Characteristics, construction and use of valves for nuclear energy

The characteristics and the constructions of the valves for nuclear energy differ largely according to the types of reactors and the kinds of coolants. For the reactors being used for power generation, the valves are constructed on the basis of standard valves by incorporating the requirements for nuclear energy use secondarily, but in sodium-cooled breeder reactors and multi-purpose high temperature reactors, the valves with special constructions have been developed in various countries. Serious accident did not occur in nuclear power stations so far, but many minor abnormalities have been reported, and those due to valves and valve-operating mechanisms amount to a quarter of them. The fault in operating function is most, and the leak from valve seats and gland packings follows. In order to reduce the probability of failure of reactors, the improvement of the reliability of valves is urgently required. As for the special valves for nuclear energy, there are main steam isolating valves, pneumatically operated relief valves, testable check valves, swing check valves for primary coolant, vacuum-breaking valves, excess flow valves and so on. The quality guarantee system in the manufacture of valves must be strengthened, but only maintenance can be relied upon regarding the secular failure of valves. (Kako, I.)