Filtered Containment Venting System Research Articles

Mass transfer enhancement and flow field simulations for a Venturi bubble generator with multiple inlet tubes

The Venturi device plays a crucial role in the Filtered Containment Venting System (FCVS), effectively preventing the release of radioactive pollutants from nuclear reactor containment during overpressure events. Various configurations of the Venturi device yield different outcomes, with mass transfer efficiency being contingent on bubble size and overall gas holdup. This study examines the impact of varying numbers of inlet tubes on the Venturi device, while keeping the inlet area constant. Specifically looking at the gas–liquid flow field, bubble behavior, and mass transfer capacity in the diverging section. By comparing Single Inlet Tube Venturi Device (SITVD) and Double Inlet Tubes Venturi Device (DITVD), we have reached the following conclusions: (1) In SITVD, the liquid flow field is biased to one side, whereas in DITVD, the liquid flows along the axial direction, resulting in bubbles experiencing stronger shear forces. (2) DITVD exhibits a higher overall gas holdup compared to SITVD, with an average axial gas holdup of 0.0317, which is greater than SITVD's 0.0247. However, SITVD's gas holdup is more evenly distributed. (3) SITVD exhibits a higher turbulence dissipation rate of 545 m2/s3, while the bubble residence time in DITVD is comparatively longer. (4) The average bubble diameter of DITVD is 1.116 mm, which is higher than the 1.011 mm of SITVD. (5) DITVD has better mass transfer than SITVD. The proposed structure of the new Venturi scrubber in this study demonstrates a significant enhancement in mass transfer capacity and filtration efficiency. This discovery provides a solid basis for the design and optimization of FCVS, thereby ensuring the safe operation of nuclear reactors.

The effect of using Filtered Containment Venting System on variation in dose with distance in the prompt accident consequence assessment

ABSTRACT In a nuclear emergency, consequence assessment based on the plant conditions using a simple method is important for a prompt response. Response Technical Manual (RTM-96) is a manual calculation method for prompt dose projection at arbitrary distances by converting pre-calculated doses with the conversion factor based on distance and weather. However, the ‘conversion factor’ in RTM-96 does not consider accident scenarios with filtered containment venting system (FCVS). Therefore, in this study, we defined the ratio of effective dose between 1 km and an arbitrary distance as the ‘Distance Conversion Factor (DCF)’ and aimed to clarify the difference between DCFs by accident scenarios, focusing on the presence or absence of FCVS. The results showed that the differences in DCFs for different accident scenarios were minor in the case of no rainfall. In contrast, in the case of rainfall, DCF differed significantly with scenarios with FCVS and those with containment failure. Therefore, the authors propose that DCFs with rainfall should be calculated separately for several representative accident scenarios rather than uniformly for all accident scenarios, as in the conventional method. The results can contribute to developing a new prompt consequence assessment method, such as RTM-96, which considers FCVS.

CFD analysis of iodine mass transfer coupled with a chemical reaction in a filtered containment venting system

The removal of iodine from flue gases through FCVS during a core meltdown in nuclear reactors is important for environmental safety. In this study, CFD analysis for iodine removal in a venturi scrubber was done on Ansys Fluent using a mathematical model that coupled the mass transfer of iodine with the reaction between iodine and thiosulfate. A user defined function (UDF) was written to couple the mass transfer with the reaction. The UDF was hooked into Ansys Fluent, and the simulation was run for three different gas flow rates. Contours for the mass fraction of iodine, tetrathionate, and iodide, along with the hydrodynamics of the venturi scrubber, were analyzed at different gas flow rates. The mass transfer rate of iodine and its overall removal efficiency were observed to increase at higher gas velocities. The results satisfied the experimental data at a high gas flow rate of 340 m3/h but overpredicted the efficiency at lower flow rates of 240 m3/h and 290 m3/h.

Novel concept for a filtered containment venting system with an ionic liquid to remove organic iodine (1)-proof of concept for organic iodine removal

ABSTRACT Ionic liquid (IL) as a chemical adsorbent used in a filtered containment venting system (FCVS) in a nuclear power plant was considered as a new mitigation method for radioactive organic iodine release in the event of a severe accident. In order to demonstrate proof of concept (PoC) for organic iodine removal with the IL, we evaluated the decontamination factor (DF) of the IL for the organic iodine at various temperatures as an index of removal performance. As a removal mechanism for organic iodine with the IL, it was assumed that the anions function to decompose organic halides such as by a Williamson ether synthesis reaction. We evaluated DF for organic iodine using the IL containing thiosulfate ions and while controlling temperature and residence time as changeable parameters. We determined the DF of the IL for the organic iodine was more than 100 in the temperature range from 393 to 433 K and residence time of 0.1 s or longer. The allowable chemical adsorption weight of organic iodine was 5.9 g kg-IL−1. It was concluded that IL was a possible candidate as an organic iodine adsorbent for a next-generation FCVS.

Influence of throat and diverging section on the performance of venturi scrubber by using computational fluid dynamics

Filtered Containment Venting System (FCVS) is a safety system of nuclear power plants whose primary objectives are control of over-pressurization and prevention of release of radioactivity in severe accidents. In a severe accident scenario, when pressure of containment exceeds a set limit, this system gets activated and part of containment steam/gases mixture is transferred to FCVS where removal of hazardous radioactive gases like iodine takes place via scrubbers and then cleaner air is vented out. Iodine removal is necessary because if discharged into environment, it can cause serious health concerns including thyroid cancer. Venturi scrubbers are a key component in FCVS for retention of iodine. Research on various parameters of venturi scrubbers is necessary in order to attain maximum removal efficiency. This research was carried out to investigate the effect of geometric parameters of venturi scrubber on iodine removal using Computational Fluid Dynamics. Parameters such as number of orifices, diameter and length of diverging section and length and diameter of throat section were studied. Influence of variation in above-mentioned geometric parameters on different operational parameters like pressure, volume fraction phase-1, velocity, mass transfer rate and iodine mass fraction was investigated. Order of effect of geometric parameters on iodine removal from lower to higher comes out to be diverging diameter, diverging length, throat length, number of orifices, and throat diameter. 5–68% increase in mass transfer rate was observed from variation in parameters. This research would be very helpful for researchers and designers in parametric optimization and design of an efficient venturi scrubber.

Removal of iodine by dry adsorbents in filtered containment venting system after 10years of Fukushima accident.

Radioactive iodine is a hazardous fission product and a major concern for public health. Special attention is paid to iodine out of 80 fission products because of its short half-life of 8.02days, high activity, and potential health hazards like its irreversible accumulation in thyroid gland and ability to cause thyroid cancer locally. Radioactive iodine can get released in the form of aerosols (cesium iodide), elemental iodine, and organic iodide after a nuclear accident and can cause off-site and on-site contamination. Filtered containment venting system (FCVS) is a safety system whose main objective is mitigation of severe accidents via controlled venting and removal of different forms of iodine to ensure safety of people and environment. After nuclear accidents like Fukushima, extensive research has been done on the removal of iodine by using dry scrubbers. This review paper presents research status of iodine removal by dry adsorbents especially after 10years of Fukushima to assess the progress, research gap, and challenges that require more attention. A good adsorbent should be cost-effective; it should have high selective adsorption towards iodine, high thermal and chemical stability, and good loading capacity; and its adsorption should remain unaffected by aging and the presence of inhibitors like CO, NO2, CH3Cl, H2O, and Cl2 and radiation. Research on different dry adsorbents was discussed, and their capability as a potential filter for FCVS was reviewed on the basis of all the above-mentioned features. Metal fiber filters have been widely used for removal of aerosols especially micro- and nanoscale aerosols. For designing a metal fiber filter, optimal size or combination of sizes of fibers, number of layers, and loading capacity of filter should be decided according to feasibility and requirement. Balance between flow resistance and removal efficiency is also very important. Sand bed filters were successful in retention of aerosols, but they showed low trapping of iodine and no trapping of methyl iodide at all. For iodine and methyl iodide removal, many adsorbents like activated carbon, zeolites, metal organic frameworks (MOFs), porous organic frameworks (POPs), silica, aerogels, titanosilicates, etc. have been used. Impregnated activated carbon showed good results but low auto-ignition temperature and decline in adsorption due to aging and inhibitors like NOx made them less suitable. Silver zeolites have been very successful in methyl iodide and iodine removal, but they are expensive and affected by presence of CO. Titanosilicates, macroreticular resins, and chalcogels were also studied and they showed good adsorption capacities, but their thermal stability was low. Other adsorbents like silica, MOFs, aerogels, and POPs also showed promising results for iodine adsorption and good thermal stability, but very limited or no research is available on their performance in severe accident conditions. This review will be very helpful for researchers to understand the merits and demerits of different types of dry adsorbents, the important operating parameters that need optimization for designing an efficient scrubber, margin of research, and foreseeable challenges in removal of different forms of iodine.

Performance of bubble column for iodine removal in a lab scale setup of filtered containment venting system

Iodine is one of the most hazardous fission products that can get released into environment after a severe nuclear accident and can cause thyroid cancer. Removal of iodine is necessary to ensure safety of people and environment. Different experiments were performed in a lab scale setup of FCVS containing a bubble column. Purpose of this research was to understand the mechanism involved in wet scrubbing in order to improve the removal efficiency of iodine. Influence of many parameters such as gas flowrate, liquid level height, gas holdup, additives, bubble diameter etc. on retention of iodine was studied. Results showed major dependance of decontamination factor on gas flowrate and liquid level height. Bubble diameter was observed to be dependent on gas flowrate, viscosity of liquid and density of liquid and gas. Decrease in bubble diameter was observed with increase in superficial gas velocity which enhanced overall mass transfer and hence, removal efficiency was increased as well. Overall, greater than 99.9% removal efficiency was achieved.

Advancement of Filtered Containment Venting System (FCVS) by Silver Zeolite

Advancement of Filtered Containment Venting System (FCVS) by Silver Zeolite

Level swell analysis of stagnant water pool in filtered containment venting systems

A filtered containment venting system (FCVS) prevents over pressurization of containment vessel and releasing of radioactive materials during the severe accidents in nuclear power plants. During the venting process, it has been reported that the two-phase mixture level in a wet FCVS tends to swell and fluctuate. The behaviors depend on inlet/boundary conditions and physical properties of the injected gas, which vary as the accident progresses. Proper controlling and monitoring of the FCVS pool water level is crucial because it affects filtration performance including scrubbing process and thermal-hydraulic stability. In order to investigate this phenomenon, the current study proposes a set of nitrogen and steam injection experiments using a vertical pipe with a diameter of 105 mm to evaluate the effects of flow conditions and physical properties of gases. Drift flux analysis was carried out to predict the two-phase mixture water level and its fluctuations. The experimental two-phase mixture level was consistent with the values predicted by the drift flux model for nitrogen and steam injection, and the model's capability was confirmed for the system pressure ranging from atmospheric to 0.20 MPa and initial water level ranging from 0.6 to 2.6 m for both small and large diameter pipe configurations. The fluctuation amplitudes in the current experiment were smaller than those observed in experiments conducted on small-diameter pipes. The mean two-phase mixture water level increased upon pressurization of the scrubbing pool. However, it was found that the effect of pressurization on the two-phase mixture level fluctuation amplitude was negligibly small.

Evaluation of filtered containment venting system (FCVS) effects on severe accident of a WWER1000 plant

To mitigate radioactive material release in nuclear facilities, some effective approaches have been suggested such as using filtered venting system (FCVS). For a nuclear containment, the FCVS reduces the overall environmental contamination. This work uses MELCOR for severe accident analysis, ORIGEN for isotope production and depletion calculation and HotSpot for health physics analysis to evaluate the progression of radionuclide release and containment structural stability during station blackout accident (SBO). In this analysis, the performance of a containment with a filter venting system is evaluated. The overall goals are assessment of FCVS effects on radionuclide release into environment and to evaluate containment integrity. In this research, three scenarios of radionuclide releases are considered. In the unmitigated case, no filtered venting system is employed. For the mitigated accident, a proper filtered venting path is considered for decontamination of the released material, and in the unfiltered case, there is a venting path but no filter is provided to absorb radionuclides. Also, the radiation dose produced after the radionuclide release based on the site meteorological condition is estimated. The main results include study of mass and decay heat of deposited radionuclides on filter and fission products release. This research proves, using FCVS saves public health and containment safety during SBO by mitigation mechanism.

Assessment of Filtered Containment Venting Strategies for Mitigating Severe Accident Consequences at a Generic Single-Unit CANDU

Abstract In many jurisdictions, filtered containment venting systems are an integral part of severe accident management guidelines but are normally only used as a last resort, to be manually activated when the containment pressure approaches the containment failure limit. This approach fails to utilize the capability of the filtered venting system to better control containment pressure throughout an accident and to create capacity for possible future pressurization based on the accident progression. In this paper, smart venting strategies are explored, using a generic single-unit Canada Deuterium Uranium (CANDU) (660 MWel) plant model in MAAP-CANDU, as a means to mitigate the consequences of a severe accident. These strategies are able to account for both current conditions as well as possible future pressurization. The use of strategic venting offers an improvement in maintaining containment integrity, as well as reducing I-131 releases to the environment by about 10% to 31% compared to last-resort venting while being feasible for manual operator actions. Overall, this comprehensive analysis demonstrates the capability of a smart venting strategy paired with a filtered containment venting system as an active mitigation tool.

Influence of variation in converging section and orifice plane on the performance of venturi scrubber by using CFD

Filtered Containment Venting System (FCVS) is an important severe accident mitigation system within a nuclear powerplant. Its main objectives are prevention of over-pressurization of containment and spread of radioactivity into environment in a severe accident scenario. After initiation of an accident, when pressure exceeds the design limit, a portion of containment air is transferred to this system. Incoming contaminated air containing hazardous gases like iodine gets scrubbed out in FCVS and clean air is vented into environment. Removal of iodine is crucial because if released to the environment, it can cause thyroid cancer. Venturi scrubbers play a very important role in removal of iodine. Study of its geometric and operational parameters is required to achieve high iodine removal efficiency. So, this study was conducted to investigate the influence of geometric parameters of venturi scrubber on removal efficiency of iodine by using Computational Fluid Dynamics. Geometric parameters such as length and diameter of converging section, position of orifice plane and orifice diameter were studied. Effect of above-mentioned geometric parameters, on various operational parameters such as pressure, velocity, mass transfer rate, volume fraction of air and mass fraction of iodine, was studied. Results showed that variation in converging section's length from 110 to 70 mm caused 9% increase in mass transfer rate of iodine. Variation of position of orifice plane from 3 to 15 mm caused 25% increase in mass transfer rate of iodine. 60% increase in mass transfer rate was achieved by change of orifice diameter from 1 to 1.8 mm. The order of influence of geometric parameters on removal efficiency of iodine from higher to lower comes out to be orifice diameter, position of orifice plane, length of converging section and converging diameter.

Mathematical model of the NPP Krško PCFV system for the RELAP5 computer code

Containment building is the final barrier for radioactive releases from a nuclear power plant (NPP). Preserving its integrity will minimize these releases even in a case of a severe accident with core degradation and melt discharge in the containment accompanied with the pressure and temperature increase. Installation of a venting system with ability to filter radioactive fission products is a preferred way to deal with the issue in present and future NPPs, especially after the Fukushima accident. Such system, called passive containment filtered venting system (PCFV), was installed in 2013 in the NPP Krško. Thermal hydraulic model of the PCFV system which included aerosol and iodine filters, associated pipings and valves was developed for the best-estimate computer code RELAP5. Main results and discussion are presented and compared with relevant plant documentation.

Study of an improved and novel venturi scrubber configuration for removal of radioactive gases from NPP containment air during severe accident

Owing to the rising concerns about the safety of nuclear power plants (NPP), it is essential to study the venturi scrubber in detail, which is a key component of the filtered containment venting system (FCVS). FCVS alleviates the pressure in containment by filtering and venting out the contaminated air. The main objective of this research was to perform a CFD investigation of different configurations of a circular, non-submerged, self-priming venturi scrubber to estimate and improve the performance in the removal of elemental iodine from the air. For benchmarking, a mass transfer model which is based on two-film theory was selected and validated by experimental data where an alkaline solution was considered as the scrubbing solution. This mass transfer model was modified and implemented on a unique formation of two self-priming venturi scrubbers in series. Euler-Euler method was used for two-phase modeling and the realizable K−ε model was used for capturing the turbulence. The obtained results showed a remarkable improvement in the removal of radioactive iodine from the air using a series combination of venturi scrubbers. The removal efficiency was improved at every single data point.

Optimized initiation criterion for a filtered containment venting in case of a severe accident in a nuclear power plant

In case of a nuclear accident with core damage, there is a high conditional probability that not only all core cooling systems are lost, but also that all containment cooling systems are lost. Thus, the containment pressurization represents a significant risk for the containment integrity. Nowadays, it is international standard that Generation 2 nuclear power plants are back-fitted with a filtered containment venting system to control the containment pressure passively in case other means have failed.In case of a core damage event, the emergency response team may have to make the decision to either initiate the filtered containment venting to avert an impending containment overpressure failure (accepting a limited fission product release), or to delay the venting to gain additional time for emergency repair works, possibly avoiding the need for the venting (but increasing the probability for an uncontrolled containment failure).In the following, a method is presented to deduce an optimized venting pressure set-point, based on an approach to minimize the cesium release risk. The result of this optimization is that a filtered containment venting shall be initiated after the containment exceeds its design pressure but before the test pressure (usually in the range of 1.2 times the design pressure) is significantly exceeded. A further delay of the venting, accepting even a very small probability for a containment over-pressure failure, significantly increases the overall fission product release risk.

Experimental Investigation on the Retention of Soluble Particles by Pool Scrubbing

Abstract In the late stage of a severe loss-of-coolant accident, the pressure in the containment building of a nuclear power plant could rise beyond the design limits and thus endanger its structural integrity. Therefore, to avoid pressure failure, it may be necessary to perform controlled venting of the containment. During the event of an accident, a large amount of fission and activation products are released into the containment as airborne particles (aerosols). These particles are filtered during the venting process, usually with the help of wet filters, in order to keep risks to the surrounding environment to a minimum. Consequently, the knowledge of the retention processes in a water reservoir (pool scrubbing) is of central importance for such filtered containment venting systems and for reactor concepts in which water reservoirs are used for pressure reduction (e.g., condensation chamber of a boiling water reactor (BWR)). Investigations on pool scrubbing are carried out in the severe accident aerosol behavior (SAAB) test facility at the Juelich Research Center in the framework of a national project (“severe accident aerosol behavior-II”). SAAB is a unique large-scale facility with the ability to perform a great variation of experiments using various measurement tools. The influence of numerous parameters, such as the height of the water pool, solubility of aerosols and concentration on the retention capacity, is investigated by means of separate effect studies on both insoluble and soluble particles. This technical brief gives a detailed overview over the facility and includes example results of the first test series with soluble particles including cesium iodine (CsI).

Numerical simulation of gas holdup in nocoalescence media of industrial-scale bubble column

A bubble column is an industrial-scale wet filtration facility that contains non-coalescence media. To overcome the experimental challenges, numerical simulation was employed to investigate the influence of various factors on the whole gas holdup εt. These include the bubble diameter ds, initial liquid height Hs, column diameter, Dc, the number of bubbling orifices N, and the configuration of bubbling orifices. Two magnitudes of the superficial gas velocity UG, were selected to represent the homogeneous and heterogeneous flow regimes, respectively. The relationship between εt and ds changed within different ds ranges. The proportion of the developing region in the total liquid height is an important factor that influences εt. For an “industrial-scale” column, εt increased with N when N < 49, but becomes insensitive to N when N > 49. The configuration of bubbling orifices significantly influences εt when N > 49. The results of this study show the need to optimize the bubble column and improve the operating performance of filtered containment venting systems.

Advancement of Filtered Containment Venting System (FCVS) by Silver Zeolite (12)

Advancement of Filtered Containment Venting System (FCVS) by Silver Zeolite (12)

Fundamental Study on Flow Characteristics of Venturi Nozzle for High Efficiency Filtered Containment Venting System

Fundamental Study on Flow Characteristics of Venturi Nozzle for High Efficiency Filtered Containment Venting System

Analysis of venting strategies and hydrogen concentration evolution during a station blackout in a BWR-6 containment using GOTHIC 8.3

After the Fukushima accident, the interest on hydrogen combustion hazard management has increased considerably. Many European nuclear plants reinforced their strategies for severe accident management with the installation of Passive Autocatalytic Recombiners (PARs) and Filtered Containment Venting Systems (FCVS), among others. In this study, the hypothesis of considering a preventive venting to try to reduce the hydrogen combustion risk is analyzed for a BWR-6 Mark III containment. The scenario chosen was the in-vessel phase of a Station Blackout accident. Cases with and without PARs have been tested.The venting action has been tested at different conditions to clarify its impact on the hydrogen concentration in the containment. One novelty of this study is to consider the difference between measuring the hydrogen concentration values present in the containment in the venting pipe rather than in the instrumentation position. The purpose is to try to understand the decisions that an operational crew can take with the instrumentation available and analyze the differences by modifying the location of the plant instrumentation.For the numerical analysis, numerous simulations have been carried out using a BWR containment model with GOTHIC 8.3. It has been observed that hydrogen concentration depends to a great extent on the containment venting strategy. The main conclusion is that the venting strategy, if properly performed, can reduce the risk associated with hydrogen for BWR-6 containments. During a SBO scenario, an early venting increases considerably the hydrogen combustion hazard, even in the cases with PARs.