STABILITY OF BOILING WATER-REACTORS - PHENOMENA, OCCURRENCES AND MONITORING

Boiling water reactors are stable under their defined operating condit ions. Instability can occur during start-up or shutdown operations if the known instability region if not avoided. The instability has a the rmal-hydraulic component which is dependent on the parallel channel co nfiguration and is mostly determined experimentally. The different fee dback mechanisms in boiling water reactors and thr applied methods to avoid instability are explained. The different incidents which occurre d during the last ten years show the need for monitoring the stability of boiling water reactors. For this purpose an international standard has been developed which is outlined in this paper.