Last update on April 2017
The PASSAM project launched in January 2013 and completed in late 2016 has investigated the possibilities for enhancing the reduction (referred to as "mitigation") of radioactive waste that may be released into the environment following the meltdown of the core of a nuclear reactor. Directed by the IRSN (the French Radioactivity Protection and Nuclear Safety Institute) as part of the European Commission's 7th Framework Program for Research and Development (FPRD), it has involved the participation of nine European partners.
Background and objectives
During an accident involving a core melt at a light-water nuclear reactor, radioactive elements emitted from fuel rods may be released into the environment, exposing the human population, fauna and flora to a risk of radiological contamination. For many years the IRSN has directed, or contributed to, research projects that aim to improve our understanding of the evolution of core melt accidents, of the kinetics of radionuclide waste and of the means to mitigate this waste. The international programs PHEBUS (completed in 2010), ISTP (completed in 2013) and STEM (continuing until 2019) have in particular increased our understanding of the behavior of nuclear fission products in a reactor's primary circuit and inside the reactor containment.
In order to reduce the risk of the massive release of radioactive elements, a venting and filtration system has been installed on certain reactors, particularly those in the French pool of nuclear-powered electrical power plants. This system enables the reactor containment to be depressurized through a filtration device that limits the release of radioactive elements into the environment.
In France, the filtration device adopted consists of a metallic pre-filter and a sand filter located respectively inside and outside the reactor confinement. This system, effective for the filtration of aerosols, was not designed to retain gaseous forms of radionuclides, particularly the gaseous forms of iodine, which nevertheless represent a major safety risk for the local population in the early days following an accident.
The PASSAM project has investigated by experiment the possibilities for enhancing the existing filtration systems, but has also tested other innovative approaches to the retention of iodine. The aim was to conduct experiments reproducing as closely as possible the actual conditions of a core melt accident, in order to investigate in particular the following aspects:
- the performance of mitigation systems;
- The long-term behavior of elements trapped by retention systems (particularly the potential for revaporization of the trapped radioactive elements).
The PASSAM project, coordinated in overall terms by the IRSN, was divided into four technical and scientific "work packages" (WPs):
- the analysis, undertaken by CIEMAT (Spain), of the current state of understanding of existing or potential filtration systems, together with the definition of the experiments to be undertaken within the scope of the project; the development, undertaken by RSE (Italy), of the first simplified calculation models, to be integrated into the calculation codes for nuclear accidents, such as
the ASTEC simulation software for a serious accident developed by the IRSN;
- experiments concerning existing filtration systems, undertaken by the PSI (Switzerland) and the IRSN;
- experiments concerning five new systems for the mitigation of waste, selected for their promising potential, and undertaken by VTT (Finland), CIEMAT and CSIC (Spain), RSE (Italy), the IRSN and Areva GmbH (Germany);
- and lastly, the final synthesis of the project, under the responsibility of the IRSN, and the dissemination of the knowledge acquired (publications, workshops, etc.).
A number of existing systems were reviewed (bubbling filters, sand
filters and metallic pre-filters), in addition to a number of innovative
systems (an acoustic agglomerator system, high-pressure pulverizers,
electrostatic precipitators, advanced zeolites, and combined wet-dry
filtration systems). Adsorption tests were conducted for the gaseous
species under investigation, mainly on a small scale, for each type of
filter, taking into account the velocity of adsorption, the maximum
trapping capacity, the temperature, the rate of humidity, etc. The
reversibility of the trapping process under the effects of gamma
ionizing radiation was also assessed.
For these experiments, a number of IRSN facilities were
used: the EPICUR test device, consisting of a gamma radiation irradiator
(with six sources of cobalt-60), was used to test the long-term
stability of the radioactive elements trapped on the different
filtration devices; the PERSÉE installation, recently inaugurated, made
it possible to conduct a large-scale test to assess the effectiveness of
the trapping of iodine compounds by zeolite filters.
PASSAM project made it possible to constitute a database of the
characteristics of each mitigation system studied. It is useful not only
to the various national nuclear safety authorities, but also to the
technical organisms responsible for safety assessments (TSOs) and to the
operators of nuclear installations, with a view to increasing the
reliability of the systems existing in nuclear power plants currently in
The experiments led to a number of important observations:
- hydrodynamics in the liquid (bubbling) filters, the system most investigated during the PASSAM project, is significantly different from the data currently entered into the calculation programs for serious accidents, and more precisely into the calculation modules specifically designed for this type of filter, particularly in the case of high velocities of gas flow.
- The effectiveness of the sand filters combined with the metallic pre-filters, installed in all French nuclear power plants, was checked for the filtration of gaseous organic iodine. It was confirmed that organic iodine is not retained by this type of filter. Furthermore, in temperature and gamma radiation conditions close to those anticipated in the event of an accident, the instability of the cesium iodide aerosols previously trapped in the sand filter was made apparent, which could lead to the retarded release of gaseous iodine.
- Among the innovative procedures, which could complement the existing systems, particularly worthy of note is the very high degree of effective trapping of both molecular iodine and organic iodine shown by zeolites, particularly the zeolite of the Faujasite-Y silver type.
The observations arising from the experiments conducted during the PASSAM project have made it possible to establish new calculation models and to enhance the existing models. These models will be subsequently integrated into the calculation programs specific to the filtration systems concerned, and then into the calculation programs for serious accidents, particularly into the European ASTEC system of programs developed by the IRSN.
The results obtained during the PASSAM project also serve to provide inputs for the
(2014-2019) directed by the IRSN. This ANR-RSNR (French National Research Agency/Digital Social Networks for Research) project also aims to improve the confinement of radioactive waste during a nuclear meltdown accident by acquiring an understanding of the filtration systems already existing all over the world, and of new effective and robust filtration systems. It is differentiated from the PASSAM project, particularly in that it undertakes in greater depth than PASSAM the R&D into innovative filtration materials, and also takes into account the trapping of gaseous ruthenium, which, according to accident scenarios, could also be a major contributor to atmospheric contamination and to short-term health consequences.