| 1. |
- Ferrando, Carlos, et al.
(författare)
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Effects of oxygen on post-surgical infections during an individualised perioperative open-lung ventilatory strategy : a randomised controlled trial
- 2020
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Ingår i: British Journal of Anaesthesia. - : ELSEVIER SCI LTD. - 0007-0912 .- 1471-6771. ; 124:1, s. 110-120
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Tidskriftsartikel (refereegranskat)abstract
- Background: We aimed to examine whether using a high fraction of inspired oxygen (FIO2) in the context of an individualised intra- and postoperative open-lung ventilation approach could decrease surgical site infection (SSI) in patients scheduled for abdominal surgery. Methods: We performed a multicentre, randomised controlled clinical trial in a network of 21 university hospitals from June 6, 2017 to July 19, 2018. Patients undergoing abdominal surgery were randomly assigned to receive a high (0.80) or conventional (0.3) FIO2 during the intraoperative period and during the first 3 postoperative hours. All patients were mechanically ventilated with an open-lung strategy, which included recruitment manoeuvres and individualised positive end-expiratory pressure for the best respiratory-system compliance, and individualised continuous postoperative airway pressure for adequate peripheral oxyhaemoglobin saturation. The primary outcome was the prevalence of SSI within the first 7 postoperative days. The secondary outcomes were composites of systemic complications, length of intensive care and hospital stay, and 6-month mortality. Results: We enrolled 740 subjects: 371 in the high FIO2 group and 369 in the low FIO2 group. Data from 717 subjects were available for final analysis. The rate of SSI during the first postoperative week did not differ between high (8.9%) and low (9.4%) FIO2 groups (relative risk [RR]: 0.94; 95% confidence interval [CI]: 0.59-1.50; P=0.90]). Secondary outcomes, such as atelectasis (7.7% vs 9.8%; RR: 0.77; 95% CI: 0.48-1.25; P=0.38) and myocardial ischaemia (0.6% [n=2] vs 0% [n=0]; P=0.47) did not differ between groups. Conclusions: An oxygenation strategy using high FIO2 compared with conventional FIO2 did not reduce postoperative SSIs in abdominal surgery. No differences in secondary outcomes or adverse events were found.
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| 2. |
- Estévez-Albuja, S., et al.
(författare)
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Modelling of a Nordic BWR containment and suppression pool behavior during a LOCA with GOTHIC 8.1
- 2020
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Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 136
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Tidskriftsartikel (refereegranskat)abstract
- Boiling water reactors use the Pressure Suppression Pool (PSP) to relieve the containment pressure in case of an accident. During the event of a Loss of Coolant Accident (LOCA), drywell air and steam are injected into the PSP through blowdown pipes. This may lead to thermal stratification, which is a relevant safety issue as it leads to higher water surface temperatures than in mixed conditions and thus, to higher containment pressures. The Effective Heat (EHS) and Momentum (EMS) Source models were previously introduced to predict the effect of small-scale direct contact condensation phenomena on the large-scale pool water circulation. In this paper, the EHS/EMS models are extended by adding the effect of non-condensable gases on the chugging regime. The EHS/EMS models are implemented in the GOTHIC code to model a full-scale Nordic BWR containment under different LOCA scenarios. The results show that thermal stratification can be developed in the PSP.
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| 3. |
- Ferrando, Carlos, et al.
(författare)
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A noninvasive postoperative clinical score to identify patients at risk for postoperative pulmonary complications : the Air-Test Score
- 2020
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Ingår i: Minerva Anestesiologica. - : EDIZIONI MINERVA MEDICA. - 0375-9393 .- 1827-1596. ; 86:4, s. 404-415
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Postoperative pulmonary complications (PPCs) negatively affect morbidity, healthcare costs and postsurgical survival. Preoperative and intraoperative peripheral oxyhemoglobin saturation (SpO(2)) levels are independent risk factors for postoperative pulmonary complications (PPCs). The air-test assesses the value of SpO(2) while breathing room-air. We aimed at building a clinical score that includes the air-test for predicting the risk for PPCs. METHODS: This is a development and validation study in patients -randomly divided into two cohorts- from a large randomized clinical trial (iPROVE) that enrolled 964 intermediate-to-high risk patients scheduled for abdominal surgery. Arterial oxygenation was assessed on room-air in the preoperative period (preoperative air-test) and 3h after admission to the postoperative care unit (postoperative air-test). The air-test was defined as positive or negative if SpO(2) was <= 96% or >96%, respectively. Positive air-tests were stratified into weak (93-96%) or strong (<93%). The primary outcome was a composite of moderate-to-severe PPCs during the first seven postoperative days. RESULTS: A total of 902 patients were included in the final analysis (542 in the development cohort and 360 in the validation cohort). Regression analysis identified five independent risk factors for PPC: age. type of surgery, pre- and postoperative air-test, and atelectasis. The area under the receiver operating characteristic curve (AUC) was 0.79 (95% CI: 0.75-0.82) when including these five independent predictors. We built a simplified score termed "air-test score" by using only the pre- and postoperative SpO(2) , resulting in an AUC of 0.72 (95% CI: 0.67-0.76) for the derivation and 0.72 (95% CI: 0.66-0.78) for the validation cohort, respectively. The air-test score stratified patients into four levels of risk, with PPCs ranging from <15% to >75%. CONCLUSIONS: The simple, non-invasive and inexpensive bedside air-test score, evaluating pre- and postoperatively SpO(2) measured on room-air, helps to predict the risk for PPCs.
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| 4. |
- Gallego-Marcos, Ignacio, et al.
(författare)
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Effective momentum induced by steam condensation in the oscillatory bubble regime
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The spargers used in Boiling Water Reactors (BWR) discharge steam from the primary coolant system into a pool of water. Direct steam condensation in subcooled water creates sources of heat and momentum determined by the condensation regimes, called “effective sources” in this work. Competition between the effective sources can result in thermally stratification or mixing of the pool. Thermal stratification is a safety concern in BWRs since it reduces the steam condensation and pressure suppression capacity of the pool. In this work, we present semi-empirical correlations to predict the effective momentum induced by steam condensation in the oscillatory bubble regime, relevant for the operation of spargers in BWRs. A Separate Effect Facility (SEF) was designed and built at LUT, Finland, in order to provide the necessary data. An empirical correlation for the effective momentum as a function of the Jakob number is proposed. The Kelvin Impulse theory was also applied to estimate the effective momentum based on information about the bubble dynamics. To do this, new correlations for the bubble collapse frequencies, maximum bubble radius, velocities, pressure gradient and heat transfer coefficient are proposed and compared to available data from the literature. The effective momentum induced by sonic steam jets appears to be constant in a wide range of studied Jakob number. However, further experimental data is necessary at larger Jakob numbers and steam mass fluxes.
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| 5. |
- Gallego-Marcos, Ignacio, et al.
(författare)
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Effective momentum induced by steam condensation in the oscillatory bubble regime
- 2019
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 350, s. 259-274
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Tidskriftsartikel (refereegranskat)abstract
- The spargers used in Boiling Water Reactors (BWR) discharge steam from the primary coolant system into a pool of water. Direct steam condensation in subcooled water creates sources of heat and momentum determined by the condensation regimes, called “effective sources” in this work. Competition between the effective sources can result in thermally stratification or mixing of the pool. Thermal stratification is a safety concern in BWRs since it reduces the steam condensation and pressure suppression capacity of the pool. In this work, we present semi-empirical correlations to predict the effective momentum induced by steam condensation in the oscillatory bubble regime, relevant for the operation of spargers in BWRs. A Separate Effect Facility (SEF) was designed and built at LUT, Finland, in order to provide the necessary data. An empirical correlation for the effective momentum as a function of the Jakob number is proposed. The Kelvin Impulse theory was also applied to estimate the effective momentum based on information about the bubble dynamics. To do this, new correlations for the bubble collapse frequencies, maximum bubble radius, velocities, pressure gradient and heat transfer coefficient are proposed and compared to available data from the literature. The effective momentum induced by sonic steam jets appears to be constant in a wide range of studied Jakob number. However, further experimental data is necessary at larger Jakob numbers and steam mass fluxes.
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| 6. |
- Gallego-Marcos, Ignacio, et al.
(författare)
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Modeling of Thermal Stratification and Mixing in a Pressure Suppression Pool Using GOTHIC
- 2016
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Konferensbidrag (refereegranskat)abstract
- The development of thermal stratification in the pressure suppression pool of a BWR is a safety issue since it can lead to higher containment pressures than in completely mixed conditions. The thermal hydraulic code of GOTHIC offers a very suitable platform to simulate the pool and containment behavior during a long term accident. However, for a computationally efficient code such as GOTHIC, direct contact condensation cannot be resolved accurately enough to obtain a good estimation of the momentum induced by the condensing steam, and thus, to predict the pool behaviour. In this paper, we present how to implement the previously validated Effective Heat Source (EHS) and Effective Momentum Source (EMS) models, developed for pool analysis during a steam injection, in GOTHIC. The implementation was done using control variables and Dynamically Linked Libraries (DLL). A time averaging model to minimize the effect of the numerical oscillations appearing in GOTHIC when steam is injected into the pool is also proposed.
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| 7. |
- Gallego-Marcos, Ignacio, et al.
(författare)
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Modeling of Thermal Stratification and Mixing Induced by Steam Injection Through Spargers Into a Large Water Pool
- 2016
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Konferensbidrag (refereegranskat)abstract
- The pressure suppression pool of a Boiling Water Reactor (BWR) is designed to protect the containment from over pressure by condensing steam. Under certain steam injection conditions, thermal stratification can develop in the pool and significantly reduce its pressure suppression capacity. In this work, we propose a model to simulate the pool behavior during a steam injection through spargers, which are multi-hole injection pipes connecting the main steam lines to the wetwell pool. The aim of the model is to predict the global pool behavior. Effective Heat and Momentum Sources (EHS/EMS) approach is used to model time averaged effects of small scale direct contact condensation phenomena on the large scale pool circulation. The model was implemented in Fluent 16.2 and validated against experimental data obtained in PANDA facility at PSI (Switzerland). The scaling of the experiments was done to address the most important physical phenomena that can occur in plant scale. The results show that the global pool behavior can be predicted using the Standard Gradient Diffusion Hypothesis (SGDH) in k-Omega turbulence model.
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| 8. |
- Gallego Marcos, Ignacio, et al.
(författare)
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Modelling of pool stratification and mixing induced by steam injectionthrough blowdown pipes
- 2018
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Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 112, s. 624-639
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Tidskriftsartikel (refereegranskat)abstract
- Containment overpressure is prevented in a Boiling Water Reactor (BWR) by condensing steam into thepressure suppression pool. Steam condensation is a source of heat and momentum. Competition betweenthese sources results in thermal stratification or mixing of the pool. The interplay between the sources isdetermined by the condensation regime, steam mass flow rate and pool dimensions. Thermal stratificationis a safety issue since it limits the condensing capacity of the pool and leads to higher containmentpressures in comparison to a completely mixed pool with the same average temperature. The EffectiveHeat Source (EHS) and Effective Momentum Source (EMS) models were previously developed for predictingthe macroscopic effect of steam injection and direct contact condensation phenomena on the developmentof stratification and mixing in the pool. The models provide the effective heat and momentumsources, depending on the condensation regimes. In this work we present further development of theEHS/EMS models and their implementation in the GOTHIC code for the analysis of steam injection intocontainment drywell and venting into the wetwell through the blowdown pipes. Based on thePPOOLEX experiments performed in Lappeenranta University of Technology (LUT), correlations arederived to estimate the steam condensation regime and effective heat and momentum sources as functionsof the pool and steam injection conditions. The focus is on the low steam mass flux regimes withcomplete condensation inside the blowdown pipe or chugging. Validation of the developed methodswas carried out against the PPOOLEX MIX-04 and MIX-06 tests, which showed a very good agreementbetween experimental and simulation data on the pool temperature distribution and containmentpressure.
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| 9. |
- Gallego-Marcos, Ignacio, et al.
(författare)
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Pool stratification and mixing during a steam injection through spargers: analysis of the PPOOLEX and PANDA experiments
- 2018
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Ingår i: Nuclear Engineering and Design. - : Elsevier. - 0029-5493 .- 1872-759X. ; 337, s. 300-316
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Tidskriftsartikel (refereegranskat)abstract
- Spargers are multi-hole injection pipes used in Boiling Water Reactors (BWR) and Advanced Pressurized (AP) reactors to condense steam in large water pools. A steam injection induces heat, momentum and mass sources that depend on the steam injection conditions and can result in thermal stratification or mixing of the pool. Thermal stratification reduces the steam condensation capacity of the pool, increases the pool surface temperature and thus the containment pressure. Development of models with predictive capabilities requires the understanding of basic phenomena that govern the behavior of the complex multi-scale system. The goals of this work are (i) to analyze and interpret the experiments on steam injection into a pool through spargers performed in the large-scale facilities of PPOOLEX and PANDA, and (ii) to discuss possible modelling approaches for the observed phenomena. A scaling approach was developed to address the most important physical phenomena and regimes relevant to prototypic plant conditions. The focus of the tests was on the low steam mass flux and oscillatory bubble condensation regimes, which are expected during a long-term steam injection transient, e.g. in the case of a Station Black Out (SBO). Exploratory tests were also done for chugging and stable jet conditions. The results showed a similar behavior in PPOOLEX and PANDA in terms of jet induced by steam condensation, pool stratification, and development of hot layer and erosion of the cold one. A correlation using the Richardson number is proposed to model the erosion rate of the cold layer as a function of the pool dimensions and steam injection conditions.
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| 10. |
- Gallego-Marcos, Ignacio, et al.
(författare)
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Pool stratification and mixing induced by steam injection through spargers : CFD modelling of the PPOOLEX and PANDA experiments
- 2019
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Ingår i: Nuclear Engineering and Design. - : ELSEVIER SCIENCE SA. - 0029-5493 .- 1872-759X. ; 347, s. 67-85
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Tidskriftsartikel (refereegranskat)abstract
- Spargers are multi-hole injection pipes used in Boiling Water Reactors (BWR) and Generation III/III+ Pressurized Water Reactors (PWR) to condense steam in large water pools. During the steam injection, high pool surface temperatures induced by thermal stratification can lead to higher containment pressures compared with completely mixed pool conditions, the former posing a threat for plant safety. The Effective Heat Source (EHS) and Effective Momentum Source (EMS) models were previously developed and validated for the modelling of a steam injection through blowdown pipes. The goal of this paper is to extend the EHS/EMS model capabilities towards steam injection through multi-hole spargers. The models are implemented in ANSYS Fluent 17.0 Computational Fluid Dynamics (CFD) code and calibrated against the spargers experiments performed in the PPOOLEX and PANDA facilities, analysed by the authors in Gallego-Marcos et al. (2018b). CFD modelling guidelines are established for the adequate simulation of the pool behaviour. A new correlation is proposed to model the turbulent production and dissipation caused by buoyancy. Sensitivity studies addressing the effect of different assumptions on the effective momentum magnitude, profile, angle and turbulence are presented. Calibration of the effective momentum showed an inverse proportionality to the sub-cooling. Differences between the effective momentum calibrated for PPOOLEX and PANDA are discussed. Analysis of the calculated flow above the cold stratified layer showed that the erosion of the layer is induced by the action of turbulence rather than mean shear flow.
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