Surveillance and maintenance of an environmentally qualified Candu nuclear plant. A view from operations

CANDU nuclear station owners are faced with an increasing amount of equipment considered to be safety related and required to operate successfully during common mode design basis events such as earthquakes, loss of coolant accidents, main steam line breaks, etc. Designers are faced with the task of either protecting this equipment from the consequences of the events or supplying equipment which will operate in the environment expected during these events. This trend has continued at Darlington NGS-A with the identification of 125 safety related systems which must perform a function during and/or following the common-mode design basis events. In addition to protecting or hardening the safety related equipment, the designers must also provide assurance that the equipment is capable of operating reliably during any of these events. At Darlington NGS-A, the effects of aging mechanisms on components of safety related equipment is also being taken into account. This paper describes the Darlington Environmental Qualification Program and discusses how it will change the nature of our safety related equipment maintenance, surveillance and replacement programs