Category Archives: Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants

Behaviour of emergency heat exchangers and isolation condensers

The removal of decay heat from a nuclear core can be accomplished by passive means using either an emergency heat exchanger or an isolation condenser (IC), depending on the system design. In some advanced pressurized water reactors (PWR), the emergency heat exchanger decay heat removal system consists of a closed loop that includes a shell and tube heat exchanger immersed […]

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Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants

As part of the IAEA’s overall effort to foster international collaborations that strive to improve the economics and safety of future water-cooled nuclear power plants, an IAEA Coordinated Research Project (CRP) was started in early 2004. This CRP, entitled Natural Circulation Phenomena, Modeling and Reliability of Passive Safety Systems that Utilize Natural Circulation, focuses on the use of passive safety […]

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SUMMARY OF REACTOR AND PASSIVE SAFETY SYSTEM CATEGORIES

The characterization of the nuclear reactor designs based on the passive (sub-) systems constitutes the objective of the present section. This can be achieved by combining the reactor descriptions given in Annexes I to XX and the passive systems identified in Sections 2 and 3. Furthermore, the ‘passive’ thermal-hydraulic phenomena characterized in Section 4 can be cross-correlated with the reactor […]

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Stratification and mixing of boron

Boric acid is introduced into the reactor coolant to control long term reactivity. Forced coolant circulation during normal operation ensures that the boric acid is homogeneously distributed in the reactor coolant system (RCS) so that the boron concentration is practically uniform. Decrease of the boron concentration results in an increase of the reactivity. Causes for decreasing of boron concentration are […]

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Containment heat removal and atmospheric mixing

Following a LOCA, large flow paths are established interconnecting the fuelling machine vaults and SG enclosures with the rest of the reactor building. These flow paths allow natural circulation flows to prevent formation of regions of locally high temperature and/or hydrogen concentration to protect the integrity of containment.

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DEFINITIONS OF PHENOMENA ASSOCIATED WITH NATURAL CIRCULATION4

Phenomena have been classified into two categories (a) phenomena occurring during interaction between primary system and containment; and (b) phenomena originated by the presence of new components and systems or special reactor configurations. This classification considers the information provided in the CSNI Report [25] which has been developed for the primary systems having in mind the safety assessment, and is […]

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Core make-up tank behaviour

Several advanced reactor designs implement core make-up tanks (CMTs) to provide natural circulation cooling to the core. CMTs are elevated tanks connected to the reactor vessel and primary loop at the top and bottom of the tank. Special lines connect the bottom of the tank with the vessel, and are termed direct vessel injection (DVI). In connection to this, an […]

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Pre-pressurized core flooding tanks (accumulators)

Pre-pressurized core flooding tanks, or accumulators, are used in existing nuclear power plants and they constitute part of the emergency core cooling systems. They typically consist of large tanks having about 75% of the volume filled with cold borated water and the remaining volume filled with pressurized nitrogen or an inert gas. As shown in Figure 1, the contents of […]

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