Pipelines safety features

Safety features at a nuclear power plant include automatic shutdown of the fission process by insertion of control rods, emergency water cooling for the cote in case of pipeline breakage, and a concrete containment shell. It is impossible for a reactor to have a nuclear explosion because the fuel enrichment in a reactor is intentionally limited to about 3% uranium-235, while almost 100% pure uranium-235 is required for a bomb. The worst accident at a PWR would be a steam explosion, which could contaminate the inside of the containment shell. 

This is a location safer than Zone I with a likelihood of concentration of explosive gases, chemical vapour or volatile liquids during processing, storage or handling. This would become a fire hazard only under abnormal conditions, such as a leakage or a burst of joints or pipelines etc. Such a condition may exist only for a short period. A standard motor with additional features, as di.scussed below, may also be safe for such locations. A non-sparking type. Ex. n , or an increased safety motor, type Ex. e , may also be chosen for such locations. 

Experimental studies of features of the alloy-structure interaction were carried out by tests of mock-ups, models and real primary components. Fuel subassemblies, control and safety system components, primary pumps, steam generators, sections of main and auxiliary pipelines and their valves have been tested. In the course of tests requirements have been worked out for the temperature conditions of heating up and cooling down modes, as well as for separate structures designed for avoiding damages at multiple condition changes. 

Many extremely hazardous substances can quite safely be employed in manufacturing processes provided they are at all times contained within the plant and not allowed to escape into the working environment. This assumes automated and bulk handling into store, then from store to process with transfer either in sealed containers or through enclosed and dedicated pipelines. An essential feature of containment is a high level of safety integrity of the plant - which in its turn demands high standards of plant maintenance. 

It should be noted that shut-off and isolation valves are not used in any reactor pipelines, except for the user circuit, i.e., all systems are in continuous operation and not just available. This feature contributes significantly to the reliability and safety of the UNITHERM. 

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