiological evaluations.Finally, the next steps of this continuous safety assessment of the FCVS that are foreseen to be installed on Belgian NPPs are highlighted at the end of this paper.

高除染性フィルターベントシステムにおける二相流安定化

Fukushima Daiichi NPP accident would be terminated, if sufficient accident countermeasures, such as water proof door, mobile power, etc. In case of Europe, it had already installed the heat removal system and filtered containment venting system (FCVS) from the lessons of TMI and Chernobyl Accidents. The new regulatory standard, the filtered vent system (FCVS) should be installed, and prevent the radioactive material in case of the severe accident and the overpressure breakage prevention of a primary containment vessel (PCV) and also stabilize the FCVS. The authors examined the severe accident process in the 2nd unit of Fukushima Daiichi NPS, and found the vent by FCVS should be done before water injection into the core. By conducting two-phase flow visualization test, the authors also pointed out the necessity of stabilization in the scrubbing pool. TRAC code analysis was also conducted to clarify the mechanism of the geysering and stabilized by using an orifice plate to pressurize the scrubbing pool.