Abstract: Uncertainty analysis is applied in the licensing process for nuclear installations to complement best estimate analysis and to verify that the upper bound value is less than the threshold corresponding to the safety parameter of interest. Metal-water reaction is a critical safety phenomenon of water-cooled nuclear reactors at accident conditions, e.g. Loss-Of-Coolant Accidents (LOCA). AISI 348 cladding is able to increase the accident tolerance comparing to Zr-based alloys and differently from other accident tolerant fuel cladding options, there is operational experience of nuclear power plants with stainless steel. In this study, a transient oxidation experiment of AISI 348 by steam was conducted and the major sources of uncertainty were addressed. An evaluation model was developed to calculate the evolution of mass gain during the experiment. Meanwhile, uncertainty propagation of experimental data was performed. The results show that the mass gain predicted by the transient metal-water reaction model lays within the experimental data uncertainty band. Furthermore, the selection of the oxidation kinetics model seems to be important whether the analysis wills to provide conservative results.

AVELAR, ALAN M.; DINIZ, CAMILA; CAMARGO, FÁBIO de; GIOVEDI, CLAUDIA; ABE, ALFREDO; CHERUBINI, MARCO; PETRUZZI, ALESSANDRO; MOURÃO, MARCELO B. Best estimate plus uncertainty analysis of metal-water reaction transient experiment. Nuclear Engineering and Design, v. 411, p. 1-12, 2023. DOI: 10.1016/j.nucengdes.2023.112414. Disponível em: http://repositorio.ipen.br/handle/123456789/34372. Acesso em: $DATA.

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Abstract: Many of the recent nuclear power plant projects use natural circulation as heat removal mechanism. The accuracy of heat transfer parameters estimation has been improved through models that require precise prediction of two-phase flow pattern transitions. Image patterns of natural circulation instabilities were used to construct an automated classification system based on Self-Organizing Maps (SOMs). The system is used to investigate the more appropriate image features to obtain classification success. An efficient automated classification system based on image features can enable better and faster experimental procedures on two-phase flow phenomena studies. A comparison with a previous fuzzy inference study was foreseen to obtain classification power improvements. In the present work, frequency domain image features were used to characterize three different natural circulation two-phase flow instability stages to serve as input to a SOM clustering algorithm. Full-Frame Discrete Cosine Transform (FFDCT) coefficients were obtained for 32 image samples for each instability stage and were organized as input database for SOM training. A systematic training/test methodology was used to verify the classification method. Image database was obtained from two-phase flow experiments performed on the Natural Circulation Facility (NCF) at Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN), Brazil. A mean right classification rate of 88.75% was obtained for SOMs trained with 50% of database. A mean right classificationrate of 93.98% was obtained for SOMs trained with 75% of data. These mean rates were obtained through 1000 different randomly sampled training data. FFDCT proved to be a very efficient and compact image feature to improve image-based classification systems. Fuzzy inference showed to be more flexible and able to adapt to simpler statistical features from only one image profile. FFDCT features resulted in more precise results when applied to a SOM neural network, though had to be applied to the full original grayscale matrix for all flow images to be classified.

Palavras-Chave: natural convection; two-phase flow; cooling systems; classification; brazilian cnen; diagrams; maps; coolant loops

MESQUITA, ROBERTO N. de; CASTRO, LEONARDO F.; TORRES, WALMIR M.; ROCHA, MARCELO da S.; UMBEHAUN, PEDRO E.; ANDRADE, DELVONEI A.; SABUNDJIAN, GAIANE; MASOTTI, PAULO H.F. Classification of natural circulation two-phase flow image patterns based on self-organizing maps of full frame DCT coefficients. Nuclear Engineering and Design, v. 335, p. 161-171, 2018. DOI: 10.1016/j.nucengdes.2018.05.019. Disponível em: http://repositorio.ipen.br/handle/123456789/28971. Acesso em: $DATA.

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Abstract: Background: Tumour hypoxia is associated with increased metastasis, invasion, poor therapy response and prognosis. Most PET radiotracers developed and used for clinical hypoxia imaging belong to the 2-nitroimidazole family. Recently we have developed novel 2-nitroimidazole-derived PET radiotracer [18F]FBNA (N-(4-[18F]fluoro- benzyl)-2-(2-nitro-1H-imidazol-1-yl)-acet-amide), an 18F-labeled analogue of antiparasitic drug benznidazole. The present study aimed to analyze its radio-pharmacological properties and systematically compare its PET imaging profiles with [18F]FMISO and [18F]FAZA in preclinical triple-negative (MDA-MB231) and estrogen receptor-positive (MCF-7) breast cancer models. Methods: In vitro cellular uptake experiments were carried out in MDA-MB321 and MCF-7 cells under normoxic and hypoxic conditions. Metabolic stability in vivo was determined in BALB/c mice using radio-TLC analysis. Dynamic PET experiments over 3 h post-injection were performed in MDA-MB231 and MCF-7 tumour-bearing mice. Those PET data were used for kinetic modelling analysis utilizing the reversible two-tissue-compartment model. Autoradiography was carried out in tumour tissue slices and compared to HIF-1α immunohistochemistry. Detailed ex vivo biodistribution was accomplished in BALB/c mice, and this biodistribution data were used for dosimetry calculation. Results: Under hypoxic conditions in vitro cellular uptake was elevated in both cell lines, MCF-7 and MDA-MB231, for all three radiotracers. After intravenous injection, [18F]FBNA formed two radiometabolites, resulting in a final fraction of 65 ± 9 % intact [18F]FBNA after 60 min p.i. After 3 h p.i., [18F]FBNA tumour uptake reached SUV values of 0.78 ± 0.01 in MCF-7 and 0.61 ± 0.04 in MDA-MB231 tumours (both n = 3), representing tumourto- muscle ratios of 2.19 ± 0.04 and 1.98 ± 0.15, respectively. [18F]FMISO resulted in higher tumour uptakes (SUV 1.36 ± 0.04 in MCF-7 and 1.23 ± 0.08 in MDA-MB231 (both n = 4; p < 0.05) than [18F]FAZA (0.66 ± 0.11 in MCF-7 and 0.63 ± 0.14 in MDA-MB231 (both n = 4; n.s.)), representing tumour-to-muscle ratios of 3.24 ± 0.30 and 3.32 ± 0.50 for [18F]FMISO, and 2.92 ± 0.74 and 3.00 ± 0.42 for [18F]FAZA, respectively. While the fraction per time of radiotracer entering the second compartment (k3) was similar within uncertainties for all three radiotracers in MDA-MB231 tumours, it was different in MCF-7 tumours. The ratios k3/(k3 + k2) and K1*k3/(k3 + k2) in MCF-7 tumours were also significantly different, indicating dissimilar fractions of radiotracer bound and trapped intracellularly: K1*k3/(k2 + k3) [18F]FMISO (0.0088 ± 0.001)/min, n = 4; p < 0.001) > [18F]FAZA (0.0052 ± 0.002)/min, n = 4; p < 0.01) > [18F]FBNA (0.003 ± 0.001)/min, n = 3). In contrast, in MDA-MB231 tumours, only K1 was significantly elevated for [18F]FMISO. However, this did not result in significant differences for K1*k3/(k2 + k3) for all three 2-nitroimidazoles in MDA-MB231 tumours. Conclusion: Novel 2-nitroimidazole PET radiotracer [18F]FBNA showed uptake into hypoxic breast cancer cells and tumour tissue presumably associated with elevated HIF1-α expression. Systematic comparison of PET imaging performance with [18F]FMISO and [18F]FAZA in different types of preclinical breast cancer models revealed a similar tumour uptake profile for [18F]FBNA with [18F]FAZA and, despite its higher lipophilicity, still a slightly higher muscle tissue clearance compared to [18F]FMISO.

SANTOS, SOFIA N. dos; WUEST, MELINDA; JANS, HANS-SONKE; WOODFIELD, JENILEE; NARIO, ARIAN P.; KRYS, DANIEL; DUFOUR, JENNIFER; GLUBRECHT, DARRYL; BERGMAN, CODY; BERNARDES, EMERSON S.; WUEST, FRANK. Comparison of three 18F-labeled 2-nitroimidazoles for imaging hypoxia in breast cancer xenografts: [18F]FBNA, [18F]FAZA and [18F]FMISO. Nuclear Engineering and Design, v. 124-125, p. 1-14, 2023. DOI: 10.1016/j.nucmedbio.2023.108383. Disponível em: http://repositorio.ipen.br/handle/123456789/34376. Acesso em: $DATA.

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Abstract: Many nuclear research reactors use or are planned with cores containing flat-plate-type fuel elements. One of the problems of this fuel element design is the mechanical stability of the fuel plates. High-velocity coolant flowing through the narrow channels that separate the plates can cause large deflections of these plates leading to local overheating, structural failure or plate collapse. In particular, in real fuel elements and experimental tests, flowinduced deflections at the leading edge and along the length of the plates have been detected. Some authors have indicated that the use of a support comb removes the leading-edge static divergence, but it has been also suggested that, even with the comb, there are significant deflections away from the inlet. In this work, a fluid-structure interaction study is conducted to examine the effectiveness of using an inlet comb on the mechanical stability of fuel plates. The system consists of two fuel plates bounded by three-equal coolant channels. The pressure loadings caused by the fluid flow are calculated using a CFD model and the structural response of the plates and the support comb are determined by means of an FEA model. The two-way fluid-structure interaction method was employed for coupling the fluid and solid solvers. The results presented here show that the static divergence at the inlet end is effectively eliminated with the installation of a support comb. Nevertheless, the main contribution of this work is the detection of deformation of the plates along their length and that it was an increasing function of the fluid velocity in the channels. As a consequence, the flow channels could be constricted or completely closed, thus affecting the safe operation of the nuclear reactor. To the best of our knowledge, this is the first numerical analysis reported in the literature that models the fluid-structure interaction phenomenon of adjacent plates with the support comb located at the midpoint of their inlet end.

Palavras-Chave: fuel plates; fuel elements; critical velocity; fluid-structure interactions; numerical data; nuclear fuels

MANTECON, JAVIER G.; MATTAR NETO, MIGUEL. Numerical analysis on stability of nuclear fuel plates with inlet support comb. Nuclear Engineering and Design, v. 342, p. 240-248, 2019. DOI: 10.1016/j.nucengdes.2018.12.009. Disponível em: http://repositorio.ipen.br/handle/123456789/30013. Acesso em: $DATA.

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Abstract: Shell-type fuel elements are widely used in nuclear research reactors. The nuclear fuel is contained in parallel shells, flat or curved, that are separated by narrow channels through which the fluid flows to remove the heat generated by fission reactions. A major problem of this fuel assembly design is the hydraulic instability of the shells caused by the high flow velocities. The objective of the study presented here is the development of a fluid-structure interaction methodology to investigate numerically the onset of hydroelastic instability of flat-shell-type fuel elements, also known as plate-type fuel assemblies, under axial flow conditions. The system analyzed consists of two nuclear fuel plates bounded by three-equal coolant channels. It is developed using the commercial codes ANSYS CFX for modeling the fluid flow and ANSYS Mechanical to model the plates. The fluid-structure interaction methodology predicts a behavior consistent with other theoretical and experimental works. Particularly, the maximum deflection of the plates is detected at the leading edge and it is a linear function of the square of the fluid velocity up to the Miller’s theoretical value. For velocities above this value, a nonlinear relationship is observed. This relationship indicates that structural changes are taking place in the plates. Furthermore, for fluid velocities greater than the Miller’s velocity, an extra deflection peak is observed near the trailing edge of the plates. Thus, structural alterations also happen along the length of the flat-shells.

Palavras-Chave: critical velocity; research reactors; computer codes; nuclear fuels; fuel elements; fuel plates; instability

MANTECON, JAVIER G.; MATTAR NETO, MIGUEL. Numerical methodology for fluid-structure interaction analysis of nuclear fuel plates under axial flow conditions. Nuclear Engineering and Design, v. 333, p. 76-86, 2018. DOI: 10.1016/j.nucengdes.2018.04.009. Disponível em: http://repositorio.ipen.br/handle/123456789/28966. Acesso em: $DATA.

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Abstract: This work aims on the development of a FORTRAN 90 code to solve the Loading Pattern Optimization Problem (LPOP) in the IEA-R1 research reactor at the Nuclear and Energy Research Institute (IPEN/CNEN-SP) in S˜ao Paulo, Brazil. The code integrates the Particle Swarm Optimization (PSO) method, with the current reactor calculation methodology. The objective function seeks to maximize the effective multiplication factor (keff), minimize the peak power factor (PPF), and achieve the most uniform neutron flux distribution possible. A comparison with the parameters of the reactor’s current configuration, and the code successfully finds solutions meeting the standard problem requirements. The new configuration enhances peak power (6.93%) and variance (9.62%), slightly increases neutron flux (0.48%), and marginally reduces in keff (0.45%). Additionally, it lowers the maximum fuel cladding temperature (0.7%), contributing to reactor safety.

SANTOS, THIAGO A. dos; GENEZINI, FREDERICO A.; STEFANI, GIOVANNI L. de. Optimization of IEA-R1 reactor core parameters using the particle swarm algorithm. Nuclear Engineering and Design, v. 415, p. 1-9, 2023. DOI: 10.1016/j.nucengdes.2023.112713. Disponível em: http://repositorio.ipen.br/handle/123456789/34374. Acesso em: $DATA.

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Abstract: The process of decommissioning nuclear reactors is a complex activity that involves various technical and administrative stages. Its main objective is to ensure the safety of the site, workers, the general public, and the environment during the execution of decommissioning activities, aiming for the release of the site from regulatory control. In the Brazilian context, it is essential to develop decommissioning strategies, taking into consideration the established technical and regulatory requirements, as well as following the guidelines of the Brazilian Nuclear Policy (BNP). Eight decommissioning strategies were proposed for small reactors, with different objectives and in different scenarios, encompassing 23 decommissioning approaches, divided into 6 groups: 1) decontamination and dismantling (DD); 2) radioactive waste (RW) management; 3) RW storage management; 4) human resources (HR) and knowledge management; 5) cost estimation; and 6) financial fund management. Additionally, 18 factors affecting the selection of these approaches were considered, taking into account particularities of the Brazilian context. A qualitative risk analysis was conducted using risk assessment techniques from the ABNT NBR ISO/IEC 31,010 standard, with a focus on the Multicriteria Decision Analysis (MCDA) technique. This qualitative analysis allowed for the evaluation of the approaches considering the current scenario and the future scenario, which includes possible changes in the BNP currently under discussion in the National Congress. The observations and results obtained in this study will be useful in guiding future efforts related to nuclear reactor decommissioning projects in Brazil. Based on the proposed strategies and considerations of safety, regulation, and governmental policies, it will be possible to plan and execute decommissioning activities more efficiently and safely.

CALDAS NETO, A.B.; SILVA, A.T. Strategies for decommissioning small nuclear reactors in Brazil. Nuclear Engineering and Design, v. 414, p. 1-14, 2023. DOI: 10.1016/j.nucengdes.2023.112608. Disponível em: http://repositorio.ipen.br/handle/123456789/34375. Acesso em: $DATA.

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