Seismic qualification of the primary loop of the non-seismically designed Belgian NPP

This paper describes the non linear time history analysis performed to seismically qualify the primary loop of the three first Belgian PWR plants. These plants (Chooz A 300 MWe - commissioned in 1966, and Doel 1/2 2 x 390 MWe - commissioned in 1974 and 1975) were not seismically designed, no seismic event being specified at that time. But, after respectively 20 years and 10 years of operation, the safety authorities required to seismically qualify the primary loop of these plants, for a SSE event. Both primary loops and, particularly, the Chooz A primary loop, have a supporting system that differs from the other seismically qualified Belgian NPP. A seismic qualification by analogy was thus not possible, but they are equipped with restraints designed for LOCA/SLB that will certainly be active in case of an SSE