Analysis of aerosol deposition in PHEBUS containment during FPT-1 experiment

The integral Phébus tests were probably one of the most important experimental campaigns performed to investigate the progression of severe accidents in light water reactors. In these tests, the degradation of a PWR fuel bundle was investigated employing different control rod materials and burn-up levels in strongly or weakly oxidizing conditions. From the results of such tests, numerical codes such as ASTEC and MELCOR have been developed to describe the evolution of a severe accident. After the termination of the experimental Phébus campaign, these two codes were furthermore expanded. Therefore, the aim of the present work is to reanalyze the first Phébus test (FPT-0) employing the updated ASTEC and MELCOR versions to ensure that the new improvements introduced in such codes allow also a better prediction of these Phébus tests. The analysis focuses on the stand-alone containment aspects of this test, and the paper summarizes the main thermal-hydraulic results and presents different sensitivity analyses carried out on the aerosols and fission products behavior. This paper is part of a series of publications covering the four executed Phébus tests employing a solid PWR fuel bundle: FPT-0, FPT-1, FPT-2, and FPT-3.

Section: Science and Technology Of Nuclear Installationsmentioning

confidence: 99%

Stand-Alone Containment Analysis of the Phébus FPT Tests with the ASTEC and the MELCOR Codes: The FPT-0 Test

Bruno

Paci

2017

“…Thus, a continuous verification and validation activity is necessary to ensure that the improvements/modifications introduced are valuable also for the analysis of older experiments, such as the Phébus FP tests. In the past, these Phèbus tests were widely investigated in independent works [7][8][9][10][11][12] or in international benchmark exercise [34,35]. Most of these activities focused on the degradation phenomena of the fuel bundle, and the subsequent release, and transport of FPs into the primary circuit.…”

Section: Discussionmentioning

confidence: 99%

“…This CV is a cylindrical shaped volume (10 m 3 free volume, 1.8 m inner diameter, and 5 m in height) with a sump on the lower part. The sump dimensions (0.584 inner diameter and 0.6 m in height) are set to reproduce a representative atmospherewater exchange surface [11]. Semiellipsoidal structures close the CV top, connect the main cylindrical zone with the sump zone, and close the bottom of the sump.…”

Section: The Phébus Fp Facilitymentioning

confidence: 99%

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

Bruno

Paci

2019

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.

“…The input was assumed to follow log-normal distribution which may be different from the distribution in the experiment. If the proportion of smaller aerosols is increased, the deposition on wall due to Brownian diffusion, diffusiophoresis, and thermophoresis will increase, deposition of gravitational settling will decrease [35], and vice versa. It can thus be concluded that the Cs mass flow rate and the aerosol size are the two main sources of uncertainties in the calculated results.…”

Section: Phenomenon Deposition Regionmentioning

confidence: 99%

Validation of Modified ART Mod 2 Code through Comparison with Aerosol Deposition of Cesium Compound in Phébus FPT3 Containment Vessel

Vechgama¹,

Silva²,

Rassame

2019

Evaluation of aerosol deposition in the containment vessel is an important step for the assessment of radioactive material release to the environment. ART Mod 2 is a calculation code that is used for evaluation of aerosol deposition in the containment vessel. The authors modified aerosol deposition models of ART Mod 2, namely, gravitational settling model, Brownian diffusion model, diffusiophoresis model, and thermophoresis model in order to increase potential of capturing the deposition phenomena. This study aims to compare the simulated results of modified ART Mod 2 with aerosol deposition of cesium compounds in the containment vessel of Phébus FPT3 experiment, in order to validate modified ART Mod 2 code. It is found that aerosol deposition using modified ART Mod 2 agrees with Phébus FPT3. Prediction of Brownian diffusion is significantly improved due to the consideration of turbulent damping process. Cesium mass flow rate and aerosol size are factors that can significantly influence the uncertainty of the results. When conditions of single volumes are carefully selected to match those of the Phébus FPT3 experiment, modified ART Mod 2 can predict aerosol deposition in Phébus FPT3 with relative accuracy.