Containment Venting System Research Articles

Effects of the Baffle Plate of the Advanced Venturi Scrubber on Decontamination Factor of the Filtered Containment Venting System

Effects of the Baffle Plate of the Advanced Venturi Scrubber on Decontamination Factor of the Filtered Containment Venting System

Stability and radioactive gaseous iodine-131 retention capacity of binderless UiO-66-NH2 granules under severe nuclear accidental conditions

In the present work, we aim to investigate the ability of the zirconium-based MOF-type compound UiO-66-NH2, to immobilize molecular gaseous iodine under conditions analogous to those encountered in an operating Filtered Containment Venting System (FCVS) line. Typically, the UiO-66-NH2 particles were exposed to 131I (beta and gamma emitters) and submitted to air/steam at 120 °C, under gamma irradiation (1.9 kGy h-1). In parallel to this experiment under simulated accidental conditions, the stability of the binderless UiO-66-NH2 granules under steam and gamma irradiation was investigated. In order to fit with the specifications required by typical venting systems, and to compare the efficiency of the selected MOF to porous materials commonly used by the industry, scale-up syntheses and UiO-66-NH2 millimetric-size shaping were realized. For this task, we developed an original binderless method, in order to analyze solely the efficiency of the UiO-66-NH2 material. The shaped MOF particles were then submitted separately to gamma irradiation, steam and temperature, for confirming their viability in a venting process. Their structural, textural and mechanical behaviors were characterized by the means several techniques including gas sorption, powder X-ray diffraction, infrared spectroscopy and crushing tests. Promising results were obtained to trap gaseous molecular iodine in severe accidental conditions.

Experimental evaluation of re-entrainment from wet scrubber filtered containment venting systems

Wet scrubber-based filtered containment venting systems (FCVSs) are commonly deployed at nuclear power plants, owing to the high degree of aerosol, iodine, and organic iodine retention that is possible through the pool scrubbing action that takes place during their operation. However, after a FCVS has been operating during a severe accident, the pool water will become extremely contaminated with previously-captured radionuclides, and the bubbling action of gases passing through the pool, could result in the re-entrainment of contaminated liquid droplets into the gas stream. This would produce a secondary source term during the late phases of an accident. As such, a set of experiments have been conducted in order to evaluate the aerosol re-entrainment rates and size distribution from a system prototypical of a pool-type FCVS. Entrainment rates were measured by tracking the carry-over of a NaCl tracer into a set of liquid traps, while the size of the re-entrained droplets was measured with a phase Doppler anemometer. The experiment employed a prototypical venturi nozzle and gas injection conditions to examine the influence of gas flow rate, liquid level, and pool water temperature. Entrainment factors between 5×10−5 and 1×10−3 were measured, and the water droplet count median diameters were between 3 and 13 µm, and fairly wide particle size distributions, with mass mean diameters were on the order of 40–140 µm. These experimental results help the assessment of the potential magnitude of the late phase source term hazards posed by the fission products retained in pool-type FCVS (secondary release), and the potential loading on the secondary dry filter stage (metal fiber filters) employed in FCVSs after the primary pool scrubbing stage. The secondary metal fiber filters should have a high efficiency in capturing water droplets produced through this mechanism, given the droplet’s relatively large size.

A method of estimating aerosol particle removal rates using one-dimensional two-fluid equations for venturi scrubbers in filtered containment venting

One-dimensional two-fluid mass, momentum, and energy conservation equations for gas and liquid droplet and the particle removal rate are formulated to estimate aerosol particle removal rates of venturi scrubbers used in filtered containment venting systems. Compared with existing one-dimensional models, present method enables describing actual two-phase interactions by calculating the local gas and droplet velocities hence local droplet diameters as well as the other physical properties. The results show that the particles are mostly removed at the entrance region of the throat where droplets are introduced and thus the two-phase velocity difference is the largest. This coincides well with previous experimental studies. The present model predicts the existing experimental data considered here better than the previous one- or two-dimensional models. Especially, in the conditions of low liquid-to-gas flow ratio, the predictions of the present model are very close to the experimental data.

Investigation of iodine removal efficiency in a venturi scrubber using mass transfer model for CFD

Filtered containment venting system (FCVS) is important for the ultimate safety of a nuclear power plant owing to its use in containment pressure reduction in case of severe accident. It vents a portion of containment air after removal of harmful radioactive products including iodine through venturi scrubber. The purpose of this research was to develop a mass transfer model for estimation of performance of a venturi scrubber for removal of elemental iodine using Computational Fluid Dynamics. A mathematical model for transfer of iodine from air to water was developed based on two film theory of mass transfer and experimentally validated. Simulations were performed for self-priming non-submerged circular venturi scrubber using Fluent and the results were compared with experimental ones. Experimental data was used for validation in which an aqueous solution of sodium hydroxide and sodium thiosulfate was used as scrubbing solution for removal of iodine. For simulation, only water was used instead of scrubbing solution for simplicity. Euler-Euler approach was used for two-phase modeling and realizable k-epsilon model was used for turbulence modeling. The results obtained from simulations had a good match with the experimental ones.

Thermal-hydraulic behaviors of a wet scrubber filtered containment venting system in 1000 MWe PWR with two venting strategies for long-term operation

Filtered containment venting system (FCVS) is one of the severe accident mitigation systems designed to release containment pressurization to maintain its integrity. The thermal-hydraulic behaviors in FCVSs are important since they affect the operation characteristics of the FCVS. In this study, a representative FCVS was modeled by RELAP5/Mod3.3 code, and the Station BlackOut (SBO) was chosen as an accident scenario. The thermal-hydraulic behaviors of an FCVS during long-term operation with two venting strategies (open-and-close strategy, open-and-non-close strategy) and the sensitivity analysis of important parameters were investigated. The results show that the FCVS can operate up to 250 h with a periodic open-and-close strategy during an SBO. Under the combined effects of steam condensation and water evaporation, the solution inventory in the FCVS increases during the venting phase and decreases during the intermission phase, showing a periodic pattern. Under this condition, the appropriate initial water level is 3–4 m; however, it should be adjusted according to the environment temperature. The FCVS can accommodate a decay heat power of 150–260 kW and may need to feed water for a higher decay heat power or drain water for a lower decay heat power during the late phase. The FCVS can function within an opening pressure range from 450 kPa to 500 kPa and a closing pressure range between 250 kPa and 350 kPa. When the open-and-non-close strategy is adopted, the solution inventory increases quickly in the early venting phase due to steam condensation and then decreases gradually due to the evaporation of water; drying-up may occur in the late venting phase. Decreasing the venting pipe diameter and increasing the initial water level can mitigate the evaporation of the scrubbing solution. These results are expected to provide useful references for the design and engineering application of FCVSs.

On Line Measurement of Organic Iodine During a Severe Nuclear Accident

A severe nuclear accident may induce a dramatic dissemination of radioactive species into the environment. In that respect, improving the nuclear safety remains an important challenge to improve the society acceptability towards this energy. A solution may consist on implementing robust and reliable measurement systems operating near the Containment Venting Systems (CVS). These devices should be able to provide real time monitoring of the emitted fission products (FPs) in the course of a hypothetical accidental sequence. In the present study, a peculiar attention was devoted to iodine species (namely CH3I) measurement by complementary techniques (photoacoustic spectroscopy and gas chromatography). The most important results will be described here.

Simulation of the Performance of the Venturi Scrubber for an Advanced Reactor Containment Venting Conditions

Abstract Post Fukushima, nuclear plants are being retrofitted with severe accident mitigation measures. For attaining depressurization of the containment and mitigate the consequences of the release of the radioactivity to the environment during a severe accident condition, filtered containment venting systems (FCVS) are proposed to be installed in existing reactors and being designed for advanced reactors. The design of FCVS is particular to the reactor type. The FVCS configuration considered in this paper comprises of a manifold of venturi scrubber enclosed in a scrubber tank along with metal fiber filter and demister for an advanced Indian reactor. This study focuses on the assessment of the design of the venturi scrubber for the reactor conditions at which venting is carried out through a numerical model. The numerical model is first validated with experiments performed for prototypic conditions. The predicted pressure drop and the iodine absorption efficiency were found to be in good match with the experimental measurements. Subsequently, the model is implemented for predicting the hydrodynamics, i.e., pressure drop, droplet sizes and distribution, and iodine absorption for prototypic conditions. The hydrodynamics, i.e., pressure profile in the venturi scrubber showed a decrease in the converging section and in the throat section. The diverging section showed decrease in recovery of pressure with the decrease in gas flow because of the increased liquid loading to the scrubber. The iodine absorption efficiency showed a value of 92% for high gas velocity which decreased to 68% for the lowest gas flow rate.

Filtration tests of gaseous ruthenium tetroxide by sand bed and metallic filters

This work presents laboratory tests on gaseous RuO4 filtration carried out at IRSN in Cadarache. The objective is to determine if gaseous ruthenium tetroxide can be trapped by metallic filter and sand bed filter, both elements being used in filtered containment venting systems implemented on French pressurized water reactors. The results show no ruthenium tetroxide trapping by physical or chemical adsorption but certain retention is observed resulting from its thermal decomposition into solid ruthenium dioxide. A thermodynamic analysis of the system tends to confirm this conclusion. Chemical stability of RuO4(g) has to be considered as it strongly impacts potential filtration and so potential releases.

Effect of Liquid Injection Arrangements on Injection Flow Rate of a Laboratory-Scale Venturi Scrubber

As the core device of a filtered containment venting system(FCVS), Venturi Scrubber is an efficient device to scrub the radioactive gases and aerosols before release into the atmosphere. The design concept of Multi-Venturi Scrubber System makes the laboratory-scale venturi scrubber research more valuable. This paper studied the injection flow rate of Venturi Scrubber in different injection arrangements. The liquid is injected horizontally and vertically to the throat at different radial position of i) at the wall of throat, ii) at the half radius of throat, and iii) at the center of Venturi Scrubber throat with a nozzle of diameter 4mm. Throat gas velocities range from 0 to 190 m/s. A constant level water tank was installed to keep water level constant during the injection process. The results showed that liquid injection modes significantly affect the injection performance. The arrangements of straight tube at center and elbow tube at center had larger injection flow rate among the others, and the injection flow rate increased as the throat gas velocity increased. The conventional wall opening (ie, straight tube at the wall) injection method had the worst injection performance. This study provides a valuable reference for the liquid injection arrangement and structural design of the Venturi Scrubber.

Numerical study on cut-off diameter of aerosol particle for filtered containment venting system in nuclear power plant

Abstract This paper presents analytical investigations of the cut-off diameter of aerosol particle for filtered containment venting system in a nuclear power plant. These analyses were done for operation conditions of the containment venting and the numerical results reveal that the particle sizes of fission products released to environment range between 10−8 m and 10−5 m and mostly distribute between 10−7 m and 10−6 m. For designing a filtered containment venting system, the collection efficiency of the filter must be high-quality in the main range 10−7 m – 10−6 m. In this research, the numerical results can offer nuclear power plant a useful reference to design and set up FCVS.

Control of accidental discharge of radioactive materials by filtered containment venting system: A review

Abstract Radioactive materials are released from the molten core into the containment at the time of a severe accident in a nuclear power plant (NPP). Filtered containment venting system is a popular and effective safety measure installed to obstruct the uncontrolled escape of radioactive materials due to the over pressurization of the containment. Different designs of filtered containment venting system (FCVS) are available today, each being the result of extensive research and development varying in one way or the other. This paper gives an elaborate description of the different types of FCVS currently being used, the current usage status in over 17 countries and the legislations regarding it. The recent researches being carried out in this field has also been discussed in detail. This present paper focuses on the critical review of existing FCVS, reports the challenges faced by it and highlights the potential developments to overcome the difficulties.

Study of level swell for a Filtered Containment Venting System at the VEFITA facility

A Filtered Containment Venting System (FCVS) is a safety system incorporated in Nuclear Power Plants (NPPs) to filter the steam and noncondensable gases released from the containment during a severe accident scenario to avoid overpressure in the containment structures while isolating most radioactive products inside. This paper presents the experimental and numerical simulation results from confirmatory tests performed in the VEFITA (Venting Filter Assessment) test facility at the Paul Scherrer Institut (PSI) in Switzerland. This facility is designed to evaluate the performance of an FCVS by assessing key phenomena and parameters such as internal recirculation patterns, changes in inventory, level swell, and the Decontamination Factor (DF) of aerosol and iodine species in simulated venting processes. The current study focuses on the level swell (gas holdup) phenomenon. The level swell during gas injection is particularly of interest since it is associated with the heights of gases and liquids in the venting vessel and thus affects the design and operation of an FCVS. The experiment is performed by injecting the noncondensable gas and steam at various mass flow rates through a sparger nozzle to the vessel, which is partially filled with washing fluid as a bubble column. The level swell and other physical variables are recorded and analyzed. System codes (RELAP5 and TRACE) input decks are developed for this facility, and experimental transients are simulated. The code simulation results, as well as previous physical gas holdup models based on homogeneous-heterogeneous regime transition, are compared with current experimental data to study the level swell in this FCVS.

Effects of the operating strategies of filtered containment venting system on Cesium-137 releases during severe accidents

The concept of Filtered Containment Venting System (FCVS) has been adopted in the Republic of Korea for Pressurized Heavy Water Reactors to prevent over-pressurization of containment and to reduce the amount of radionuclides released to the environment. This strategy is considered suitable for Pressurized Light Water Reactors as well. As the effects of the FCVS on depressurization and decontamination differ, depending not only on nuclear power plant type but also on accident scenarios and venting strategies, this study analyzes the effects of FCVS operating strategies and accident scenarios on Cesium (Cs) release during severe accidents. Conservatively, the most extreme accident scenarios are chosen, namely, Station Blackout and Loss of Coolant Accident, without any mitigating measures except for the safety injection tank. Continuous and cyclic operation of the FCVS are investigated as operating strategies. In conclusion, installation of the FCVS allows the plant to meet the regulatory requirements, limiting the release of Cs-137 to under 100 TBq for limiting cases such as those considered here. Operating the FCVS to open at higher pressure in cyclic mode is found to be more effective in reducing the amount of Cs-137 release to the environment.

Prevention of contamination around the NPS and Emergency Evacuation by a High Efficiency Filtered Containment Venting System during a Severe Accident

Prevention of contamination around the NPS and Emergency Evacuation by a High Efficiency Filtered Containment Venting System during a Severe Accident

Fundamental study on the filtered containment venting system for decommissioning of the Fukushima Nuclear Power Plant

Fundamental study on the filtered containment venting system for decommissioning of the Fukushima Nuclear Power Plant

Performance evaluation of venturi scrubber used in filtered containment venting system

Performance evaluation of venturi scrubber used in filtered containment venting system

CFD investigation of iodine mass transfer in venturi scrubbing solution of Filtered Containment Venting System

Removal of elemental iodine from gases using Filtered Containment Venting System (FCVS) was studied. Iodine was scrubbed from gases by passing it through venturi placed in scrubbing solution. This task was performed using ANSYS 14.0 FLUENT. Scrubbing solution was aqueous solution of sodium hydroxide and sodium thiosulphate in water. Two phase Euler-Euler multiphase model was used while transfer of iodine from gaseous phase to liquid phase was modelled using species transport model. No specific model was available in any CFD software package to model mass transfer of iodine in scrubbing solution. Therefore, a user defined function (UDF) for iodine mass transfer based on mathematical model proposed by Majid et al. was developed and implemented through FLUENT. Droplet diameter effect on mass transfer of iodine was studied. Large decrease in gas phase iodine, large mass transfer rate and sharp increase in liquid phase iodine was observed on decreasing droplet diameter. About 98% removal efficiency was observed in case of 1 micron droplet diameter while it decreased as the droplet diameter was increased. Thus, validating the mass transfer model for removal of iodine as removal efficiency lies within range reported in previously published experimental results. Increase in liquid volume fraction along venturi length was also noted due to mass transfer of iodine. Liquid droplets of smaller diameter achieved peak velocity close to gas phase. This peak velocity shifted more towards the diverging section as droplet diameter was increased.

Numerical simulation of injection characteristics, hydrodynamics and absorption of iodine vapour in a venturi scrubber operating in self-priming mode

Abstract Post Fukushima, many utilities are planning to install the Filtered Containment Venting System (FCVS) to protect the nuclear reactor containment under severe accident scenarios. FCVS aims at depressurizing the reactor containment and filtering the radioactive gas leaving the containment boundary under such scenarios. A key component of FCVS is the venturi scrubber. The hydrodynamics of the fluid flow inside the FCVS is complex involving multi-phase and multi-component systems with droplets formed by entrainment of high velocity gas stream with liquid jet. The size of droplets and their trajectories are critical with regard to decontamination of iodine which combines with the droplets inside the venturi. Thus, understanding the injection characteristics, hydrodynamics and absorption of iodine vapour with the droplets in the venturi scrubber is very important. There are very limited studies on this aspect. In view of this, a CFD simulation study has been performed in this work for understanding of venturi scrubber operation and performance in self-priming mode. The interaction of the continuous gas phase and droplets is assumed to occur through drag force. The gas flow rate is varied from 1700 to 3400 lpm for two submergence heights of 3 m and 4 m. The liquid loading is estimated from pressure drop at the nozzles observed in the experiments. The retention of iodine in venturi scrubber is calculated assuming instantaneous mass transfer at gas droplet interface. The mass transfer coefficient is evaluated from Steinberg and Treybal correlation. Our results indicate that the liquid loading to the scrubber increases at lower flow rates of 1700 lpm gas flow and further decreases with the increase in gas flow. The two phase pressure profile predicted is close to measured values for each case. The pressure decreases in the converging section; decreases sharply in the throat section due to liquid injection as droplets and shows negligible recovery in the diverging section of the venturi scrubber. The retention of iodine in the venturi scrubber increases with the increase in gas flow rate in the venturi scrubber. This indicates that the participation of venturi scrubber in the iodine retention increases as the air flow rate increases.

Performance evaluation of venturi scrubber for the removal of iodine in filtered containment venting system

Filtered containment venting system (FCVS) is an essential technology in nuclear power plants for the removal of iodine. A laboratory scale venturi scrubber has been designed, developed and fabricated.The maximum removal efficiency of iodine is obtained as 82.32% at 3×10−3kmol/m3 of KI solution, used as the scrubbing liquid for the throat gas velocity of 18m/s and liquid flow rate of 0.033kg/s with iodine inlet concentration of 0.39kg/m3. A semi-empirical model has been developed to predict the removal efficiency of iodine scrubbing using the experimental results and the variables which show the impact on the scrubber performance.