Results 1 - 10 of 2083
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[en] Plant traits reflect their evolutionary history and influence physiological processes (Reich 2014). For example, the embolism risk taken by plants, called the embolism safety margin, is a good predictor of stomatal conductance, and hence photosynthesis (Skelton et al. 2015). Trait-science has grown dramatically in the last decade as we have found universal patterns governing the carbon and nutrient economies of plants (Bloom et al. 1985). Perhaps the greatest value of studying plant functional traits is that they yield understanding of plant functional processes.
[en] This report includes the description and development plan for a Risk Informed Safety Margins Characterization (RISMC) toolkit and methodology that will evaluate multihazard risk in an integrated manner to support the operating nuclear fleet.
[en] The Fukushima accident occurred quite simultaneously with the launching of ASTRID preconceptual design phase (March 2011). Thus the workprogram has been able to take into account the main lessons from the Fukushima accident at the very early stages of ASTRID project. The paper presents the main lessons retained from the Fukushima accident, and the safety orientations deduced for ASTRID design. The major items are identified with a focus on the consideration of natural hazards, and the post-accidental management. On each item, safety orientations defined for ASTRID are presented. One of the most important orientation concerns the consideration of extreme natural hazards with the objective to increase safety margin before cliff-edge effect in terms of radiological releases into the environment. Principles for identifying among the safety provisions a “hardened safety core” of features resistant to extreme natural hazards are described. In this context, favorable intrinsic behavior of the concept is underlined. (author)
[en] According to the president of the French ASN (Authority of Nuclear Safety) there is a before and an after Fukushima and the most important lesson learnt from Fukushima is that we have to increase in a short-term basis the robustness of the facilities beyond the safety margins they already have in order to be able to face extreme situations. ASN is willing to impose to nuclear facility operators 4 dispositions: 1) the implementation of a core of dispositions that will assure vital functions in any situation; 2) the creation of a rapid intervention force that will be able to bring extra means in cooling, power and assistance to any damaged nuclear facility in a very short time; 3) the implementation of new dispositions to reduce the risk of dewatering of the fuel assemblies in spent fuel pools; and 4) the realization of feasibility studies for new equipment to protect underground waters in case of a sever accident in a nuclear facility. (A.C.)
[en] In France the seismic risk in the design of nuclear facilities is taken into account through regulations, rules and design criteria that are stricter than for other installations even dams. Benchmarks and feedback experiences from seismic areas from around the world have shown high resistance to earthquakes particularly for building and piping. Nevertheless it appears weaknesses on the electric equipment side like electrical cabinets or electrical relays. All the studies show that the standards for the dimensioning of nuclear structures provide large safety margins. (A.C.)
[en] In radiation therapy, a plan is robust if the calculated and the delivered dose are in agreement, even in the case of different uncertainties. The current practice is to use safety margins, expanding the clinical target volume sufficiently enough to account for treatment uncertainties. This, however, might not be ideal for proton therapy and in particular when using intensity modulated proton therapy (IMPT) plans as degradation in the dose conformity could also be found in the middle of the target resulting from misalignments of highly in-field dose gradients. Single field uniform dose (SFUD) and IMPT plans have been calculated for different anatomical sites and the need for margins has been assessed by analyzing plan robustness to set-up and range uncertainties. We found that the use of safety margins is a good way to improve plan robustness for SFUD and IMPT plans with low in-field dose gradients but not necessarily for highly modulated IMPT plans for which only a marginal improvement in plan robustness could be detected through the definition of a planning target volume.
[en] Changes of reload core design for economic efficiency, such as extended reload cycle, power uprate and license renewal, can cause the changes in safety margins, peak power and burn-up trends in the core. The changes of reload core design can increase the risk of various kinds of unusual core power distribution such as AOA (Axial Offset Anomaly) and, at worst, CILC (Crud Induced Localized Corrosion). In short, because the importance of reload fuel change management is emerging as a major configuration management issue, nuclear utilities should have an appropriate self-review and work process for reload design or reload fuel change management. From this background, this study will be conducted by choosing the US utility Exelon as a leading fuel management organization and comparing their fuel change package and reload design management know-how with our core group
[en] This report describes the work that has been performed on flooding fragility, both the experimental tests being carried out and the probabilistic fragility predictive models being produced in order to use the text results. Flooding experiments involving full-scale doors have commenced in the Portal Evaluation Tank. The goal of these experiments is to develop a full-scale component flooding experiment protocol and to acquire data that can be used to create Bayesian regression models representing the fragility of these components. This work is in support of the Risk-Informed Safety Margin Characterization (RISMC) Pathway external hazards evaluation research and development.
[en] Original intent: The original intent of this task was ''support of the Risk-Informed Safety Margin Characteristic (RISMC) methodology in order'' ''to address ... efficiency of computation so that more accurate and cost-effective techniques can be used to address safety margin characterizations'' (S. M. Hess et al., ''Risk-Informed Safety Margin Characterization,'' Procs. ICONE17, Brussels, July 2009, CD format). It was intended that ''in Task 1 itself this improvement will be directed toward upon the very important issue of Loss of Offsite Power (LOOP) events,'' more specifically toward the challenge of efficient computation of the multidimensional nonrecovery integral that has been discussed by many previous contributors to the theory of nuclear safety. It was further envisioned that ''three different computational approaches will be explored,'' corresponding to the three subtasks listed below; deliverables were tied to the individual subtasks.
[en] As a consequence of the Fukushima accident, all the operators of nuclear facilities in France were asked by IRSN (Institute for radiation protection and nuclear safety) to perform a complementary safety assessment (CSA) of their installation in case of extreme situations (seism, flood, loss of coolant...). IRSN presents its approach for the analysis of the CSA reports. The main aim of CSA is to enable the operator to identify the safety functions that have to be assured in any situation to avoid the happening of feared consequences (core melting, dewatering of spent fuel in fuel pools, important releases of radioactive or toxic matter in the environment...). The identification of the safety functions will lead to the definition of a hard core of equipment or systems necessary in any situation to perform these safety functions. In most cases this hard core will be composed of reinforced already existing systems and of new dedicated systems. This hard core will have to be protected from aggressions from a greater level than to which the installation was designed. (A.C.)