1.2. GENERAL CONSIDERATIONS

General considerations for the incorporation of inherent and passive safety design features into SMRs are not different from those of advanced reactors of any capacity and type. Clearly, the implementation of inherent and passive safety design features can facilitate improved defence in depth. It can also positively affect plant economy through:

— Reduced design complexity and reduced necessity for human intervention resulting in fewer potentially unsafe actions;

— Reduced investment requirements, due to a reduction in qualifications as well as operation and maintenance and, depending on specific design and regulations, reduced off-site emergency planning;

— Increased operability and capacity factors.

It is also noted that the use of inherent and passive safety features can facilitate advantages in areas other than economy, for example:

— Reduced adverse environmental impacts, for example through a reduced number of systems requiring maintenance and associated waste;

— Reduced vulnerability to sabotage through semi-autonomous operation, better reactor self-control in accidents, and ‘passive shutdown’[2] capabilities;

— Deployment in developing countries through simplified infrastructure requirements matching human resource limitations in such countries.

In the view of SMR designers, smaller capacity reactors have the following generic features, potentially contributing to a particular effectiveness in the implementation of inherent and passive safety features:

— Larger surface-to-volume ratio, facilitating easier decay heat removal, specifically, with a single phase coolant;

— An option to achieve compact primary coolant system design, e. g. the integral pool type primary coolant system, which could contribute to the effective suppression of certain initiating events;

— Reduced core power density, facilitating easy use of many passive features and systems, not limited to natural convection based systems;

— Lower potential hazard that generically results from lower source term owing to lower fuel inventory, less non-nuclear energy stored in the reactor, and a lower decay heat generation rate.

Section 2.2. below summarizes considerations of SMR designers regarding inherent and passive safety features that could be easier to achieve in a reactor of smaller capacity for each reactor line considered in this report.