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Thermodynamic Properties and Equations of State
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
However, the amount of moisture the air can hold increases with increasing temperature because the saturation pressure PSAT increases with this temperature as well. If the temperature inside a containment building drops, the amount of water the air can hold will drop as well and the remaining water may condense out of the air in the form of a liquid film on the containment building walls. The reason why this process is important in the study of nuclear engineering is that it sometimes comes into play following a reactor loss-of-coolant accident (or LOCA). As the air–steam mixture cools down, water condenses out of the mixture and builds up on the containment building floor. We will examine the mechanics of this process when we discuss the physics of LOCAs in Chapter 34.
Pumping in Nuclear Plants
Published in Maurice L. Adams, Power Plant Centrifugal Pumps, 2017
As Dahlheimer et al. (1984) explain, the primary function of the residual heat removal system (RHRS) is to transfer heat energy from the reactor core and reactor coolant system (RCS) during plant cooldown and refueling operations. The RCS temperature is reduced to 140°F (60°C) within 20 hours following reactor shutdown. The RHRS may also be used to transfer refueling water between the refueling cavity and the refueling water storage tank at the beginning and end of refueling operations. The residual heat removal pumps are also utilized as part of the safety injection system for emergency core cooling in the event of a loss-of-coolant accident (LOCA).
Nuclear Energy
Published in Efstathios E. Michaelides, Energy, the Environment, and Sustainability, 2018
In all nuclear power plants, the LOCA represents an unacceptable risk because it may have catastrophic consequences for the population of a vast geographic region in the vicinity of the reactor. Nuclear power plants are designed with a primary cooling circuit and one or two separate and independent emergency cooling circuits, designed to continuously operate, even when the plant does not produce electric power. The reliability and effectiveness of the primary and emergency cooling systems of the reactor are of paramount importance to the safe operation of any nuclear power plant.
Measurements of Droplet Size and Velocity Distributions During Rod Bundle Core Reflood
Published in Nuclear Science and Engineering, 2023
Grant R. Garrett, Brian R. Lowery, Molly K. Hanson, Douglas J. Miller, Turki Almudhhi, Fan-Bill Cheung, Stephen M. Bajorek, Kirk Tien, Chris L. Hoxie
A loss-of-coolant accident (LOCA) is one of the most serious hypothetical accidents to occur in a nuclear power plant. In the event of a LOCA, a break occurs in the primary system that results in the loss of available coolant to the core. The reactor is then shut down from voiding of the coolant, but energy is still released from the fuel via decay reactions. In order to ensure the integrity of the fuel and cladding and prevent core melt, a secondary source of water is introduced to the core. During this core reflood, entrained liquid droplets play an essential role in the energy transfer from the rods to the coolant, especially in the dispersed flow film boiling regime where no liquid is directly in contact with the hot rods. The total entrained liquid and the droplet sizes determine the interfacial area available between the liquid and vapor phases. The energy removal from the hot rods is directly dependent on the interfacial area. Hence, increased interfacial area from increased entrainment and/or smaller droplets will assist in maintaining fuel and cladding temperatures below their safety limits. However, increased entrainment will delay overall quench times as the liquid entrained exits the core and is no longer available to quench the rods.
A Risk Approach to the Management for the Pre-Defueled Phase in the Decommissioning Transition Stage
Published in Nuclear Technology, 2023
Po-Jung Chiu, Chung-Kung Lo, Tai-Hung Wu
The classification of IEs is based on similarities in the responses of the plant systems that can affect the progression of an AS. Transients, loss-of-coolant accidents (LOCAs), DHR-related, and special events are the four principal groups of generic IEs. Varied configurations of the reactor/SFP and different demands on mitigating systems characterize these four groups of IEs. To identify initiators that will disable safety or mitigation systems, failure mode and effects analyses (FMEAs) are performed for electrical, air, and cooling systems.7,8 First, transients are perturbations of the operation of the plant’s normal or alternative heat removal systems. Second, a LOCA is an event involving an uncontrolled loss of reactor coolant. Third, the cooling systems of different DHR capabilities, such as the RHR and SFPACS, will contribute to the DHR-related IEs.
Development of Advanced Instrumentation for Transient Testing
Published in Nuclear Technology, 2019
A loss-of-coolant accident38 (LOCA) represents an important DBA undercooling event of great interest to transient testing experiments for LWR systems. A LOCA is caused by a break in a reactor’s coolant pressure boundary. Automatic emergency shutdown of the reactor will be activated, but the temperature of the reactor continues to rise due to stored thermal energy, loss of coolant, and radioactive decay in the fuel. As cladding temperatures may reach over 1000°C, it may plastically deform due to the decrease of pressure across the cladding wall and deteriorating mechanical properties, resulting in possible ballooning and rupture. At these high temperatures, the Zircaloy cladding also undergoes phase transformation and oxidizes in reaction with the coolant (steam) forming a brittle structure. Emergency core cooling systems are engaged that reflood the reactor causing the potential for brittle failure of the cladding during rapid quenching. Ballooning and rupturing of cladding can block coolant channel flow and eventual loss of coolable geometry of the core.