Experimental investigation in the TOSQAN facility of heat and mass transfers in a spray for containment application

TOSQAN is an experimental program undertaken by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in order to perform thermal hydraulic containment studies. The TOSQAN facility is a large enclosure devoted to simulate typical accidental thermal hydraulic flow conditions in nuclear-pressurized water reactor (PWR) containment. The TOSQAN facility which is highly instrumented with non-intrusive optical diagnostics is particularly adapted to nuclear safety CFD code validation. The present work is devoted to studying the interaction of a water spray injection used as a mitigation means in order to reduce the gas pressure and temperature in the containment, to produce gases mixing and washout of fission products. In order to have a better understanding of heat and mass transfers between spray droplets and the gas mixture, and to analyze mixing effects due to spray activation, we perform detailed characterization of the two-phase flow.     

The effect of thermal annealing on the adherence of Al2O3-films deposited by low-pressure,metal-organic,chemical-vapor deposition on AISI 304

Thin alumina films, deposited at 280°C by low-pressure, metal-organic, chemical-vapor deposition on stainless steel, type AISI 304, were annealed at 0.17 kPa in a nitrogen atmosphere for 2,4, and 17 hr at 600, 700, and 800°C. The effect of the annealing process on the adhesion of the thin alumina films was studied using a scanning-scratch tester, type SST-101, developed by Shimadzu. The best mechanical properties were obtained with unannealed samples. After thermal annealing the critical load decreased, proportional to annealing time and/or temperature. This effect was probably due to the presence of a high thermal stress and to preferential segregation of sulfur near the oxidealloy interface.     

OECD International Standard Problem ISP-47 on containment thermal-hydraulics—Conclusions of the TOSQAN part

The main objective of the ISP-47 is to assess the capabilities of Lumped-Parameter and Computational Fluid Dynamics codes in the area of nuclear containment thermal-hydraulics. Three experimental facilities TOSQAN, MISTRA and ThAI were involved in this project. The present paper summarizes the specifications, the results and the conclusions obtained for the TOSQAN open benchmark exercise.Wall condensation, steam injection in air or air/helium atmospheres, and buoyancy were addressed under well-controlled initial conditions in the simple TOSQAN geometry. Detailed gas velocity and gas concentration (air, steam and helium) fields were obtained for the first time in such an exercise.It is found that the model predictions fit with a generally good accuracy the experimental results obtained during condensation steady-state conditions, but the flow conditions in the transition regime are not well reproduced by the calculations: some of the major transient phenomena are not always correctly modelled and if so, the transient evolutions or the levels of the concerned variables are not the same in the calculations and in the experiment. Furthermore, two kinds of measurements were specific for TOSQAN: boundary layer measurements and turbulence variables, which were addressed for the first time in such an exercise. It is concluded that more sophisticated modelling in CFD codes for the boundary layers should be developed and that turbulence variables should be addressed more intensively in further exercises.     

Progress of IRSN R&D on ITER Safety Assessment

The French “Institut de Radioprotection et de S?reté Nucléaire” (IRSN), in support to the French “Autorité de S?reté Nucléaire”, is analysing the safety of ITER fusion installation on the basis of the ITER operator’s safety file. IRSN set up a multi-year R&D program in 2007 to support this safety assessment process. Priority has been given to four technical issues and the main outcomes of the work done in 2010 and 2011 are summarized in this paper: for simulation of accident scenarios in the vacuum vessel, adaptation of the ASTEC system code; for risk of explosion of gas-dust mixtures in the vacuum vessel, adaptation of the TONUS-CFD code for gas distribution, development of DUST code for dust transport, and preparation of IRSN experiments on gas inerting, dust mobilization, and hydrogen-dust mixtures explosion; for evaluation of the efficiency of the detritiation systems, thermo-chemical calculations of tritium speciation during transport in the gas phase and preparation of future experiments to evaluate the most influent factors on detritiation; for material neutron activation, adaptation of the VESTA Monte Carlo depletion code. The first results of these tasks have been used in 2011 for the analysis of the ITER safety file. In the near future, this R&D global programme may be reoriented to account for the feedback of the latter analysis or for new knowledge.     

Experimental and numerical approaches of aerosol removal in spray conditions for containment application

TOSQAN is an experimental program undertaken by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in order to perform thermal hydraulic containment studies. The TOSQAN facility is a large enclosure devoted to simulate typical accidental thermal hydraulic flow conditions in nuclear pressurized water reactor (PWR) containment. The TOSQAN facility, which is highly instrumented with non-intrusive optical diagnostics, is particularly adapted to nuclear safety code validation. The present work is devoted to study a water spray injection used as a mitigation means in order to washout aerosol fission products.     

Research works on contamination transfers through cracked concrete walls

This study takes place within the framework of nuclear facilities containment assessment. The aims are to determine gaseous flow, two-phase flow and aerosol deposition models through a crack network by using the most realistic and representative crack network characteristics. For this, the crack network is considered as two infinite parallel plates. First of all, airflow experiments are performed on three concrete walls (128 cm in width, 75 cm in height and 10 cm in thickness), cracked by shear stresses. The results enable determining aeraulic crack network characteristics, thanks to the Poiseuille model in laminar compressible flow, and elaborating an experimental friction factor correlation for the transition flow, validated up to a Reynolds number of 250. Next, aerosol deposition experiments were performed with one of the previous concrete walls in order to determine a global aerosol deposition model in a crack network. The first experiments with an aerosol diameter of 60 nm showed that the aeraulic crack network characteristics are suitable for the aerosol physics. Therefore, geometrical crack network characteristics were determined by using several types of experiment and enable – thanks to aerosol deposition experiments – constituting and validating a global model of aerosol deposition in a crack network.