Application of best estimate plus uncertainty in review of research reactor safety analysis

To construct and operate a nuclear research reactor, the licensee is required to obtain the authorization from the regulatory body. One of the tasks of the regulatory authority is to verify that the safety analysis fulfils safety requirements. Historically, the compliance with safety requirements was assessed using a deterministic approach and conservative assumptions. This provides sufficient safety margins with respect to the licensing limits on boundary and operational conditions. Conservative assumptions were introduced into safety analysis to account for the uncertainty associated with lack of knowledge. With the introduction of best estimate computational tools, safety analyses are usually carried out using the best estimate approach. Results of such analyses can be accepted by the regulatory authority only if appropriate uncertainty evaluation is carried out. Best estimate computer codes are capable of providing more realistic information on the status of the plant, allowing the prediction of real safety margins. The best estimate plus uncertainty approach has proven to be reliable and viable of supplying realistic results if all conditions are carefully followed. This paper, therefore, presents this concept and its possible application to research reactor safety analysis. The aim of the paper is to investigate the unprotected loss-of-flow transients "core blockage" of a miniature neutron source research reactor by applying best estimate plus uncertainty methodology. The results of our calculations show that the temperatures in the core are within the safety limits and do not pose any significant threat to the reactor, as far as the melting of the cladding is concerned. The work also discusses the methodology of the best estimate plus uncertainty approach when applied to the safety analysis of research reactors for licensing purposes

PREMIUM, a benchmark on the quantification of the uncertainty of the physical models in the system thermal-hydraulic codes: methodologies and data review

The objective of the Post-BEMUSE Reflood Model Input Uncertainty Methods (PREMIUM) benchmark is to progress on the issue of the quantification of the uncertainty of the physical models in system thermalhydraulic codes by considering a concrete case: the physical models involved in the prediction of core reflooding. The present document was initially conceived as a final report for the Phase I “Introduction and Methodology Review” of the PREMIUM benchmark. The objective of Phase I is to refine the definition of the benchmark and publish the available methodologies of model input uncertainty quantification relevant to the objectives of the benchmark. In this initial version the document was approved by WGAMA and has shown its usefulness during the subsequent phases of the project. Once Phase IV was completed, and following the suggestion of WGAMA members, the document was updated adding a few new sections, particularly the description of four new methodologies that were developed during this activity. Such developments were performed by some participants while contributing to PREMIUM progress (which is why this report arrives after those of other phases). After this revision the document title was changed to “PREMIUM methodologies and data review”. The introduction includes first a chapter devoted to contextualization of the benchmark in nuclear safety research and licensing, followed by a description of the PREMIUM objectives. Next, a description of the Phases in which the benchmark is divided and its organization is explained. Chapter two consists of a review of the involvement of the different participants, making a brief explanation of the input uncertainty quantification methodologies used in the activity. The document ends with some conclusions on the development of Phase I, some more general remarks and some statements on the benefits of the benchmark, which can be briefly summarized as it follows: - Contribution to development of tools and experience related to uncertainty calculation and promotion of the use of BEPU approaches for licensing and safety assessment purposes; - Contribution to prioritization of improvements to thermal-hydraulic system codes; - Contribution to a fluent and close interaction between the scientific community and regulatory organizations. Appendices include the complete description of the experimental data FEBA/SEFLEX used in the benchmark and the methodologies CIRCÉ and FFTBM and the general requirements and description specification used for Phase I. Due to the revision of the document, four extra appendixes have been added related to the methods developed during the activity, MCDA DIPE, Tractebel IUQ and PSI methods

Evaluation of uncertainty connected with Transient thermal-Hydraulics Calculations

Three approaches for the evaluation of uncertainty expected in calculations performed by system thermal-hydraulic codes are discussed : a) The statistical approach initially proposed by United States Nuclear Regulatory Commission, later on made robust by GRS (Geselschaft fur Reaktosicherhet) in Germany with the introduction of the Wilks’ formula. The approach is also known as propagation of code input errors. b) The deterministic approach based on the propagation of code output error, including the methodologies UMAE (Uncertainty Method based on the Accuracy Extrapolation) and the CIAU (Code with capability of Internal Assessment of Uncertainty), proposed by UNIPI (University of Pisa). c) The third approach is based on ASAP (Adjoint Sensitivity Analysis Procedure) and GASAP (Global Adjoint Sensitivity Analysis Procedure) initially proposed by Cacuci D. and later on extended by Petruzzi and D’Auria (UNIPI) including concepts from DAA (Data Adjustment and Assimilation). The three approaches are discussed here for possible interaction with uncertainty methods proposed within the Computational Fluid Dynamics (CFD) community

Updated Analyses for the In Progress NUREG on ”Analysis of the OSU-MASLWR 001 and 002 Test by Using the TRACE Code”

MULTI-APPLICATION SMALL LIGHT WATER REACTOR OSU-MASLWR test facility OSU MASLWR Testing Capability-Previous Testing Brief Description of the OSU-MASLWR 001 test OSU-MASLWR TRACE Model Description Post Test Analysis of the OSU-MASLWR 001 Test Conclusion

Small Modular Reactors and insights on passive mitigation strategy modeling

In the last decades, taking into account the operational experience of fission nuclear reactors, the nuclear international technical community started the development of advanced reactor designs in order to satisfy the demand of the people to improve the safety of NPPs and to take into consideration the industry needs to improve the economic efficiency and reduce the capital costs of nuclear power technology. In this framework Small Modular Reactors (SMR) adopting light water as coolant, taking advantage of the experience developed in current larger scale LWR, can bring advantages in terms of increasing “inherent safety” due to the integral type configuration, lower nominal power, and the adoption of passive mitigation strategy. Starting from some of the research activities on code applications developed by the authors along the last decade, and available in the public scientific literature, the target of this paper is to give some insights and recommendations for the future development of new research activities, in national and international frameworks, in relation to thermal hydraulics of SMRs

Design, Synthesis, and Biological Evaluation of Potent Dual Agonists of Nuclear and Membrane Bile Acid Receptors

Bile acids exert genomic and nongenomic effects by interacting with membrane G-protein-coupled receptors, including the bile acid receptor GP-BAR1, and nuclear receptors, such as the farnesoid X receptor (FXR). These receptors regulate overlapping metabolic functions; thus, GP-BAR1/FXR dual agonists, by enhancing the biological response, represent an innovative strategy for the treatment of enteroendocrine disorders. Here, we report the design, total synthesis, and in vitro/in vivo pharmacological evaluation of a new generation of dual bile acid receptor agonists, with the most potent compound, <b>19</b>, showing promising pharmacological profiles. We show that compound <b>19</b> activates GP-BAR1, FXR, and FXR regulated genes in the liver, increases the intracellular concentration of cAMP, and stimulates the release of the potent insulinotropic hormone GLP-1, resulting in a promising drug candidate for the treatment of metabolic disorders. We also elucidate the binding mode of the most potent dual agonists in the two receptors through a series of computations providing the molecular basis for dual GP-BAR1/FXR agonism

Binding Mechanism of the Farnesoid X Receptor Marine Antagonist Suvanine Reveals a Strategy To Forestall Drug Modulation on Nuclear Receptors. Design, Synthesis, and Biological Evaluation of Novel Ligands

Here, we report suvanine, a marine sponge sesterterpene, as an antagonist of the mammalian bile acid sensor farnesoid-X-receptor (FXR). Using suvanine as a template, we shed light on the molecular bases of FXR antagonism, identifying the essential conformational changes responsible for the transition from the agonist to the antagonist form. Molecular characterization of the nuclear corepressor NCoR and coactivator Src-1 revealed that receptor conformational changes are associated with a specific dynamic of recruitment of these cofactors to the promoter of OSTα, a FXR regulated gene. Using suvanine as a novel hit, a library of semisynthetic derivatives has been designed and prepared, leading to pharmacological profiles ranging from agonism to antagonism toward FXR. Deep pharmacological evaluation demonstrated that derivative <b>19</b> represents a new chemotype of FXR modulator, whereas alcohol <b>6</b>, with a simplified molecular scaffold, exhibits excellent antagonistic activity

Notulae to the Italian native vascular flora: 2

In this contribution new data concerning the Italian distribution of native vascular flora are presented. It includes new records, exclusions, and confirmations to the Italian administrative regions for taxa in the genera Arctostaphylos, Artemisia, Buglossoides, Convolvulus, Crocus, Damasonium, Epipogium, Ficaria, Filago, Genista, Heptaptera, Heracleum, Heteropogon, Hieracium, Myosotis, Ononis, Papaver, Pilosella, Polygonum, Pulmonaria, Scorzonera, Silene, Trifolium, Vicia and Viola

OECD/NEA/CSNI/WGAMA PERSEO benchmark: main outcomes and conclusions

In the framework of the OECD/NEA/CSNI/WGAMA, an activity on the "Status report on thermal-hydraulic passive systems design and safety assessment" has been conducted. Within this activity, a benchmark exercise, based on the experimental data developed in the full scale PERSEO (in-Pool Energy Removal System for Emergency Operation) component separate effect test facility, built at SIET (Piacenza, Italy), has been proposed and carried out. An "OPEN" benchmark exercise, hosted by ENEA, has been conducted. Twelve results from eleven Organizations were submitted. PERSEO is a full-scale separate effect test facility designed to study a new passive decay heat removal system operating in natural circulation. Test 7 is a full pressure test (7 MPa) and investigates the system stability and the system operation. The accuracy of the calculated results has been evaluated both qualitatively and quantitatively. The latter has been conducted adopting the Fast Fourier Transform Based Method. The present paper summarizes the main features of the PERSEO facility and Test 7 and discusses the main results and outcome of the benchmark exercise