Light Water Reactor Containment Research Articles

CFD analysis of the erosion of a light gas stratification by means of a hot air jet in the MiniPanda facility

Following the Fukushima-Daiichi accident, many countries decided to strengthen the safety systems of their nuclear power plants in order to increase the capabilities of managing severe nuclear accidents. To achieve this goal detailed analysis of postulated design and beyond-design-basis accidents is essential. The main tools available for the analysis of these complex scenarios are Advanced Lumped Parameters (LP) and Computational Fluid Dynamics (CFD) codes. Currently, the most limiting factor in the application of these tools is their validation. This activity is performed in support of the development and validation of a CFD model, built in the numerical environment of OpenFOAM, for hydrogen behavior in the containment of Light Water Reactors. For validation purpose, numerical simulations of the erosion of a light gas stratification by means of a hot air jet have been performed, and results of the simulations were analysed and compared against experimental results obtained by Ritterath (2012) in the MiniPanda facility. Two different scenarios have been considered, each characterized by a different value of the mass flow rate of the jet used to erode the stratification.

Experimental investigation of gas transport induced by containment spray activation during a scaled severe accident scenario

Abstract We present the results of an experimental study on the activation of sprays representative of those used in a generic light water reactor containment for severe accident mitigation. Depending on the initial conditions, the spray nozzle type and the spray water flow rates, the spray may cause higher hydrogen concentration during depressurization due to steam condensation, or it may erode the hydrogen stratification by enhanced mixing. To investigate these phenomena, the tests were performed in the PANDA facility at Paul Scherrer Institut, Switzerland in the frame of the ERCOSAM-SAMARA project. The experiments followed a test sequence based on a postulated severe accident scenario scaled from a nuclear power plant design. The scaled scenario consisted of the formation of a stratified helium-rich (substitute for hydrogen) atmosphere in one of the PANDA vessels followed by the activation of a spray. Temporal evolution and spatial distribution of the gas temperature and the gas concentrations at selected positions were measured using thermocouples and mass spectrometers. Four tests were performed with two different spray nozzle types, two spray flow rates and two initial vessel wall temperatures of 105 °C and 135 °C, which created condensing and non-condensing environments, respectively. The different initial conditions lead to different density stratification. The effect of these different initial and boundary conditions on the transport and mixing of gases in the vessels due to the activation of the spray is revealed by these tests. The spray causes a fast breakup of the stratification and a complete mixing in the vessel in which it was injected. The concentration measurements in the adjacent connected vessel showed the presence of helium at the bottom of the vessel suggesting the possibility of hydrogen transport to the lower parts of the containment in a three gas mixture environment.

A First Orienting Investigation of the Interaction of Cable Fire Products with Passive Autocatalytic Recombiners

Passive autocatalytic recombiners (PARs) have been installed inside light water reactor containments in many countries to remove hydrogen and, thus, to mitigate the combustion risk during a severe accident (SA). Due to the challenging SA boundary conditions, PARs are exposed to several deactivation risks during operation, which may cause a reduction of the hydrogen removal capacity. Such a deactivation may occur through different mechanisms and could in principle affect the start-up behavior up to the full loss of catalytic activity. To assess the interaction of PARs with the products of cable fires, a set of PAR catalyst samples has been introduced to the atmosphere of cable fire tests performed at Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France. The subsequent surface analyses performed at Forschungszentrum Jülich (Germany) reveal a significant amount of carbon, chlorine (a constituent of polyvinyl chloride), zinc, and antimony (a flame retardant) on all catalyst samples compared to reference samples. The subsequent performance tests confirm that all catalyst sheets suffer a significant start-up delay of between 17 and 45 min compared to the reference samples. However, after burning off the soot deposition, the catalyst samples reach full conversion capacity and show immediate start-up behavior in a subsequent test. The present results clearly demonstrate the adverse effect of cable fire products on the efficiency of hydrogen conversion in a PAR. To further understand and quantify the impact of cable fire products and to assess their relevance for SA scenarios, further experimental as well as theoretical investigations are required. In particular, the combined influence of cable fire products and humidity, which has intentionally been omitted in the present study, should be investigated in the future due to the possible corrosive impact on the catalyst as well as the influence of humidity on the nature of the soot deposition.

Validation and Application of the REKO-DIREKT Code for the Simulation of Passive Autocatalytic Recombiner Operational Behavior

In order to reduce the accumulation of hydrogen and thus to mitigate the risk of combustion, many countries have installed passive autocatalytic recombiners (PARs) within light water reactor containments. The severe hydrogen combustion events of the recent Fukushima Daiichi accident are likely to incentivize an increased demand in upgrading nuclear power plants with PARs. Numerical simulation is an important tool for assessing PAR operation during a severe accident in terms of efficiency and proper installation. Advanced numerical PAR models are required for the challenging boundary conditions during a severe accident, for example, low oxygen amount, high steam amount, and presence of carbon monoxide. The REKO-DIREKT code has been developed in order to provide a PAR model capable of simulating complex PAR phenomena and at the same time being suitable for implementation in thermal-hydraulic codes.The development of REKO-DIREKT was supported by small-scale experiments performed at Forschungszentrum Juelich in the REKO facilities. These facilities allow the study of PAR-related single phenomena such as reaction kinetics under different conditions including variation of steam, oxygen, and carbon monoxide (REKO-3) and the chimney effect (REKO-4). Recently, the code has been validated against full-scale experiments performed in the Thermal-Hydraulics, Hydrogen, Aerosols, Iodine (THAI) facility at Eschborn, Germany, in the framework of the Organisation for Economic Co-operation and Development/Nuclear Energy Agency THAI project. By this, the code has proven its applicability for different PAR designs and for a broad range of boundary conditions (pressure of up to 3 bars, steam amount up to 60 vol %, low-oxygen conditions). REKO-DIREKT has been successfully implemented in the commercial computational fluid dynamics code ANSYS-CFX as well as in the LP code COCOSYS [Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Germany].

THAI test facility for experimental research on hydrogen and fission product behaviour in light water reactor containments

The test facility THAI (thermal-hydraulics, hydrogen, aerosol, and iodine) aims at addressing open questions concerning gas distribution, behaviour of hydrogen, iodine and aerosols in the containment of light water reactors during severe accidents. Main component of the facility is a 60m3 stainless steel vessel, 9.2m high and 3.2m in diameter, with exchangeable internals for multi-compartment investigations. The maximal design pressure of the vessel is 14bar which allows H2 combustion experiments at a severe accident relevant H2 concentration level. The facility is approved for the use of low-level radiotracer I-123 which enables the measurement of time resolved iodine behaviour.The THAI test facility allows investigating various accident scenarios, ranging from turbulent free convection to stagnant stratified containment atmospheres and can be combined with simultaneous use of hydrogen, iodine and aerosol issues. THAI experimental research also covers investigations related to mitigation systems employed in light water reactor containments by performing experiments on, e.g. pressure suppression pool hydrodynamics, performance behaviour of passive autocatalytic recombiners, and spray interaction with hydrogen–steam–air flames in phenomenon orientated and coupled-effects experiments.The THAI experimental data have been widely used for the validation and further development of Lumped Parameter and Computational Fluid Dynamics codes with 3D capabilities, e.g. International Standard Problems ISP-47 (thermal hydraulics, gas distribution) and ISP-49 (hydrogen combustion), EU-SARNET/SARNET2 code-benchmark exercises involving THAI data on iodine/surface interactions, iodine mass transfer, passive autocatalytic recombiner performance, iodine oxide behaviour and iodine transport in multi-compartment behaviour.The present paper provides an overview of the THAI experiments related to hydrogen and fission products issues performed in the frame of national and international projects. From the comprehensive THAI experimental database, a selection of typical results is presented to illustrate the multi-functionality of the THAI facility and the broad variety of the experimental investigations.

Impact of oxygen starvation on operation and potential gas-phase ignition of passive auto-catalytic recombiners

A large amount of hydrogen can be released into the containment of light water reactors during a severe accident. Passive Auto-catalytic Recombiners (PARs) aim to avoid flame acceleration and excessive pressure loads on the containment in case of hydrogen combustion. Their operation is based on the catalytic recombination of hydrogen into steam in the presence of oxygen. Thus, the recombiners reduce the hydrogen but also the oxygen content in the containment atmosphere. As a consequence, the oxygen/nitrogen ratio diverts more and more from the standard 21vol.% in air. This decreasing ratio may impact on the PAR efficiency. Additionally, the exothermic surface chemical mechanism leads to the overheating of the catalytic plates and activates the natural convection inside the recombiners. This heat source can also create local conditions for hydrogen combustion in the gas phase, as igniters do. Hence, the oxygen/nitrogen ratio may also determine the conditions for the gas-phase ignition inside PARs. This study deals with the numerical simulation of the impact of the oxygen starvation (i.e. low oxygen/nitrogen ratio) on the PAR efficiency and on the PAR gas-phase ignition limit. Calculations are performed with a dedicated CFD code named SPARK. We focus on the interaction of recombiners with any H2/O2/N2/H2O mixtures and thus establish a quite complete understanding of PAR operation. Calculations confirm the experimental oxygen surplus (i.e. twice more oxygen than stoichiometry) necessary to ensure an optimal PAR efficiency (XO2≈XH2) independently of the steam content. The PAR gas-phase ignition limit is then determined numerically in the classical H2/Air/H2O ternary diagram with a very good agreement with the available experimental database. It points out the importance of catalyst heat radiation, and more secondarily of species thermal diffusion (i.e. Soret effect). Finally, the PAR gas-phase ignition limit is determined for all oxygen/nitrogen ratios. The ignition domain appears to strongly contract when the oxygen content decreases, so that the steam threshold for inertization of the containment with respect to the recombiners ignition becomes very low.

Synthesis of I-131 labelled iodine species relevant during severe nuclear accidents in light water reactors

Summary Methods for the small scale synthesis of I-131 labelled iodine species relevant to severe nuclear accidents in light water reactors have been developed. The introduced methods allow the synthesis of impurity free, volatile, inorganic elemental iodine and volatile, organic iodides such as methyl- and ethyl iodide, as well as butyl iodide, chloroiodomethane, allyl iodide and benzyl iodide with ease. The radioactive iodine containing products are sufficiently stable to allow their storage for later use. Due to their volatility the liquid species can be easily converted into gaseous species and thus can be used in research in liquid and gaseous phase. The primary motivation for the development of these synthesis methods is to study the behaviour of volatile iodine species under the conditions of a severe nuclear accident in a light water reactor. Thus, the chemicals involved in the synthesis are chosen in a way to not generate impurities (chlorine and organic solvents) in the products which interfere with competing reactions relevant during a severe nuclear accident. Teknopox Aqua VA epoxy paint, which is used in Swedish light water reactor containments, and its reactions with the produced iodine species are described. The synthesised iodine species undergo chemisorption on paint films. Different to elemental iodine, the organic iodides are non-reactive with copper surfaces. The sorbed iodine species are partly re-released mainly in form of organic iodides and not as elemental iodine when the exposed paint films are heat treated. The partitioning and hydrolysis behaviour of gaseous methyl- and ethyl iodide between containment gas phase and water pools is found to be similar. The methods have been designed to minimise the use of harmful materials and the production of radioactive waste.

Corrosion and Corrosion Control in Light Water Reactors

Serious corrosion problems have plagued the light water reactor (LWR) industry for decades. The complex corrosion mechanisms involved and the development of practical engineering solutions for their mitigation will be discussed in this article. After a brief overview of the basic designs of the boiling water reactor (BWR) and pressurized water reactor (PWR), emphasis will be placed on the general corrosion of LWR containments, flow-accelerated corrosion of carbon steel components, intergranular stress corrosion cracking (IGSCC) in BWRs, primary water stress corrosion cracking (PWSCC) in PWRs, and irradiation-assisted stress corrosion cracking (IASCC) in both systems. Finally, the corrosion future of both plants will be discussed as plants extend their period of operation for an additional 20 to 40 years.

Experiments on basic thermalhydraulic phenomena relevant for LWR containments: Gas mixing and transport induced by buoyant jets in a multi-compartment geometry

In the frame of the OECD SETH project twenty-four experiments have been carried out on basic gas transport and mixing phenomena in the large-scale, multi-compartment PANDA facility. The experiments consist of several series based on the flow configuration driving the gas transport including plume and jet injection of saturated or superheated steam. A variety of test configurations with well-defined initial and boundary conditions have been investigated, including the parametric effects of the geometry of the injection, the composition and velocity of the injected mixture, the initial ambient composition, the vent location and the initial temperatures. The tests have been designed to be used for the validation of computer codes that are capable of analyzing the thermalhydraulic safety of the containment of light water reactors (LWRs). The results obtained form an extensive database especially valuable for the assessment of the capabilities of three-dimensional simulation tools. The present work reports on a specific test series of the aforementioned experimental program, the so-called Free-Plume Series featuring vertical injection of buoyant steam driving the gas transport. The experimental data is presented showing its quality and the trends in the experiments are analyzed. The phenomena whose prediction might be challenging for codes are emphasized. After the expiration of the confidentiality period, the experimental data is now available for the broad scientific community to be used for code validation purposes.

Simulation of containment jet flows including condensation

The validation of a CFD code for light-water reactor containment applications requires among others the presence of steam in the different flow types like jets or buoyant plumes and leads to the need to simulate condensation phenomena. In this context the paper addresses the simulation of two “HYJET” experiments from the former Battelle Model Containment by the CFD code CFX. These experiments involve jet releases into the multi-compartment geometry of the test facility accompanied by condensation of steam at walls and in the bulk gas. In both experiments mixtures of helium and steam are injected. Helium is used to simulate hydrogen. One experiment represents a fast jet whereas in the second test a slow release of helium and steam is investigated. CFX was earlier extended by bulk and wall condensation models and is able to model all relevant phenomena observed during the experiments. The paper focuses on the simulation of the two experiments employing an identical model set-up. This provides together with other validation exercises the information on how well a wider range of flowing conditions in a full containment simulation can be covered with a single set of models (e.g. turbulence and condensation model). Some aspects related to numerical and modelling uncertainties of CFD calculations are included in the paper by investigating different turbulence models together with the modelling errors of the differencing schemes applied.

PARIS project: Radiolytic oxidation of molecular iodine in containment during a nuclear reactor severe accident: Part 1. Formation and destruction of air radiolysis products—Experimental results and modelling

In case of a hypothetical severe accident in a nuclear LWR (light water reactor), the high radiation fields reached in the reactor containment building due to the release of fission products from the reactor core could induce air radiolysis. The air radiolysis products could, in turn, oxidise gaseous molecular iodine into aerosol–borne iodine–oxygen–nitrogen compounds. Thereby, this reaction involves a change of iodine speciation and a decrease of iodine volatility in the reactor containment atmosphere. Kinetic data were produced within the PARIS project on the air radiolysis products formation and destruction, and on their reaction with molecular iodine, with the objective of developing and validating existing kinetic models. The current paper includes the non-iodine tests of the PARIS project whose objective was to determine the rates of formation and destruction of air radiolysis products in the presence of both structural containment surfaces (decontamination coating (“paint”) and stainless steel), aerosol particles such as silver rich particles (issued from the control rods) in boundary conditions representative for LWR or PHEBUS facility containments. It is found that the air radiolysis products concentration increases with dose and tend to approach saturation levels at doses higher than about 1 kGy. This behaviour is more evident in oxygen/steam atmospheres, producing ozone, than in air/30% (v/v) steam atmospheres, the latter favouring the model-predicted on-going production of nitrogen dioxide even at very high doses. No significant effect of temperature, dose rate and hydrogen addition (4%, v/v) was observed. Furthermore, the inserted surfaces do not exhibit significant effects on the air radiolysis concentrations. However, these “non-noticeable influence” could be due to a masking of small effects by the appreciable scattering of the experimental air radiolysis product concentrations. The PARIS results are then analysed using two different kinetic models, an empirical and a mechanistic one. The kinetic constants within an empirical model including formation and destruction of air radiolysis products, derived from PARIS results, are in reasonable agreement with those determined previously for lower steam fractions. From the mechanistic model IODAIR-IRSN, it is concluded that ozone is the predominant air radiolysis product at low doses in air/steam atmospheres. At doses higher than 1 kGy, nitrogen dioxide becomes increasingly important, both due to an increase in its concentration and due to a simultaneous decrease in ozone concentration.

COCOSYS: Status of development and validation of the German containment code system

For the simulation of severe accident propagation in containments of nuclear power plants it is necessary to assess the efficiency of severe accident measures under conditions as realistic as possible. Therefore the German containment code system COCOSYS is under development and validation at GRS. The main objective is to provide a code system on the basis of mostly mechanistic models for the comprehensive simulation of all relevant processes and plant states during severe accidents in the containment of light water reactors covering the design basis accidents, too. COCOSYS is being used for the identification of possible deficits in plant safety, qualification of the safety reserves of the entire system, assessment of damage-limiting or mitigating accident management measures, support of integral codes in PSA level 2 studies and safety evaluation of new plants. COCOSYS is composed of three main modules, which are separate executable files. These modules are covering thermal hydraulics including hydrogen combustion, fission products mainly aerosols and iodine behaviour, and corium behaviour with molten corium concrete interaction. The communication between these modules is realized via PVM (parallel virtual machine). COCOSYS is subject to an ongoing internal and external validation process. At present this validation process is mainly based on tests being performed in the German ThAI facility. Experiments to be performed in ThAI dealing with hydrogen combustion, recombiner behaviour and aerosol and iodine issues are currently subject of the just started OECD-THAI project. Examples given for the successful validation are the participation in the OECD/NEA ISP-47 and the benchmark for the CCI-2 test in the frame of the OECD-MCCI project. For example COCOSYS has been used in licensing procedure performed for the installation of catalytic recombiners in German nuclear power plants. At present COCOSYS is in use for the licensing process of the new Finnish EPR plant on the industrial side. Improvements and model extensions like pyrolysis processes, direct containment heating and the combined use with CFD models are just ongoing.

Integral large scale experiments on hydrogen combustion for severe accident code validation-HYCOM

A joint research project was carried out in the EU Fifth Framework Programme, concerning hydrogen risk in a nuclear power plant. The goals were: Firstly, to create a new data base of results on hydrogen combustion experiments in the slow to turbulent combustion regimes. Secondly, to validate the partners CFD and lumped parameter codes on the experimental data, and to evaluate suitable parameter sets for application calculations. Thirdly, to conduct a benchmark exercise by applying the codes to the full scale analysis of a postulated hydrogen combustion scenario in a light water reactor containment after a core melt accident. The paper describes the work programme of the project and the partners activities. Significant progress has been made in the experimental area, where test series in medium and large scale facilities have been carried out with the focus on specific effects of scale, multi-compartent geometry, heat losses and venting. The data were used for the validation of the partners CFD and lumped parameter codes, which included blind predictive calculations and pre- and post-test intercomparison exercises. Finally, a benchmark exercise was conducted by applying the codes to the full scale analysis of a hydrogen combustion scenario. The comparison and assessment of the results of the validation phase and of the challenging containment calculation exercise allows a deep insight in the quality, capabilities and limits of the CFD and the lumped parameter tools which are currently in use at various research laboratories.

Hydrogen removal from LWR containments by catalytic-coated thermal insulation elements (THINCAT)

In the THINCAT project, an alternative concept for hydrogen mitigation in a light water reactor (LWR) containment is being developed. Based on catalytic coated thermal insulation elements of the main coolant loop components, it could be considered either as an alternative to backfitting passive autocatalytic recombiner devices, or as a reinforcement of their preventive effect. The present paper summarises the results achieved at about project mid-term. Potential advantages of catalytic thermal insulation studied in the project are: • reduced risk of unintended ignition, • no work space obstruction in the containment, • no need for seismic qualification of additional equipment, • improved start-up behaviour of recombination reaction. Efforts to develop a suitable catalytic layer resulted in the identification of a coating procedure that ensures high chemical reactivity and mechanical stability. Test samples for use in forthcoming experiments with this coating were produced. Models to predict the catalytic rates were developed, validated and applied in a safety analysis study. Results show that an overall hydrogen concentration reduction can be achieved which is comparable to the reduction obtained using conventional recombiners. Existing experimental information supports the argument of a reduced ignition risk.

Containment behaviour in the event of core melt with gaseous and aerosol releases (CONGA)

The CONGA project concentrated on theoretical and experimental studies investigating the behaviour of advanced light water reactor containments containing passive containment heat removal systems and catalytic recombiners expected to be effectively operational during a hypothetical severe accident involving large quantities of aerosol particles and noncondensable gases. The central point of interest was the investigation of the effect of aerosol deposition on the condensation heat transfer of specially designed finned-type heat exchangers (HX) as well as the recombination efficiency of catalytic recombiners. A conceptual double-wall Italian PWR design and a SWR1000 design from Siemens were considered specifically as the reference Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) designs. An assessment of selected accident scenarios was performed in order to define the range of boundary conditions necessary to perform the experimental studies of the other work packages. Experimental investigations indicated that aerosol deposition accounted for up to 37% loss in the heat removal capacity of the two-tube-layer BWR HX units. However, no significant heat transfer degradation could be observed for the PWR HX units. These results can be attributed to the important differences in the designs and operating conditions of the two units. The tests to study the effect of hydrogen (simulated by helium) on the heat transfer rate for heat exchanger units designed for BWR and PWR applications indicated a degradation less than 30% under various conditions. This was found to be acceptable within the over capacity designed for the heat exchangers or containment characteristics. The tests performed to study the long-term aerosol behaviour in the pressure suppression chamber of the current operating BWRs indicated that the water pool scrubs the aerosol particles effectively and reduces the ultimate aerosol load expected on the off-gas system. The efficiency of the catalytic recombiner system designed by Siemens for the off-gas system was found to be insensitive to the aerosol deposited in the recombiner. A computation code, HTCFOUL, was developed to predict the heat transfer rate of a finned-type heat exchanger subjected to a steam–noncondensable gas mixture containing airborne aerosol particles. The model predicts the non-aerosol part of two tests within a variation of 26% and the aerosol part within 32%.

00/02548 Global rupture of a nuclear reactor lower head with elevated temperature due to severe accidents

The CONGA project concentrated on theoretical and experimental studies investigating the behaviour of advanced light water reactor containments containing passive containment heat removal systems and catalytic recombiners expected to be effectively operational during a hypothetical severe accident involving large quantities of aerosol particles and noncondensable gases. The central point of interest was the investigation of the effect of aerosol deposition on the condensation heat transfer of specially designed finned-type heat exchangers (HX) as well as the recombination efficiency of catalytic recombiners. A conceptual double-wall Italian PWR design and a SWR1000 design from Siemens were considered specifically as the reference Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) designs. An assessment of selected accident scenarios was performed in order to define the range of boundary conditions necessary to perform the experimental studies of the other work packages. Experimental investigations indicated that aerosol deposition accounted for up to 37% loss in the heat removal capacity of the two-tube-layer BWR HX units. However, no significant heat transfer degradation could be observed for the PWR HX units. These results can be attributed to the important differences in the designs and operating conditions of the two units. The tests to study the effect of hydrogen (simulated by helium) on the heat transfer rate for heat exchanger units designed for BWR and PWR applications indicated a degradation less than 30% under various conditions. This was found to be acceptable within the over capacity designed for the heat exchangers or containment characteristics. The tests performed to study the long-term aerosol behaviour in the pressure suppression chamber of the current operating BWRs indicated that the water pool scrubs the aerosol particles effectively and reduces the ultimate aerosol load expected on the off-gas system. The efficiency of the catalytic recombiner system designed by Siemens for the off-gas system was found to be insensitive to the aerosol deposited in the recombiner. A computation code, HTCFOUL, was developed to predict the heat transfer rate of a finned-type heat exchanger subjected to a steam–noncondensable gas mixture containing airborne aerosol particles. The model predicts the non-aerosol part of two tests within a variation of 26% and the aerosol part within 32%.

C101 触媒式可燃性ガス再結合装置性能評価モデルの開発

The passive autocatalytic recombiner for flammable gas control in the light water reactor containment during postulated accident, has the unique feature which does not require any external driving force. However, the system performance has close interaction with thermal-hydraulic condition inside containment, and empirical correlations have been applied to date. Authors have developed mechanistic model which is applicable to extended atmospheric condition such as inerted containment. The new model has been incorporated into 3-dimensional CFD code, and verified against existing performance test data ranges from small to large scale. The analytical result shows good agreement with test data, and supports the model capability of recombiner performance prediction.

A model of silver–iodine reactions in a light water reactor containment sump under severe accident conditions

Metallic silver and iodine form insoluble AgI in the containment sump which has a major impact on iodine volatility and hence on the source term to the environment. Resistance-in-series models are developed and validated against separate-effects tests. The reaction between I 2 and Ag is limited by mass transfer in the liquid. The rate does not follow a parabolic law for the duration of the experiments. The extent of oxidation of the silver sample seems to play a decisive role for reactions with I − which proceed via a two-step process. The initial, rapid step is controlled by the reaction with the surface silver oxide with a contribution of mass transfer in the liquid. The subsequent, slow step is limited by reaction between I − and Ag + at the solid–liquid interface. The reaction is probably negligible for pH > 7 and in the absence of oxidising conditions.

Molecular dynamics simulation of displacement cascades in matrix of french light water reactor waste containment glass

A simplified nuclear glass containing the major elements of the French light water reactor containment glass was prepared from a molecular dynamics standpoint using Born-Mayer-Hugins potentials. Accelerating an atom in the simulation cell with an energy below 1.5 keV was the first step in addressing the problem of ballistic damage induced along the path of a recoil nucleus in the glass. Among the observations made for these simulations, it was noted that displaced alkali metal atoms were found around the periphery of the damage zone, that collective displacements occurred in the glass network and were in fact more energy-effective than individual displacements. Finally, a phenomenon of general reduction of network connectivity in the damage zones was revealed.

Feasibility Study for a Containment to Resist Core-Melt Accidents

A feasibility study has been performed for a light water reactor containment able to resist even severe accidents by passive means. Upper-bound design loads have been considered for all physically possible scenarios after a core-melt accident as determined by Kernforschungszentrum Karlsruhe. The essential layout of this containment is presented. Based on the main system features of a German 1,300-MW Convoy reactor type, internal static pressure, hydrogen detonation, failure of the pressure vessel under high pressure, and steam explosion, respectively, have been regarded as well as such external loads as an airplane crash, earthquake, gas explosion, and so forth. The containment can remove the decay heat by purely passive means, and it is believed that the design can be realized at reasonable costs.