The ultimate in safety

摘要

Large-scale expansion of nuclear power must be based on reactors that meet two main requirements: "ultimate" safety and highly efficient fuel utilisation. The heavy water gas-cooled reactor concept developed over recent decades in the former USSR fulfils these goals. "Ultimate" safety may have a variety of safety definitions, often inconsistent. For this project, it means eliminating the possibility of radioactivity releases from the plant that have significant environmental impact, allowing in principle for the possibility of core damage and even core complete melt. Reducing this probability to an acceptable level is also of importance from the viewpoints of financial risk and public acceptance. To achieve this it is necessary to consider the safety impact and the likely challenges to it. The internal challenges to the envelope are: 1. Sudden pressure buildup, due either to a power excursion caused by prompt neutrons or a sudden release of internal energy stored in the primary coolant. 2. Gradual pressure increase to a level exceeding design limits. 3. Explosive chemical reactions in an emergency. 4. Ablation by molten core debris.