Use of Fuel Assembly/Backfill Gas Effective Thermal Conductivity Models to Predict Basket and Fuel Cladding Temperatures Within a Rail Package During Normal Transport

Abstract

Two-dimensional finite element thermal simulations of a generic rail package designed to transport twenty-one spent PWR assemblies were performed for normal transport conditions. Effective thermal conductivity models were employed within the fuel assembly/backfill gas region. Those conductivity models were developed by other investigators assuming the basket wall temperature is uniform. They are typically used to predict the maximum fuel cladding temperature near the package center. The cladding temperature must not exceed specified limits during normal transport. This condition limits the number and heat generation rate of fuel assembles that can transported. The current work shows the support basket wall temperatures in the periphery of the package are highly non-uniform. Moreover the thermal resistance of those regions significantly affects the maximum fuel clad temperature near the package center. This brings the validity of the fuel/backfill gas thermal conductivity models into question. The non-uniform basket wall temperature profiles quantified in this work will be used in future numerical and experimental studies to develop new thermal models of the fuel assembly/backfill gas regions. This will be an iterative process, since the assembly/backfill model affects the predicted basket wall temperature profiles.

Simulation of thermal state of containers with spent nuclear fuel: multistage approach

“…Because of slow changes of decay heat of spent fuel assemblies during the storage, the modelling of thermal processes inside containers with spent nuclear fuel is generally accepted to carry out in the quasi-static formulation [5][6][7][8][9][10]. The system of quasi-static differential equations that describes the conjugate heat transfer problem consists of the following equations [15][16][17]: -Continuity equation:…”

“…Unfortunately, all existing known works in field of thermal simulation at dry spent nuclear fuel storage have some limitations. For example, the moving of filled medium inside storage basket is not considered [5,6], or the problem was solved in two-dimensional formulation [7][8][9]. There are some researches that use simplified geometry structure and equivalent thermal properties for CFD simulation [9,10], but this way of investigations does not allow to obtain the detailed information about thermal processes inside storage containers even with usage of CFD methodology.…”

Geometrically-Accurate-Three-Dimensional Simulations of a Used Nuclear Fuel Canister Filled With Helium

“…Multiple simulations are performed to determine the cask thermal capacity, which is the fuel heat generation rate that causes the cladding to reach its temperature limit. In some models, the fuel and basket are replaced by a smeared region with an Effective Thermal Conductivity (ETC) and an effective porosity [8][9][10][11][12][13][14]. Other models use an accurategeometry computational domain where the fuel rods, gas and the baskets are modeled separately [15][16][17][18][19][20][21][22][23][24][25].…”

Use of Regular Rod Arrays to Model Heat Transfer From BWR Fuel Assemblies Inside Transport Casks

“…The fuel cladding temperature increases as the fuel heat generation rate increases. Finite element (FE) cask models [3] are used to predict the cladding temperature and determine the maximum heat generation rate that does not cause the cladding to exceed its integrity temperature limit of 400°C [4]. In the past, resources were not available to construct and use computational cask models that accurately represent the fuel geometry.…”