In severe accidents with primary-to-secondary leakages, the retention of fission products in horizontal steam generators is poorly understood. The understanding of fission product deposition in realistic steam generator conditions is needed in realistic release estimates in PSA studies, and to design efficient accident management procedures. This is considered very important because steam generator tube rupture sequences are included in the risk dominant sequences.



Tube dimensions of the HORIZON model steam generator and Loviisa VVER-440 steam generators are approximately same. Thus it can be assumed that experiments give realistic results.



In addition to the steam generator section itself, the HORIZON facility includes a lot of equipment needed for steam and aerosol generation, and for measuring the thermal-hydraulic parameters as well as the aerosols concentrations.



The inlet and outlet chamber aerosol mass concentration is monitored with Tapered Element Oscillating Microbalance (TEOM) on-line mass monitor and the particle size distribution is measured on-line with the Electrical Low Pressure Impactor (ELPI). Aerosol sampling system includes heated sampling lines, two diluters (first diluter in system pressure is computer controlled and uses heated dilution air), pressure reducer and sampling valves. It is possible to change sampling point between inlet and outlet chambers.

Facility is dismanteled.

The influence of containment sprays on atmosphere behaviour is being investigated both experimentally and theoretically. Experiments are being performed on the TOSQAN and MISTRA experimental facilities. The main objective of the CEA's MISTRA programme was to study condensation on the walls and the water droplets (from spraying) in a geometry larger than that of TOSQAN and with the possibility of compartments.
The experiments, carried out at MISTRA within SARNET, followed the same basic pattern. First, a well-defined (in terms of pressure, temperature and atmosphere composition) initial state was obtained, with a quiescent atmosphere. Then, sprays were activated with all boundary conditions remaining constant. The tests lasted typically less than two hours.
Facility is in operation.

The experiment objective was to study the physical phenomena that affect hydrogen distribution in the reactor containment such as: steam wall condensation, heat mass and momentum exchanges with the sump or with the containment spray systems. These different phenomena have been studied during specific test phases.
TOSQAN facility is highly instrumented both in terms of measurement density and diversity. Most of instrumentation is based on innovative optical diagnostics, which allows to measure accurately and non-intrusively the multiphase flow composed of various gases (air, steam, and helium used as a surrogate of hydrogen), water droplets, and aerosols simulating the fission products.
Facility is in operation.

The catalyst sheets (stainless steel coated with washcoat/platinum catalyst material) are arranged in parallel forming vertical rectangular flow channels. Such a set-up represents a box-type recombiner section of AREVA design. Inside of the configuration the distribution of the catalyst temperatures and the gas com- position in vertical flow direction are measured. The correlation of the hydrogen conversion and catalyst temperatures with the experimental parameters serve basically to clarify the interactions of reaction kinetics, heat and mass transfer, and the flow conditions inside the recombiner.

Facility is in operation.

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–nitrogencompounds. 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 Program on Air Radiolysis and Iodine adsorption on Surfaces (PARIS) was therefore initiated in 2002 by IRSN in collaboration with AREVA NP, as part of the research programs performed to improve severe accident modelling and evaluation of subsequent fission product release into the environment with specific objective of measuring:
• the rate and amount of ARP production and destruction,
• rate and extent of radiolytic oxidation of molecular iodine into iodine oxides,
• the effect of the containment structural surfaces, namely decontamination coating (“paint”) and stainless steel, on radiolytic oxidation of I2,
• the effect of silver, representing silver-containing aerosol particles, on radiolytic oxidation of I2.
Important new features of the PARIS project were: (1) more realistic low iodine concentrations, (2) surface to volume ratios of paint, steel and silver surface area to containment volume ratio representative of LWR or PHEBUS containments, (3)higher steam fractions and (4) representative dose rates. The PARIS database, containing about 400 tests, was intended to provide data to develop and validate empirical models, and finally to derive a simplified model for ASTEC Code and other severe accident iodine codes.
Facility is not operating.

This programme will help to better estimate the quantity of radioactive iodine released during a core meltdown accident taken into account when elaborating specific emergency plans. The programme results will also be used to better define the means and measures required to limit releases into the environment.



A study on ruthenium chemistry – another radiotoxic product – in the reactor containment under accidental conditions was conducted as part of the ISTP. About twenty tests were performed to assess the effect of irradiation on the volatilisation of ruthenium from the sump or deposits on painted containment surfaces. This study provided experimental data used to determine ruthenium quantities released into the environment in the event of an accident.



Various materials can be irradiated so as to determine the impact of the received dose on the variation in certain properties. This application could be used to study the ageing of polymers, greases and other compounds, which would help improve existing computer models and make it possible to make more informed decisions on the reactor life extension for example.

Facility is in operation.

The purpose of the SISYPHE (Simulation du Système Phébus Enceinte) facility at Cadarache was to build a 1:1 replica of the Phébus FP experimental containment vessel, assisting the Phébus test interpretation, for all phenomena concerning thermal-hydraulics and fission product behaviour.



All systems of the Phébus FP containment vessel are reproduced, except radiation. Instrumentation improved as compared to Phébus, by special optical instruments.



The objective of the testing foreseen in this vessel was manifold:

• A: Thermal Hydraulics Studies: these tests are simulating phenomena like: condensation on condensers and walls, convection, humidity up to 100%, presence of hot/cold sump, steam condensation on aerosols, diffusiophoresis, and iodine affinity with water. B: Aerosol Behaviour Programme: multicomponent aerosols from POLYR generator, soluble or non-soluble. Study on wall deposits or electrophoresis.
• B: Iodine Programme: studying the presence of molecular gaseous iodine, transfer to surfaces, interactions with paint, re-emission from sump by radiolysis, iodine aerosol interaction, and interface with hydrogen.
• C: Mass Transfer Programme: effect of evaporating or non-evaporating sump on molecular iodine mass transfer (in preparation to FPT2 & FPT3). Oxygen is the simulant for iodine. Ultimate goal: mass-transfer model to predict MT coefficient for oxygen and hence for iodine.

Duration of the programme: post-FPT1, between 1995 and 2003.

Facility is dismanteled, part of Phébus.

Iodine is a fission product of major importance, because volatile species can be formed under severe nuclear reactor accident conditions, and may potentially be released into the environment, leading to significant radiological consequences. The CAIMAN programme was devoted to studying the radiochemistry of iodine in the reactor containment in case of a severe accident occurring in a Pressurised Water Reactor; this is a data base of prime importance for the validation of codes, namely IODE, which is a module of the integral ASTEC (Accident Source Term Evaluation Code) code, jointly developed by the IRSN and the GRS. These computations are generally used to predict the radiological consequences of such an accident. The experimental programme, which ran from 1996 to 2002, concerned eighteen experiments in a facility of intermediate scale (300 dm3), where labelled iodine, 131I, was used to perform -counting. The CAIMAN tests are here analysed, and the main experimental observations and trends are described. For each experiment, IODE computations were performed and compared with experimental results in order to assess the possible weak points of the present modelling and to identify key parameters. Broadly speaking, the gaseous concentrations predicted are quite consistent with the experimental ones; the remaining gaps have been identified.
Facility is not operating.

Steam generator reliability and performance are serious concerns in the operation of pressurized water reactors. The aim of the SGTR project was to provide a database of fission product retention in steam generator tube rupture sequences and models, which could be applied to estimate the effectiveness of different accident management strategies in these kind of accidents.
The SGTR project made an important step forward to resolve uncertainties of physical models, especially in the aerosol deposition and mechanical resuspension in turbulent flows. There was one sampling at the injection line for the Optical Particle Counter (OPC) aimed at determining the aerosol size distribution and quantifying the mass concentration at the inlet. Within the vessel atmosphere eight samplings were taken to six filters and two cascade impactors, from which the mass concentration exiting the tube mini-bundle was estimated.
The test mini-bundle is a scaled mock-up of the first stage of the steam generator tube bundle. It consists of a squared arrangement housing inside a total of 117 tubes plus four supporting rods placed in the corners. The mini-bundle allows two possible locations of the broken tube. One place is just at the centre of the structure and the other place is three tubes away from the centre.

This emission has an impact on the iodine chemistry (AgI) and on the behavior of aerosols in the reactor primary circuit and in the containment. The presence of control rod material influences the source term potentially present in a PWR containment and likely to in the atmosphere.


In a French 900 PWR the AIC material can make up as much as 2 tons.


The results of these experiments should help in establishing computer models on the AIC source term, part of the ESCADRE (later ASTEC) code system. They should also be used as an experimental input for the AIC injection into VERCORS fuel release experiments.

Facility is not operating.