In-service inspection of PWR reactor coolant loops - A challenging project

There are four reactors at the Ringhals Nuclear Power Plant. Three of those are PWRs of Westinghouse design. Inservice Inspection of the primary loops and reactor coolant pumps at the three PWRs has over the years been performed to a limited extent due to the difficulties to inspect heavy wall cast stainless steel materials. Effective January 1995, a new code for Inservice Inspection with more stringent requirements was imposed by the Swedish regulator, the SKi. The new code includes requirements to inspect the full volume of each inspection area for the purpose of detecting possibly remaining manufacturing defects as well. as a requirement to qualify the inspection techniques (performance demonstration). In order to meet the new requirements Ringhals has formed a project which aims at performing Inservice Inspection of the primary loops with qualified inspection techniques starting 1997. This paper describes the project and the different activities which are performed in order to meet the project objectives. A Round Robin test has been carried out in order to assess the possibility to inspect applicable materials. Also fracture mechanic calculations are carried out in order to determine acceptable flaw sizes and inspection intervals. A system for Risk Based Inservice Inspection is used to select the welds to be inspected and a full size mock-up is planned for the qualification of the robotics and the inspection techniques.