1,720,974 research outputs found
ELSY Neutronic Analysis by deterministic and Monte Carlo methods: an innovative concept for the control rod systems
No full textThis paper deals with the neutronic design of ELSY (the European Lead-cooled SYstem), a 600 MWe Fast Reactor developed within the 6th EURATOM Framework Programme. ELSY aims at being an “adiabatic” system (as far as possible) in order to fulfill both the requirements of sustainability and proliferation resistance. It represents the European solution for the Lead Fast Reactor (LFR), one of the six candidate typologies proposed by the Generation-IV International Forum (GIF).
The analysis of the ELSY reference configuration, with typical pure MOX loading, is here presented. An introductory investigation of the adiabatic and, possibly, the burner options viability is also achieved by providing a rough estimate of the Minor Actinides (MAs) equilibrium concentrations and time constants. One of the main challenge-points in the design of the core, made up of wrapper-less square Fuel Assemblies (FAs) according to the common scheme of PWRs, is the small delta-T between the coolant average outlet temperature (480 °C) and the allowable cladding one (550 °C): it requires a rather flat radial power distribution, obtained by segmenting the core in three zones with different enrichments.
Three different control sets have been introduced in order to achieve the required reliability for reactor shutdown and safety systems: eight traditional concept Control Rod (CR) assemblies together with two independent systems of sparse control “Finger Absorber” Rods (FARs), small B4C rods that can be inserted, in principle, in the center of each FA.
One of the two finger absorber systems includes a subset of rods devoted to the regulation of the criticality swing during the cycle: their number can be limited indeed since the small reactivity swing (some hundreds pcm) due to the about unitary breeding ratio. Such an innovative solution can also be positioned in order to maintain an optimal power flattening during the fuel cycle.
To verify the feasibility of this solution, a very detailed neutronic analysis, adopting both deterministic and stochastic approaches, has been carried out. It becomes crucial indeed to estimate accurately the self-shielding phenomenon of the innovative FARs in order to achieve the aimed performances (a reactivity worth of about 3000 pcm for scram)
Extension of the FAST code system for the modelling and simulation of MSR dynamics
No full textIn this work, the PSI FAST code system is extended for the modeling and simulation of Molten Salt Reactor (MSR) dynamics. The thermal-hydraulic code TRACE has been provided with a module for 1-D Delayed Neutron Precursor (DNP) balance and decay heat modeling in fluid fuel, and with built-in MSR materials. The reactor power is determined by means of a Point-Kinetics approach that makes use of power-weighted values of temperature and DNP distributions in the core. To validate the module, models for the comparison with experiments performed in the Molten Salt Reactor Experiment (MSRE) have been developed. The MSRE was a graphite moderated reactor built and operated in the sixties at Oak Ridge National Laboratory (ORNL). The neutronic characteristics of the reactor have been determined by means of the Monte Carlo code SERPENT. Two models of the MSRE plant with different detailing have been set up in order to determine the importance of the plant components. In particular, different descriptions of the external cooling loop have been tested and compared. Some significant transients have been considered for the module assessment, by comparison with available experimental data from ORNL, both in time and frequency domain
MSFR TRU-BURNING POTENTIAL AND COMPARISON WITH AN SFR
No full textTransmutation of the legacy TRansUranics (TRU) from Light Water Reactor operation has become in recent years a main objective for the development of Fast Reactors (FR). In fact, an effective TRU-burning requires fuel multi-recycling and a fast-neutron-spectrum reduces the endogenous generation of Cm and Cf isotopes, thus
benefitting fuel handling and in-core radiotoxicity generation. However, achievement of high TRU-burning rates requires low-Conversion-Ratio (CR) reactors with a high fraction of Minor Actinides (MA) in the core, requiring remote fuel fabrication behind thick shielding.
Problems of fuel handling are exacerbated if Th is used as fertile isotope (e.g. to enhance safety or TRU-burning rate), since Th-232 irradiation causes the build-up of U-232, whose progeny emits high energy gamma rays. Use of a liquid fuel with online reprocessing would avoid most of the issues related to reprocessing, manufacturing and transporting highly radioactive recycled fuel. The logical technology for the adoption of liquid fuel is the Molten Salt Reactor (MSR). Among MSRs, the Molten Salt Fast Reactor (MSFR) is in principle better suited for TRU burning as it combines the advantages of a liquid fuel with those of a fast-spectrum and of Th use. Objective of this work is to evaluate the MSFR potential benefits in terms of TRU burning through a comparative analysis with a sodium-cooled FR. The comparison is
based on TRU- and MA-burning rates, as well as on the in-core evolution of radiotoxicity and decay heat.
Solubility issues limit the TRU-burning rate to 1/3 that achievable in traditional low-CR FRs. The softer spectrum also determines notable radiotoxicity and decay heat of the equilibrium actinide inventory. On the other hand, the liquid fuel suggests the possibility of using a Pu- free feed composed only of Th and MA, thus maximizing the MA burning rate. This is generally not possible in traditional low-CR FRs due to safety deterioration and decay heat of reprocessed fuel. In addition, the high specific power and the lack of out-of-core cooling times foster a quick transition toward equilibrium, which improves the MSFR capability to burn an initial fissile loading, and makes the MSFR a promising system for a
quick (i.e., in a reactor lifetime) transition from the current U-based fuel cycle to a novel closed Th cycle
THE MSFR AS A FLEXIBLE CR REACTOR: THE VIEWPOINT OF SAFETY
No full textIn recent years efforts have been spent in the development of innovative reactors capable of operating with flexible Conversion Ratio (CR). Fast Reactors (FR) are natural candidates since they allow to achieve high CR, as well as an efficient TRU burning through a low CR and the closure of the fuel cycle. Among the fast-spectrum systems, a peculiar role is played by the Molten Salt Fast Reactor. This reactor lacks the sound technological basis available for the solid-fuelled liquid-metal-cooled FRs, but it shows fuel cycle potential benefits: it uses Th, which features vast natural resources and mitigates waste management issues due to a low generation of TRUs; it can naturally operate with flexible CR without design modifications thanks to the online reprocessing system; it can achieve high CR, with doubling times of the order of
40 years or lower; it can achieve good TRU-burning rates and very high burning rates of minor actinides. However, such fuel cycle flexibility implies a wide variety of fuel salt compositions. Along with the variation of the fuel salt properties, concerns arise for the varying safety features of the core, especially when using the MSFR as TRU- burner. This work first summarizes results regarding the fuel cycle performances of the MSFR when used as breeder, iso-breeder or burner reactor. Subsequently, safety parameters are computed for each fuel cycle option and a simple approach based on reactivity and energy balances is employed to predict the reactor steady-state after major accidental transient initiators, thus giving indications of its inherent safety features for different fuel cycle strategies
Hybrib Spectrum Molten Salt Reactor
No full textThe Molten Salt Reactor (MSR) concept has a unique feature, if compared to the majority of other reactor designs, that its fuel is liquid. This property creates, on one hand, several technical challenges; on the other hand, it offers flexibility in shaping and designing of the active core. Accordingly, single fuel fluid can, for instance, circulate through several core zones with different moderation ratios. This possibility was already considered in the past; however, in relation to the thermal MSR. In the presented study, an extreme case of hybrid spectrum MSR is proposed and preliminarily analyzed. It is concluded that hybrid spectrum may provide several advantages and could be applicable especially during the initial phase of the fuel cycle or by the transition to equilibrium cycle
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thorium-based Fast Reactors: Potential Benefits and Challenges
No full textUse of thorium in Fast Reactors (FR) is gaining consideration in the scientific community thanks to its potential benefits in terms of waste management. The present paper investigates the performance of Th in three FRs: a TRU-burner sodium-cooled FR, an iso- breeder lead-cooled FR and a fast-spectrum Molten Salt Reactor (MSR). The study confirms the relatively low actinide radiotoxicity generated by Th fuel in a closed cycle that could result beneficial to waste management. In addition, notably improved safety parameters are generally observed, which in turn allows increasing the TRU-burning rate while complying with safety requirements. The MSR emerges as the most promising option from the safety features standpoint and thanks to the unique flexibility fostered by a liquid fuel
Analysis of thorium and uranium fuel cycles in an iso-breeder lead fast reactor using extended-EQL3D procedure
No full textUse of thorium in fast reactors has typically been considered as a secondary option, mainly thanks to a possible self-sustaining thorium cycle already in thermal reactors and due to the limited breeding capabilities compared to U–Pu in the fast neutron energy range. In recent years nuclear waste management has become more important, and the thorium option has been reconsidered for the claimed potential to burn transuranic waste and the lower build-up of hazardous isotopes in a closed cycle. To ascertain these claims and their limitations, the fuel cycle isotopic inventory, and associated waste radio-toxicity and decay heat, should be quantified and compared to the case of the uranium cycle using realistic core configurations, with complete recycle of all the actinides. Since the transition from uranium to thorium fuel
cycles will likely involve a transuranic burning phase, this transition and the challenges that the evolving fuel actinide composition presents, for instance on reactor feedback parameters, should also be analyzed. In the present paper, these issues are investigated based on core physics analysis of the Lead-cooled Fast Reactor ELSY, performed with the fast reactor ERANOS code and the EQL3D procedure allowing full-core characterization of the equilibrium cycle and the transition cycles. In order to compute radio-toxicity and decay heat, EQL3D has been extended by developing a new module, which has been assessed against ORIGEN-S and is presented here. The capability of the EQL3D procedure to treat full-core 3D geometries allowed to explicitly account for aspects related to core dimensions and safety parameters in the analysis, giving a better insight into the pros and cons of the thorium option
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
