Experiments performed by others measured the temperature of twelve heated vertical rods within a constant temperature, internally finned cylindrical enclosure. Measurements were performed for a range of air and helium pressures and a range of rod heat generation rates. In the current work, three-dimensional computational fluid dynamics simulations of natural convection and radiation heat transfer within this domain were conducted to benchmark the simulation techniques. These calculations accurately reproduced the local and average temperatures when the heat generation rate was sufficiently low that the velocity field is steady. Future simulations will be used to design experiments that model spent nuclear fuel within non-isothermal cells of storage packages.
Experiments and computational fluid dynamics/radiation heat transfer simulations of an 8×8 array of heated rods within an aluminum enclosure are performed with nitrogen and helium as backfill gases in both horizontal and vertical orientations. This configuration represents a region inside the channel of a boiling water reactor fuel assembly between two consecutive spacer plates. The rods can be oriented horizontally or vertically to represent transport or storage conditions. The measured and simulated rod temperatures are compared for three different rod heat generation rates to assess the accuracy of the simulation technique. Simulations show that temperature gradients in the air are much steeper near the enclosure walls than they are near the center of the rod array. The measured temperatures of rods at symmetric locations are not identical, and the difference is larger for rods close to the wall than for those far from it. Small but uncontrolled deviations of the rod positions away from the design locations may cause these differences. The simulations reproduce the measured temperature profiles. For nitrogen experiment in horizontal orientation and a total rod heat generation rate of 500 W, the maximum rod-to-enclosure temperature difference is 138°C. The maximum measured heater rod and enclosure wall temperatures 375°C and 280°C, are measured in 2-inch insulated, nitrogen backfill vertical experiment for 1 atm internal pressure. Linear regression shows that the simulations slightly but systematically under predict the hotter rod temperatures but accurately predict the cooler ones. For all rod locations, heat generation rates, nitrogen and helium backfill gases, and apparatus orientations, 95% of the simulated temperatures are within 11°C of the correlation values. These results can be used to assess the accuracy of using simulations to design spent nuclear fuel transport and storage systems.
The Container Analysis Fire Environment computer code is used to simulate the response of a truck package designed to transport one PWR fuel assembly to 7.2-m-diameter pool fires. Simulations are performed with the package centered over the fire, and offset axially from that location by 1 and 2.5 m. In all simulations the package body is 1 m above the fuel pool. The simulations predict the package containment seal exceeds its temperature of concern for all three package locations. Simulations of a no-impact-limiter version of the package are also performed to quantify the level of thermal protection provide by the limiter. The minimum fire duration that causes the seal to reach its temperature of concern is determined for each configuration. When the center of the no-impact limiter package is within 2.5 m of the pool center, fires shorter than 0.7 hour are capable of causing the seal to reach its temperature of concern. By contrast, the intact package protects the seal in fires that last roughly 2 hours. These results will help risk analysts better understand the effect of package position and the role of the impact limiters on accident consequences.
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