Experimental characterization of VVER-440 reactor containment type spray nozzle

This paper presents the experimental characterization of a spray produced by a VVER-440 nuclear reactor type nozzle. Several droplet size and velocity profiles have been obtained at different pressure supplies and different heights below the outlet of the spray nozzle. Repeatability and stability have been checked. A log-normal size distribution can be fitted on the experimental results. Correlations between droplet velocities and sizes at different locations are also given, showing that for small droplet sizes (below 300 μm) no clear size-velocity correlation exists below 0.7 m from nozzle outlet, but for larger droplets, a classical evolution of this correlation is observed. It is concluded that the experimental data obtained at 300 mm from the nozzle outlet can be used as spray boundary conditions for numerical calculations with CFD codes. The other experimental data (at 500 and 700 mm from the nozzle outlet) can serve for detailed code validation, if the correlations between sizes and velocities are considered in the validation procedure: indeed, the averaging of droplet sizes and velocities can mask some typical spray results on droplet sizes and velocities evolutions. If a good code validation of the size-velocity correlations is obtained at 500 and 700 mm from the nozzle outlet, the concerned code may then be used with good confidence to extrapolate the results at other distances (for example, 3 m, 5 m) which cannot be obtained easily experimentally. © 2016 by Begell House, Inc

EXPERIMENTAL CHARACTERIZATION OF VVER-440 REACTOR CONTAINMENT TYPE SPRAY NOZZLE

International audienceThis paper presents the experimental characterization of a spray produced by a VVER-440 nuclear reactor type nozzle. Several droplet size and velocity profiles have been obtained at different pressure supplies and different heights below the outlet of the spray nozzle. Repeatability and stability have been checked. A log-normal size distribution can be fitted on the experimental results. Correlations between droplet velocities and sizes at different locations are also given, showing that for small droplet sizes (below 300 μm) no clear size-velocity correlation exists below 0.7 m from nozzle outlet, but for larger droplets, a classical evolution of this correlation is observed. It is concluded that the experimental data obtained at 300 mm from the nozzle outlet can be used as spray boundary conditions for numerical calculations with CFD codes. The other experimental data (at 500 and 700 mm from the nozzle outlet) can serve for detailed code validation, if the correlations between sizes and velocities are considered in the validation procedure: indeed, the averaging of droplet sizes and velocities can mask some typical spray results on droplet sizes and velocities evolutions. If a good code validation of the size-velocity correlations is obtained at 500 and 700 mm from the nozzle outlet, the concerned code may then be used with good confidence to extrapolate the results at other distances (for example, 3 m, 5 m) which cannot be obtained easily experimentally. © 2016 by Begell House, Inc

Achievements of spray activities in nuclear reactor containments during the last decade

International audienceDuring the course of a severe accident in a nuclear power plants, spray systems are used in the containment in order to prevent overpressure and to wash-out fission products. Spray will also have an impact on the gas mixing in case of the presence of hydrogen. This paper presents the current achievements of spray activities during the last decade. Spray systems in nuclear reactors are described and an overview of the knowledge gained on these sprays during the last decade is given. During this period, more and more studies devoted to CFD simulations (Computational Fluid Dynamics) of real containment severe accident conditions have been published. In order to give confidence to such calculations, code validation is mandatory. As a result, experiments have been performed in order to validate the spray models. A review of experimental programs, in CARAIDAS, CALIST, TOSQAN (IRSN) and MISTRA (CEA) facilities is presented here. Spray models developed for the codes involved in the above mentioned simulations of these experimental programs are also discussed, as well as international benchmarking activities performed during the last decade. CFD calculations at real scale with well validated phenomena on separate-effect tests are recommended in order to bring some insights for different configurations typical for safety concerns. © 2014 Published by Elsevier Ltd

SARNET-2: Droplet Heat And Mass Transfer Elementary Benchmark - Comparison Report

In the past, validation of spray modelling has been performed on large-scale facilities (CVTR, NUPEC, CSE) using several spray nozzles. More specific studies have been proposed in the frame of SARNET-1 (on TOSQAN and MISTRA facilities), where it has been concluded that the level of validation obtained for spray modelling was encouraging for their use for risk analysis. However, further activities were well encouraged on this topic, such as benchmarks based on separate-effect tests. Three different separate-effect tests, so-called elementary tests, have thus been proposed by IRSN during the first SARNET-2 WP7-2 meeting in April 2009: heat and mass transfer (HMT) tests, momentum transfer on large spray, and aerosol collection on single droplet. This document presents the results for the first elementary benchmark on HMT tests. Code-experiment as well as code-to-code comparisons are presented here

Sprays in Containment: Final results of the SARNET Spray Benchmark

The influence of containment sprays on atmosphere behaviour, a sub-task of the Work Package WP12-2 CAM (Containment Atmosphere Mixing), has been investigated through benchmark exercises based on TOSQAN (IRSN) and MISTRA (CEA) experiments. These tests are being simulated with lumped-parameter (LP) and Computational Fluid Dynamics (CFD) codes. Both atmosphere depressurization and mixing are being studied in two phases: a ‘thermalhydraulic part’, which deals with depressurization by sprays (TOSQAN 101 and MISTRA MASPn), and a ‘dynamic part’, dealing with light gas stratification break-up by spray (TOSQAN 113 and MISTRA MARC2b). In the thermalhydraulic part of the benchmark, participants have found the appropriate modelling to obtain good global results in terms of experimental pressure and mean gas temperature, for both TOSQAN and MISTRA tests. It can thus be considered that code users have a good knowledge of their spray modelling parameters. On a local level, for the TOSQAN test, single droplet behaviour is found to be well estimated by some calculations, but the global modelling of multiple droplets, i.e. of the spray, specifically for the spray dilution, is questionable in some CFD calculations. It can lead to some discrepancies localized in the spray region and can thus have a high impact on the global results, since most of the heat and mass transfers occur inside this region. In the MISTRA tests, wall condensation mass flow rates and local temperatures were used for code-experiment comparison and show that improvement of the local modelling, including initial conditions determination, is needed. In this dynamic part, a general result, in both tests, is that calculations do not recover the same kinetics of the mixing. Furthermore, concerning global mixing, LP contributions seem not suitable here. For the TOSQAN benchmark, the one-phase CFD calculations recover partially the phenomena involved during the mixing, whereas the two-phase flow CFD contributions generally recover the phenomena. Moreover, one important result is also that none of the contributions finds the exact amount of helium remaining in the dome above the spray nozzle in the TOSQAN 113. Discrepancies are rather high (above 5%vol of helium). Results are thus encouraging, but the level of validation should be improved. The same kind of conclusions can be drawn for the MISTRA MARC2B tests. As a conclusion of this SARNET spray benchmark, the level of validation obtained here is encouraging for the use of spray modelling for risk analysis. However, some more detailed investigations are needed to improve model parameters and decrease the uncertainty for containment applications as well as to increase the predictability of the phenomena within the containment analyses. Further activities are well encouraged on this topic, such as numerical benchmarks on analytical separate-effect experiments

Generic Containment: Detailed comparison of containment simulations performed on plant scale

One outcome of the OECD/NEA ISP-47 activity was the recommendation to elaborate a ‘Generic Containment’ in order to allow comparing and rating the results obtained by different lumped-parameter models on plant scale. Within the European SARNET2 project (http://www.sar-net.eu), such a Generic Containment nodalisation, based on a German PWR (1300 MWel), was defined. This agreement on the nodalisation allows investigating the remaining differences among the results, especially the ‘user-effect’, related to the modelling choices, as well as fundamental differences in the underlying model basis in detail. The methodology applied in order to compare the different code predictions consisted of a series of three benchmark steps with increasing complexity as well as a systematic comparison of characteristic variables and observations