Nowadays, several integral Pressurised Water Reactor (iPWR) designs are close to the licencing stage since they are based on the well-established technology of large Light Water Reactors (LWRs), incorporating evolutionary design features aimed at enhancing the inherent safety of the plant through integral configurations and adoption of passive safety systems. However, a sound demonstration of iPWRs’ capability to address Severe Accident (SA) should be carried out for a comprehensive safety review process. In this context, the international scientific community is increasingly focusing on assessing SA integral codes in simulating typical iPWRs’ phenomenology during postulated accidental scenarios. The Horizon Euratom project “Safety Analysis of SMR with Passive Mitigation strategies – Severe Accident” (SASPAM – SA), coordinated by ENEA, investigates the applicability, the transfer of the large LWR knowledge and know-how to iPWRs, in view of SA and Emergency Planning Zone (EPZ) licensing analyses needs. In this regard, the present work carried out within the SASPAM-SA project presents a comparative analysis between the SA codes MELCOR and ASTEC. The goal of the study is to evaluate the capability of the codes in simulating the dominant thermal–hydraulic phenomena during a postulated Design Basis Accident (DBA) scenario in a generic 300 MWe iPWR, considering the full availability of the reactor passive safety systems. The code-to-code benchmark highlights the main consistencies and possible discrepancies between the codes.
In this paper, a mechanism-based continuum damage model for the in-plane analysis of masonry structures is presented. Each of the considered damage mechanisms is characterized by a damage criterion ruled by few mechanical parameters easily obtainable from small-scale tests on masonry components. In the proposed model, the most prominent ones, involving opening/sliding of the joints and failure of the bulk, are taken into account. A decomposition of the strains into mechanism-relevant contributions is introduced, leading to the definition of a set of five damage variables governed by cohesive-frictional laws. An ad-hoc damage activation strategy is devised to guarantee that the active damage mechanisms are independent of each other. Accordingly, the evolution of each single damage variable can be independently evaluated following its closed-form evolution law. The set of the active damage variables rules the evolution of the constitutive matrix coefficients, resulting in a secant orthotropic damage model. The numerical implementation of the proposed damage model resorts to a mixed strain–displacement finite element formulation, already proved effective to deal with mesh dependency issues. The proposed model is tested on several masonry shear wall benchmarks and compared with a state-of-the-art damaging block-based model adopted as reference. A good agreement is obtained between the two models in terms of peak loads, post-peak evolution and damage mechanisms evolutions.
Hydrothermal carbonisation (HTC) of lignocellulose could improve its pyrolytic behaviour, but to date, few studies have evaluated the effect of HTC (150 degrees C and 200 degrees C) on fast pyrolysis. To fill this gap, this paper investigated how HTC affects the chemical composition of fir sawdust and, in turn, how these changes affect biooil yield and composition. HTC significantly alters the chemical properties of the solid material, affecting the content and acetylation degree of hemicellulose while removing inorganics (primarily K2O and CaO). Whereas the relative mass yield of pyrolysis products was not strongly affected by HTC, the pyrolytic behaviour was influenced by the HTC pre-treatment. HTC alters the rheological behaviour of the reacting material during fast pyrolysis, yielding hydrochar that displays an apparently melting and bed agglomeration, similarly to pure lignin, with ultimate fluidisation impairment. Fast pyrolysis products were characterised with an array of analytical techniques, allowing for the identification of changes in pyrolysis pathways and providing the tentative identification of novel holocellulose-derived oligomers in the aqueous phase portion of bio-oil. Beyond the obvious effects related to hemicellulose removal/deacetylation, results showed a meaningful change in biooil composition, with a strong increase in the share of anhydrosugars, which may be due to ash removal. Pyrolytic lignin was the least affected fraction, presenting only a slight reduction in molecular weight and a slight demethoxylation of its components. Results show that HTC at 150 degrees C/200 degrees C extracts or hydrolyses part or all of the hemicellulose and converts biomass into a material with different pyrolytic behaviour. In particular, hydrochar obtained at 200 degrees C behaves similarly to a heterogeneous mixture of pure lignin and cellulose, highlighting the approach's potential (increased selectivity toward anhydrosugars) and pitfalls (in-bed melting of the material).
Growing interest in sustainable bio-lubricants as alternatives to conventional mineral oils has increased the demand for renewable feedstocks that do not compete with agricultural land use. In this study, waste cooking oil (WCO) was chemically modified through transesterification/partial hydrogenation (H-FAME), partial hydrogenation (H-WCO_l and H-WCO), estolide formation (E-WCO), and epoxidation (EOs) followed by ethanol ringopening (POs) to produce potential bio-lubricants. The thermal, physicochemical, and rheological properties of the resulting products were evaluated and compared with a commercial mineral lubricant (ISO VG 46), representative of oils used in industrial hydraulic systems. Tribological tests were performed as a preliminary comparative screening to determine friction and wear behaviour under selected pin-on-disc conditions. The WCO-derived products exhibited a broad range of properties depending on the applied chemical modification. Most samples showed thermal stability in air equal to or greater than ISO VG 46. Rheological analysis over 25-100 degrees C revealed Newtonian behaviour for H-FAME and POs, while E-WCO and EOs exhibited shearthinning behaviour, indicating fluid-like and grease-like structures, respectively. Kinematic viscosity at 40 degrees C ranged from 3.61 to 286 cSt, with polyols (POs) displaying viscosity indices between 111 and 133, exceeding that of ISO VG 46 (107). Friction coefficients were similar across all samples, although WCO, H-WCO_l, and H-WCO showed slightly lower values. Wear testing demonstrated comparable or reduced wear for E-WCO and almost fully epoxidized oil (EO_100) relative to ISO VG 46. These results highlight the potential of WCO-derived products as sustainable bio-lubricant candidates with tuneable properties, while further tribological testing under varied load, speed, and temperature conditions will be required to assess their application-specific performance.
We collect several results related to the Symmetrized Fractional Variation model for signal and image denoising (shortly denoted SFV): a variational approach based on L1 fitting data term together with regularizing terms exploiting a distributional version of Riemann-Liouville fractional derivatives. We enhance the analysis of the one-dimensional case through the study of the space BV*s of admissible signals on a bounded interval, say the functions with bounded variation of both sides fractional derivatives for a prescribed real positive order s. We show that the embedding in BV*s of the Sobolev space of the same fractional order is strict. We exhibit some nontrivial borderline examples of admissible or non admissible functions in the space BV*s. We prove several relationships between related fractional calculus and the integral transforms. The SFV model is discretized based on a second-order consistent Grunwald Letnikov scheme and coupled with an automatic selection procedure of all model parameters relying on the whiteness principle: some numerical simulations are presented to show the efficacy of the proposed approach in denoising one-dimensional signals corrupted by impulsive noise modelled by the Laplace distribution.
