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Considering the world energy demand increase in order to fulfill an environmental and economic sustainability, the energy policy of each country has to diversify the sources of energy and use stable, safe energy production option able of producing electricity in a clean way contributing in cutting the CO2 emission. In the framework of the sustainable development, today the use of advanced nuclear power plant, have an important role in the environmental and economic sustainability of country energy strategy. In the last 20 years, in fact, the international community, taking into account the operational experience of the nuclear reactors, starts the development of new advanced reactor designs considering also the use of natural circulation for the cooling of the core in normal and transient conditions. In this framework, Oregon State University (OSU) has constructed, under a U.S. Department of Energy grant, a system level test facility to examine natural circulation phenomena characterizing the Multi-Application Small Light Water Reactor (MASLWR) design, a small modular integral pressurized light water reactor relying on natural circulation during both steady state and transient operation. It includes an integrated helical coil steam generator as well. Starting from an experimental campaign in support of the MASLWR concept design verification, the planned work, will be not only to specifically investigate the concept design further but also advance the broad understanding of integral natural circulation reactor plants and accompanying passive safety features as well. An IAEA International Collaborative Standard Problem (ICSP) on “Integral PWR Design Natural Circulation Flow Stability and Thermo-hydraulic Coupling of Containment and Primary System During Accidents” is hosting at OSU and the experimental data will be developed at the OSU-MASLWR facility. The purpose of this IAEA ICSP is to provide experimental data on single/two-phase flow instability phenomena under natural circulation conditions and coupled containment/reactor vessel behavior in integral-type light water reactors. These data can be used to assess thermal hydraulic codes for reactor system design and analysis as well. The first planned test investigates a stepwise reduction in the primary mass inventory of the facility while operating at reduced power (decay power). The second planned test, investigates a loss of feed water transient with subsequent primary blowdown due to automatic depressurization system actuation and long term cooling phase. The target of this paper is to contribute to the thermal hydraulic analysis of the expected phenomena of these transients on the basis of the TRACE V5 Patch 01 calculated data developed during the double-blind phase of the ICSP.

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In order to reduce the spread of SARS-CoV-2 infection and the burden of disease, since 27 December 2020, Sicily has introduced a regional COVID-19 vaccination campaign. This study aimed at estimating the effectiveness of mRNA COVID-19 vaccines on SARS-CoV-2 infections and COVID-19. A retrospective cohort study was carried out on 3,966,976 Sicilian adults aged 18 years or more, who were followed-up from 1 January 2021 to 30 September 2021. The risk of SARS-CoV-2 infection, severe COVID-19, and COVID-19 death or intubation during the study period was compared among vaccinated with two mRNA doses and unvaccinated individuals. Cox regression, adjusted for age and sex, and a joint-point analysis on rate trends were performed. Overall, 2,469,320 (62.2%) subjects have been vaccinated and a total of 103,078 (2.6% of the entire population) SARS-CoV-2-positive subjects have been observed including 4693 (0.12%) severe COVID-19, 277 (0.01%) intubated, and 2649 (0.07%) deaths. After two months from vaccination, adjusted vaccine effectiveness was 81.3% against SARS-CoV-2 infection, 96.1% against severe COVID-19, and 93.4% against intubation/death. During the eight-month follow-up, statistically significant decreasing effectiveness trends were observed for all the evaluated outcomes (−4.76% per month against SARS-CoV-2 infection; −2.27% per month against severe COVID-19 and −2.26% per month against COVID-19 intubation/death). The study results confirm that mRNA COVID-19 vaccines have high real-world effectiveness, especially in the first months after vaccination. The vaccine effectiveness decreases over time and, even if the decrease is relatively small against severe outcomes, the increasing protection wane suggests the need for booster vaccination campaigns.

BACKGROUND AND OBJECTIVES On June 4, 2021, Italy launched the COVID-19 vaccination of adolescents to pace down the COVID-19 spread. Although clinical trials have evaluated mRNA vaccine effectiveness in adolescents, there is limited literature on its real-world effectiveness. Accordingly, this study aimed to estimate the effectiveness of mRNA COVID-19 vaccines against SARS-CoV-2 infection and mild or severe COVID-19 in a cohort of Sicilian adolescents within a six-month observation period. METHODS A retrospective cohort study was conducted with adolescents aged 12–18, residents of Sicily, that were followed from July 15 to December 31, 2021. SARS-CoV-2 infections, mild and severe COVID-19, and COVID-19-related intubation or deaths during the study period were compared between subjects vaccinated with two doses of mRNA vaccines and unvaccinated individuals. The Cox regression analysis, adjusted for age and sex, was performed to compare the two groups. RESULTS Overall, the study included a total at-risk population of 274,782 adolescents with 61.4% (168,633) of them having completed the vaccination cycle by the end of the study. Unvaccinated subjects had higher incidence rates of SARS-CoV-2 (1,043 x 10,000 vs. 158.7 x 10,000 subjects), mild COVID-19 (27.7 x 10,000 vs. 1.8 x 10,000 subjects) and severe COVID-19 (1.41 x 10,000 vs. 0 subjects) compared to the vaccinated population. The estimated adjusted vaccine effectiveness against SARS-CoV-2 infection was 71.2%, reaching 92.1% and 97.9% against mild and severe COVID-19, respectively. CONCLUSIONS This study provides rigorous evidence of the mRNA COVID-19 vaccines effectiveness in protecting adolescents from both SARS-CoV-2 infection, and mild or severe COVID-19.