Trip and test units

Trip units provide a positive trip signal with a fail safe feature vdien a certain measured parameter level goes beyond the preset range. The trip level should be continuously variable with a provision for locking after the levels are set. 

Available technology offers a minimum of four types of safety logic systems, based on diverse logic elements, for use in reactors. The relay logic which has been tried out extensively in the safety systems of many research and power reactors has established its reliability and availability beyond doubt. However, relay logic systems are bulky. 

Finally, the use of duplicated or triplicated microprocessor systems for the safety channels of a research reactor is likely to be effective and economical. However, microcomputers have not been tried out in large numbers in reactor systems. Their introduction into safety systems poses many questions regarding reliability and unsafe failures, and as reported, when used, have presented some operational problems. 

In all safety systems using semiconductor logic, or semiconductor components, unsafe failure cannot be ruled out. It is therefore necessary in such systems to provide continuous reliable impulse testing to monitor performance of the system. 

It is not necessary to require safety system redimdancy (duplication) in alarm systems, however, it is necessary to keep reliable alarm (warning) systems, by the use of appropriate buffering systems if necessary. Alarm systems can not compromise the functionality of safety systems. 

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