1,721,006 research outputs found
Conceptual Design of a Large, Passive Pressure-Tube Light Water Reactor
No full textA design for a large, passive, light water reactor has been developed.
The proposed concept is a pressure tube reactor of similar design to
CANDU reactors, but differing in three key aspects. First, a solid
Sic-coated graphite fuel matrix is used in place of pin-rod bundles to enable
the dissipation of decay heat from the fuel in the absence of primary
coolant. Second, the heavy water coolant in the pressure tubes is replaced by
light water, which serves also as the moderator. Finally, the calandria
tank, surrounded by a graphite reflector, contains a low pressure gas
instead of heavy water moderator, and the normally-voided calandria is
connected to a light water heat sink. The cover gas keeps the light water out
of the calandria during normal operation, while during loss of coolant or
loss of heat sink accidents it allows passive calandria flooding. Calandria
flooding also provides redundant and diverse reactor shutdown. The entire
primary system is enclosed in a robust, free standing cylindrical steel
containment cooled solely by buoyancy-induced air flow, and surrounded by
a concrete shield building.
It is shown that the proposed reactor can survive loss of coolant
accidents without scram and without replenishing primary coolant
inventory, while the safe temperature limits on the fuel and pressure tube
are not exceeded. It can cope with station blackout and anticipated
transients without scram - the major traditional contributors to core
damage frequency - without sustaining core damage. The fuel elements
can operate under post-CHF conditions even at full power, without
exceeding fuel design limits. The heterogeneous arrangement of the fuel
and moderator ensures a negative void coefficient under all circumstances.
Although light water is used as both coolant and moderator, the reactor
exhibits high neutron thermalization and a large prompt neutron lifetime,
similar to DgO moderated cores. Moreover, the extremely large neutron
migration length results in a strongly coupled core with a flat thermal flux
profile, and inherent stability against xenon spatial oscillations.United States. Dept. of Energ
Effective Thermal Conductivity of Prismatic MHTGR Fuel
No full textThe Reactor Cavity Cooling System (RCCS) is an essential passive safety feature of the Modular High Temperature Gas-Cooled Reactor (MHTGR). Its function is to assure the protection of both public safety and owner investment. As shown schematically in Figure 1.1, the system relies upon all three of the classic modes of heat transfer: conduction through the graphic core dominates energy transport to the reactor vessel, from which radiation is the principal mechanism for heat transfer to the riser tubes, inside which natural convection transfers heat to ambient air which provides the ultimate heat sink. The latter two steps have been the subject of past and on-going analyses at MIT in the support of the MHTGR program, as document in references 1 through 10. In this report we focus attention on the in-vessel aspects of this sequence
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Plant Design and Cost Estimation of a Natural Circulation Lead-Bismuth Reactor with Steam Power Conversion Cycle
No full textThe analysis of an indirect steam power conversion system with lead-bismuth natural circulation primary system has been performed. The work of this report is focused on 1) identifying the allowable design region for the important design parameters, 2) selecting the set of design parameter values for the steam secondary system which leads to the lowest electricity generation cost and 3) comparing this approach to alternative fast systems. An analysis was performed to examine the capital cost of the ABR and the sensitivity of the capital cost to key design parameters: degree of superheat, secondary system pressure and reactor chimney height. These capital cost estimation and sensitivity analyses were based on the cost estimate of the ALMR report. The following optimal design parameter values for the steam secondary system were established by parameter studies presented in this report. - Pb-Bi in-tube design for the steam generator - Triangular tube lattice in the steam generator - Superheat in steam generator (30°C superheat) - Secondary pressure (70 bar) in the steam generator - No recirculation in the steam generator - Steam generator coolant inlet temperature. The ABR capital cost shows around 15% reduction compared to the ALMR. This is mainly due to the lower cost of the coolant systems due to elimination of the intermediate heat transport system and main coolant pump. Whether, the same ration of reduced cost can be expected in comparison to S-PRISM which is not known but is likely given that the same simplification apply. The ABR capital cost sensitivity analysis shows that the capital cost does not change with degree of superheat, increases with secondary system pressure and decreases with increased reactor chimney height. This report is restricted to the capital cost of the ABR. A previous report has estimated ABR fuel cycle cost. Future economic analysis will include the O&M costs and updated capital estimates based on comparison with the SPRISM.Idaho National Engineering and Environmental Laborator
Variations on the Author
Get PDF“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
Conceptual Design of a Lead-Bismuth Cooled Fast Reactor with In-Vessel Direct-Contact Steam Generation
No full textThe feasibility of a lead-bismuth (Pb-Bi) cooled fast reactor that eliminates the need for steam generators and coolant pumps was explored. The working steam is generated by direct contact vaporization of water and liquid metal in the chimney above the core and then is sent to the turbine. The presence of a lighter fluid in the chimney drives the natural circulation of the Pb-Bi within the reactor pool. Three key technical issues were addressed:
The maximum thermal power removable by direct contact heat transfer without violating the fuel, clad and vessel temperature limits;
The consequences of Pb-Bi aerosol transport on the design and operation of the turbine;
The release of radioactive polonium (a product of coolant activation) to the steam.
Modeling of the multi-phase phenomena occurring in the chimney confirmed the effectiveness of the direct contact heat transfer mode within a well-defined design envelope for the reactor power, chimney height and steam superheat. A 1260MWth power is found possible for 10m chimney height and 25ºC superheat. The temperature of the low-nickel steel clad is maintained below 600ºC, which results in limited corrosion if tight control of the coolant oxygen concentration is adopted.
Generation, transport and deposition of Pb-Bi aerosols were also modeled. It was found that the design of a chevron steam separator reduces the heavy liquid metal in the steam lines by about three orders of magnitude. Nevertheless, the residual Pb-Bi is predicted to cause embrittlement of the turbine blades. Four solutions to this problem were assessed: blade coating, employment of alternative materials, electrostatic precipitation and oxidation of the Pb-Bi droplets.
An experimental campaign was conducted to investigate the polonium release from a hot Pb-Bi bath to a gas stream. The thermodynamics of the polonium hydride formation reaction (free-energy vs. temperature) as well as the vapor pressure of the lead-polonide were measured and then utilized to model the polonium transport in the reactor. It was found that the polonium concentration in the steam and on the surface of the power cycle components is significantly above the acceptable limits, which makes the very concept of a direct contact reactor open to question.Idaho National Engineering and Environmental Laborator
Plant Design and Cost Estimation of a Natural Circulation Lead-Bismuth Reactor with Helium Power Conversion Cycle
No full textThe analysis of an indirect helium power conversion system with lead-bismuth natural circulation primary system has been performed. The work of this report is focused on 1) identifying the allowable design region for the important design parameters and 2) selecting the set of design parameter values for the helium secondary system which lead to the lowest electricity generating cost. An analysis was also performed to examine the capital cost of the ABR/GT and the sensitivity of the capital cost to key parameters. These capital cost estimation and sensitivity analyses were based on available cost estimates of the ALMR and a published HTGR/GT design.
The following optimal design parameter values for the helium secondary system were established by this report.
Pb-Bi in-tube design for the heat exchanger
Triangular tube lattice in the heat exchanger
Helium heat exchanger inlet temperature: 250 °C
Helium heat exchanger outlet temperature: 500 °C
Compression ratio: 3
The ABR/GT capital cost per unit electrical output with helium secondary system is about 36% above that of the steam secondary system case. Sensitivity analyses show about 10% reduction in cost is achieved by increasing the chimney height from 8 m to 15m, 22% cost reduction by increasing the capacity factor from 70-90% and 13% cost reduction by decreasing the construction time from 7 to 3 years. These cost reductions are comparable to those which can be achieved for the ABR with a steam secondary system. The increased cost for the helium versus the steam secondary side results principally from the thermal efficiency difference and the cost difference between steam cycle and helium cycle components.
This report is restricted to the capital cost of the ABR/GT. A previous report has estimated the ABR fuel cycle cost. Future economic analysis will include the O&M costs and updated capital estimates based on comparison with the S-PRISM primary system.Idaho National Engineering and Environmental Laborator
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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