Ex-Vessel Break in the ITER Divertor Cooling Loop Using the ECART Code

This work is related to the application of the CESI and Edf ECART code on the analysis of a large ex-vessel break in the divertor cooling loop of the ITER reactor. These activities are carried out in the general framework of the validation phase of the ECART code, initially developed by ENEL and EdF for integrated analysis of severe accidents in LWRs, for its application on incidental sequences related to the ITER fusion plant. ECART was originally designed and validated for traditional NPP safety analyses and it is internationally recognized as a relevant nuclear source term code for nuclear fission plants. It permits the simulation of chemical reactions and transport of radioactive gases and aerosols under two-phase flow transients in generic flow systems, using a built-in thermal-hydraulic model. A comparison of the ECART data with the results obtained by NFR Studsvik Nuclear AB (Nyköping, Sweden), utilising the MELCOR code in its fusion version for the same sequence, has been also performed during the present task. This comparison gives a quite good qualitative and quantitative agreement in the results, both for the thermal-hydraulics main parameters and the environmental radioactive releases

Analysis of External Radioactive Releases for an In-Vessel Break in the Power Plant Conceptual Study Using the ECART Code

This work is related to the application of the CESI and EdF ECART code on the analysis of the tritium and dusts external releases for an in-vessel break in the helium cooling loop of the first wall / blanket for the Power Plant Conceptual Study (PPCS). In particular the influence on the releases of a Detritiation System (DS) and of a dust scrubber with constant decontamination factor, not implemented in the original PPCS design, are analysed. Furthermore, some parametrical analysis on the influence, on the external releases, of the mass fraction of dust resuspended inside the VV at the beginning of the sequence have been also performed. These analyses are the follow-up of a previous DIMNP study about the phenomenological behaviour of the PPCS containment (vacuum vessel walls and expansion volume walls), giving the first indications on the amount of the external radioactive releases. The activities have been also carried out in the general framework of the validation phase of the ECART code, initially developed for integrated analysis of severe accidents in LWRs, for its application on incidental sequences related to fusion plants. ECART was originally designed and validated for safety analyses of fission NPPs and is internationally recognized as a relevant nuclear source term code for these fission plants. It permits the simulation of chemical reactions and transport of radioactive gases and aerosols under two-phase flow transients in generic flow systems, using a built-in thermal-hydraulic model

SARNET2 Severe Accident Phenomenology Course - January 2011

The first SARNET2 “Severe Accident Phenomenology Short Course” was organized from 10 to 14 January 2011 by CEA and UNIPI and hosted by Pisa University, with the participation of about 100 students from 20 different countries. This was a 1-week course on phenomenology, focused on disseminating the knowledge gained on severe accidents in the last two decades to students, young engineers and researchers. The goal was also to refresh participants memories after 5 years and SARNET new outcomes, with a program covering severe accident phenomenology and progression in current watercooled Gen. II NPPs, but also the different design solutions in Gen. III ones. Lecturers were experts from 8 different countries, with large skills and knowledge on Gen. II and III plants and on the progression of a severe accident. The course was open to university students with a discount fee and contributed for 3 ECTS with a strong link among SARNET2 and ENEN

Analysis of the THAI Iod-11 and Iod-12 tests: Advancements and limitations of ASTEC V2.0R3p1 and MELCOR V2.1.4803

This work is related to the application of the ASTEC V2.0R3p1 and MELCOR V2.1.4803 codes to the analysis of the THAI Iod-11 and Iod-12 containment tests characterised by an iodine release. The main scope of these two tests was to investigate the steel interaction on dry and wet surfaces, with an interaction supposed to be a two-steps process: an initial faster and reversible physisorption followed by a slower, and irreversible, chemisorption of the physisorbed I2. The aim of the present work is to highlight advancements and limitations of the current ASTEC and MELCOR code versions respect to the older code versions employed during the European SARNET projects. The investigation was carried out as a code-to-code comparison vs. the experimental THAI data, focusing on the evaluation of the code models treating the iodine behaviour. A similar spatial nodalisation was employed for both codes. As main result, ASTEC had shown an overall good agreement compared to the iodine related experimental data while, on contrary, MELCOR had shown poor results, probably due to unsolved numerical issues and unsatisfactory iodine modellisation

Standalone Containment Analysis of Four Phébus Tests with the ASTEC and the MELCOR Codes

After the severe accident (SA) occurred at the Three-Miles Island Nuclear Power Plant (NPP), important efforts on the investigation of the different phenomena during this kind of accidents have been started. Several experimental campaigns investigating one phenomenon at time or the combination of two or more phenomena have been performed. Today, the Phébus experimental campaign is probably the most important activity on the evaluation of the coupling among different phenomena. Four out of five tests investigated the degradation of an intact Pressurized Water Reactor (PWR) fuel bundle and the subsequent transport of Fission Products (FP) and Structural Materials (SM) through the primary circuit and into the containment, while the fifth test was only the degradation of a bed of PWR fuel bundle debris. These tests were performed between 1990 and 2010 at the CEA Cadarache laboratories (France) in a 5000:1 scaled facility. The main four tests varied the employed control rod materials, the fuel burn-up, and the oxidizing conditions of the atmosphere (strongly or weakly). The outcomes of this experimental campaign created a solid base for the understanding of the involved phenomena and allowed the development of models and software codes capable of simulating the evolution of a SA in a real NPP. ASTEC and MELCOR were two of the main SA codes profiting from the results of this Phébus campaign. These two codes were further improved in the latest years to account for the findings obtained in more recent experimental campaigns. A continuous verification and validation work is then necessary to check how the newer code's versions reproduce the tests performed in these older experimental campaigns such as Phébus one. The present work is intended to be the final step of a series of publications covering the activities carried out at University of Pisa with the ASTEC and the MELCOR SA codes on the four Phébus tests employing an intact PWR fuel bundle. Because of the complexity and the extent of these tests, only the containment aspects were considered in the precedent works, i.e., only the thermal-hydraulics transient and its coupling with the FP and SM behavior. Then, general conclusions based on the outcomes of these precedent works are summarized in this work

Normal and Accidental Scenarios Analyses with MELCOR 1.8.2 and MELCOR 2.1 for the DEMO Helium-Cooled Pebble Bed Blanket Concept

As for Light Water Reactors (LWRs), one of the most challenging accidents for the future DEMOnstration power plant is the Loss of Coolant Accident, which can trigger the pressurization of the confinement structures and components. Hence, careful analyses have to be executed to demonstrate that the confinement barriers are able to withstand the pressure peak within design limits and the residual cooling capabilities of the Primary Heat Transfer System are sufficient to remove the decay heat. To do so, severe accident codes, as MELCOR, can be employed. In detail, the MELCOR code has been developed to cope also with fusion reactors, but unfortunately, these fusion versions are based on the old 1.8.x source code. On the contrary, for LWRs, the newest 2.1.x versions are continuously updated. Thanks to the new features introduced in these latest 2.1.x versions, the main phenomena occurring in the helium-cooled blanket concepts of DEMO can be simulated in a basic manner. For this purpose, several analyses during normal and accidental DEMO conditions have been executed. The aim of these analyses is to compare the results obtained with MELCOR 1.8.2 and MELCOR 2.1 in order to highlight the differences among the results of the main thermal-hydraulic parameters

Stand-alone containment analysis of the Phébus FPT-0 test with the ASTEC V2.1 and the MELCOR v2.2 codes

During the last 40 years, several efforts have been carried out to investigate the different phenomena occurring during a severe accident in a Nuclear Power Plant (NPP). Within this framework, the execution of different experimental campaigns, investigating only specific phenomena or the coupling among two or more phenomena, has been one of the main activity and the integral Phébus FP tests were probably the most important experiences in this field. In these tests, the degradation of a PWR fuel bundle and the related phenomena in the primary circuit and in the containment system were investigated, employing different control rod materials and fuel burn-up levels in strongly or weakly oxidizing conditions. Such Phébus integral tests were of fundamental importance to understand the key aspects of each phenomena and to develop numerical codes capable to simulate the evolution of a severe accident in a real NPP. Two of the main codes international employed (ASTEC and MELCOR) for severe accident analysis were intensively benchmarked basing on the findings of the different Phébus FP tests. In the latest years, these two codes were furthermore improved, to implement the more recent research findings after the termination of the Phébus experimental campaign, as the results obtained in the SARNET projects. Therefore, a continuous verification and validation work is still needed for the codes to check that the new improvements introduced in such codes really allow a better prediction of the Phébus tests and of the other tests forming the validation test matrix. The aim of the present paper is to re-analyze the first Phébus FPT-0 test employing the latest ASTEC V2.1 and MELCOR V2.2 code versions. The performed analysis focuses on the thermal-hydraulics /aerosol coupling, and only the stand-alone containment aspects of the test have been investigated. Three different spatial nodalizations of the Phébus containment vessel have been employed, showing that at least 15/20 control volumes are necessary for the vessel spatial schematization to correctly predict thermal-hydraulics and aerosol behavior. Furthermore, the paper summarizes the main thermal-hydraulic results and presents the different sensitivity analyses carried out on the iodine and aerosols behavior. When possible, a comparison among the results obtained during this work and by different authors in previous works is also performed, to highlight the improvements in the physical models implemented in the two codes

MUSA WP4 Second Intermediate Reporting

General information Description of the reference case Development of the SA code and ut coupling and status Description of the input uncertainty parameters and the uncertainty methodology Development of uncertainty analysis - first results Issues to be reported Conclusion

An attempt to introduce a resuspension model in MELCOR 1.8.6 for fusion applications

During normal plasma operation the erosion of the ”plasma facing components” occurs and the dusts formed tends to deposit onto the divertor surface. In case of an In-vessel LOCA, these dusts may resuspend and transported to the VV Pressure Suppression System. Define the maximum amount of mobilized dust is an issue of main concern. MELCOR v1.8.6 hasn’t a resuspension model and an attempt to introduce a resuspension model in MELCOR was performed

Optimal index related to the shoreline dynamics during a storm: the case of Jesolo beach

Abstract. The paper presents an application of shoreline monitoring aimed at understanding the response of a beach to single storms and at identifying its typical behaviour, in order to be able to predict shoreline changes and to properly plan the defence of the shore zone. On the study area, in Jesolo beach (northern Adriatic Sea, Italy), a video monitoring station and an acoustic wave and current profiler were installed in spring 2013, recording, respectively, images and hydrodynamic data. The site lacks previous detailed hydrodynamic and morphodynamic data. Variations in the shoreline were quantified in combination with available near-shore wave conditions, making it possible to analyse the relationship between the shoreline displacement and the wave features. Results denote characteristic patterns of beach response to storm events, and highlight the importance of improving beach protection in this zone, notwithstanding the many interventions experimented in the last decades. A total of 31 independent storm events were selected during the period October 2013–October 2014, and for each of them synthetic indexes based on storm duration, energy and maximum wave height were developed and estimated. It was found that the net shoreline displacements during a storm are well correlated with the total wave energy associated to the considered storm by an empirical power law equation. A sub-selection of storms in the presence of an artificial dune protecting the beach (in the winter season) was examined in detail, allowing to conclude that the adoption of this coastal defence strategy in the study area can reduce shoreline retreat during a storm. This type of intervention can sometimes contribute to prolonging overall stability not only in the replenished zone but also in downdrift areas. The implemented methodology, which confirms to be economically attractive if compared to more traditional monitoring systems, proves to be a valuable system to monitor beach erosive processes and provide detailed indications on how to better plan beach-maintenance activities. The presented methodology and the proposed results can therefore be used as a basis for improving the collaboration between coastal scientists and managers to solve beach erosion problems, in locations where data are scattered and sporadic