NPP Containment Research Articles

Simulation of the removal of radioactive aerosols from the atmosphere of NPP containment by spray system droplets using the MAVR-TA code

Simulation of the removal of radioactive aerosols from the atmosphere of NPP containment by spray system droplets using the MAVR-TA code

3D Modeling of NPP Containment Medium Mixing During the Development of Severe Accidents

3D Modeling of NPP Containment Medium Mixing During the Development of Severe Accidents

Simulation of Aerosol Removal from the Atmosphere of an NPP Containment using a Sprinkler System

Simulation of Aerosol Removal from the Atmosphere of an NPP Containment using a Sprinkler System

Simulations of PANDA and SPARC experiments on containment atmosphere mixing caused by vertical gas injection

Several experiments of interaction of air or steam jet with a horizontal helium rich layer in a closed vessel representing a NPP containment, which were performed in PANDA and SPARC experimental facilities, are simulated on the local instantaneous scale using the Unsteady Reynolds Averaged Navier Stokes approach. Axisymmetric two-dimensional and three-dimensional numerical models of cylindrical vessels are developed, and the effects of numerical domain reduction are studied. The mixing process is simulated as a single-phase flow with common momentum and energy equations. Consequently, an additional term accounting for enthalpy diffusion due to compositional changes is implemented into the energy equation. Included gas species mass fractions are considered as passive scalars and are calculated using the transport equation. However, the term describing the molecular diffusion cannot be neglected and had to be added to the diffusion equation implemented in the default OpenFOAM computational fluid dynamics code that was used. The k-ε turbulence model with additional turbulence generation and dissipation due to buoyancy is used for turbulence modelling. The comparison of simulation and experimental results shows that the improved physical model is able to successfully describe the phenomena in several experiments performed in different facilities with different initial and boundary conditions.

Effect of the Operation of a Polar Crane on the Stress-Strain State of NPP Containment

Effect of the Operation of a Polar Crane on the Stress-Strain State of NPP Containment

Application of Conditional Spectra to Seismic Fragility Assessment for an NPP Containment Building based on Nonlinear Dynamic Analysis

Application of Conditional Spectra to Seismic Fragility Assessment for an NPP Containment Building based on Nonlinear Dynamic Analysis

РАСЧЕТ ПАРАМЕТРОВ ГАЗОВОЙ СРЕДЫ В КОНТЕЙНМЕНТЕ АЭС С УЧЕТОМ ПОЛНОГО АДИАБАТИЧЕСКОГО СГОРАНИЯ ВОДОРОДА КОДОМ КУПОЛ-М

An important factor for the analysis of hydrogen safety is to take into account the effect of possible hydrogen combustion on the parameters of NPP containment atmosphere. In order to evaluate this effect a model of adiabatic isochoric complete combustion (AICC) of hydrogen was developed and implemented in the KUPOL-M containment code. With the model of adiabatic isochoric complete combustion of hydrogen included in the KUPOL-M code, this code will become applicable for the VVER NPP safety analysis performed with the aim to estimate possible thermal mechanical loads on the containment in case of hydrogen burning. This model is simple, conservative and based on the laws of conservation of mass and energy. The following assumptions are made in the model of adiabatic isochoric complete combustion of hydrogen: the volume in which burning takes place is constant; there is no heat transfer; the limiting component (in most cases it is hydrogen) burns down completely; intermediate stages of chemical transformations are not considered. The test results of this model on experimental data are presented in the article. There is a good agreement between the data of calculations and experiments in a wide range of hydrogen concentrations in gas mixtures. Based on the test results it can be concluded that implementation of AICC model in the KUPOL-M code allows conservatively evaluating the parameters in the containment atmosphere without significantly increasing the calculation time.

Thermal hydraulic modelling of grating effect for application to 3-dimensional analysis of hydrogen behavior in NPP containment

For three-dimensional analysis of the thermal hydraulic phenomena associated with hydrogen behavior in a containment building, geometry modelling that reflects the three-dimensional features of the containment building is required. A lot of equipment and concrete structures are installed in the containment building, and gratings are also installed on a large floor area. Gratings in the containment can affect gas flow and heat transfer, so modelling of the grating is required for three-dimensional analysis of hydrogen behavior in the containment. As a method of modelling gratings, many computational mesh nodes are required to directly simulate gratings made of steel plates several millimeters thick, so a large amount of computation is required for accident analysis. Therefore, simple modelling of gratings is required to properly control the size of the three-dimensional mesh. In this study, a method of simulating porous media for gratings was adopted, and the model was extended to allow for consideration of heat transfer of the gratings. To verify the porosity-based grating model, analyses of the H2P1_10_2 experiment recently performed through the international joint project OECD/NEA HYMERES-2 were conducted. Through a comparison with the H2P1_10_2 experimental data, it was confirmed that the porous media-based model showed calculation results very similar to those of the direct simulation of the grating, and that the porous media-based model reduced the mesh size by 1/5 and the calculation time by 1/5 compared to those values in the direct simulation of the grating.

Експериментальні дослідження повітропроникності бетону стиснутої зони захисної оболонки енергоблоків № 1 і 2 ВП «Южно-­Українська АЕС»

The determination of the air permeability of concrete in the compressed zone of NPP’s containment under conditions of excessive air pressure in the subshell space of the reactor compartment under a maximum design basis accident is necessary to confirm the localizing functions of the containment when extending the lifetime of power units. Approaches to determining the localizing ability (air permeability) of concrete in the compressed zone of the containment of NPPs with WWER-1000 type reactors under the impact of excessive air pressure under conditions of maximum design basis accident are discussed in the article. The designed testing installation for experimental studies of the air permeability of concrete by the method of stationary radial filtration is described and the results of experimental researches of the air permeability on the installation are presented for samples simulating the composition of concrete used under construction of the containment for Power Units No. 1, 2 (series B-302 and B-338, respectively) SD “South-Ukrainian NPP”. A comparative analysis of the results of abovementioned experimental researches with the results of experimental and theoretical work on the study of air permeability of the similar samples-imitators of concrete by the method of stationary linear filtration, as well as the results of measurements for samples of concrete sampled directly from the compressed zone of containment for Power Unit No. 2 of SD “South-Ukrainian NPP” was fulfilled. The results are explained by processes of compaction of the concrete structure under a complex stress state that occurs under specific hardening conditions and during longtime compression by pre-stressed reinforcing ropes, which takes place under conditions of real containment operation. It was concluded that the simulators made according to the currently accepted technology cannot provide a correct determination of the localizing ability of the NPP’s containment, since the conditions and time of containment concrete hardening, as well as the longtime constant compressive action of reinforcing ropes, cannot be correctly modeled in full under the formation of samples-imitators. The issue of the containment concrete samplesimitators creating in laboratory conditions requires additional study, improvement of technology and the development of new approaches with maximum physical modeling of the conditions characteristic of the operation of the NPP containment.

Numerical modeling of deformation and destruction of NPP containment at impact of falling aircraft engines

Numerical modeling of deformation and destruction of NPP containment at impact of falling aircraft engines

О возможности применения инфракрасных кристаллических световодов для передачи сигнала температуры от подшипников внутри гермообъема АЭС

The flexible fiber made of crystal systems AgBr – TlI and AgBr – TlBr0,46I0,54 has radioresistance properties, can be produced with permissible length, characterized by low optical losses with a small number and large radius of curves. This allows to use it for transmission of temperature signal from the surface of NPP equipment, including moving parts installed in the containment of NPP. Implementation of this method allows to avoid the operation of activated sensing elements in conditions of gamma and neutron fields of NPP containment. The optical fiber, suggested in the paper, is produced by the method of extrusion from single-crystal of silver and thallium halides and transparent in the mid-infrared band from 2,0 to 25,0 µm which is equivalent to the temperature range of -200…+1100°C.

Modeling the emergency processes proceeding in the containment of NPP with water-water energy reactor

The article presents the results of computational modeling of the development of accidents in the containment of NPP with water-water energy reactor (WWER) using the COCOSYS software. The containment of the Balakovo NPP with WWER-1000/V-320 was selected as the object of study. The results of the calculation of environmental parameters in the containment during a beyond design basis accident with a “large” leak from the primary circuit at the following initial events: break of the main circulation pipeline DN850 with a full cross section at the reactor inlet, with simultaneous failure of all AC sources including diesel generators for a long period, without operating personnel intervention. A comparison of the results of calculations with the results obtained using the ANGAR software certified by Rostekhnadzor is performed. The calculation results are in good agreement: emergency scenarios are similar; the maximum deviation from absolute pressure values is less than 10 %. Thus, it was concluded that the analysis of processes occurring in the NPP containment during an accident can be performed using the COCOSYS code. This software can be used to independent safety assessment of NPP required by the IAEA standards.

Study on the NPP Containment Structure Subjected to Different Loading Conditions

Study on the NPP Containment Structure Subjected to Different Loading Conditions

Review of the potential sources of organic iodides in a NPP containment during a severe accident and remaining uncertainties

In case of a severe accident in a nuclear power plant, organic iodides (RI) are one of the volatile iodine species that can be released in the environment thus possibly contributing to the radiotoxicity by inhalation. The formation and decomposition reactions of organic iodides have been studied through various experimental programs whose objectives were to understand their behavior and develop phenomenological models able to predict their volatility. Four potential sources of RI formation have been reviewed: (1) the reactor coolant system (RCS), (2) the containment sump, (3) the paints in the containment and (4) the containment gaseous phase. A review of the knowledge, chemical mechanisms leading to RI formation and decomposition and the remaining uncertainties is performed in order to recommend remaining needed experimental investigations. It has been identified that significant uncertainties remain on RI formation in the gaseous phase through reaction of iodine with volatile organic compounds (VOC, like methane) and that additional data should be obtained to improve its modeling as it can be a significant RI source during days after the beginning of the accident.

Evaluation of the thermal strain of an NPP containment structure during leakage rate tests

A strategy for isolating the thermal strain due to solar radiation from the total measured strain during the Integrated Leak Rate Test of a nuclear containment structure is presented in this paper. In the proposed method, a series of numerical models are developed to estimate the temperature change on the prestressed concrete containment structure and to predict the strain due to temperature and applied pressure. The effects of the solar radiation, heat exchange with internal and external air and heat conduction are considered in the proposed method. The developed method is validated by reproducing the total strain profiles measured from the leak rate tests conducted at the Point Lepreau CANDU®11CANDU (CANada Deuterium Uranium Reactor) is a registered trademark of the Atomic Energy of Canada Limited (AECL), used under exclusive license by Candu Energy Inc. 6 containment structure.

Influence of Rheological Characteristics of Concrete on the Stress-Strain State of NPP Containment

A comparative analysis is presented of the influence of the rheological characteristics of concrete on the stress strain state of NPP containment shells. It is based on creep and shrinkage tests performed on concrete, field observations, and calculations of the strains and stresses engendered in the reinforcement and concrete by the shrinkage and creep of concrete. The results showed discrepancies in the obtained data. For this reason, it is recommended that field data and detailed working models, in which the cross-section parameter and the pitch of the reinforcement rods correspond to the nominal values, be used in evaluating the stress-strain state of NPP containment under operational and accidental loads.

Unusual Attenuation Recovery Process After Fiber Optic Cable Irradiation

At present, the number of optical cables in nuclear power plants has been increasing. Fiber optic cables are commonly used at nuclear power plants in instrumentation and control systems but they are usually used in environments without radiation. Nevertheless, currently, the number of applications in NPP containment with radiation is increasing. One of the most prevalent effects of radiation exposure is an increase of signal attenuation (signal loss). This is the result of fiber darkening due to radiation exposure and it is the main limitation factor in application of fiber optics in radiation environment. However, after the irradiation, the fiber optics go through a “recovery process” during which the optical properties improve again; i.e. attenuation decreases. However, we have found cable, where the expected healing process after few days changed its trend and the attenuation increased again to a value well above the attenuation just after the irradiation. This paper describes experiments that were carried out to explain this unusual recovery behaviour.

Evaluation of CANDU NPP containment structure subjected to aging and internal pressure increase

The objective of this study is to investigate the long-term performance of a typical CANDU®1®Registered trademark of Atomic Energy of Canada Ltd. (AECL) used under exclusive license by Candu Energy Inc., a Member of the SNC-Lavalin Group.1 containment structure. A three-dimensional nonlinear finite element model was built to realistically evaluate the performance of the structure under service load as well as a hypothetical beyond-design level internal pressure. Consideration is given to the time-dependent effects, such as shrinkage, creep, and relaxation of prestressing tendons, over a 60-year timeframe. In addition, the sensitivity of the response of the containment structure against support condition, internal temperature profile and temporary construction openings was also investigated. The accuracy of the numerical model was validated against structural measurements made during a routine leak rate test. The analysis results show that the containment structure would develop a ductile mechanism if the internal pressure significantly exceeded the design pressure. The pressure-deformation relationship of the structure is sensitive to the considered time-dependent parameters.

Analysis of the Dynamic Behavior and Stress-Strain State of NPP Containment under Nonstationary Impacts

The paper presents the analysis of dynamic behavior of the reinforced concrete containment of NPP unit under the combined effect of internal pressure shock caused by the accident in the reactor hall and seismic impact of design-basis earthquake using the finite element method (FEM) and DIPROS software. Using the modal analysis and numerical solution of the FEM equations of containment concrete, the stress-strain state of the building structure in the post-accident period was defined. It is shown that the maximum intensity of the stresses in the steel liner of the containment does not exceed the yield strength of the steel liner material. Accordingly, the liner integrity is preserved, the containment remains operable and ensures compliance of radiation safety requirements.

등가선형 및 비선형 납-고무받침 모델을 이용한 면진된 원전구조물의 지진응답의 비교

등가선형 및 비선형 납-고무받침 모델을 이용한 면진된 원전구조물의 지진응답의 비교