Development, Use, and Accuracy of a Homogenized Fuel Region Model for Thermal Analysis of a Truck Package Under Normal and Fire Accident Conditions

In the current work, a geometrically-accurate two-dimensional model is developed of an isolated fuel assembly within isothermal compartment walls. Finite difference thermal simulations are performed to determine the cladding temperature for a range of compartment wall temperatures and assembly heat generation rates. The results for zero-heat-generation-rate are used to determine a temperature-dependent effective thermal conductivity of the fuel region. The effective volumetric specific heat of the region is determined from a lumped capacity model. These effective properties are then applied to a two-dimensional model of a legal weight truck cask with homogenized (smeared) fuel regions. Steady-state normal conditions of transport simulations are performed for a range of fuel heat generation rates. The generation rate that brings the zircaloy cladding to its radial-hydride formation temperature, predicted by the homogenized model, is greater than that determined by simulations that employ an accurate-geometry fuel region model. Transient regulator fire accident simulations are then performed for a range of fire durations. The critical fire duration is defined as the minimum that brings the fuel cladding to its burst-rupture temperature. That duration is found to decrease as the fuel heat generation rate increases. The critical durations predicted by the homogenized fuel-region model are shorter than those predicted by the accurate-geometry model.

Download Full-text

Development and Use of a Homogenized Fuel Region Model for Thermal Analysis of a Truck Package Under Normal and Fire Accident Conditions

Volume 7: Operations, Applications and Components ◽

10.1115/pvp2012-78370 ◽

2012 ◽

Author(s):

Krishna Kumar Kamichetty ◽

Venkata Venigalla ◽

Miles Greiner

Keyword(s):

Heat Generation ◽

Effective Properties ◽

Generation Rate ◽

Two Dimensional ◽

Dimensional Model ◽

Geometry Model ◽

Capacity Model ◽

Two Dimensional Model ◽

Accident Conditions ◽

Fire Accident

In the current work, a geometrically-accurate two-dimensional model is developed of an isolated fuel assembly within isothermal compartment walls. Finite difference thermal simulations are performed to determine the cladding temperature for a range of compartment wall temperatures and assembly heat generation rates. The results for zero heat generation rate are used to determine a temperature-dependent effective thermal conductivity of the fuel region. The effective volumetric specific heat of the region is determined from a lumped capacity model. These effective properties are then applied to a two-dimensional model of a legal weight truck cask with homogenized (smeared) fuel regions. Steady-state normal conditions of transport simulations are performed for a range of fuel heat generation rates. The generation rate that brings the zircaloy cladding to their radial hydride formation temperature predicted by the homogenized model is greater than that determined by an accurate geometry model. Transient regulator fire accident simulations are performed for a range of fire durations. The minimum fire durations that bring the fuel cladding to its burst rupture temperatures are estimated. These results are compared to simulations which employ cask models with geometrically-accurate fuel region models.

Download Full-text

Prediction of Cladding Temperatures Within a Used Nuclear Fuel Transfer Cask Filled With Rarefied Helium

Volume 7: Operations, Applications and Components ◽

10.1115/pvp2014-29048 ◽

2014 ◽

Author(s):

Ernesto T. Manzo ◽

Rachel Green ◽

Mustafa Hadj Nacer ◽

Miles Greiner

Keyword(s):

Nuclear Fuel ◽

Heat Generation ◽

Generation Rate ◽

Two Dimensional ◽

Atmospheric Conditions ◽

Heat Generation Rate ◽

Pressurized Water ◽

Model Calculations ◽

Used Nuclear Fuel ◽

Helium Gas

During the used nuclear fuel vacuum drying process, helium is evacuated to pressures as low as 70 Pa, to promote water vaporization and removal. At these low pressures the gas is rarefied to the extent that there is a temperature jump thermal resistance between the surface and gas. This occurs when the mean free path of a molecule becomes a comparable to the characteristic length of a system. In order to correctly apply this jump model to a nuclear transfer cask, a two dimensional model of parallel plates and concentric cylinders were created using ANSYS/Fluent package. Heat generation was plotted against a variety of relevant pressures. The results in these simple geometries are compared to kinetic model calculations, performed by other investigators, to determine the appropriate collision diameters to use in rarefied helium gas simulations within complex geometries. A two dimensional mesh of a transfer cask containing 24 pressurized water reactor used fuel assemblies is then constructed, and the rarefied gas model was implemented in the helium-filled regions between the fuel and basket support structures. Steady state simulations with a fuel heat generation rate of 710 W/m/assemble shows that the cladding is measurably hotter when the helium gas pressure is reduced from atmospheric conditions ∼105 Pa to 500 Pa. The heat generation rate that brings the peak cladding temperature to a hydride dissolution temperature of 400°C is as much as 10% lower when the gas is at 500 Pa than under atmospheric conditions.

Download Full-text

Commitment to pro- versus counter-attitudinal behavior and the dynamics of social representations

Swiss Journal of Psychology ◽

10.1024//1421-0185.61.1.34 ◽

2002 ◽

Vol 61 (1) ◽

pp. 34-44 ◽

Cited By ~ 8

Author(s):

Eric Tafani ◽

Lionel Souchet

Keyword(s):

Higher Education ◽

Social Representations ◽

Cognitive Restructuring ◽

Social Representation ◽

Two Dimensional ◽

Dimensional Model ◽

Social Actions ◽

The Social ◽

Two Dimensional Model ◽

Students Attitudes

This research uses the counter-attitudinal essay paradigm ( Janis & King, 1954 ) to test the effects of social actions on social representations. Thus, students wrote either a pro- or a counter-attitudinal essay on Higher Education. Three forms of counter-attitudinal essays were manipulated countering respectively a) students’ attitudes towards higher education; b) peripheral beliefs or c) central beliefs associated with this representation object. After writing the essay, students expressed their attitudes towards higher education and evaluated different beliefs associated with it. The structural status of these beliefs was also assessed by a “calling into question” test ( Flament, 1994a ). Results show that behavior challenging either an attitude or peripheral beliefs induces a rationalization process, giving rise to minor modifications of the representational field. These modifications are only on the social evaluative dimension of the social representation. On the other hand, when the behavior challenges central beliefs, the same rationalization process induces a cognitive restructuring of the representational field, i.e., a structural change in the representation. These results and their implications for the experimental study of representational dynamics are discussed with regard to the two-dimensional model of social representations ( Moliner, 1994 ) and rationalization theory ( Beauvois & Joule, 1996 ).

Download Full-text