Mesure de la réactivité de réacteurs sous-critiques pilotés par accélérateur par l'analyse d'expériences d'interruptions de faisceau programmées

Radioactive waste originating from nuclear power plants are a major societal issue. In order to reduce their radiotoxic impact on the environment, it is envisaged to incinerate minor actinides using neutron-induced nuclear reactions.The potential of Accelerator-Driven Systems (or ADS) to burn minor actinides is being investigated. Many studies, both experimental and theoretical, are being carried out to evaluate the feasibility of these hybrid systems which couple a subcritical reactor to an external neutron source. One of the points investigated concerns the reactivity of the reactor, an essential parameter for the safety of the facility, and its online monitoring that requires the evaluation of appropriate methods. This thesis deals with the analysis of the neutron population evolution over time, measured by several fission chambers located in the reactor, during short interruptions of the beam delivered by the accelerator that provides the external neutron source. Data from experiments carried out at the GUINEVERE facility located at the SCK•CEN center (Mol, Belgium) in the framework of the FREYA project (FP7 Euratom), are analyzed, then interpreted and successfully corrected using neutron transport codes. The results are discussed and used to provide recommendations regarding the use of such experiments to measure the reactivity. Finally, an interpretation of the experiments based on a modal decomposition of the neutron flux is proposed.Les déchets radioactifs produits par les centrales nucléaires électrogènes sont une source de préoccupation sociétale majeure. Afin de réduire leur impact sur l'environnement en matière de radiotoxicité, il est envisagé d'incinérer les actinides mineurs en leur faisant subir des réactions nucléaires induites par des neutrons. Ce processus présente cependant des contraintes particulières du point de vue neutronique qui justifient l'intérêt porté aux réacteurs sous-critiques pilotés par accélérateur (Accelerator-Driven Systems ou ADS). Ce type de système hybride, qui couple un réacteur sous-critique à une source externe de neutrons, fait l'objet de nombreuses activités de recherche et développement. Parmi les points étudiés, on compte la mesure en ligne de la réactivité du réacteur, paramètre essentiel à la sûreté de l'installation et qui nécessite la mise en place de méthodes adaptées. Ce travail porte sur la mesure de la réactivité à partir de l'évolution de la population neutronique, mesurée par des chambres à fission placées dans le réacteur, durant de brèves interruptions du faisceau délivré par l'accélérateur qui fournit la source externe de neutrons. Les données issues d'expériences menées auprès de l'installation GUINEVERE au centre SCK•CEN (Mol, Belgique), dans le cadre du projet FREYA du 7ème PCRD Euratom, sont ainsi analysées, puis interprétées et corrigées avec succès à l'aide de codes de transport neutronique. Les résultats obtenus sont discutés et permettent d'apporter des recommandations quant à l'utilisation d'expériences de ce type pour la mesure de la réactivité. Enfin, une interprétation des expériences basée sur une décomposition modale du flux neutronique est proposée

Mesure de la réactivité de réacteurs sous-critiques pilotés par accélérateur par l'analyse d'expériences d'interruptions de faisceau programmées

Radioactive waste originating from nuclear power plants are a major societal issue. In order to reduce their radiotoxic impact on the environment, it is envisaged to incinerate minor actinides using neutron-induced nuclear reactions.The potential of Accelerator-Driven Systems (or ADS) to burn minor actinides is being investigated. Many studies, both experimental and theoretical, are being carried out to evaluate the feasibility of these hybrid systems which couple a subcritical reactor to an external neutron source. One of the points investigated concerns the reactivity of the reactor, an essential parameter for the safety of the facility, and its online monitoring that requires the evaluation of appropriate methods. This thesis deals with the analysis of the neutron population evolution over time, measured by several fission chambers located in the reactor, during short interruptions of the beam delivered by the accelerator that provides the external neutron source. Data from experiments carried out at the GUINEVERE facility located at the SCK•CEN center (Mol, Belgium) in the framework of the FREYA project (FP7 Euratom), are analyzed, then interpreted and successfully corrected using neutron transport codes. The results are discussed and used to provide recommendations regarding the use of such experiments to measure the reactivity. Finally, an interpretation of the experiments based on a modal decomposition of the neutron flux is proposed.Les déchets radioactifs produits par les centrales nucléaires électrogènes sont une source de préoccupation sociétale majeure. Afin de réduire leur impact sur l'environnement en matière de radiotoxicité, il est envisagé d'incinérer les actinides mineurs en leur faisant subir des réactions nucléaires induites par des neutrons. Ce processus présente cependant des contraintes particulières du point de vue neutronique qui justifient l'intérêt porté aux réacteurs sous-critiques pilotés par accélérateur (Accelerator-Driven Systems ou ADS). Ce type de système hybride, qui couple un réacteur sous-critique à une source externe de neutrons, fait l'objet de nombreuses activités de recherche et développement. Parmi les points étudiés, on compte la mesure en ligne de la réactivité du réacteur, paramètre essentiel à la sûreté de l'installation et qui nécessite la mise en place de méthodes adaptées. Ce travail porte sur la mesure de la réactivité à partir de l'évolution de la population neutronique, mesurée par des chambres à fission placées dans le réacteur, durant de brèves interruptions du faisceau délivré par l'accélérateur qui fournit la source externe de neutrons. Les données issues d'expériences menées auprès de l'installation GUINEVERE au centre SCK•CEN (Mol, Belgique), dans le cadre du projet FREYA du 7ème PCRD Euratom, sont ainsi analysées, puis interprétées et corrigées avec succès à l'aide de codes de transport neutronique. Les résultats obtenus sont discutés et permettent d'apporter des recommandations quant à l'utilisation d'expériences de ce type pour la mesure de la réactivité. Enfin, une interprétation des expériences basée sur une décomposition modale du flux neutronique est proposée

Vinblastine chemotherapy in adult patients with langerhans cell histiocytosis: a multicenter retrospective study

Abstract Background Vinblastine is the standard treatment for children with Langerhans cell histiocytosis (LCH). Whether this treatment could be extended to adults with LCH is questionable. This retrospective multicenter study included 35 adult patients (median age 33 years; 23 men; 80% with multisystem LCH) who were treated with vinblastine + steroids as a first-line chemotherapy and followed for a median time of 83 months. The objectives were to determine the overall response rate (based on the Histiocyte Society criteria), disease reactivation rate, toxicity, permanent consequences, and survival rate corresponding to this treatment. The lung involvement outcome was based on serial lung function tests. The distribution of right-censored end points was estimated by the Kaplan-Meier method. Univariate Cox model with time-fixed and time-varying covariates was used for the predictive analysis of reactivation in the responders. Univariate analyses of risk factors for neurotoxicity were based on nonparametric Wilcoxon rank sum tests and exact Fisher tests. Results The median duration of the first course of vinblastine was 7.6 months, with a median cumulative dose of 160 mg [IQR 120–212]. Seventy percent of the patients were responders at the end of this treatment. Subsequently, LCH reactivation occurred with a 5-year cumulative incidence of 40%. During the study, 27 reactivations were observed in 17 patients, and half of these episodes were retreated with vinblastine. At the end of the last vinblastine treatment, 70% of the patients were responders. None of the patients with impaired lung function improved. No grade 3–4 peripheral neuropathy was observed. At the final vinblastine treatment, permanent LCH consequences, primarily pituitary stalk involvement, were present in 15 (43%) patients, and all were present at the time of vinblastine initiation. The 10-year survival rate was 86.2% (95CI, 71.8–100%), and the 2 patients who died from LCH had risk organ localizations. Conclusions Vinblastine is an effective and well-tolerated first-line treatment for adult LCH except in patients with lung involvement and impaired lung function. However, a significant portion of patients experienced LCH reactivation during long-term follow up. As in childhood LCH, the presence of risk organ involvement has a negative impact on patient prognosis

Monte Carlo MSM correction factors for control rod worth estimates in subcritical and near-critical fast neutron reactors

The GUINEVERE project was launched in 2006, within the 6th Euratom Framework Program IP-EUROTRANS, in order to study the feasibility of transmutation in Accelerator Driven subcritical Systems (ADS). This zero-power facility hosted at the SCK·CEN site in Mol (Belgium) couples the fast subcritical lead reactor VENUS-F with an external neutron source provided by interaction of deuterons delivered by the GENEPI-3C accelerator and a tritiated target located at the reactor core center. In order to test on-line subcriticality monitoring techniques, the reactivity of all the VENUS-F configurations used must be known beforehand to serve as benchmark values. That is why the Modified Source Multiplication Method (MSM) is under consideration to estimate the reactivity worth of the control rods when the reactor is largely subcritical as well as near-critical. The MSM method appears to be a technique well adapted to measure control rod worth over a large range of subcriticality levels. The MSM factors which are required to account for spatial effects in the reactor can be successfully calculated using a Monte Carlo neutron transport code

Effects of Fluid Resuscitation With Colloids vs Crystalloids on Mortality in Critically Ill Patients Presenting With Hypovolemic Shock

International audienceIMPORTANCE:Evidence supporting the choice of intravenous colloid vs crystalloid solutions for management of hypovolemic shock remains unclear.OBJECTIVE:To test whether use of colloids compared with crystalloids for fluid resuscitation alters mortality in patients admitted to the intensive care unit (ICU) with hypovolemic shock.DESIGN, SETTING, AND PARTICIPANTS:A multicenter, randomized clinical trial stratified by case mix (sepsis, trauma, or hypovolemic shock without sepsis or trauma). Therapy in the Colloids Versus Crystalloids for the Resuscitation of the Critically Ill (CRISTAL) trial was open label but outcome assessment was blinded to treatment assignment. Recruitment began in February 2003 and ended in August 2012 of 2857 sequential ICU patients treated at 57 ICUs in France, Belgium, North Africa, and Canada; follow-up ended in November 2012.INTERVENTIONS:Colloids (n = 1414; gelatins, dextrans, hydroxyethyl starches, or 4% or 20% of albumin) or crystalloids (n = 1443; isotonic or hypertonic saline or Ringer lactate solution) for all fluid interventions other than fluid maintenance throughout the ICU stay.MAIN OUTCOMES AND MEASURES:The primary outcome was death within 28 days. Secondary outcomes included 90-day mortality; and days alive and not receiving renal replacement therapy, mechanical ventilation, or vasopressor therapy.RESULTS:Within 28 days, there were 359 deaths (25.4%) in colloids group vs 390 deaths (27.0%) in crystalloids group (relative risk [RR], 0.96 [95% CI, 0.88 to 1.04]; P = .26). Within 90 days, there were 434 deaths (30.7%) in colloids group vs 493 deaths (34.2%) in crystalloids group (RR, 0.92 [95% CI, 0.86 to 0.99]; P = .03). Renal replacement therapy was used in 156 (11.0%) in colloids group vs 181 (12.5%) in crystalloids group (RR, 0.93 [95% CI, 0.83 to 1.03]; P = .19). There were more days alive without mechanical ventilation in the colloids group vs the crystalloids group by 7 days (mean: 2.1 vs 1.8 days, respectively; mean difference, 0.30 [95% CI, 0.09 to 0.48] days; P = .01) and by 28 days (mean: 14.6 vs 13.5 days; mean difference, 1.10 [95% CI, 0.14 to 2.06] days; P = .01) and alive without vasopressor therapy by 7 days (mean: 5.0 vs 4.7 days; mean difference, 0.30 [95% CI, -0.03 to 0.50] days; P = .04) and by 28 days (mean: 16.2 vs 15.2 days; mean difference, 1.04 [95% CI, -0.04 to 2.10] days; P = .03).CONCLUSIONS AND RELEVANCE:Among ICU patients with hypovolemia, the use of colloids vs crystalloids did not result in a significant difference in 28-day mortality. Although 90-day mortality was lower among patients receiving colloids, this finding should be considered exploratory and requires further study before reaching conclusions about efficacy