Investigation of ex-vessel core catcher for SBO accident in VVER-1000/V528 containment using MELCOR code

To mitigate consequences of core melting,an ex-vessel core catcher is investigated in this study.Instructions should be obeyed to cool down the corium caused by core melting.The corium destroys the reactor containment and causes radioactive materials to be released into the environment if it does not cool down well.It is important to build a core catcher system for the reception,localization,and cool down of the molten corium during a severe accident resulting from core melting.In this study,the role of a core catcher in the VVER-1000/v528 reactor containment during a station black out(SBO)accident is evaluated using the MELCOR1.8.6 code.In addition,parametric analyses of the SBO for(i)SBO accidents with emergency core cooling system(ECCS)operation,and(ii)without ECCS operation are performed.Furthermore,thermal–hydraulic analyses in dry and wet cavities with/without water are conducted.The investigations include the reduction of gases resulting from molten–corium–concrete interactions(H_(2),CO,CO_(2)).Core melting,gas production,and the pressure/temperature in the reactor containment are assessed.Additionally,a full investigation pertaining to gas release(H_(2),CO,CO_(2))and the pressure/temperature of the core catcher is performed.Based on MELCOR simulations,a core cavity and a perimeter water channel are the best options for corium cooling and a lower radionuclide release.This simulation is also theoretically investigated and discussed herein.The simulation results show that the core catcher system in addition to an internal sacrificial material reduces the containment pressure from 689 to 580 kPa and the corresponding temperature from 394 to 380 K.Furthermore,it is observed that the amount of gases produced,particularly hydrogen,decreased from 1698 to 1235 kg.Moreover,the presence of supporting systems,including an ECCS with a core catcher,prolonged the core melting time from 16,430 to 28,630 s(in an SBO accident)and significantly decreased the gases produced.

Release of ZrO2 nanoparticles from ZrO2/Polymer nanocomposite in wastewater treatment processes

The widespread use of nano-enabled water treatment composites(NWTCs)can result in the release of nanoparticles(NPs)into environmental waters.Studying the release of NPs from NWTCs is of great significance for evaluating the material stability,and environment and biological safety.This work evaluated the amount and species of Zr released from a NWTC,a ZrO2/polymer composite(HZO@D201),during the treatment of electroplating wastewater.About 5 g of the HZO@D201 particles,consisting of porous spheres(0.8 mm in diameter)loaded with ZrO2 NPs,were packed into a glass column(130 mm in length and20 mm in diameter)and treated with wastewater at a flow rate of 25 mL/hr.The release of Zr occurred mainly in the initial stages of water treatment,decreased with the increase of treatment volume,and approached an equilibrium value of approximately 3.79μg/L at the treatment volume of about 800 bed volumes.The total amount of Zr released in the effluent was in the range of 2.62-140μg/L,which was mainly present in the form of ZrO2 NPs.The amounts of Zr released under acidic and alkaline conditions were markedly higher than that under neutral conditions,while the presence of humic acid significantly inhibited the release of Zr.Our study implied that the NWTCs could be a source of engineered NPs in environmental waters,and should be considered in evaluating the safety of ZrO2/polymer composites in water treatment.

Integration of production and use information into an exposure-based screening approach to rank chemicals of emerging Arctic concern for potential to be planetary boundary threats

Planetary boundaries delimit a‘safe operating space for humanity’that should not be overstepped to maintain stable Holocene-like conditions on Earth.Some chemical pollutants have the potential to pose a planetary boundary threat to the functioning of vital Earth system processes as so-called‘novel entities’.Recently,an exposure-based prioritization scheme was developed that uses model-estimated data on persistence and degree of mobility in air and water to identify and prioritise chemical substances that may be planetary boundary threats.As a case study,chemicals of emerging Arctic concern identified by the Arctic Monitoring and Assessment Programme(AMAP)were used to develop the scheme.The exposure-based prioritization scheme cannot address all scenarios for a chemical to pose an unknown planetary boundary threat,but it does allow for prioritization of chemicals according to environmental fate and exposure profiles.A key limitation of the scheme is that the quantity of chemical potentially released to the environment was not considered in the prioritization.Here,we use data on chemical production and use reported under the European chemicals regulation REACH,and an emission scoring system developed by the European Food Safety Authority(EFSA)to attempt to add information about estimated emissions to the exposure-based prioritization scheme.Using REACH data and the EFSA scoring system,we ranked the AMAP substances according to their potential for environmental release and combined that information with the previously reported exposure-based prioritization that considers persistence and long-range transport potential.Our method successfully assigned‘high priority’to known ozone-depleting substances(methyl chloride and dichloromethane)and identified chemicals of concern recently under consideration for nomination as persistent organic pollutants under the Stockholm Convention(octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane).The EFSA scoring system offers a useful starting point that provided useful additional information in the case study for chemicals of emerging Arctic concern,but lack of information to estimate potential releases of chemicals was a major limitation.