• Energy Research

Modelling of sodium-evaporation and formation of sodium-oxide aerosols from a sodium-pool fire is of fundamental importance for the assessing of the radiological consequences in Sodium-cooled Fast Reactors severe accidents. This paper summarizes the derivation of a simple model to estimate the amount and size of particles being generated from Na-pool fires and its performance assessment, once implemented in an integral severe accident tool (ASTEC-Na), against available large-scale separate effect tests. The model has been transposed in analytical correlations which implementation in lumped-parameter severe accident codes is straightforward. According to the comparisons to data set, the correlations do not adversely impact the code estimates with respect to other more empirical alternative approaches and, in addition, the correlations remove any need of user-defined ad-hoc parameters in the input deck concerning Na-based particles behaviour, as other alternates do. Regarding code behaviour, the model predictions yield the same order of magnitude both in terms of suspended aerosol concentration and diameter as data and capture the reliable measured data trends.

Abstract The OECD/NEA Sandia Fuel Project provided unique thermal-hydraulic experimental data associated with Spent Fuel Pool (SFP) complete drain down. The study conducted at Sandia National Laboratories (SNL) was successfully completed (July 2009 to February 2013). The accident conditions of interest for the SFP were simulated in a full scale prototypic fashion (electrically heated, prototypic assemblies in a prototypic SFP rack) so that the experimental results closely represent actual fuel assembly responses. A major impetus for this work was to facilitate severe accident code validation and to reduce modeling uncertainties within the codes. Phase I focused on axial heating and burn propagation in a single PWR 17 × 17 assembly (i.e. “hot neighbors” configuration). Phase II addressed axial and radial heating and zirconium fire propagation including effects of fuel rod ballooning in a 1 × 4 assembly configuration (i.e. single, hot center assembly and four, “cooler neighbors”). This paper summarizes the comparative analysis regarding the final destructive ignition test of the phase I of the project. The objective of the benchmark is to evaluate and compare the predictive capabilities of computer codes concerning the ignition testing of PWR fuel assemblies. Nine institutions from eight different countries were involved in the benchmark calculations. The time to ignition and the maximum temperature are adequately captured by the calculations. It is believed that the benchmark constitutes an enlargement of the validation range for the codes to the conditions tested, thus enhancing the code applicability to other fuel assembly designs and configurations. The comparison of lumped parameter and CFD computer codes represents a further valuable achievement.

The PASSAM (Passive and Active Systems on Severe Accident source term Mitigation) project was launched in the frame of the 7th framework programme of the European Commission. Coordinated by IRSN, this four year project (2013–2016) involved nine partners from six countries: IRSN, EDF and university of Lorraine (France); CIEMAT and CSIC (Spain); PSI (Switzerland); RSE (Italy); VTT (Finland) and AREVA GmbH (Germany). It was mainly an R&D project of experimental nature aimed at investigating phenomena that might enhance source term mitigation in case of a severe accident in a Nuclear Power Plant (NPP). Both existing systems (i.e., water scrubbing and sand bed filters plus metallic pre-filters) and innovative ones (i.e., high pressure sprays, electrostatic precipitators, acoustic agglomerators and, advanced zeolites and combined wet-dry filtration systems), were experimentally studied in conditions as close as possible from those anticipated for severe accidents. This paper presents the main experimental results of the project which represent a significant extension of the current database on these existing or innovative mitigation systems. Application of some of these data for improving existing models or developing new ones should eventually enhance the capability of modelling Severe Accident Management measures and developing improved guidelines.

Abstract The characterization of spent fuel in dry storage is fundamental to assess and assure the cladding integrity as one of the main safety criteria. To do that, reliable methodologies based on applicable analytical tools are pursued. The present paper shows an easy to apply methodology to characterize dry stored fuel from a realistically conservative approach. It has been validated through EOL rod internal pressure data from PWR fuel rods. The application to old and current designs of discharged fuel rods shows cladding stresses below the limit usually applied for embrittlement due to hydride radial reorientation (90 MPa). An analysis of the stress reduction with respect to enveloping conditions (licensing limits concerning irradiation and stored heat load) points out the importance of approaching realistic power histories (stress reduction higher than 30%), whereas the realism sought in the stored heat load is shown to be less important (stress reduction around 12%).

Artículos en revistas . Sodium fast reactors (SFRs) potential to meet Gen. IV requirements is broadly acknowledged worldwide. The scientific and technological experience accumulated by operating test reactors and, even, by running commercial reactors, makes them be considered as the closest Gen. IV option in the near future. In the past their balance of plant has been always based on Rankine cycles. This paper investigates the potential use of supercritical recompression CO2 cycles (S-CO2) in SFRs on the basis of the working parameters foreseen within the European Sodium Fast Reactor (ESFR) project. A wide range of configurations have been explored, from the simplest one to combined cycles (with organic Rankine cycles, ORC), and a comparison has been set in terms of thermal efficiency. As a result, it has been found out that the most basic configuration could reach a thermal efficiency as high as 43.31%, which is comparable to that obtained through super-critical Rankine cycles proposed elsewhere. A sensitivity analysis together with an exergy study of this configuration, pointed the pre-cooler and IHXNa CO2 as key components in the cycle performance. These results highlight a main conclusion: the potential use in SFRs of recompression S-CO2 cycles for their balance of plant, whenever a sound and extensive database is built-up on S-CO2 turbo-machinery and IHX performance. info:eu-repo/semantics/publishedVersion

The 5th FWP EURSAFE Project highlighted iodine chemistry in the containment as one of the issues requiring further research in order to reduce source term uncertainties. Consequently, a series of studies was launched in the 6th FWP SARNET Project aimed at improving the predictability of iodine behaviour during severe accidents via a better understanding of the complex chemical phenomena in the containment. In particular, SARNET has striven to foster common interpretation of integral and separate effect test data, production of new or improved models where necessary, and compilation of the existing knowledge of the subject. The work has been based on a substantial amount of experimental information made available from bench-scale projects (PARIS and EPICUR), via intermediate-scale tests (CAIMAN) to large-scale facilities (SISYPHE, THAI and PHEBUS-FP). In the experimental field, particular attention has been paid to two specific issues: the effects of radiation on both aqueous and gaseous iodine chemistry, and the mass transfer of iodine between aqueous and gaseous phases. Comparisons between calculations and results of the EPICUR and CAIMAN experiments suggest that the aqueous phase chemistry is reasonably well understood, although there are still some areas of uncertainty. Interpretation of integral experiments, like PHEBUS-FPT2, indicated that radiation-induced conversion of molecular iodine into particulate species (IxOy) could be responsible for the gaseous iodine depletion observed in the long-term. However, the results of much simpler, small-scale experiments have shown that further improvements in understanding and modelling are still needed. Mass transfer modelling has been extended to cover evaporating sump conditions based on SISYPHE data; however, application of this model to the larger scale THAI experiments seems not to be straightforward. In addition to these two major issues, some specific studies have been carried out concerning the potential effect of passive autocatalytic hydrogen recombiners on iodine volatility. The RECI analytical experiments have shown that metal iodides (namely CsI and CdI2) are not stable and yield gaseous iodine when heated, in a humid atmosphere, at temperatures representative of recombiner operation. Another important undertaking successfully carried out has been the compilation of an Iodine Data Book, which provides a critical review of the experimental data and modelling approaches that have been used in the development of iodine source term methodologies. This should assist in a proper use of such models, and inform their future development.