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RISS 인기검색어
- 검색키워드
- 저자 : Zullo G. (검색결과 6 건)
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Zullo G.,Pizzocri D.,Magni A.,Van Uffelen P.,Schubert A.,Luzzi L. 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.8
When assessing the radiological consequences of postulated accident scenarios, it is of primary interest to determine the amount of radioactive fission gas accumulated in the fuel rod free volume. The state-ofthe-art semi-empirical approach (ANS 5.4e2010) is reviewed and compared with a mechanistic approach to evaluate the release of radioactive fission gases. At the intra-granular level, the diffusiondecay equation is handled by a spectral diffusion algorithm. At the inter-granular level, a mechanistic description of the grain boundary is considered: bubble growth and coalescence are treated as interrelated phenomena, resulting in the grain-boundary venting as the onset for the release from the fuel pellets. The outcome is a kinetic description of the release of radioactive fission gases, of interest when assessing normal and off-normal conditions. We implement the model in SCIANTIX and reproduce the release of short-lived fission gases, during the CONTACT 1 experiments. The results show a satisfactory agreement with the measurement and with the state-of-the-art methodology, demonstrating the model soundness. A second work will follow, providing integral fuel rod analysis by coupling the code SCIANTIX with the thermo-mechanical code TRANSURANUS
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G. Zullo,D. Pizzocri,L. Luzzi 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.4
Recent developments on spectral diffusion algorithms, i.e., algorithms which exploit the projection of thesolution on the eigenfunctions of the Laplacian operator, demonstrated their effective applicability in fasttransient conditions. Nevertheless, the numerical error introduced by these algorithms, together with theuncertainties associated with model parameters, may impact the reliability of the predictions on shortlived volatile fission product release from nuclear fuel. In this work, we provide an upper bound on thenumerical error introduced by the presented spectral diffusion algorithm, in both constant and timevarying conditions, depending on the number of modes and on the time discretization. The definitionof this upper bound allows introducing a methodology to a priori bound the numerical error on shortlived volatile fission product retention.
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Zullo G.,Pizzocri D.,Magni A.,Van Uffelen P.,Schubert A.,Luzzi L. 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.12
The behaviour of the fission gas plays an important role in the fuel rod performance. In a previous work, we presented a physics-based model describing intra- and inter-granular behaviour of radioactive fission gas. The model was implemented in SCIANTIX, a mesoscale module for fission gas behaviour, and assessed against the CONTACT 1 irradiation experiment. In this work, we present the multi-scale coupling between the TRANSURANUS fuel performance code and SCIANTIX, used as mechanistic module for stable and radioactive fission gas behaviour. We exploit the coupled code version to reproduce two integral irradiation experiments involving standard fuel rod segments in steady-state operation (CONTACT 1) and during successive power transients (HATAC C2). The simulation results demonstrate the predictive capabilities of the code coupling and contribute to the integral validation of the models implemented in SCIANTIX.
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A surrogate model for the helium production rate in fast reactor MOX fuels
Pizzocri D.,Katsampiris M.G.,Luzzi L.,Magni A.,Zullo G. 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.8
Helium production in the nuclear fuel matrix during irradiation plays a critical role in the design and performance of Gen-IV reactor fuel, as it represents a life-limiting factor for the operation of fuel pins. In this work, a surrogate model for the helium production rate in fast reactor MOX fuels is developed, targeting its inclusion in engineering tools such as fuel performance codes. This surrogate model is based on synthetic datasets obtained via the SCIANTIX burnup module. Such datasets are generated using Latin hypercube sampling to cover the range of input parameters (e.g., fuel initial composition, fission rate density, and irradiation time) and exploiting the low computation requirement of the burnup module itself. The surrogate model is verified against the SCIANTIX burnup module results for helium production with satisfactory performance
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Physics-based modelling and validation of inter-granular helium behaviour in SCIANTIX
Giorgi R.,Cechet A.,Cognini L.,Magni A.,Pizzocri D.,Zullo G.,Schubert A.,Van Uffelen P.,Luzzi L. 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.7
In this work, we propose a new mechanistic model for the treatment of helium behaviour at the grain boundaries in oxide nuclear fuel. The model provides a rate-theory description of helium inter-granular behaviour, considering diffusion towards grain edges, trapping in lenticular bubbles, and thermal resolution. It is paired with a rate-theory description of helium intra-granular behaviour that includes diffusion towards grain boundaries, trapping in spherical bubbles, and thermal re-solution. The proposed model has been implemented in the meso-scale software designed for coupling with fuel performance codes SCIANTIX. It is validated against thermal desorption experiments performed on doped UO2 samples annealed at different temperatures. The overall agreement of the new model with the experimental data is improved, both in terms of integral helium release and of the helium release rate. By considering the contribution of helium at the grain boundaries in the new model, it is possible to represent the kinetics of helium release rate at high temperature. Given the uncertainties involved in the initial conditions for the inter-granular part of the model and the uncertainties associated to some model parameters for which limited lower-length scale information is available, such as the helium diffusivity at the grain boundaries, the results are complemented by a dedicated uncertainty analysis. This assessment demonstrates that the initial conditions, chosen in a reasonable range, have limited impact on the results, and confirms that it is possible to achieve satisfying results using sound values for the uncertain physical parameters.
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A reduced order model for fission gas diffusion in columnar grains
Pizzocri D.,Di Gennaro M.,Barani T.,Silva F.A.B.,Zullo G.,Lorenzi S.,Cammi A. 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.11
In fast reactors, restructuring of the fuel micro-structure driven by high temperature and high temperature gradient can cause the formation of columnar grains. The non-spheroidal shape and the non-uniform temperature field in such columnar grains implies that standard models for fission gas diffusion can not be applied. To tackle this issue, we present a reduced order model for the fission gas diffusion process which is applicable in different geometries and with non-uniform temperature fields, maintaining a computational requirement in line with its application in fuel performance codes. This innovative application of reduced order models as meso-scale tools within fuel performance codes represents a first-of-a-kind achievement that can be extended beyond fission gas behaviour.
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