Containment passive protection systems

Secondary containment systems are best described as passive protective systems. They do not eliminate or prevent a spill or leak, but they can significantly moderate the impact without the need for any active device. Also, containment systems can be defeated by manual or active design features. For example, a dike may have a drain valve to remove rain water, and the valve could be left open. A door in a containment building could be left open. 

Besides the inherent safety characteristics of SMART, its safety is further enhanced by highly reliable engineered safety systems. These are designed to function passively on demand and consist of a reactor shutdown system, passive residual heat removal system (PRHRS), emergency core cooling system (ECCS), safeguard vessel, reactor overpressure protection system (ROPS) and containment overpressure protection system (COPS). 

Although the first industrial application of anodic protection was as recent as 1954, it is now widely used, particularly in the USA and USSR. This has been made possible by the recent development of equipment capable of the control of precise potentials at high current outputs. It has been applied to protect mild-steel vessels containing sulphuric acid as large as 49 m in diameter and 15 m high, and commercial equipment is available for use with tanks of capacities from 38 000 to 7 600000 litre . A properly designed anodic-protection system has been shown to be both effective and economically viable, but care must be taken to avoid power failure or the formation of local active-passive cells which lead to the breakdown of passivity and intense corrosion. 

A passive fire protection system requires no action to occur for it to function per its design intent. Examples of passive fire protection methods are fireproofing, spill containment, and physical separation of units and buildings. 

Solid floors in multilevel process structures can provide a passive means of containing any spilled liquids or solids and preventing materials from falling onto lower levels. To maximize the effectiveness of solid floors, the floor design should include appropriately located drainage for spills and fire water runoff. Fire protection systems can be designed to effectively manage liquid pool fires. 

The remaining safety-grade functions are performed by the reactor protection system (it initiates opening of the scram valves to achieve a reactor scram), the containment isolation system (it initiates isolation of the containment by closing isolation valves), the reactor vessel safety valves (based on pressure-activated components), and the passive reactor pool cooling function. These functions are not needed for the protection of the core, however. 

In the case of LOCA, some primary coolant and steam-gas mixture from the pressurizer are discharged to the containment. The emergency core protection system acts in response to the signals of pressure transducers. Leakage proceeds until the pressure values in the reactor and in the containment are equalized (about 2 MPa after 10 minutes of the transient). The amount of coolant remaining in the reactor is sufficient to maintain circulation in the main coolant circuit. The reactor is passively cooled via the intermediate circuit and the independent heat removal circuit without time limitation. The component cooling system removes heat from the containment. 

Additionally, a passive containment cooling ancillary water storage tank and two recirculation pumps are provided for onsite storage of additional passive containment cooling system cooling water, to transfer the inventory to the passive containment cooling water storage tank, and to provide a back-up supply to the fire protection system seismic standpipe system. 

The APIOOO does not need a containment spray system to cool the containment atmosphere, because this function is performed by the passive containment cooling system. The principal means of post-accident isotope control for the APIOOO relies on natural forces, like natural convection, condensation and conduction, to transfer decay heat from the lower regions of the containment to the containment walls, which are cooled (there is also a containment spray utilising the fire protection system (see Section 8.4.3.10), as a backup for this function. The resulting steam condenses onto the containment wall, and then returns to IRWST or to the containment sump by gravity. Through analysis and testing, it has been shown that the soluble and suspended isotopes move with the water, and thus finish up in the water in the IRWST or the lower portions of the containment. 

Anticorrosion paints containing polyaniline. As the first actively passivating anticorrosion system, a newly developed PAni primer could perform the important environmental protection function of conserving energy-intensive and raw-material-intensive assets (Section VII.B). 

Tantalum is not resistant to substances that can react with the protective oxide layer. The most aggressive chemicals are hydrofluoric acid and acidic solutions containing fluoride. Fuming sulfuric acid, concentrated sulfuric acid above 175°C, and hot concentrated aLkaU solutions destroy the oxide layer and, therefore, cause the metal to corrode. In these cases, the corrosion process occurs because the passivating oxide layer is destroyed and the underlying tantalum reacts with even mild oxidising agents present in the system. 

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