Applying SHARK-X to perform data assimilation with the LWR-PROTEUS Phase II integral experiments

Data assimilation methods have recently been implemented in the sensitivity analysis and uncertainty quantification tool SHARK-X. This paper presents how they were used with sensitivity coefficients and randomly-sampled nuclear data to simulate integral parameters from the LWR-PROTEUS Phase II experiment. The adjusted calculated values of the integral parameters showed small differences between the two implemented data assimilation methods, GLLS and MOCABA. The differences were statistically significant, but were caused by round-off errors. The experiment was also analyzed to search for sources of bias in the simulations. Analysis of the chi-squared parameter showed that many of the integral parameters have biases that were inconsistent with their high correlation. This indicates that the bias likely arose from sources other than nuclear data, like the modeling of the fuel burnup, the 2D model in CASMO-5M, or from experimental methods. The nuclear data adjustments were analyzed and ranked according to how they improved the computational bias and reduced its uncertainty.

Development of the control assembly pattern and dynamic analysis of the generation IV large gas-cooled fast reactor (GFR)

Gaëtan Girardin

During the past ten years, different independent factors, such as the rapidly increasing worldwide demand in energy, societal concerns about greenhouse gas emissions, and the high and volatile prices for fossil fuels, have contributed to the renewed interest in nuclear technology. It is in this context that the Generation IV international forum (GIF) launched the initiative, in 2000, to collaborate on the research and development (R&D) efforts needed for the next generation, i.e. Generation IV, of nuclear reactors. These advanced systems will be ideally deployed beyond the year 2030, following the Generation III or III+ nuclear power plants, which are mainly based on light water technology and are currently entering deployment. A particular goal set for Generation IV systems is closure of the nuclear fuel cycle. Thus, apart from improvements in safety, they are expected to offer a better utilization of natural resources, as also a minimization of long-lived radioactive wastes. Among the systems selected by the GIF, the Gas-cooled Fast Reactor (GFR) is a highly innovative system with advanced fuel geometry and materials (fuel pellets of mixed uranium-plutonium carbide within a plate-type, honeycomb structure made of SiC). It is in the context of the large, 2400 MWth reference GFR design that the present doctoral research has been conducted, the principal aim having been to develop and qualify the control assembly (CA) pattern and corresponding CA implementation scheme for this system. The work has been carried out in three successive and complementary phases: (1) validation of the neutronics tools, (2) the CA pattern development and related static analysis, and (3) dynamic core behavior studies for hypothetical CA driven transients. The deterministic code system ERANOS and its associated nuclear data libraries for fast reactors were developed and validated for the previous generation of sodium-cooled reactors. The validation of ERANOS for GFR applications was, therefore, the first task to be realized in the present research. This has entailed a systematic reanalysis of the GFR-relevant, integral data generated at PSI during the GCFR-PROTEUS experimental program of the 1970's. Thus, during the first phase of the thesis, the reference PROTEUS test lattice from these experiments has been analyzed with ERANOS-2.0 and its associated, adjusted nuclear data library ERALIB1, in order to derive a reference computational scheme to be used later for the GFR analysis. Additionally, benchmark calculations were performed with the Monte Carlo code MCNPX, allowing one to both check the deterministic results and to analyze the sensitivity to different modern data libraries. It has been found that, for the main reaction rate ratios, the new analysis of the GCFR-PROTEUS reference lattice generally yields good agreement – within 1σ measurement uncertainty – with experimental values and with the Monte Carlo simulations. As shown by the analysis, the predictions were in somewhat better agreement in the case of the adjusted ERALIB1 library. The applicability of ERANOS-2.0/ERALIB1 as the reference neutronics tool for the GFR analysis could thus be demonstrated. Furthermore, neutronics aspects related to the novel features of the GFR, for which new experimental investigations are needed, were highlighted. In the second phase of the research, the CA pattern was developed for the GFR, based on iterative neutronics and thermal-hydraulics calculations, 2D and 3D neutronics models for the reactor core having first been set up using the reference ERANOS-2.0/ERALIB1 computational scheme. For the thermal-hydraulics analysis, the CEA code COPERNIC was used. This design work was followed by the study of an appropriate CA implementation scheme (number of CAs and corresponding positions within the core). Detailed neutronics studies revealed the existence of large CA interaction effects, so-called shadowing/anti-shadowing effects leading to an amplification/reduction of the CA worth. The interactions between the absorber pins within a CA, and between the CAs themselves, were investigated in detail, with the goal to optimize the CA efficiency, in terms of the absorber fraction and minimization of the associated heterogeneity effects. The proposed CA pattern consists of 54 absorber pins placed in a triangular lattice. Each absorber pin is a stainless-steel tube filled with highly enriched 10B boron carbide pellets. As a result of the detailed investigations, the absorber pin diameter could be chosen such as to minimize the pin-to-pin influence within the assembly. In particular, a central part of the CA was designed without any absorber pins (zone filled with stagnant helium). A final reduction of the heterogeneity effect (difference between homogeneous and heterogeneous treatments) to 13% was achieved through this feature. Of special importance, the neutronics investigations performed for the reference GFR core ("2004-Core"), especially those related to the CA interactions, have directly contributed to a new core design ("2007-Core"), with the height-to-diameter ratio having been increased to 0.6, compared to 0.3 for the reference core. During the third phase, detailed coupled, 3D neutron-kinetics (NK) and 1D thermal-hydraulics (TH) models were developed for the GFR core, the aim being to arrive at an in-depth understanding of the 3D core behavior during CA driven transients, especially from the viewpoint of spatial effects. The coupled models were developed using the PARCS code for the 3D NK and the TRACE code for the 1D TH modeling. Particular attention was paid to have each individual fuel sub-assembly and CA represented, in order to allow the analysis of local deformations of the 3D distributions of power and safety related parameters, such as the coolant, cladding and fuel temperatures. The validation of the coupled full-core models was performed against reference ERANOS-VARIANT calculations. In particular, the CA worth and reactivity feedbacks were benchmarked, the discrepancies being shown to be relatively low (

EPFL2009

Etudes numériques et expérimentales de caractéristiques d'un système rapide sous-critique alimenté par une source externe

Michaël Plaschy

One of the principal research axes related to nuclear energy concerns the management of nuclear wastes. In this context, certain innovative pathways are being explored to provide options which could lead to a major reduction of the quantities of radioactive nuclides requiring long-term geological storage. An important aspect is the development of advanced nuclear systems which allow the transmutation of long-lived minor actinides, the ADS (accelerator driven system) concept often being proposed for the purpose. Various important developments are necessary for these new systems, one of the principal needs being the qualification of calculational tools to enable the reliable design of an ADS demonstrator. In the present research, related numerical and experimental studies have been carried out in the framework of the MUSE4 programme, which was developed on the MASURCA facility at Cadarache, France. This programme consists of investigations of a reference critical configuration (MOX fuel with sodium), and several subcritical configurations driven by an external neutron source. The source is obtained with the help of a deuton accelerator, called GENEPI, which produces neutrons via a nuclear reaction, either with a tritium target (14.1MeV neutrons), or with a deuterium target (2.7MeV neutrons). The experimental techniques implemented in this research address the study of spectral variations via foil activation measurements near interfaces characteristic of ADSs. The additional value of such experimental results, compared to standard fission rate traverses obtained using fission chambers (which were also analysed), has been highlighted. An important novel set of integral parameters has thus been made available for the validation of different numerical codes and nuclear data. The activation and fission rate measurements carried out, as also experimental results for other parameters such askeff, βeff and φ*, have been interpreted using various calculational codes (mainly ERANOS and MCNP) and several different nuclear data libraries (JEF-2.2, ERALIB1, ENDF/B6v2). Supplementary information on the performance of the calculational methods has been obtained in the context of the MUSE4 benchmark exercise, conducted by the NEA. The present investigations have led to the resolution of various problems encountered during the earlier MUSE3 programme at MASURCA, viz. uncertainties related to description of the intrinsic source description, difficulties in interpreting fission traverses near the external source, etc. A detailed study has thus been made possible of the important factors which characterise subritical fast systems driven by an external source, i.e. influence of the subcriticality level and of the external source intensity. The various analyses carried out have permitted to establish several recommendations concerning the modeling of the external source and the accelerator tube, as well as the most appropriate numerical methods and data sets to be applied. In this context, the specificity of subcritical configurations, as regards the prediction of parameters such as spatial indices and absolute reaction rates, has been clearly brought out. Certain difficulties (interpretation of high threshold reactions, absolute flux determination, etc.) have thereby been highlighted, pointing at the need for further numerical and experimental investigations. Finally, some recent ERANOS developments have allowed a study to be carried out of the representativity of MUSE4 configurations with respect to alternative ADS concepts proposed in the framework of the international PDS-XADS project. In brief, the representativity of the MUSE4 configurations is found to be quite satisfactory for XADS-Na and XADS-gas. However, in the case of the XADS-Pb/Bi system, effects of the significant uncertainties associated with the nuclear data of lead and bismuth have been clearly highlighted, indicating the desirability of new, more specific experiments for XADS-Pb/Bi validation.

EPFL2004

Characterization of input uncertainties in strategic energy planning models

Michel Bierlaire, Victor Codina Gironès, François Maréchal, Stefano Moret

Various countries and communities are defining strategic energy plans driven by concerns for climate change and security of energy supply. Energy models can support this decision-making process. The long-term planning horizon requires uncertainty to be accounted for. To do this, the uncertainty of input parameters needs to be quantified. Classical approaches are based on the calculation of probability distributions for the inputs. In the context of strategic energy planning, this is often limited by the scarce quantity and quality of available data. To overcome this limitation, we propose an application-driven method for uncertainty characterization, allowing the definition of ranges of variation for the uncertain parameters. To obtain a proof of concept, the method is applied to a representative mixed-integer linear programming national energy planning model in the context of a global sensitivity analysis (GSA) study. To deal with the large number of inputs, parameters are organized into different categories and uncertainty is characterized for one representative parameter per category. The obtained ranges serve as input to the GSA, which is performed in two stages to deal with the large problem size. The application of the method generates uncertainty ranges for typical parameters in energy planning models. Uncertainty ranges vary significantly for different parameters, from [-2%,2%] for electricity grid losses to [-47.3%, 89.9%] for the price of imported resources. The GSA results indicate that only few parameters are influential, that economic parameters (interest rates and price of imported resources) have the highest impact, and that it is crucial to avoid an arbitrary a priori exclusion of parameters from the analysis. Finally, we demonstrate that the obtained uncertainty characterization is relevant by comparing it with the assumption of equal levels of uncertainty for all input parameters, which results in a fundamentally different parameter ranking. (C) 2017 Elsevier Ltd. All rights reserved.

Elsevier Sci Ltd2017