The paucity of evidences about the long-term durability of currently available transcatheter prostheses is one of the main issues of transcatheter aortic valve implantation (TAVI). We sought to ...assess 3-year clinical and echocardiographic outcomes of patients undergoing TAVI with the third generation CoreValve prosthesis (Medtronic Incorporation, MN, USA).
From the Italian CoreValve registry, 181 who underwent TAVI from June 2007 to August 2008 and eligible for 3-year follow-up were analysed. All outcomes were defined according to the Valve Academic Research Consortium. All-cause mortality at 1, 2, and 3 years was 23.6, 30.3, and 34.8%, respectively. Cardiovascular death at 1, 2, and 3 years was 11.2, 12.1, and 13.5%, respectively. The actuarial survival free from a composite of death, major stroke, myocardial infarction, and life-threatening bleeding was 69.6% at 1 year, 63.5% at 2 years, and 59.7% at 3 years. Patients with renal insufficiency had a higher mortality at 3-year follow-up (49.0 vs. 29.2%, P = 0.007); moreover, patients experiencing post-procedural major or life-threatening bleeding had a higher rate of mortality already seen at 30 days (21.6 vs. 2.8%; P < 0.001) and this result was sustained at 3-year follow-up (62.2 vs. 27.7%; P < 0.001). Mean pressure gradients decreased from 52.2 ± 18.1 mmHg (pre-TAVI) to 10.3 ± 3.1 mmHg (1-year post-TAVI) (P < 0.001); aortic valve area increased from 0.6 ± 0.2 cm(2) (pre-TAVI) to 1.8 ± 0.4 cm(2) (1-year post-TAVI); these results remained stable over the 3 years of follow-up. Paravalvular leak was observed in the majority of patients. There were no cases of progression to moderate or severe regurgitation. No cases of structural valve deterioration were observed.
This multicentre study demonstrates that TAVI with the 18-Fr CoreValve ReValving System is associated with sustained clinical and functional cardiovascular benefits in high-risk patients with symptomatic aortic stenosis up to 3-year follow-up. Non-cardiac causes accounted for the majority of deaths at follow-up.
In ITER, the evaluation of the activated water radiation source and its impact on the radiological levels is necessary to demonstrate compliance with the safety requirements. The use of simplified or ...conservative approaches often results in the application of expensive constraints on the installation that impact its economics, operations, and construction schedule. In this work, we propose a novel methodology to calculate the activated water source term with a higher degree of realism. The methodology is based on the coupling of a system-level code with a Computational Fluid Dynamics (CFD) code in an explicit, one-way approach. We apply this methodology to the evaluation of the 16N radioisotope within the ITER Vacuum Vessel Primary Heat Transfer System (VV-PHTS) cooling circuit in a steady-state and transient scenarios. We chose this system since previous analyses of the VV-PHTS were done with simple, ad-hoc calculations that yielded results that differed by up to a factor of five, underscoring a higher level of uncertainty. As a result, we generate a computational model of the source term that can be used to evaluate the radiological condition surrounding the cooling systems during the operations.
•Coupling of CFD and system codes to calculate the 16N radiation source in ITER.•16N study of ITER Vacuum Vessel primary circuit, in steady state and transient.•Production of the 16N computational model for radiation protection studies.
Concomitant mitral regurgitation (MR) impaired prognosis in patients undergoing transcatheter aortic valve implantation (TAVI). It has been suggested that the use of first generation self-expandable ...valve in patients with significant MR is associated with worse outcome as compared with balloon expandable valve. However, the impact of newer generation transcatheter devices on MR has not been investigated so far. We aim to assess the prognostic impact of MR in patients undergoing TAVI with the first-generation vs. the latest generation of self-expandable valves.
We analyzed 2964 consecutive patients who underwent TAVI. Patients were classified into 4 groups according to the degree of baseline MR and the generation of self expandable valve implanted.
Of 1234 patients with moderate or severe MR, 817 were treated with first generation and 417 patients with second generation valves. Whereas, of 1730 patients with no or mild MR, 1130 were treated with first generation and 600 patients with second generation valves. Although, concomitant moderate-severe MR was found to be an independent predictor of mortality after TAVI, the use of newer generation self expandable valves was associated with higher survival rate at 1 year irrespective of the degree of preprocedural MR. At multivariable analysis the use of newer generation valve was associated with MR improvement throughout 1 year follow-up.
Baseline moderate-severe MR is associated with an increase in mortality after TAVI. However, the degree of preprocedural MR doesn't impact survival when a second generation self expandable valve is used.
•Moderate-severe preoperative MR is an independent predictors of mortality after TAVI.•Significant preoperative MR is associated with worse outcome in particular among patients treated with first generation self-expandable valves.•Whit the second generation device the degree of MR at baseline did not affect mortality at 1 years even with the use of self expandable valves.
In this work, the Monte Carlo burn-up code SERPENT-2 has been extended and employed to study the material isotopic evolution of the Molten Salt Fast Reactor (MSFR).
This promising GEN-IV nuclear ...reactor concept features peculiar characteristics such as the on-line fuel reprocessing, which prevents the use of commonly available burn-up codes. Besides, the presence of circulating nuclear fuel and radioactive streams from the core to the reprocessing plant requires a precise knowledge of the fuel isotopic composition during the plant operation.
The developed extension of SERPENT-2 directly takes into account the effects of on-line fuel reprocessing on burn-up calculations and features a reactivity control algorithm. It is here assessed against a dedicated version of the deterministic ERANOS-based EQL3D procedure (PSI-Switzerland) and adopted to analyze the MSFR fuel salt isotopic evolution.
Particular attention is devoted to study the effects of reprocessing time constants and efficiencies on the conversion ratio and the molar concentration of elements relevant for solubility issues (e.g., trivalent actinides and lanthanides). Quantities of interest for fuel handling and safety issues are investigated, including decay heat and activities of hazardous isotopes (neutron and high energy gamma emitters) in the core and in the reprocessing stream. The radiotoxicity generation is also analyzed for the MSFR nominal conditions.
The production of helium and the depletion in tungsten content due to nuclear reactions are calculated for the nickel-based alloy selected as reactor structural material of the MSFR. These preliminary evaluations can be helpful in studying the radiation damage of both the primary salt container and the axial reflectors.
A varying degree of eccentricity always exists in the initial configuration of a nuclear fuel rod. Its impact on traditional LWR fuel is limited as the radial gap closes relatively early during ...irradiation. However, the effect of misalignment is expected to be more relevant in rods with highly conductive fuels, large initial gaps and low conductivity filling gases. In this paper, we study similar characteristics in the experimental setup of two fuel disc irradiation campaigns carried out in the OECD Halden Boiling Water Reactor. Using the multi-dimensional fuel performance code OFFBEAT, we combine 2-D axisymmetric and 3-D simulations to investigate the effect of eccentricity on the fuel temperature distribution. At the same time, we illustrate how the advent of modern tools with multi-dimensional capabilities might further improve the design and interpretation of in-pile separate-effect tests and we outline the potential of such an analysis for upcoming experiments.
This paper presents an assessment of three deterministic core simulators with the focus on the neutronic performance in steady-state calculations of small Sodium cooled Fast Reactor cores. The ...selected codes are DYN3D, PARCS and the novel multi-physics solver GeN-Foam. By using these codes, the multi-group diffusion solutions are obtained for the selected twenty control rod worth measurements performed during the isothermal physics tests of the Fast Flux Test Facility (FFTF). The identical set of homogenized few-group cross sections applied in the calculations is generated with the Serpent Monte Carlo code. The numerical results are compared with each other as well as with the measured values. The obtained numerical results, such as the multiplication factors and control rod worth values, are in good agreement as compared to the experimental data. Furthermore, a comparison of the radial power distributions is presented between DYN3D, PARCS and GeN-Foam. Ultimately, the power distributions are compared to the full core Serpent solution, demonstrating an adequate performance of the selected deterministic tools. In overall, this study presents a verification and validation of the neutronic solvers applied by DYN3D, PARCS and GeN-Foam to steady-state calculations of SFR cores.
At EPFL, the CROCUS reactor has been used to carry out experiments with vibrating fuel rods. The paper presents a first attempt to employ the measured data to validate CORE SIM+, a neutron noise ...solver developed at Chalmers University of Technology. For this purpose, the original experimental data are processed in order to extract the necessary information. In particular, detector recordings are scrutinized and detrended, and used to estimate CPSDs of detector pairs. These values are then compared with the ones derived from the CORE SIM+ simulations of the experiments. The main trend of the experimental data along with the values for some detectors are successfully reproduced by CORE SIM+. Further work is necessary on both the experimental and computational sides in order to improve the validation process.
► Multi-physics modelling for the single-channel analysis of LFR transients. ► Neutronics, thermal-elasticity and fluid-dynamics coupling in the same environment. ► Purpose-made diffusion model with ...point-wise neutron cross-sections dependence. ► Assessment of the accuracy of the neutronic model through Monte Carlo simulations. ► Steady-state and transient analyses of the ELSY single-channel.
This paper presents a multi-physics and time-dependent model for single-channel transient analysis of a Lead Fast Reactor (LFR). The work focuses on the coupling among the neutronic, the thermal-elastic and the fluid-dynamic phenomena in the considered reactor channel, benefiting from a finite-element scheme of analysis that is implemented in the same simulation environment (COMSOL Multiphysics®), and within a computational domain featured by a moving mesh. A purpose-made six-group neutron diffusion model is developed, which allows to take into account the local dependency of the neutron macroscopic cross-sections on the temperature and density fields. The potential of the multi-physics model to estimate the effective neutron multiplication factor, by means of a comparison with the Monte Carlo code SERPENT, is assessed. A special attention is given to the capability to implicitly catch the thermal-hydraulic and thermal-expansion feedbacks on reactivity, without relying on cross-sections corrective factors. The proposed multi-physics model is employed to investigate the active-core average conditions of the ELSY (European Lead cooled System) reactor, both in steady-state operation and during two transient scenarios. It is shown that the presented model represents a suitable simulation tool for a preliminary investigation of the LFR dynamics, and allows to simultaneously evaluate a wide set of the reactor channel parameters.
Modelling and simulation (M&S) have gradually become irreplaceable tools in the field of Nuclear Science and Technology (NS&T), including nuclear energy systems. This is partly due to growing ...computational resources and advances in computational science and partly to the difficulties to finance, build and license new experimental facilities. However, the utilization of M&S for research and development (R&D) and education and training (E&T) applications is somewhat hampered by limited accessibility to controlled and sensitive nuclear M&S tools as well as by the desires of the developers of these tools to retain their intellectual property (IP). Open-source software and open-access data are growingly perceived as means to accelerate innovation by promoting synergistic collaborative developments while lowering the barriers associated to code distribution, modification, and sharing. Open-source software development is ideal for R&D and E&T purposes because it permits the enhancement of understanding, the use of advanced computational methods and it promotes the cooperation among researchers and scientists, without rigorous constraints on quality assurance or reliance on proprietary data for technology-specific validation. As a fundamental research tool, this helps to mitigate constraints related to dual use of such technology. It is in this context that an initiative is being launched under the aegis of the International Atomic Energy Agency (IAEA) to promote the development and application of open-source multi-physics simulation in support of R&D and E&T in NS&T. This paper presents scope and objectives of this initiative.
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