Enhancing TRU burning and Am transmutation in Advanced Recycling Reactor

This paper presents about conceptual designs of Advanced Recycling Reactor (ARR) focusing on enhancement in transuranics (TRU) burning and americium (Am) transmutation. The design has been conducted in the context of the Global Nuclear Energy Partnership (GNEP) seeking to close nuclear fuel cycle in ways that reduce proliferation risks, reduce the nuclear waste in the US and further improve global energy security. This study strives to enhance the TRU burning and the Am transmutation, assuming the development of related technologies in this study, while the ARR based on mature technologies was designed in the previous study. It has followed that the provided TRU burning core is designed to burn TRU at 28 kg/TW_thh, by adding moderator pins of B₄C (Enriched B-11) and the Am transmutation core will be able to transmute Am at 34 kg/TW_thh, by locating Am blanket of AmN around the TRU burning core. It indicates that these concepts improve TRU burning by 40-50% than the previous core and can transmute Am effectively, keeping the void reactivity acceptable.     

THETRIS: A micro-scale temperature and gas release model for TRISO fuel

The dominating mechanism in the passive safety of gas-cooled, graphite-moderated, high-temperature reactors (HTRs) is the Doppler feedback effect. These reactor designs are fueled with submillimeter-sized kernels formed into tristructural-isotropic (TRISO) particles that are imbedded in a graphite matrix. The best spatial and temporal representation of the feedback effect is obtained from an accurate approximation of the fuel temperature. Micro-scale models of TRISO particles are necessary in order to obtain accurate predictions during fast transients or when parameters internal to the TRISO are needed. Most accident scenarios in HTRs are characterized by large time constants and slow changes in the fuel and moderator temperature fields. In these situations, a meso-scale, or pebble- and compact-scale, solution provides a good approximation of the fuel temperature as the fission thermal energy transports out of the kernel and into the surrounding matrix with a much shorter time constant. Therefore, in most cases, the matrix can be assumed to be in quasi-static equilibrium with the kernels. These models, however, fail to provide accurate information on the state of the various components of the TRISO during the early stages of transients. Since the coated particles constitute one of the fundamental design barriers for the release of fission products, it becomes important to understand the transient behavior inside this containment system. An explicit TRISO fuel temperature model named THETRIS has been developed and incorporated into the CYNOD–THERMIX-KONVEK suite of coupled codes. The code includes gas-release models that provide a simple predictive capability of the internal pressure during transients. The new model yields similar results to those obtained with other micro-scale fuel models of TRISO particles, but with the added capability to analyze gas release, internal pressure buildup, and effects of a gap in the TRISO. Analysis of bounding benchmark transients yield good agreement with other codes in which the TRISO particles are modeled explicitly. In addition, a sensitivity study of the potential effects on the transient behavior of high-temperature reactors due to the presence of an inter-layer gap is included. Although the formation of a gap occurs under special conditions, its consequences on the dynamic behavior of the reactor can yield responses during fast transients that depart significantly from those in which no gap is present in the model. The new model was applied to an extreme (beyond design basis) scenario in order to observe the behavior of the fuel during a large prompt critical reactivity insertion. Although a large amount of fission energy was deposited rapidly into the fuel, the kernel temperature is shown to stay well below the melting point and the silicon carbide layer remained well below the temperature above which failure is expected to occur. The explicit treatment of the TRISO particle geometry leads to much lower estimations of power peaking during the transient and a greater degree of negative Doppler feedback.     

European supercritical water cooled reactor

The High Performance Light Water Reactor (HPLWR), how the European Supercritical Water Cooled Reactor is called, is a pressure vessel type reactor operated with supercritical water at 25 MPa feedwater pressure and 500 °C average core outlet temperature. It is designed and analyzed by a European consortium of 10 partners and 3 active supporters from 8 Euratom member states in the second phase of the HPLWR project. Most emphasis has been laid on a core with a thermal neutron spectrum, consisting of small fuel assemblies in boxes with 40 fuel pins each and a central water box to improve the neutron moderation despite the low coolant density. Peak cladding temperatures of the fuel rods have been minimized by heating up the coolant in three steps with intermediate coolant mixing. The containment design with its safety and residual heat removal systems is based on the latest boiling water reactor concept, but with different passive high pressure coolant injection systems to cause a forced convection through the core. The design concept of the steam cycle is indicating the envisaged efficiency increase to around 44%. Moreover, it provides the constraints to design the components of the balance of the plant. The project is accompanied by numerical studies of heat transfer of supercritical water in fuel assemblies and by material tests of candidate cladding alloys, performed by the consortium and supported by additional tests of the Joint Research Centre of the European Commission. Besides the scientific and technical progress, the HPLWR project turned out to be most successful in training the young generation of nuclear engineers in the technologies of light water reactors. More than 20 bachelor or master theses and more than 10 doctoral theses on HPLWR technologies have been submitted at partner organizations of this consortium since the start of this project.     

Phébus-FP: Results and significance for plant safety in Switzerland

Phébus-FP is a multi-national collaborative programme comprising four integral and one debris bed melting and fission product release experiments. The integral experiments simulate the heat-up, degradation and fission product release and transport, thermal hydraulic response, aerosol behaviour and iodine chemistry in the containment. The total programme, including interpretation effort, runs from 1993 to ca. 2007. The experiments demonstrated new characteristics of core degradation, fission product and iodine chemistry and accident integral behaviour. PSI has participated extensively through planning support, interpretation of data from the experiments and analyses of the results to establish confidence in the models being used for plant application. A significant part of the PSI effort was performed to interpret the significance of silver iodide as an effective retention agent under typical reactor conditions. The conclusions are of an interim nature, since the data reduction and interpretation are not yet complete. The significance of the Phébus results for plant safety will be fully realised only after successful benchmarking of the computer codes against Phébus, and application to plant sequences. Such work remains in progress within the Phébus project and in various national programmes.     

Validation of CATHARE V2.5 thermal-hydraulic code against full-scale PERSEO tests for decay heat removal in LWRs

The PERSEO experimental program was performed in the framework of a domestic research program on innovative safety systems with the purpose to increase the reliability of passive decay heat removal systems implementing in-pool heat exchangers. The conceived system was tested at SIET laboratories by modifying the existing PANTHERS IC-PCC facility utilized in the past for testing a full scale module of the GE-SBWR in-pool heat exchanger. Integral tests and stability tests were conducted to verify the operating principles, the steadiness and the effectiveness of the system. Two of the more representative tests have been analyzed with CATHARE V2.5 for code validation purposes. The paper deals with the comparison of code results against experimental data. The capabilities and the limits of the code in simulating such kind of tests are highlighted. An improvement in the modeling of the large water reserve pool is suggested trying to reduce the discrepancies observed between code results and test measurements.     

Suspension and solution thermal spray coatings

The emerging methods of coating deposition by suspension and solution thermal spraying are described. The liquid suspensions of fine powders and liquid precursors are injected into flames and/or jets generated in the torches. The formulation and stability of suspensions as well as the methods of fine powders synthesis are briefly described. Typical solutions, being often the liquid organo-metallics are also briefly described. An important problem of injection of liquids into jets and flames is then presented. Two principal modes of injection, used at present, are outlined, i.e.: (i) atomization; and, (ii) injection of a continuous jet. Subsequently, the phenomena occurring in flames and plasma jets are discussed and the major differences to these occurring during conventional spraying are stressed up. The build up of coatings starting from the impact of fine particles on the substrate is described and typical microstructures of suspension and solution sprayed coatings are shown. Some properties of the sprayed coatings, including mechanical, electrical, chemical, and thermophysical ones are collected and presented. Finally, the emerging applications of coatings are shown and the possible future applications are discussed.