Heat and Mass Transfer in Reactor Core During a Loca-Single Channel Analysis (Mixed Convection, Numerical, Flow, Thermal-Hydraulics)
Pien, Shyh-Jye
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https://hdl.handle.net/2142/70134
Description
Title
Heat and Mass Transfer in Reactor Core During a Loca-Single Channel Analysis (Mixed Convection, Numerical, Flow, Thermal-Hydraulics)
Author(s)
Pien, Shyh-Jye
Issue Date
1985
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Abstract
Ability to predict the scenario following a loss-of-coolant accident (LOCA) is of central importance in the safety analysis of water reactors. During LOCA, the reactor core is uncovered and the residual water inventory is boiled off by fission products decay heating. For the Three Mile Island (TMI-2) reactor, it was reported that the steam oxidation of Zircaloy reached such an extent that radioactive gases leaked from the interior of the fuel rod and contaminated the primary coolant system. To assess the potential hazard of hydrogen and the concomitant structural damage to fuel cladding, as well as the extent of fission products release, a detailed study of the heat and mass transfer processes during LOCA was made.
As a first step, the analysis was made for a single flow channel of equivalent annular geometry. During the early stage of the core uncovery, the flow is everywhere upward and the governing conservation equations are parabolic. Toward the late stages, the net outflow at the channel exit is small and flow recirculation ensues. The governing equations are elliptic. Because of the unusually large length-to-diameter ratio of the flow channel which may exceed 200, a hybrid elliptic-parabolic computational scheme was developed taking advantage of the time when the maximum fuel rod temperature reaches a dangerously high value, the flow in the channel is elliptic only in a small portion of the long channel and parabolic in the remaining portion.
Results presented include information on the core water level at various times following the start of core uncovery, the corresponding steam generation rate, velocity, and temperature profiles of the mixture flow as well as the mass fraction profiles for hydrogen and fission products across the channel. Also included are the variations of friction factor, Nusselt number, and Sherwood numbers along the length of the uncovered rod. The axial distribution of the Zircaloy cladding temperature and the generation rates of hydrogen and fission products are also given. For conditions pertinent to the TMI-2 reactor, the solutions showed that when the current water level receded to 2.50 m from the top of the active core, the maximum cladding temperature would have reached 1843 K which is very close to the break-away oxidation temperature of Zircaloy. (Abstract shortened with permission of author.)
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