The loss of primary coolant from a pressurized water reactor as a result of an instantaneous rupture of a main circulating line' is called a LOCA and is perhaps the most serious accident in terms of radioactivity release from the fuel to the outer containment system that can be realistically postulated. Emergency Core Cooling Systems (ECCS) are provided to maintain continuity of energy removal from the reactor core following such an event. Paramount to the evaluation of the ECCS is knowledge of the fuel and fuel-clad temperatures at the end of the coolant loss period of 8 to l4 seconds. Heat-transfer data have not been available for the conditions of heater power (heat flux) and of transient coolant pressure, velocity, and temperature comparable to the environment around a fuel-rod bundle during a loss-of-coolant transient. Appropriate transient heat-transfer data have now been obtained with single Zircaloy clad heaters (0.5-in.-CD x 2-ft-long) and a seven-rod cluster in a closed cycle, circulating, 1500 psi pressurized, water loop at power levels of 17.5 kw/ft (^50,000 Btu/hr»ffc s) with cooling water near 500°P inlet and 1500 psi during a 12-second depressurization and coolant loss. Flow regimes associated with bulk-nucleate boiling and with thin film surface evaporation are clearly discernible where the temperature difference and heat flux data are considered. The high heat-transfer coefficients were observed for times .. greater than the heat-removal time constants of the heater rods and suggest that assumptions made in current calculations are conservative.
The author acknowledges the help of H. Tjehrend III in helping with the data taking and computing and the help of D. G. Thomas in data taking. UNCLASSIFIED
Calculations are presented to show the effect of uraniumbearing scale deposits on the HRE-2 core wall temperature, heat flux, and the temperature of patches proposed for sealing the holes of the HRE a 2 core vessel. Flow behavior in the HRE-2 core mockup with simulated patches installed and simulated corrosion pits drilled in the vessel wall was determined.A plausible mechanism was advanced to account for hot spots due to sedimentation of solids on metal surfaces projecting from the core wall. Patch designs with reduced. metal projections from the core wall are presented.
NOTICEThis document contains information of a preliminary nature and was prepared primarily for internal use at the Oak Ridge Notional Laboratory. It is subiect to revi sion or correction and therefore does not represent a final report. The information is not to be abstracted, reprinted or otherwise given public dissemination without the approval of the ORNL potent branch, Legal and Information Control Department.
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